FORESTS AND WATER. 


effects of forest 

management 

on floods, 

sedimentation, 

and water supply 

HENRY W. ANDERSON, MARVIN 0. HOOVER, 

KENNETH G. REINHART 

PACIFIC 

SOUTHWEST 

Forest and Range Experiment Station 

FOREST SERVICE. 

U. S.DEPARTMENT OF AGRICULTURE 

P. 0. BOX 245, BERKELEY, CALIFORNIA 94701 

USDA FOREST SERVICE 

GENERAL TECHNICAL 

REPORT PSW- 18I1976 
CONTENTS 

Page 

Introduction.............................................. 1 


I-Hydrologic Processes ................................... 3 


Hydrology in the Forest ................................ 6 


Water Inputs ......................................... 6 


Precipitation Measurement ........................... 6 


Snowfall ........................................... 7 


Interception Processes ................................. 7 


Snow Interception ................................... 8 


Interception and Floods .............................. 8 


Variability of Interception ............................ 9 


Surface Storage .......................................10 


Infiltration Processes .................................. 11 


Watershed Storage ..................................12 


Subsurface Flow ....................................15 


Peak Flows .........................................15 


Evapotranspiration ....................................17 


Transpiration.......................................17 


Evaporation ........................................20 


Water Yield ..........................................20 


Groundwater .......................................20 


Streamflow.........................................20 


Modifiers of the Forest Influence ........................23 


Storm Size .........................................23 


Watershed Size .....................................23 


Physiography.......................................23 


Geology ........................................... 24 


Forest and Frost .................................... 24 


Forestry, Erosion. and Water Quality ....................25 


Erosion and Sedimentation ........................... 25 


Water Temperature ..................................27 


Water Chemistry ....................................27 


Integrating Hydrologic Processes ........................28 


11-Forest Treatment and Water ............................. 30 


Timber Harvesting .................................... 30 


Interception ........................................30 


Snow Accumulation .................................30 

Surface Detention ................................... 32 


Infiltration. Overland Flow. Erosion. and Sedimentation . . 32 


Evapotranspiration..................................37 


Soil-Water Storage .................................. 37 


Quantity of Streamflow .............................. 38 


Peak Flows and Stormflow Volumes ................... 42 


Water Temperature .................................. 44 


Water Chemistry .................................... 45 


Summary .......................................... 45 


Regeneration and Tree Planting ......................... 46 


Interception ........................................ 46 


Infiltration. Overland Flow. Erosion. and Sedimentation ..... 47 


Soil-Water Storage .................................. 47 


Evapotranspiration and Streamflow .................... 48 


Peak Flows ......................................... 48 


Summary .......................................... 49 


Type Conversions ..................................... 49 


Fertilizers. Herbicides. and Insecticides ................... 52 


Fertilizers .......................................... 52 


Herbicides ......................................... 52 


Insecticides......................................... 52 


Fire ................................................. 53 


Interception ........................................ 53 


Infiltration. Overland Flow. Erosion. and Sedimentation . . 53 


Soil-Water Storage ..................................55 


Evapotranspiration..................................56 


Quantity of Streamflow ...............................56 


Peak Flows .........................................56 


Summary ..........................................57 


Grazing..............................................57 


Interception and Evapotranspiration ................... 57 


Infiltration. Overland Flow. Erosion. Sedimentation. 

and Peak Flow .................................... 57 


Summary .......................................... 58 


Forest-Land Disposal of Wastes .......................... 58 


Insects. Diseases. and Weather ..........................59 


Minimum-Treatment Management .......................60 


111-Special Problems .....................................61 


Southern California and Arizona Chaparral ...............61 


Fire-Flood Erosion ..................................61 


Erosion Without Fire ................................62 


Erosion After Fire ...................................63 


Control and Rehabilitation ........................... 63 


Arizona Chaparral .................................. 64 


Wetland Forests .......................................65 


Wetflats ...........................................65 


Bays ..............................................65 


Swamps and Upland Ponds ...........................65 


Bottomlands .......................................66 


Phreatophytes ........................................66 


Surface Mining .......................................67 

IV-Potentials for Management ............................. 68 


Conflicting Objectives ................................. 68 


Management for Water Yield ........................... 68 


Management for Maximum Water Yield ................ 69 


Water-Yield Increase Resulting from Multiple Use ........ 69 


Cost of Increasing Water Yield ........................ 70 


Management for Flood Reduction ....................... 71 


Forest Management and Rainfall Floods ................ 71 


Conversion of Open Land to Forest .................... 72 


Snow Management .................................. 72 


Management for Maintaining Water Quality ................ 72 


Erosion and Sedimentation ........................... 73 


Erosion Control-Logging ........................... 74 


Microbiological..................................... 75 


Erosion Control-Fire ............................... 75 


Regional Characteristics and Possibilities: The East ......... 76 


Water Chemistry and Temperature ..................... 77 


Northeastern Conifers and Hardwoods .................78 


Central-Southeastern Hardwoods ...................... 80 


Southeastern Pines .................................. 81 


Regional Characteristics and Possibilities: The West ........ 82 


West Coast Forests .................................. 83 


Rocky Mountain Forests ............................. 87 


Southwestern Brushlands ............................. 89 


V-Tomorrow's Forestry and Water ......................... 91 


Water Yield .......................................... 91 


Selection of Areas for Cutting .........................91 


Antitransoirants and Antievaporants ...................91 


Recreation Use and Environmental Quality ............... 92 


Comparison with Alternatives ......:..................92 


Potential Role of the Forest ...........................93 


Flood Prevention ......................................93 


Forest Role ......................................... 93 


Protection and Reforestation .......................... 93 


Research ...........................................94 


Erosion-Sedimentation-Water Quality ................. 94 


VI- Literature Cited ...................................... 96 

Anderson, Henry W., Marvin D. Hoover, and Kenneth G. Reinhart. 

1976. Forests and water: effects of forest management on floods, 

sedimentation, and water supply. USDA Forest Sew. Gen. Tech. Rep. 

PSW-18, 115 p., illus. Pacific Southwest Forest and Range Exp. 

Stn., Berkeley, Calif. 

From the background of more than 100 years' collective experience 

in watershed research and from comprehensive review of the literature of 

forest hydrology, the authors summarize what is known about the forest's 

influence on the water resource, particularly the effects of current forestry 

practices. They first examine the fundamental hydrologic processes in the 

forest. They then discuss how water supply, floods, erosion, and water 

quality are affected by timber harvesting, regeneration, tree planting, type 

conversion, fire, grazing, and the application of fertilizers and pesticides. 

They consider and present the special problems of fire-prone chaparral, 

phreatophytes, wetland forests, and surface-mined sites. Finally, they 

assess potential increases in water yield that might be achieved by forest 

management in each of six major forest regions in the United States and 

venture some predictions about future management of watersheds. Nearly 

600 references provide a fairly comprehensive overview of the literature. 

Oxford; 116.1 907.3 :(73) 

Retrieval Terms: forest influences, water yield, flood control, erosion, 

sedimentation, water quality, multiple-use, watershed management, forest 

fire, logging, forest grazing, wetlands, phreatophytes, surface mining. 

The Authors 

were, until their retirement, research hydrologists with various Experiment 

Stations of the Forest Service, U.S. Department of Agriculture. HENRY W. 

ANDERSON served at the Pacific Southwest Forest and Range Experiment 

Station, headquartered in Berkeley, California, from 1946 to 1976. He was 

formerly in charge of the Station's research on hydrologic processes in 

mountain watersheds. He earned bachelor's (1943) and master's (1947) 

degrees in forestry at the University of California, Berkeley. MARVIN D. 

HOOVER served on the research staff on the Southeastern Forest Experiment 

Station, Asheville, North Carolina, and later at the Rocky Mountain Forest 

and Range Experiment Station, Fort Collins, Colorado, from 1940 until 

1973. He received forestry degrees at the University of Michigan (bachelor's 

1938) and the University of California, Berkeley (master's, 1939). He is 

currently a consultant. KENNETH G.REINHART received his bachelor's 

(1937) and master's (1938) degrees from Yale University. Except for military 

service, he was employed by the Forest Service from 1939 to 1973, the 

last 18 years of which were with the Northeastern Forest Experiment Station, 

Upper Darby, Pennsylvania. 

ACKNOWLEDGMENTS 

Preparation of this paper was started by Dr. Howard W. Lull, formerly 

hydrologist at the Northeastern Forest Experiment Station, Forest Service, U.S. 

Department of Agriculture, Upper Darby, Pennsylvania. Before his retirement in 

1970, Dr. Lull prepared an outline for the whole report, wrote the first draft, and 

recruited the coauthors. Because of his nonparticipation in the writing after retirement and the many subsequent changes in the manuscript in response to reviews 

and for other reasons, Dr. Lull suggested that he not be listed as an author. 

Many other scientists contributed to this publication, and we gratefully thank 

them all. Special acknowledgment for formal manuscript review is due numerous 

colleagues in the Forest Service and to these specialists outside the Service: 

Dr. Arthur R. Eschner, State University of New York 

Dr. John D. Hewlett, University of Georgia 

Dr. Earl L. Stone, Cornell University 
Relationships between forest and water- both Coweeta Hydrologic Laboratory in western North 

imagined and real - have played an important 

part in the conservation movement. In Europe 

these relations were recognized as early as the 13th 

century. In the United States they were embodied 

in 19th century legislation to conserve the forest. 

In 1876, concern for water motivated the first 

attempt by Congress to create national forests 

from public domain in the West: "for the preservation of the forests of the national domain 

adjacent to the sources of the navigable waters 

and other streams of the United States," and to 

determine what should be reserved in order to 

prevent such rivers from becoming "scant of 

water." Legislation early in 1897 for reservation 

of forested public lands was followed the same 

year by an act that specified their water-control as 

well as timber-supply functions: "no public reservation shall be established except to improve and 

protect the forest within the reservation or for the 

purpose of securing favorable conditions of water 

flows and to furnish a continuous supply of 

timber." 

The ascribed roles of the forest in relation to 

water were employed even more strongly to justify 

the purchase of 23 million acres of forest lands 

in the East for national forests. Out of this effort, 

but not without considerable controversy, came 

the 1911 Weeks Law that provided "for the protection of the watersheds of navigable streams and 

to appoint a commission for acquisition of lands 

for the purpose of conserving the navigability of 

navigable rivers." At question, both before and 

after passage, was the thesis that streamflow is 

regulated by the forest. Conservationists taking 

the affirmative side had little more to offer for 

justification than observation and intuition; 

engineers, in opposition, had no better argument 

than some exceptions to observations and a strong 

disapproval of the intuitive approach. No firm 

data were available to support either side. 

Obviously, the subject required research, and in 

1909 the first forest watershed study in the United 

States was started at Wagon Wheel Gap, Colorado. 

Increasing flood damage throughout the next two 

decades kept the forest and flood issue alive. In 

the early 1930's, the U.S. Forest Service started 

additional research at the San Dimas Experimental 

Forest in southern California, the Sierra Ancha 

Experimental Forest in central Arizona, and the 

Carolina. 

Before many results were forthcoming, however, 

the Omnibus Flood Control Act passed in 1936 

gave the Forest Service responsibility "for conducting flood control surveys on forested watersheds to determine the measures required for runoff and water-flow retardation." Of necessity 

research programs were expanded, and in the 

1940's their results began to set forth the forest's 

influence on water yield, floods, and erosion. Out 

of this research came two salient conclusions: 

(1) forest cutting and forest growth can have a 

major influence on water yield; and (2) the forest, 

because of its full occupancy of site, provides the 

maximum opportunity for controlling runoff 

from flood-producing rainfalls; even so, the forest 

cannot prevent all floods. 

By the 1950's watershed management research 

divisions had been established at all nine Forest 

Service Experiment Stations. By the 1960's the 

number of forested experimental watersheds under 

study reached 150. By 1970 almost 2,000 papers 

had been published describing results of research 

on watershed management. In addition, courses 

in forest influences, forest hydrology, or forest 

watershed management were being offered at 25 

of the 32 accredited forestry schools (Sopper 

1970), two textbooks had been published, and two 

international symposia in forest hydrology had 

been held. 

Out of this growing body of knowledge about 

the forest's influence on streamflow came a new 

subject matter in forestry; namely, forest watershed management. Legal recognition came in the 

Multiple-Use Sustained-Yield Act of 1960, which 

authorized the establishment and administration 

of national forests "for outdoor recreation, range, 

timber, watershed, and wildlife and fish purposes." 

In the 1970's there is growing awareness of the 

forest's influence on water yield, floods, and water 

quality. Water shortages are becoming prevalent 

and threaten to become more so, when flood 

damages have reached new peaks, and when pollution of water supplies is causing increased concern. 

Knowledge about relationships between forestry 

and water has been greatly enhanced during the 

last three decades. This report summarizes and 

evaluates research evidence and other information 

pertinent to the forest's influence on water, 
I 

especially on how this influence can be managed 

for man's benefit so as to increase water yield, 

reduce floods, and improve water quality.' Though 

we hope our summary will be useful to fellow 

forest hydrologists, our principal aim is to provide 

students, practicing foresters, and other professionals an insight into current knowledge of 

relations between forestry and water. These 

persons need help in water supply management 

because of present and predictable increased pressures on forest land and the emphasis today on 

multiple use of these lands. We make no claim 

that the findings reported here or our interpretations of them is a basis for any management 

decision. Management is site specific and the 

Forestry is the science, art, and practice of managing forest 

lands and their natural resources. Since the dividing line 

between forest and nonforest is often hazy, precise definition 

is not easy. The term "forests," as used herein, includes all 

tree and shrub lands where canopy cover is greater than about 

15 percent of the land surface. 

research results were site specific. But since sites 

are generally different, integrating sites and 

management is a task for professionals. 

After that brief introduction, this report (1) discusses the hydrologic processes that govern the 

movement of water in the forest, (2) considers 

forest treatment and water, the effects of management practices and other agents on the water 

resource; and (3) discusses some local and regional 

extreme situations. Next, the paper discusses 

generally the potentials for management -first 

with respect to water yield, floods, and water 

quality; then it presents the possibilities for improving hydrologic management in three regions 

in the East and three regions in the West. Finally, 

the report assesses the place of forestry and water 

in tomorrow's society. 

In reporting quantitative results we have retained 

common U.S. rather than metric units to avoid 

problems of duplicate numbers and problems of 

significant figures, and because we still "think" in 

nonmetric units. 
I - HYDROLOGIC PROCESSES 


Forestry and water are inseparable. Forests and 

water occur together and they interact. Plant a 

tree and it will use water; cut a tree and its water 

use ceases. Trees mark where water is: the greater 

water-providing regions of the United States are 

largely tree-covered. These forests require a minimum of about 20 inches of water per year but use 

much more than that if it is available. Water in 

excess of this use penetrates the permeable forest 

soil to underground storage and streamflow except 

for a small amount that evaporates from the forest 

floor or snowpack. Water released from the forest 

is generally a beneficial component of the water 

supply needed by man, but occasionally an excess 

of water from forest lands contributes to damaging 

floods. 

The wide range among forest types in the 

United States, in the amount of precipitation they 

WESTERN FOREST TYPES 

Sugar pine - ponderosa pine 

Western larchwestern white pine -


receive and in the quantity of streamflow they 

yield (fig. I), complicates the evaluation of the 

hydrologic processes in forests. (The maps here 

show only the conterminous United States; if 

Alaska and Hawaii were included, the range would 

be even greater.) 

The circulation of water from the seas to the 

atmosphere, to the ground, and back to the seas, 

is called the "hydrologic cycle." This cycle can 

be considered a system of water-storage compartments (the atmosphere, the soilmantle, the stream, 

etc.) and the flows of water (either solid, liquid, or 

gas) within and between them (fis. 2). We call 

these individual storages and flows "hydrologic 

processes." Division of the cycle and the naming 

of its components make it easier to study how 

water and energy enter the system, and how they 

are stored, lost, and delivered. We hope, too. 

EASTERN FOREST TYPES 

Lodgepole pine Spruce-firtwith hardwoods) Oak-chestnut-yellow poplar 

Ponderosa pine Birch-beech-maple-hemlock Oak-pine 

Pinon-juniper White, red and jack pine River bottom hardwoods and cypress 

Chaparral Oak-hickory Longleaf-loblolly-slosh pine 

Figure 1-A-Major forest types in the Western United States consist chiefly of softwoods; in the 

Eastern United States, the major types include both softwoods and hardwoods. 
w s mm a -rnrn 

0- 10 0 - 254 m40- 60 1016- 1524 


=lo-20 

1

254- 508 -60-100 1524-2540 


20-30 508- 762 

-Over 100 Over 2540 


30-40 1016- 1524 


Figure 1-B-Average annual precipitation in the conterminous United States ranges from less than 10 inches to 

more than 100 inches. 

AVERAGE ANNUAL STREAMFLOW 

*S mm 

Figure 1-C-Average annual streamflow in the conterminous United States range 

from less than 1 inch to more than 40 inches. 
WATER STORAGE IN ATMOSPHERE 


OUTPUT INPUT 

(Gaseous) 

OUTPUT 

(Liquid) 

Figure 2-The hydrologic cycle consists of a system of water-storage compartments and the solid, 

liquid, or gaseous flows of water within and between the storage points. 
that the processes are additive so we can predict 

water supply, floods, and water quality by summing 

the data on the individual processes. 

Measurements of individual processes are subject to considerable error, biases, and faulty 

criteria of evaluation. In reporting their results, 

researchers usually have not worried much about 

rejecting a hypothesis when it was proved to be 

true (Type I1 Error); they say, "The differences 

were not significant." The results reported here, 

then, require further scrutiny by the user; this 

report is essentially an introduction. 

Hydrologic processes are usually studied in 

what appears to be their logical time sequence, 

such as the inputs from precipitation, interception 

by vegetation, surface storage and flow, subsurface storage and flow, groundwater flow, and 

streamflow. Of course, each of these processes 

may be subdivided; for example, precipitation, the 

first phase of the hydrologic cycle, may be 

subdivided into rain and snow. Our understanding 

of hydrologic processes has improved by study of 

the energy relations that affect them; for example, 

the energetics of rainfall impact on the soil, the 

effects of solar radiation on snowmelt, and the 

sources of energy required to evaporate water. 

Each hydrologic process in the forest ecosystem is 

influenced by the type, size, age, and arrangement 

of trees. Forest units are highly diverse, and this 

complicates their management for water as well as 

for other goods and services. How precisely has 

the forest hydrologist determined the relations 

between water and the forest? Let us examine the 

evidence. 

Hydrology in the Forest 

The conditions under which the forest functions 

hydrologically differ greatly in time and space. 

Forest types and stand conditions, forest soils, 

and even forest topography have developed from 

diverse parent geologic material through a long 

succession of tectonic events, variable climate, 

and sequences of other violent natural events. 

One 40-acre tract may perform like another 40 

acres, but probably not like the 40 immediately 

above or below it on the slope, or like the one on 

the facing slope. And each tract may perform 

differently from all others. 

The hydrologist seeks quantitative measurements 

of each process, the conditions that influence 

each, and of the interactions between processes. 

He uses relationships derived from these data to 

predict the performance of the processes in other 

areas where he can determine the conditions that 

control them. The result is a series of estimates 

ranging from distribution of rainfall and snowfall, 

through the role of energy in the water balance, to 

the flow of water within and out of the forest areas 

under consideration. 

This report updates the knowledge of processes 

that was so well documented by Kittredge (1948) 

in Forest Influences, Geiger (1965) in The Climate 

Near the Ground, and Molchanov (1963) in The 

Hydrological Role of Forests. What have we 

learned in the years since these texts were published? Forest hydrology has operated as before; 

however, our improved understanding and quantification of its processes have provided a better 

basis for deciding how to manage forests for water 

supply and control. 

Three broad groups of interacting hydrologic 

processes are those that affect (a) rainfall, snowfall, fog drip, and condensation; (b) water storage 

and delivery; and (c) energy transfer, especially in 

evaporation. For each process, we present some 

measurement results and their variability and discuss how these affect the management of forests 

for water supply and control. We will describe 

how the hydrologic processes affect each other, 

and the limitations of our ability to measure the 

processes and integrate them into models of 

watershed performance. 

Water Inputs 

Precipitation Measurement 

Water introduced into the hydrologic cycle may 

be as rain, atmospheric moisture, or snow. 

Measurements of this moisture are subject to sizable 

and unknown error - particularly for snowfall, 

misty rain, or fog. Even rainfall may be subject to 

large errors in measurement. Court (1960) wrote: 

"Two identical rain gages 10 feet apart on a windy 

ridgetop can differ consistently in catch by 50 

percent of the smaller." Glander (1966) reported 

average errors of 18 percent and maximum errors 

of 40 percent in measurements of precipitation. 

Variation of precipitation in time and space can 

mislead one in estimating the average precipitation 

for watersheds. These variations are associated 

with different synoptic events in complex ways. 

Riser (cited by Singh 1968) lists six types of events 

that produce precipitation in Illinois: cold front, 

warm front, stationary front, squall line, warm air 

mass, and cold air mass. Singh (1968) pointed out 
that each type of storm can produce different 

streamflow responses from a basin. 

Atmospheric moisture other than precipitation 

can be a direct input of water into forest hydrologic systems. Condensation on snow or vegetation 

surfaces can add significantly to water contributions. (Condensation on vegetation surfaces is 

discussed below under "Interception Processes.") 

In maritime climates the vapor gradient may be 

toward snow surfaces on most nights through the 

year and during much of the winter. In California, 

West (1959) measured as much as 0.07 inch per 

day of moisture condensing on snow. 

Snowfall 

Accurately measuring the distribution of rain is 

difficult, but measuring the distribution of snow 

and the processes that determine it are doubly so. 

We do not know how to measure this input: it 

does not remain stationary, and additions and 

subtractions occur in amounts that surprise us. 

Rarely does snow just fall. It swirls about until it 

finds a surface to rest upon -usually a tree or 

the snow-covered ground. Depending on its path, 

the individual snow crystal may take only a few 

seconds or as much as a few weeks to reach the 

ground; then it may take off again into the 

atmosphere or to a new ground location. 

The term "falling snow" is almost a misnomer; 

Kuz'min (cited by Miller 1964) reported that the 

average angle of falling snowflakes is only 4 

degrees from the horizontal. Wind almost always 

accompanies snowfall in western forests; for 

example, Court (1957) found that in the Sierra 

Nevada only 2 percent of the precipitation fell 

during calm periods. Wind affects measurement 

of interception of rain and snow by trees. 

Interception Processes 

Part of the rain that enters the tree canopy 

adheres to leaves and branches; the tree may 

absorb some of this. The remainder either falls 

directly to the ground or flows along and drips 

from the leaves and branches (called throughfall), 

or it flows down stems to the ground (called 

stemflow). 

The water films and drops held on the foliage 

and other surfaces are subject to evaporation. The 

amount of water that evaporates is called 

"interception loss." Interception loss is actually a 

part of total evapotranspiration, but its distinct 

implications in forest management necessitate 

discussing it separately here. 

When rain falls, it wets the forest soil, but not 

uniformly. For some tree forms, the amount of 

water that drips from the branch margin is one 

and one-half times the average amount that 

reaches the ground under the tree. More than the 

average amount also reaches the ground at the 

stem. Different species perform differently, and a 

single tree may perform differently in different 

storms. A windy storm may shake droplets from 

limbs and foliage and thus promote a more even 

distribution of rain reaching the soil under the 

tree (Grah and Wilson 1944). A misty rain may 

drop most of its water on the windward margins of 

each tree (Kittredge 1948). 

What happens to the rain intercepted by the 

foliage and stems? A few years ago this question 

had a very simple answer -it just evaporated; 

nobody considered complicated energy and mass 

relations. Now, interpretations of interception 

losses vary as widely as the measured amounts. 

Miller (1967) stated that only trivial amounts of 

snow can be lost by interception because there is 

not enough energy for evaporation. Conversely, 

other workers have reported interceptions of as 

much as 5 to 6 inches per year; losses by 

interception have exceeded estimated potential 

evaporation by a factor of 4 or 5 (Rutter 1967, 

Leonard and Eschner 1968, Leyton and Rodda 

1972, Helvey 1967). The interpretation of interception losses has changed over the years. Even 

the process of interception is being questioned. Is 

water absorbed into leaves? Is water transferred 

downward through leaves ultimately to dry soil? 

Does the energy required to evaporate intercepted water reduce the energy available for 

transpiration (Murphy and Knoerr 1975)? What is 

the surface detention of interception? Is it 

represented by the regression constant in Zinke's 

(1967) equation 

Interception = function (storm precipitation) 

In misty rains and clouds, is interception 

negative? 

Unfortunately, evaporative loss is difficult to 

measure (Hoover 1971). It is conventionally 

approximated by exposing several rain gages 

under the forest canopy and one or more gages in 

a nearby opening in the forest. The average 

difference in catch between these exposures 

(usually corrected for stemflow) is an estimate of 

the interception loss. 
Studies of interception by mature hardwoods 

(Helvey and Patric 1965) and by white, shortleaf, 

and loblolly pines (Lawson 1967, Helvey 1967), 

estimated from 1-day rainfall frequencies of 

storms greater than 0.10 inch, have shown an 

annual interception of 4.3 inches by hardwoods, 

or 8 percent of the annual precipitation; and 9.2 to 

12.1 inches for pines, or 17 to 22 percent of the 

precipitation, in South Carolina's Piedmont 

(Swank 1968). When 6-month growing and 

dormant seasons have equal amounts of rainfall, 

about 60 percent of interception on hardwoods 

occurs during the growing season. 

In most of western North America, even where 

snow is the dominant form of precipitation, 

interception losses from rainfall are significant in 

spring, summer, and fall and during an occasional 

rainstorm in winter. Western conifers intercept 

about the same amount of rainfall as some eastern 

pine stands. Interception by old-growth Douglasfir in Oregon in summer averaged 24 percent; 

during the frequent rainy periods of winter 

months it was 14 percent (Rothacher 1963). Price 

(1958) obtained almost identical seasonal values 

(22 and 14 percent) in a dense mixed pine-fir 

stand in central Arizona. During two summers, 

mature lodgepole pine in Colorado intercepted 30 

percent of the rainfall (Wilm and Niederhof 1941). 

In the drier part of the West, more widely 

spaced conifers intercept less preciptation. Ponderosa pine in the southern Sierra Nevada of 

California intercepted 12 percent of annual 

rainfall (Rowe and Colman 1951). In central 

Arizona the discontinuous canopies of alligator 

and Utah junipers intercepted 10 and 17 percent, 

respectively, of the precipitation over a 1-year 

period (Skau 1964). Chaparral in the Sierra 

Nevada and in southern California intercepts from 

5 to 12 percent of annual rainfall (Hamilton and 

Rowe 1949). 

Snow Interception 

The influence of wind on the differential 

deposition of snow in the forest and on the 

transport of snow from tree crowns is readily 

seen. Thus, values for interception that are 

derived by comparing the difference between 

snow accumulation within the forest and in the 

open are known to overestimate the evaporation 

loss of snow held on the canopy (Hoover and Leaf 

1967). 

Differences between maximum snow water 

accumulations in the open and those under 

hardwood and pine stands have been used as 

rough estimates of snow interception; these 

differences suggest that the forest intercepts 

about the same proportion of snowfall as of rain 

(Sartz and Trimble 1956, Hart 1963, Dunford and 

Hiederhof 1944, Rowe and Hendrix 1951). In New 

Hampshire, snow water contents of 5.5 and 5.7 

inches, respectively, were measured in 40-yearold red pine and white pine stands; 7.0 inches in a 

hardwood stand; and 6.8 inches in the open, 

equivalent to an 18 percent interception by pine 

(Hart 1963). In the Adirondacks, maximum snow 

water contents were 9.0 inches under large 

hardwoods and 6.9 inches under red spruce and 

balsam fir, or 23 percent less in the conifers (Lull 

and Rushmore 1960). Bringfelt and Harsmar 

(1974) in Sweden reported an interception loss, in 

a pine stand having about 50 percent canopy 

cover, equivalent to 26 percent of the precipitation 

in the open. 

Mature conifers in western snowpack zones 

intercepted 10 to 30 percent of the snowfall; some 

examples are: 

Interception Reference 

Percent 

Rocky Mountain Area 

Lodgepole pine, 

Colorado 23 Dunford and 

Niederhot 1944 

Ponderosa pine, 

Idaho 

Central Sierra Nevada, 

California 

Ponderosa pine 10 Anderson 1976 

White fir 12 Kittredge 1953 

Red fir 20 Kittredge 1953 

Sugar-Ponderosa 

pine 28 Kittredge 1953 

Interception and Floods 

The forest's initial influence on a flood-producing rainstorm is the amount it intercepts and 

stores in the canopy. This interception is a major 

influence only in light showers; it is most effective 

for brief storms, but its effectiveness dwindles 

rapidly as storm size increases. 
Few data on the interception of flood-producing 

rainstorms are available; very likely interception 

loss in such heavy storms would be little more 

than the 0.2 to 0.4 inch estimated for 2-inch 

storms (Helvey and Patric 1965, Helvey 1967, 

Lawson 1967, Rogerson and Bymes 1968). For 

instance, in the Douglas-fir region on the Pacific 

Coast, interception averaged only 4 percent of the 

rainfall in storms 8 inches or more (Rothacher 

1963). 

Interception loss, of course, reduces the 

amount of flood-producing rainfall that reaches 

the stream; but, as Hoover (1962) noted, "when it 

is remembered that most land areas have some 

type of plant growth similar to tree foliage, which 

intercepts rain, it is doubtful whether canopy 

interception by forests is of significance in 

reducing flood peaks." So much for the interception of rain; condensation of vapor during rainfall 

may be much more important during rain-onsnow storms. 

Variability of Interception 

Interception is a subtraction by trees or other 

vegetation from total precipitation and thus 

reduces the amount of moisture that reaches the 

forest floor. In certain situations trees can also 

trap moisture from saturated airflow. This 

phenomenon, found worldwide, is variously called 

fog drip or negative interception; it may be called 

horizontal precipitation if it is liquid and rime, or 

hoarfrost if it is solid. In the upper-slope forests of 

eastern Washington, for instance, horizontally 

intercepted moisture, forming rime and hoarfrost 

on lodgepole pine, amounts to 0.05 to 0.06 inch 

per day, and accumulates 3 to 4 inches of water 

during a winter (Berndt and Fowler 1969). In 

northern New Mexico, the amount of rime falling 

from an aspen canopy to the snow surface ranged 

from 0.02 to 0.2 inch per storm. The annual 

amount of moisture addition at this high-elevation 

site was estimated to be 1.0 inch (Gary 1972). 

Kittredge (1948, p. 117-118) reported that May to 

October fog drip under a 40-foot big cone spruce 

and 80-foot ponderosa pine, at 5,850 feet 

elevation on Mt. Wilson in southern California, 

was approximately 25 and 38 inches, respectively 

-so that total catches under the trees were 2.11 

to 2.65 times the catches of precipitation gages in 

the open. 

Forested coastal areas particularly may trap 

substantial atmospheric moisture. In Japan, small 

trees were 6 to 10 times more effective than grass 

or bare ground in trapping sea mists (Hori 1953 

and Reynolds 1967). The front surface of the 

forest was about three times as effective as the 

top surface. Also, a tall, open, broad-leaved 

forest, collecting as much as 0.03 inch per hour, 

was almost as efficient as spruce forest. On the 

Oregon coast during a period of 142 days, total 

precipitation was 45 percent greater under a stand 

of Sitka spruce and western hemlock than in the 

open: 36 inches under the trees and 25 inches in 

the open. Describing this study and others, 

Kittredge (1948) concluded that "In regions of 

frequent fogs of fine misty rains . . . fog drip may 

at certain seasons increase the precipitation 

reaching the ground by amounts up to two to 

three times the precipitation in the open." 

Further substantiation came when Ekern (1964) 

reported on a 3-year study of a cloud-swept ridge 

in Hawaii; cloud drip plus rain averaged 130 

inches per year under Norfolk Island pine, 

whereas precipitation in the open averaged only 

50 inches. It is interesting to note that 30 inches of 

the 80-inch increase occurred during rainless 

days. This water was largely saved for irrigation 

use, for little infiltrated into the iron-pan soil in 

this rather unusual case. Fog drip is largely a 

forest-margin phenomenon, but condensation of 

atmospheric moisture on vegetation may be more 

important than has been realized. Condensation 

on snow was discussed earlier. 

In conclusion, there is no question of difference 

in precipitation catch between gages under forest 

canopy and those in protected openings. The soil 

beneath dense canopies generally receives less 

rainfall than the soil in openings, and more snow 

is caught in openings and their margins. This 

redistribution of incoming precipitation is an 

important influence of the forest (Anderson 

1967b, Hoover 1973, Haupt 1973). In snow 

conditions, part of the evaporated water may be 

recondensed on the snow held on foliage, and 

thus increase the melt and drip to snow cover 

beneath; part may similarly be transferred from 

tree to atmosphere to snow cover. In neither 

case does intercepted water become wholly an 

evaporative loss. The amount of evaporative loss 

from precipitation held on the canopy is in 

question. With rain, even the water evaporated 

from foliage is not entirely lost because intercep- 
tion of moisture and subsequent evaporation are 

to some degree in lieu of transpiration. However, 

intercepted water may evaporate at rates much 

higher than transpiration rates. Nor is interception peculiar to trees. A wheat field or a 10-story 

building can intercept as much of the rainfall per 

unit area as a hardwood forest. Interception to 

some degree is a function of being. There would 

have to be exceptions; the hauli Koa of the dry 

side of Hawaii folds its leaves at the first drop of 

rain, presumably to avoid interception. 

Surface Storage 

The term "surface storage" includes temporary storage as surface detention-water 

enroute over the soil surface, water in the forest 

floor or litter, water ponded in depressions in the 

soil surface, and water held in the snowpack. 

Water stored in vegetation is also sometimes 

considered to be in surface storage. 

Trees store little water internally. Mature 

beech and yellow birch on a good site may contain 

7 to 15 thousand gallons per acre in their stems 

and branches at summer's end (Satterlund 1959), 

equivalent to a depth of about 1/4 to 1/2 inch of 

water; and old-growth redwood may contain as 

much as 150,000 gallons, an area-depth of about 

5-1/2 inches.l 

Snowpacks may contribute to surface storage 

both in the frozen phase and as free water. The 

volume and duration of detention depend on such 

conditions as depth of snow, air temperature, 

pore size, and initial free water content (Corps of 

Engineers 1956, Smith and Halverson 1969, and 

Smith 1974). Greatest detention is in the warm 

snowpacks of the Sierra Nevada and the Pacific 

slopes of the northern Rocky Mountains. Some 

water may be detained over winter, only to be 

released when the snow melts. 

Snowmelt detention time is about 5 hours in the 

4-square-mile Castle Creek Basin in the Sierra 

Nevada; measured daily runoff is equivalent to 

about 0.8 inch of water over the whole basin. 

Maximum free water in snowpacks may be as 

much as 18 percent of a 48-inch pack with 29 

Zinke, Paul J., and Peter E. Black. 1964. Soil moisture 

observations around old-growth redwoods. (Paper presented 

before the Hydrology Section of the American Geophysical 

Union, Western Regional Meeting, Seattle, Washington, Dec. 

1964.) 

inches water equivalent; Anderson and others 

(1963a) reported that 5 inches of free water was 

detained in the pack. In a test of simulated rain on 

snow, 10.56 inches of water was applied to a 

66-inch pack of 30 percent density; 8.9 inches of 

the applied water were held by the pack (Smith 

and Halverson 1969). 

Forest cover delays snowmelt by shading and 

thus extends the time that the snow is held in 

surface storage. Conifers with persistent foliage 

naturally delay melt more than deciduous 

hardwoods. In the study of a 3-day rainfallsnowmelt flood in Oregon, Anderson (1969) 

estimated that forest shading reduced the melt 

rate by 40 percent (and flood flow by 10 percent). 

Studies of two California rain-on-snow floods gave 

similar results (Anderson 1970a). 

Though snow under forest cover melts later and 

persists longer than snow in the open, it may melt 

more rapidly once it begins. This happens 

because melting occurs later in the season when 

temperatures may be much higher. A mixture of 

forest and open areas on a watershed may 

promote snowmelt at different times and thus 

reduce streamflow peaks. Topography also desynchronizes melting-snow on southerly aspects 

may disappear before much of the snow melts on 

northerly aspects. 

Surface storage of water generally affects the 

rate of runoff more than the water yield. Surface 

detention is clearly a significant phenomenon in 

the hydrology of snow-zone forests. The paths and 

flow rates of much of this detained water are 

related to energy disposition within the forest 

environment, to soils and to local topography; the 

management of these forests may be effective or 

not, depending on how these paths, rates, and 

amounts of detention are modified. 

Water stored on the surface of the soil 

eventually leaves the surface as overland flow, 

evaporates to the atmosphere, or infiltrates into 

the soil. 

Almost all of the precipitation that reaches the 

ground sooner or later either infiltrates into the 

soil or leaves the surface as overland flow, often 

ambiguously termed surface runoff. The amount 

of overland flow is largely determined by the 

relation between infiltration capacity, storage 

opportunity, and rainfall intensity. Thus those 

forest practices and conditions that severely limit 

the infiltration capacity of the soil increase 

overland flow. 
Infiltration Processes 

Infiltration capacity is the rate at which water 

can enter the soil surface, and is usually specified 

for a particular condition of rainfall or snowmelt, 

soil frost, soil-water content, and wettability. 

How is infiltration capacity measured? A wide 

variety of infiltrometers has been invented; they 

all use either artificial rainfall or surface flooding 

of relatively small areas. In general, their 

determinations serve only as indexes of broad 

differences of surface conditions which may or 

may not affect infiltration processes under natural 

rainfall in forests. Another technique involves 

analysis of hydrographs, in which rapid rises in 

the streamflow hydrograph are assumed to have 

resulted from rainfall rates that exceed infiltration 

capacity. 

East or West, rainfall in the undisturbed forest 

rarely produces overland flow that results solely 

from limited infiltration capacity. Where storage 

capacity remains, the forest floor developed under 

uncut, unburned, and ungrazed forest readily 

absorbs and transmits downward the water from 

even extreme intensities of rainfall. Because of 

the persuasive logic of the infiltration concept of 

streamflow generation, which applies to many 

nonforest areas, even forest hydrologists were 

slow to recognize that overland flow is virtually 

absent from the mature undisturbed forest. 

Realization of this fact grew from reports by 

Hoover and Hursh (1944) for North Carolina 

forests, of Anderson (1962b) for California, 

Rothacher (1965a) for Oregon, Muller (1966) in 

the Allegheny Plateau of New York, Hewlett and 

Hibbert (1967) confirming the North Carolina 

observation, Yevjevich (1968) for Colorado, and 

Tsukamoto (1966a) for Japanese forests. From 

these general conclusions and many specific 

reports, the admonition of Hewlett and Hibbert 

(1967) seems appropriate: "In the case of forest 

land begin with the assumption that all flow is 

subsurface flow until there is evidence otherwise," 

A test in southeastern Alaska provided the 

ultimate demonstration: Over a 30-day period 

more than 400 inches of water was sprinkled over 

a steep brush-covered slope without producing 

overland flow; about two-thirds reached the 

channel as subsurface flow; the remainder was 

lost to deep seepage or evapotranspiration (Patric 

and Swanston 1968). 

Overland flow seldom occurs in the forest even 

during flood-producing rainfall. For instance, 

field examinations following the flood caused by 

Hurricane Diane in August 1955 revealed very 

little overland flow in the Poconos of Pennsylvania 

or in New England. Signs of such flow were found 

only on slopes greater than 50 percent at points 

where, presumably, subsurface flow intersected 

the surfacee3 Of course, local areas have 

overland flow, produced chiefly by roads, skid 

trails, rocky areas, and many small areas where 

infiltration is impaired. 

Infiltration capacities of forest land not only 

exceed rainfall intensities; they may, for example, 

also absorb overland flow from adjacent natural 

rock outcrops, agricultural lands, and roads. In 

the driftless area of southern Wisconsin, most 

overland flow from open fields on ridges 

infiltrates into the forest slopes below and does 

not reach the valley. Over a 4-year period, 187 

storm runoffs of 10 cubic feet or more were 

measured at gages above forest boundary; only 18 

of these runoff volumes were recorded by gages in 

the valley below the forest. Overland flow from 

the upland fields infiltrated into the forest floor 

and seeped into valley bottoms (Curtis 1966). 

Packer's (1967a) study of the ability of the forest 

floor to absorb runoff from roads showed that the 

width of the protection strip required to keep 

runoff and sediment out of streamflow depends on 

several soil, cover, and topographic factors. 

There are sure to be exceptions to any 

generalization in forest hydrology. Overland flow 

may occur in the forest under some special 

conditions. Recent research in Nevada, California, and Arizona has shown that sometimes 

there is a nonwettable soil layer 112 to 1 inch 

below the surface, formed by decomposition of 

organic matter (DeBano and others 1967, Cory 

and Morris 1968, Scholl 1975). Forest fire may 

cause the development or intensification of such a 

layer. Although the phenomenon has been 

observed during small-scale tests when water was 

artificially applied to undisturbed forest soils 

under red fir, its extent and importance in 

unburned soils have not been demonstrated 

because once wetted, these same soils showed 

Varney, G. L. 1955. Some aspects of forest land behavior 

during the floods of August 1955. (Report on file, Northeast. 

For. Exp. Stn., Upper Darby, Pa.) 
high infiltration rates. Nonwettability of burned 

areas is discussed later. 

There are occasional reports of overland flow 

across a shingle-like cover of hardwood litter 

(Pierce 1967, Hoover 1962). This is a local 

phenomenon, and the flow infiltrates the soil 

within a short distance. Whipkey (1969) observed 

several such overland flows in a hardwood forest 

where simulated rainfall was applied at intensities 

of 5 to 30 inches per hour for periods of 60 to 150 

minutes. 

Evidence of apparent overland flow, such as 

small piles of leaves and twigs, and even exposure 

of the mineral soil, can often be noted in smaller 

draws or the drainageways between microndges. 

Closer obsewation usually shows that water 

infiltrated the upper slope and reappeared 

downslope or in the draw. This happens not 

because of limited infiltration capacity but 

because of limited capacity for storage and 

percolation and channel expansion; no amount of 

improvement in infiltration capacity at the point 

where the rain fell will mend it. Subsurface 

storage and detention become the dominant 

hydrologic processes. 

Watershed Storage 

The storage capabilities of a watershed largely 

determine what proportion of a flood-producing 

rainfall will reach any damage point downstream 

and at what rate. In its broadest sense, storage 

includes all aspects of retention and detention: 

interception; surface storage on the soil; storage 

in the vegetation, soil, and underlying rock; and 

storage in the channel. Interception and surface 

storage have already been discussed; detailed 

discussion of channel storage is beyond the scope 

of this report. 

Soil-water storage accounts for the water from 

the time it infiltrates the soil until it leaves to go to 

groundwater, to streamflow or other surface 

water, or to the atmosphere by evaporation 

from the soil surface or transpiration from foliage. 

Storage is of two types, detention and 

retention. These are relative terms, detention 

denoting that moisture in the soil is detained only 

temporarily as it makes its way towards groundwater or streamflow, retention being that water 

retained, against gravitational forces, and later 

discharged to the atmosphere. Substitution and 

exchange, which occur among all comp'onents of 

storage and delivery, impose problems of 

measurement. 

Measurements of soil water range from laboratory 

analysis of soil samples: through such 

physical indicators of field water content as 

resistance, capacitance, and "adsorption" of 

neutrons, to inference of soil water from 

hydrograph analysis. Tracing with chemicals and 

tritium has added some information about the 

paths and rates of flow within the soil. 

Detention storage, drained by gravity, and 

retention storage, held against gravity, have often 

been equated to the amounts greater and less 

than field capacity, respectively. Field capacity 

has been defined as the amount of water held in a 

soil after excess gravitational water has drained 

away and after the downward movement has 

materially decreased (Veihmeyer and Hendrickson 1931). More than 25 years ago, Edlefson and 

Bodman (1941) reported that the simple drainage 

of soillwater to moisture contents less than 

normal field capacity was an important source of 

long-term discharge of water. More recently, 

Hewlett (1961) and others have demonstrated that 

slow drainage of soil moisture in the range of field 

capacity may be the source of a large proportion of 

the base flow of headwater streams. 

Forest soils are generally less dense than similar 

soils not covered by forest and may have greater 

capacity for detention but less capacity for retention. Thus, for Coastal Plain soils of Mississippi 

the drainage capacity (total pore volume minus 

volume held at 113 atmosphere tension) for surface 

forest soils has been found to average 35 percent 

by volume, contrasted to 20 percent for old fields 

and pastures. Retention capacities (difference in 

volume between the amounts held at 113 and at 15 

atmospheres of tension) averaged 14 percent for 

surface soils of the forest and 17 and 14 percent 

for old-field and pasture soils (Broadfoot and 

Burke 1958). In forest soils, the density, the retention capacity, and the total volume of stored 

water are highly affected by the amount of 

In laboratory tests of soil, water held against gravitational 

forces (retention capacity) is taken as the amount held against 

a tension of 113 atmosphere. Water held too tightly for extraction by transpirational forces ,is taken as the amount held 

against a tension of 15 atmospheres. Maximum storage is taken 

as the water content when all pores are occupied. Detention 

storage capacity is taken as the water content when all pores 

are occupied. Detention storage capacity is taken as the 

difference between maximum storage and retention capacity. 
Table 1-Representative soil depths of forested watersheds 

1 Watershed location Soil depth 

and reference Subsoil 

weathering1 

1 Feet Feet 

(1) Northern United States -

(2) Mid-South United States -

(3) N. Sierra Nevada, Calif. To 70 ft 

(4) Northern Coast, Calif. Yes 

(5) Hubbard Brook, N.H. -

(6) Fernow, W. Va. -

(7) Coweeta, N.C. -

(8) H. L. Andrews Exp. Forest, Yes Oreg. 

(9) San Dimas Exp. Forest, Yes Calif. 

(10) Fraser, Colo. 1 It02 - To 14 ft 

(1 1) Central Sierra Nevada, 1 to 9+ Calif. 

'Dash indicates no data available; "yes" 

variable. 

(1) U.S. Dep. Agric. 1952 

(2) Zahner 1956 

(3) Ziemer 1968 

(4) Gardner 1958 

(5) U.S. Dep. Agric. 

Forest Serv. 1964b 

organic matter in the soil. Additions of from 1.2 

to 10 percent of organic matter have increased 

the amount of water retained in clay soils by 34 

percent, in fine sand by 150 percent, and coarse 

sand by 780 percent (Feustel and Byers 1936). 

Coile (1938) found similar increases. Organic 

matter decreases soil density, and therefore has a 

direct effect on soil depth. 

Depth of forest soils throughout the country 

varies widely but generally ranges between 2 and 8 

feet. Some reported soil depths to parent material, 

or to impermeable layers, are summarized in 

table 1. The mid-South and the Pacific Northwest 

have deeper forest soils. For the upland pine 

forests of the mid-South, Zahner (1956) considered 

the upper 6 feet of surface soil to be the effective 

root zone. In deep soils and under intense climatic 

stress rooting is deeper. At 2900 feet elevation in 

the Sierra Nevada, Ziemer (1968) found summer 

depletion under pine to depths greater than 15 feet. 

In the redwood-Douglas-fir region of northern 

California, soils as deep as 4 to 5 feet rest on 

weathered, shattered, water-holding parent materials 

indicates weathering occurs but depth is 

(6) Reinhart and others 1963 

(7) U.S. Dep. Agric. Forest Serv. 1957 

(8) Rothacher and others 1967 

(9) Rowe 1963 

(10) Love and Goodell 1960 

(1 1) Anderson and Richards 1961 

(Gardner 1958) which may furnish water to the 

trees during periods of soil moisture stress. 

The maximum opportunity for soil-water storage 

that the forest can generate at any one point is 

essentially the difference between field maximum 

and field minimum moisture contents throughout 

the rooting depth. Several of these maximums, 

derived from soil-water studies, are given in 

table 2. They range from 2 to 23 inches and, 

according to soil texture, from 1 to nearly 4 inches 

per foot of depth. The maximum soil-water 

depletion measured (Ziemer 1968) was 22.6 inches 

for an isolated pine in the Sierra Nevada. 

Retention storage capacity varies greatly, 

especially with soil depth and texture. Although 

many forest soils are often classified as shallow 

(from 5 or 10 to 20 or 30 inches deep), they can 

retain several inches of water after prolonged 

drying. However, when flood rainfall occurs, the 

first extraction from rainfall at any one point 

depends not so much upon the capacity as upon 

the amount of drying since the last significant 

rainfall, i.e., the retention opportunity. 
A watershed's maximum opportunity for soilwater retention can be estimated from the difference between storm rainfall following a prolonged 

drying period, and storm discharge. Estimates 

differ widely between Eastern and Western watersheds. Some characteristic values are: 

Maximum 

storage Conditwn Reference opportuni@ 

Location: Inches 

Northeast 4.0-4.5 During major 

storms Hoytand 

Langbein 

(1955) 

East 1.5-2.5 During major 

storms Hoyt (1942) 

4.0-5.5 After long 

drying Reinhart 

(1 Wa) 

N. Sierra Nevada 20 After summer 

drying Anderson 

(1963) 

8 After midwinter drying Anderson 

(1963) 

San Gabriel Mts., 

Calif. . 22 After long 

drying Rowe' 

Opportunity for retention storage varies seasonally in the East. When the soil has been 

recharged by autumn rainfall after the growing 

season, retention opportunity is at a minimum 

until spring. Frequent rainfall during the growing 

season in the East can severely limit the retention 

opportunity for flood rainfall. For example, estimates of maximum retention opportunities on the 

Fernow Experimental Forest in West Virginia 

were based on daily water-budget estimates over 

11 growing seasons (April-N~vember).~ Even in 

the dryest season (1957), for the 10-inch retention 

capacity, opportunity was more than 2 inches on 

only 61 days of the 244-day season; the mean for 

the season was 1.3 inches. The mean retention 

opportunity in 1956 (a wetter season) was only 

0.25 inches. 

' Rowe, Percy B. 1955. Rainfall disposition by hydrologic 

years 1938-39 through 1952-53, Volfe Canyon, Watershed IX, 

San Dimas Experimental Forest. (Unpublished report on file, 

Pacific Southwest Forest and Range Exp. Stn., Berkeley, 

Calif.) 

Unpublished report, Northeast. Forest Exp. Stn., Parsons, 

West Virginia. 

Table 2-Maximum soil-water storage under selected forest 

stands 

Location and forest cover 

Feet Inches 

(1) New Jersey Coastal Plain 

Shortleaf pine 10 8 

(2) Southeastern Ohio 

Oak 3.3 7 to 9 

(3) Western North Carolina 

Appalachian hardwoods 7 11 

(4) Piedmont of South Carolina 

Loblolly pine 5 -5 5 

Loblolly pine-hardwood 5-5 9 

(5) Missouri 

Oak-hickory 3.3 9 

(6) Southern Arkansas 

Southern red and post 

oaks, sweetgum; 

loblolly and 

shortleaf pines 4 12 

(7) Texas 

Post and blackjack oaks 2 5 

(8) Cascades, Oregon 

Douglas-fu, western 

hemlock 2 to 6 2 to 23 

(9) Central Sierra Nevada, Calif. 

Red fir (subalpine) 4 to 10 8 to 16 

(10) Southern Sierra Nevada, Calif. 

Woodland chaparral 3 7 

Ponderosa pine 6 11 

(1 1) San Dimas, Calif. 

Mixed chaparral 5 11 

Compiled as follows: 

(1) ~ull and Axley 1958 (7) Koshi 1959 

(2) Gasier 1952 (8) Rothacher and 

(3) Helvey and Hewlett 1959 others 1967 

(4) Metz and Douglass 1959 (9) Knoerr 1960 

(5) Lull and Fletcher 1962 (10) Rowe and Goldman 1951 

(6) Moyle and Zahner 1954 (11) Rowe and Colman 195 1 

Farther south on deeper soils, opportunities for 

storage are much greater. In the Piedmont of 

South Carolina, for instance, daily soil-water 

measurements for 3 years under a 50-year-old 

shortleaf pine-hardwood stand (Metz and Douglass 1959) recorded median storage opportunity 

for two soil-water seasons: January to April, 

about 2 inches and May to December, about 6 

inches. 

In major river basins on the west side of the 

Sierra, the soil-water deficit in the fall has been 

estimated to range from 4 to 10 inches. Rock 

storage varies from negligible amounts in granite 

batholith to 45 inches or more in highly fractured 

igneous rock and unconsolidated alluviums 

(Anderson 1962b). The retention for whole large 
watersheds has exceeded 20 inches in early winter 

storms and 8 inches in succeeding midwinter floodproducing storms (Anderson 1%3). When compared 

with the yearly evapotranspiration loss (Rothacher 

and others 1967)* data from Dyrness (1969) on the 

maximum storage opportunity at the end of 

summer in the H.J. Andrews Experimental Forest 

indicate that the opportunity must be restored 

several times during the year to account for a loss 

of as much as 33 inches. 

These measurements of retention storage 

opportunity and recovery of retention capacity* 

in one case in the middle of winter and in the 

other case repeatedly throughout the year* cast 

some doubt on the validity of the simple concept 

of maximum retention storage in these watersheds. 

This concept is the familiar single linear reservoir 

with a single spillway whose discharge is proportional to the storage; however* Sugawara (1967) 

showed that multiple reservoirs in series and 

parallel* with complex outlets to each other* are 

necessary to simulate streamflow hydrographs; 

equally complex analogues may be needed to explain 

adequately the performance of forests in flood 

prevention and streamflow yield generally. Thus* 

maximum retention storage may never be achieved 

in some of these watersheds* for some areas may 

always have retention capacity that does not 

become full because of the lack of input water or 

because of input channels which require heads of 

longer duration. On some watersheds* nearmaximum retention opportunity may be achieved 

only after a long drought; on others* only when 

water is available for percolation throughout the 

year will some of this excess retention storage be 

filled. The nature of these multiple reservoirs and 

their different input and output channels controls 

storage and its product* subsurface flow. 

Subsurface Flow 

Subsurface movement of. detained water on 

forested slopes has been widely studied in recent 

yeari* yet we still know little about its rates of 

movement. Water entering the surface soil sometimes flows downward until it reaches a layer of 

different texture. Then it flows downhill along 

this interface until it finds opportunity for further 

penetration. Such lateral flow has been measured 

and described by Whipkey (1%9)* McDonald 

(1967)* Minshall and Jamison (1965)* and Smith 

(1972). At other times the flow is simple drainage 

from the lower slope reaches* such as Hewlett 

and Hibbert (1967) reported* rather than flow 

occumng at the top of the B horizon or at a 

layer of finer soil texture. Ragan7s analysis (1968) 

showed that only a small area of the forested 

watershed he studied contributed flow to the storm 

hydrograph. The contributing area* a function of 

storm duration and intensity* was not uniformly 

distributed along the channel* but was localized in 

only a few zones. This subsurface drainage* together with rainfall on saturated soils and on 

water surfaces* accounted for the occasional very 

high floodflows discharged from upland forest 

watersheds in the absence of widespread appreciable 

overland flow. Martinec (1975)* from a study of 

the tritium content of subsurface flow* concluded 

that this flow included some water that had been 

in subsurface storage for several years. 

Despite the considerable progress in both the 

conceptual and the experimental studies of subsurface flow* the rates of flow and the spatial 

distribution of the flow paths are basically unmeasureable. Techniques measuring these flows 

must be developed because knowledge of these 

rates and distributions are crucial to understanding 

and predicting water use by vegetation* zones of 

saturation and soil instability* and the potential 

of parts of any watershed to generate flood peak 

flows. 

Peak Flows 

Subsurface flow in the forest can produce 

substantial peak flows in streams. Thus* completely 

or partly forested watersheds have produced floods 

periodically (table 3). Hursh (1943) reported a peak 

of 167 am (ft3/s/mi2) from a small* forested* highelevation watershed in western North Carolina 

during a low-intensity storm in which infiltration 

was not limiting. In New Hampshire* in October 

1959* peak discharges from two well-forested 

watersheds of 105 and 39 acres were 451 and 462 

csm respectivelyy during a 7-inch storm; maximum 

measured 1-hour rainfall was just over 1 inch.' 

Storm flows* calculated by the procedure of 

Hewlett and Hibbert (1967)* were 76 percent of 

rainfall for the larger watershed and 85 percent 

for the smaller. From much larger watersheds 

(45 to 143 square miles) peak flows of 126 to 

' Storm peaks and storm damage of October 23-25, 1959, 

Hubbard Brook Experimental Forest and White Mountain 

National Forest, New s amp shire. (Report on file at Northeast. 

For. Exp. Stn., Durham, N.H.) 
Table 3-Record peak flows and percentage of forest cover for watersheds approximating 25, 100, 500, and 1000 square miles 

Stream Station I Drainage Peak Forest area I flow I cover 

Mi2 Ft^/s/mi2 Percent 

North Atlantic Slope Drainage 

Ellis River Jackson, N.H. 28 529 100 

Rondout Creek Lackawack, N.Y. 100 267 80 

Rapidan River Culpepper, Va. 465 125 5 3 

N. Branch Potomac River Cumberland, Md. 875 102 82 

South Atlantic and Western Gulf of Mexico Drainage 

Morgan Creek Chapel Hill, N.C. 27 1110 61 

Henry Fork Henry River, N.C. 80 391 88 

Yadkin River Wilkesboro, N.C. 493 324 90 

Rocky River Norwood, N.C. 1370 113 55 

Ohio River Basin 

Elk Creek Elk Park, N.C. 42 655 67 

Watauga River Sugar Grove, N.C. 91 560 6 2 

Watauga River Butler, Tenn. 427 168 64 

Cheat River Rowlesburg, W. Va. 972 129 87 

Pacific Slope Basins in California 

San Antonio Creek Claremont, Calif. 17 1267 6 3 

W. Fork San Gabriel River Camp Ricon, Calif. 102 334 100 

Los Angeles River Los Angeles, 

Calif. 512 131 28 

N. Fork American River Rattlesnake Branch, 

Calif. 999 95 90 

Pacific Slope Basins in Washington and Upper Columbia Basin 

N. Fork Skokomish River Hoodsport, Wash. 60 388 75 

Wynooche River Montesano, Wash. 105 238 90 

Skykomish River Gold Bar, Wash. 5 35 148 78 

Sauk River Sauk, Wash. 7 14 96 77 

Source: Linsley and others 1949 

more than 300 csm were registered. Corbett and days, 1.9 inches in 6 hours) on a 237-acre waterothers (1975) studied flow from a 20-acre water- shed of Douglas-fir and western hemlock produced 

shed in Pennsylvania where artificial rainfall was a peak of 139 ft3/s/mi2 (Rothacher and others 

applied to three areas: ridge, midslope, and near- 1967). This peak runoff is the equivalent of only 

channel. Quickflow dominated the flow regime, 0.22 inch per hour, about two-thirds of the 

being 65 to 85 percent of the total flow, irrespective average rainfall rate of 0.32 inch per hour in the 

of the part of the watershed to which the simulated 6-hour period. The modifying influence of the 

rainfall was applied. forested watershed on flood peaks from small 

Subsurface flow from low-intensity, long- experimental watersheds was strikingly illustrated 

duration rainstorms in Oregon may have maximum in the storm that produced the Rapid City flood 

rates of runoff that are as much as 80 percent on June 9, 1972. Although prior rainfall was 

of the average rate of measured rainfall for the "apparently enough to fill available soil storage 

preceding 12 to 24 hours. For shorter durations, capacity and cause flow to respond almost immedithe maximum rainstorm of record (12.5 inches in 3 ately" to the additional high-intensity rain of 2.12 
to 3.25 inches in 1 hour (Orr 1973), the records 

show that maximum hourly flow never exceeded 

about 15 percent of the maximum hourly rain. 

Tsukamoto's study (1975) of the role of forest 

floor litter in reducing peak flows showed that 

removal of litter increased peak flows from storms 

of less than 4 inches by 168 percent. 

However, a high-elevation, steep, completely 

forested watershed without appreciable overland 

flow may produce greater volumes of stormflow 

per unit rainfall than many pastures and cultivated 

areas at lower elevations (Hewlett and Hibbert 

1967). In the Northeast, generally, the greater the 

proportion of watershed that is forested, the 

greater the streamflow (Lull and Sopper 1967). 

These high flows, and the others tabulated above, 

do not show a negative "forest influence" but 

rather the integrated influence of the forest-occupied 

environment -with steeper topography, shallower 

soils, and more rain. 

Erosion and sedimentation are discussed in 

detail elsewhere in this report. We must recognize 

here, however, that transported sediment stemming 

from erosion bulks flood flows and may increase 

flood stages. Even more important is the fact that 

deposits of sediment in stream channels reduce the 

carrying capacity and increase the frequency and 

severity of overbank flooding. Dirty flood water 

is more damaging than relatively clean water, and 

sediment left by a flood can cause a substantial 

part of its total damage. It follows, then, that as 

forest cover inhibits erosion, it significantly contributes to preventing flood damage. 

Evapotranspiration creates storage opportunity 

in the soil so may affect floods and soil and slope 

stability, but also withdraws potential water supply. 

Evapotranspiration 

Evapotranspiration from the forest is powered 

by solar energy. It includes the evaporation of rain 

and snow intercepted by the canopy, the vaporizing 

of water that reaches the leaf surface in the transpiration, and the evaporation of moisture from 

bare areas, the wetted forest floor, or snow cover. 

Transpiration 

Transpiration accounts for most of the vaporization from the forest-perhaps 80 percent in 

hardwoods and 60 percent in conifers. The remainder is evaporation from rainfall and snowfall 

intercepted in the canopy, from snow and wet 

litter on the forest floor, and from the soil 

beneath. Transpiration is difficult to measure and 

is most often estimated indirectly from the difference between precipitation and streamflow during 

selected time periods, or estimated from a water 

budget developed from periodic measurements of 

soil water and precipitation, or estimated from 

aerodynamic or energy budgets. 

Radiant energy is primarily responsible for 

evapotranspiration. The energy used is drawn 

from net radiation, which is the difference between 

incoming and outgoing solar and thermal radiations. 

Net radiation energy is used to heat air, soil, 

water, and vegetation; it is also used in photosynthesis, respiration, and evapotranspiration. By 

far the greatest portion of the energy is used in 

evapotranspiration and in heating the air. Evapotranspiration from thoroughly wetted forest soil 

is limited by the energy supply; during soil 

drought and high climatic stress evapotranspiration 

is primarily limited by the water supply, but the 

trees exercise some physiological control (Lee 1967). 

Powered by radiant energy and dependent on 

available moisture, forest evapotranspiration tends 

to be greatest in warm and wet climates and least 

in cold, dry ones. This is indicated in the several 

comparisons of potential evapotranspiration 

(Thornthwaite and Mather 1957) for points 

centrally located in major forest types (table 4 and 

fig. 3).' The longleaf-slash location, the warmest, 

has the greatest potential; the lodgepole pine 

location, the coldest, has the least potential; and 

the more humid the climate, the more likely it is 

that actual evapotranspiration will approach the 

potential. Similar average potentials are a feature 

of such diversely located types as spruce-fir in 

Maine (21 inches) and ponderosa pine in Arizona 

(23 inches), of maple-birch-beech in New York (26 

inches) and redwood in California (25 inches). 

Slope and aspect combinations markedly affect 

the amount of solar radiation received on any 

given area and thus markedly affect evapotranspiration. In studying these relationships, Lee (1964), 

describing watersheds in terms of their average 

exposure and potential insolation, found strong 

negative correlation between the radiation indexes 

and annual streamflow from adjacent basins. He 

Potential evapotranspiration is an estimate of maximum 

possible evapotranspiration, the evapotranspiration that would 

occur if water were fully available. 
Maple-birch- beech 

Jamestown, N.Y. 

Loblolly - shortleaf pine 8 - Athens, Go. 

....... 
 - .....a. -

2 - ..... -

4 

w

O . i 1 i 1 I 1 1 1 , , , 

:.A

l 4 1 ~ ~ ~ ~ ~ ~ ~ ~ (U - -c Douglas-fir Lodgepole pine 

.

532 -... Canary, Ore. Maran, Wyo. -

10 - ........ 
 -

8 -

-

6 -

-

4 2 - .-.1 ~ 1

- .......... 
 01 1 1 i 1 1 1 t 1 I 1 i 

Redwood 

Month 

\ .............Precipitation -Potential evapotranspiration 

Month 

Figure 3-Mean annual potential evapotranspiration and precipitation at points 

centrally located in some major forest types. 

Table 4-Mean annual potential evapotranspiration, precipitation, and air temperature at 

points centrally located in selected major forest types 

Potential Air 

Forest type Location evapo- Precipitation temperature 

transpiration 

I Inches Inches OF 

Longleaf-slash pine Lake City, Fla. 

Loblolly-shortleaf pine Athens, Ga. 

Maple-birch-beech Jamestown, N.Y. 

Douglas-fir Canary, Oreg. 

Redwood Eureka, Calif. 

Red fir Teakettle, Calif. 

Ponderosa pine Williams, Ariz. 

Spruce-fir Greenville, Maine 

Lodgepole pine Moran, Wyo. 
assumed these differences to be attributable to 

differences in evapotranspiration. Because of differences in the energy they receive, slopes and 

aspects differ markedly in potential evapotranspiration. In southern Missouri, for instance, where 

the soil-water storage capacity is 10 inches, the 

calculated moisture deficit on a horizontal surface 

for a normal year was 3.9 inches; a 40O north 

slope had a deficit of 1.9 inches, and a 40' southwest slope had a deficit of 5.9 inches (Nash 1963). 

These studies did not consider the influence of 

advected energy. In attempting to use space- and 

time-integrated air temperatures, Chang and Lee 

(1969) used chemical sensors to integrate temperature with soil information and seasonal responses 

of plants. They believed that using this technique 

enabled them to prepare better estimates of 

water balance. 

The amount of water evapotranspired from 

mature forests also depends on the amount of 

moisture available in the soil, which in turn is 

largely a function of soil texture and depth, and, 

of course, climate. With some exceptions (Anderson and Gleason 1960, Ziemer 1968, Rothacher 

and others 1967) the upland forest, regardless of 

type, receives sufficient radiant energy during the 

growing season to deplete most if not all of the 

available moisture. For example, in Arkansas 

(Moyle and Zahner 1954), South Carolina (Metz 

and Douglass 1959), Michigan (Urie 1959), and 

Colorado (Brown and Thompson 1965), the 

amounts of soil water withdrawn under conifers 

and hardwoods during the growing season were 

very similar, almost equally depleting moisture. 

Annual evaporative losses from white pine stands 

at Coweeta were greater than from hardwoods 

(Helvey 1967). This was ascribed to greater interception by the persistent foliage of the pine and 

not solely to greater depletion of soil water. The 

differences in the many phenological characteristics 

of individual tree species as they influence water 

use are as yet little known. 

To some degree the trees themselves control 

transpiration-by controlling water loss through 

the stomates, which cover from 1 to 3 percent of 

the leaf surface. With an average density of 100 to 

300 stomates per square millimeter, this loss can 

approach the rates of evaporation from free water 

(Slavik 1965). Opening and closing of stomates are 

controlled primarily by the water content of the 

leaf, but increases in light and rising temperatures 

also stimulate opening. The rates of water loss at 

specific stomatal openings are not constant but 

depend on atmospheric conditions. Lee (1967) 

suggested that careful study of the microstructure 

of leaf types and of their abilities to control 

transpiration seasonally would provide a rational 

basis for managing vegetation to increase water 

yield. Other investigators are far less optimistic 

(Idso 1968, Van Bavel1968). 

One influence on the stomatal mechanism is the 

available energy, which is determined in part by 

such forest characteristics as color, size, phenology, 

and vigor. The darker the forest, the lower its 

albedo; i.e., less of the incoming solar radiation is 

reflected. For example, summer albedos for birchmaple and white pine stands in New Hampshire 

were 0.17 and 0.14, respectively (Federer 1968); 

the pine had 3.6 percent more energy available 

for evapotranspiration. According to one estimate, 

darkening of the foliage by wetting can reduce 

albedo by 40 percent (Goodell 1967, citing Scholte 

Ubing). Stands having taller trees usually capture 

more radiant energy and have a lower albedo. 

Phenological differences are another factor: in 

Michigan, for instance, red pine stands rapidly 

deplete moisture in April and May, whereas 

hardwood stands do not begin until June, when 

their leaves are fully developed (Urie 1959). Finally, 

there is some evidence that the stage of growth 

influences water use. Black (1967) found that 

second-growth redwood stands depleted soil moisture more rapidly than old-growth stands, and 

Knoerr earlier (1960) reported that young red fir 

depleted soil moisture more than older stands. 

Kittredge (1948) showed that trees reach the 

culmination of their growth rate and their maximum 

leaf surface in fully stocked stands at between 15 

and 60 years, and that transpiration is related to 

area of foliage. 

Though we are accustomed to thinking that 

growing and dormant seasons control transpiration, 

even in some temperature climates-e.g., along 

the Pacific Coast-a true dormant season may 

not exist. Even when snow is on the ground, 

daytime air temperatures may reach 55 OF; tests of 

water transport through the trunks of pines, using 

heat pulse velocity and radioactive tracers, have 

indicated that sizable quantities of water are 

transpired during winter, spring, and early 

summer (Swanson 1967, Smith 1972). Such use 

may help explain why evapotranspiration in 

Douglas-fir forests (Rothacher and others 1967) is 

three to four times the maximum depletion of 

retention storage reported by Dyrness (1969), and 

may explain how 8 inches of soil moisture deficit 
could have been created in winter in the Sierra 

Nevada (Anderson 1963). 

Evaporation 

Evaporation from the forest floor or from snow 

surfaces can add significantly to transpiration as 

an evaporative loss at some places. Evaporative 

losses from the forest floor vary greatly. Aldon 

(1968) reported losses amounting to as much as 

1.09 inches of moisture during a 30-day period of 

summer thunderstorms. Similarly, Rowe (1955) 

reported that about 0.1 inch of water was stored 

per inch depth of forest litter. In a 4-year period 

when annual precipitation averaged 49 inches, the 

water evaporated from the forest floor ranged 

from 3.0 to 5.2 percent of the precipitation for 

floor depths of 1 inch to 3.6 inches. Litter on the 

forest floor may range from negligible amounts 

to more than 20 tons of oven-dry material per acre 

(Kittredge 1948). The loss from 1inch of litter was 

about 15 times the storage capacity; from 3.6 

inches it was about 7 times the storage capacity. 

Total replenishable storage deficit was greater for 

bare soil than for soil covered by 1-1/4 inches of 

pine litter; the bare soil lost 10.7 inches of water 

per year by evaporation; soils covered by 1/2 inch 

or more of litter lost about 7 inches (Rowe 1955). 

In the Appalachians, evaporation of moisture 

from litter of hardwoods and white pine is only 

about 2 inches (Helvey and Patric 1965, Helvey 

1967). 

Evaporation of snow under the. canopy can be 

slow: in a 3-year study, annual evaporation from 

January to as late as June under a dense 

lodgepole pine-red fir stand in the central Sierra 

Nevada amounted to only 0.4 to 1 inch of water 

(West 1962). In the southern Sierra Nevada, the 

3-year average annual evaporation from snow was 

zero within the red fir forest, 0.5 inch in small 

forest openings, and 1.8 inches in large open 

areas (Anderson and Richards 1961). Intercepted 

snow in trees may evaporate as much as three 

times faster than snow on the ground because of 

the much lower albedo of the snow-foliage 

moisture (Leonard and Eschner 1968). 

Water Yield 

The water yield of an area is that part of 

precipitation that is not used on the watershed. 

Water used by the forest is derived from the 

combination of dormant season precipitation, soil 

water stored during the dormant season, plus 

summer rainfall. The minimum annual requirement of moisture for forest growth is about 20 

inches of precipitation; from this the forest 

,transpires about 15 inches. In the precipitationevapotranspiration-water yield relationship, 

evapotranspiration is the most nearly constant 

element; each year it subtracts what the forest 

"needs" from total precipitation, which is 

variable. The residue, water yield, is the most 

variable element in the cycle; it includes both 

streamflow and groundwater recharge. 

Groundwater 

Water that seeps through the soil mantle and 

adjacent rock strata may move directly to a stream 

or into a groundwater aquifer. Most of the water 

that goes into aquifer storage eventually turns up 

as streamflow (though perhaps below the point 

where a particular watershed is gaged) or is 

utilized from wells. 

Most research on small watersheds has 

necessarily been conducted in areas where the 

true groundwater component is relatively small. 

However, several European studies show the 

effects of forests on groundwater. In one study, 

clearcutting a stand that had 100 mY ha of pine 

caused the water level to rise as much as 40 cm 

(16 inches) (Heikurainen 1967). Thinning also 

raises the water level; the amount of rise 

depended upon the intensity of thinning. 

Mustonen and Seuna (1971) reported increased 

streamflow of 0.9 inch per year from peatlands 

after clearcutting of trees. 

Streamflow 

Average annual streamflow from major forest 

regions varies throughout the country from 5 to 50 

inches, and monthly amounts vary from near zero 

to 25 percent of the annual total. Records of 

annual and monthly streamflows from eight 

forested experimental watersheds show some 

important characteristics (table 5 and fig. 4). 

Differences in streamflow result mostly from the 

climatic differences among major forest regions. 

Maximum annual precipitation of 94 inches is 

about 4 times the minimum value, which is 22 

inches; streamflow, as would be expected, varies 

more-from 61 to 2 inches; so the ratio of the 

maximum to the minimum is more than 30. 
Table 5-Mean annual precipitation and streamflow for selected forested watersheds 

Precipitation 

Location Forest cover 1 Area 1 elevation 1 Precipitation Streamflow 1 1 less

Acres 

Hubbard Brook Exp. Forest Northern hardwoods 105 

West Thornton, N.H. 

(Watershed 3) 

Fernow Exp. Forest Central Appalachian 

Parsons, W. Va. hardwoods 96 

(Watershed 4) 

Coweeta Hydrologic Lab. Southern Appalchian 

Franklin, N.C. hardwoods 31 

(Watershed 18) 

Marcel1 Exp. Forest Bog black spruce 24 

Grand Rapids, Minn. 

(Watershed S-2) 

Fraser Exp. Forest Lodgepole pine, 

Fraser, Colo. spruce-fir 714 

(Fool Creek) 

Sierra Ancha Exp. Forest Ponderosa pineAriz. (Middle Fork) white fir 521 

Three Bar Exp. Watersheds Chaparral 80 

Ariz. (Watershed D) 

H. L. Andrews Exp. Forest 149 

Blue River, Oreg. 

(Watershed 2) 

Fifty to 65 percent of precipitation appears as 

streamflow in northern hardwoods, Appalachian 

hardwoods, lodgepole pine-spruce-fir, and 

Douglas-fir; slightly more than 20 percent in bog 

black spruce in Minnesota, and less than 10 

percent in ponderosa pine-white fir and chapparral in Arizona (table 5). 

Monthly precipitation and corresponding 

montly streamflow differ widely among regions 

(fig. 4). The West and Southwest show the 

greatest seasonal variations. Streamflow from 

rainfall and snowmelt exceeds monthly precipitation in northern hardwopds during April, and in 

lodgepole pine-spruce-fir during June. Uniform 

winter streamflow in the lodgepole pine-sprucefir, bog black spruce, and ponderosa pine-white 

fir types attests to cold winters with little 

snowmelt; in the chaparral, low streamflow is due 

to low monthly precipitation. The Appalachian hardwoods produce high winter and spring 

flows, mostly from rainfall, followed by greatly 

streamflow 

Feet Inches Inches Inches 

2,050 48 27 21 

reduced summer flow despite no decrease in 

rainfall. The Douglas-fir region is notable for high 

winter and spring precipitation and streamflow, 

and low summer rainfall and streamflow. Even 

within regions streamflow varies with topography 

and geologic conditions. 

Streamflow also varies from year to year. 

Variations in the annual discharge by major forest 

regions are least in the Northeast and on the 

Pacific Coast; somewhat greater in the South, 

Midwest, and Rocky Mountains; and greatest in 

the Southwest (Busby 1963). In the southern 

Sierra Nevada in California, year-to-year variation 

in streamflow was least from high-elevation forest 

and alpine areas; streamflow from mid-elevation 

mixed-conifer forest was next in variation, and 

low elevation woodland and brush produced the 

most variable flow (Anderson 1963). Throughout 

northern California, the years of extreme low 

flow, the 10-year minimum flow, occurred 

progressively from high elevation to low, from 
8 

Fernow E. F.,W.Va. -1 

\ - Marcell E.F., Minn. 4 10 

Coweeta Hydrol. Lab., N.C. 

18 [- Fraser E.F., Col 6 H. J. Andrews E.F.. Ore. -1

14 

12 

10 

-Bar Ex. Watershed D, Ariz. 

4 8 

2 6 

4 O J F M A M J J A S O N D 

2 

[Precipitation 1streamflow 0 

J F M A M J J A S O N D 

Month 

Figure 4-Mean annual precipitation and streamflow for selected experimental forests 

(E.F.) and other watersheds. Forest types are: Appalachian hardwoods at Fernow 

and Coweeta, northern hardwoods at Hubbard, bog-black spruce at Marcell, lodgepole pine and spruce-fir at Fraser, ponderosa pine and white fir at Siera Ancha, 

chaparral at 3-Bar, and Douglas-fir at Andrews. 

northern latitudes to southern, from steep average annual stre amflow of small watersheds varies 

watersheds to less steep, and from watersheds from 24 to 52 inches over an elevation difference of 

with serpentine to watersheds with granite only 900 feet and a difference in average annual rain- 

(Anderson 1975d). fall of 14 inches. 

Streamflow reflects local differences in physiography and climate. For example, in 137 Within major forest regions some evidence 

watersheds in the Northeast, the average annual water shows that streamflow differs by forest type, 

yield among seven physiographic units ranged from particularly between hardwoods and conifers. In 

19 to 24 inches. Both annual and seasonal differences Michigan, water yield (as determined by groundamong regions were statistically significant at the 1- water measurements) from a 28-year-old jack pine 

percent level, as were differences between clusters of plantation was 12.4 inches compared to 15.3 

watersheds within units (Lull and Sopper 1967). inches from 40-to 60-year-old deciduous stands 

Yields can vary greatly within short distances. The nearby (Urie 1966). At Coweeta, streamflow from 

same study recorded significant differences in annual a mature white pine plantation, considering the 

and seasonal discharge within clusters of watersheds difference in interception between pine and 

within a 30-mile radius. At the 4,700-acre Coweeta hardwoods, might be as much as 12 inches less 

Hydrologic Laboratory in western North Carolina, than flow from the same site during an earlier 
period when it was covered by a hardwood stand 

(Swank 1968). After fifteen years, annual streamflow was 7.9 inches less in the pine-covered 

watershed; the decrease occurred in each month 

but was greatest in the dormant and early 

growing seasons (Swank and Douglass 1974). 

Among partly forested watersheds in the 

Northeast, those having a higher proportion of 

forest have more streamflow. This has been 

attributed not directly to the influence of the 

forest but to associated climatic, topographic, and 

edaphic conditions that usually increase flow (Lull 

and Sopper 1967). 

Modifiers of the 

Forest Influence 

The effects of hydrologic processes on streamflow are determined partly by scale-storm size, 

watershed size, and topographic differences; but 

the effect of these three factors on the forest 

influence is usually less important than physiographic controls. 

Storm Size 

The effect of the forest on streamflow is 

frequently stated as a percentage rather than an 

absolute amount. It should be apparent at this 

point that some forest influences are relatively 

more important for stormflow resulting from 

small storms: interception accounts for a larger 

proportion of small rainfalls, and soil-water 

storage opportunity of any given magnitude 

subtracts a greater proportion from the smaller 

rainfalls. Some forest processes thus have less 

effect, proportionately, on extreme events. 

The situation may be different when rainfall 

augments snowmelt; then the forest's effect on 

largelows may be equal to or greater than that on 

smaller ones, especially on large and diverse 

watersheds. 

One may well argue that the forest retains or 

detains some portion of any rainstorm, including 

the general and protracted storms described 

above, and thus somewhat reduces flood discharge and its peak. In a general sense this 

argument has merit: the forest does this. To some 

degree and in some places improved forest 

conditions do it better, provided that management 

accomplishes the needed forest improvement or 

that it reduces creation of additional poor forest 

conditions to the minimum. 

Watershed Size 

Many hydrologists reason that forests have 

greater influence on flood peaks from small 

watersheds than from large ones. Hoyt and 

Langbein (1955) explained it this way: "The 

larger the drainage area, the longer it takes flood 

waters to assemble in the lower reaches of the 

main stem. For this reason detention of infiltrated 

water for any given length of time has a lesser 

effect upon flood runoff as the size of the basin 

increases. " 

The situation is not always that simple. The 

effect forests have on flood peaks depends on the 

location of the forests and on the dominant 

processes of flood generation upon which they 

operate. The opportunity to prevent flood waters 

from collecting in the lower reaches by establishing or manipulating forest has been little 

appreciated, for American forests generally 

occupy the headwaters of rivers, a position 

favorable for delaying delivery of floodwater. 

Physiography 

Forest stormflow can differ according to 

physiographic region. For instance, for 137 

watersheds in the Northeast, all of them 100 

square miles or less in area and largely forested, 

the average annual number of daily discharges of 

more than 10 csm ft3/s/mi2 ranged from eight 

in northern New England to only one in the 

Coastal Plain (Lull and Sopper 1967). 

Local stormflow can be related to elevation, 

which can indicate storage possibilities. At 

Coweeta, for example, forested primary ridges at 

5,000 feet deliver almost 18 inches of direct runoff 

per year, whereas forest land at lower elevations 

delivers only 2.5 inches (Hewlett 1967b). Rainfalls 

of 8.4 to 10.8 inches in a December storm on three 

watersheds above 3,000 feet produced 5.0 to 8.8 

inches of flow and maximum peaks of 68 to 167 

csm. Rainfall on three watersheds below 3,000 

feet was 6.8 to 7.0 inches; flow was 1.6 to 2.3 

inches; and peaks were 22 to 32 csm (Hoover and 

Hursh 1944). 

The classic stream morphological variables 

developed by R.E. Horton (1945) accounted for 

differences of 57 percent in flood peaks from large 
storms on southern California watershed 

(Anderson and Trobitz 1949, Anderson 1950). 

Shape of watersheds influenced annual maximum 

daily flow, the 10-year flood, and the annual low 

flow, but not the average annual flow (Anderson 

1975d). 

Geology 

Extreme differences in flood peaks were 

associated with differences in both topography 

and geology of watersheds in the northwestern 

United States (Anderson and Hobba 1959). 

North-sloping watersheds and those having 

unconsolidated sedimentary rock types produced 

smaller floods. 

Dillon and Kirchner (1975) found greater 

differences in water chemical quality associated 

with different geologic rock types in watersheds 

rather than between land uses. 

Both annual and low flows differed greatly on 

northern California watersheds located on nine 

different geologic types (Anderson 1975d). Some 

types (e.g., Cenozoic nonmarine) consistently had 

high values for all elements of streamflow. In 

contrast, granitic areas produced the least annual 

discharge and low flows but the highest 10-year 

flooding. Basalt had high annual discharge and 

low flows, but low 10-year floods. Serpentine 

areas had the greatest low flows, but other 

streamflow characteristics were low. Different 

geologic types produced differences in streamflow 

from as little as 30 percent of average to more 

than three times average for daily maximum as 

well as for average flows. Low flows were even 

more varied among geologic types; granitic rocks 

yielded low flows only 1 to 3 percent as high as 

those from the basic and ultrabasic rock type 

(Basalt and Serpentine). 

Potter (1961) found it necessary to prepare 

separate predictions of peak flows for zones of 

loess and glacial till, sandstone and shale, 

limestone, and schist. White and Reich (1970) 

showed that floods are relatively low in limestone 

basins in Pennsylvania. 

It has been well documented that forests, along 

or in combination with such structures as 

reservoirs and dikes, do not completely prevent 

the flooding of great valleys, but they play an 

important role. Forests augment reservoir storage 

with watershed storage by preventing debris from 

bulking flood flows, and by minimizing the loss of 

channel and impoundment capacity by 

sedimentation. 

Forest and Frost 

The occurrence of frost in the forest in winter in 

the more northerly latitudes has been thought to 

influence several hydrologic processes. Many 

foresters have believed that "concrete frostwwet soil, solidly frozen-in the forest increases 

flood runoff. If concrete frost should form in the 

forest, it could prevent infiltration and cause 

overland flow. This may be concluded from 

evidence from nonforested areas. For instance, 

overland flow from concretely frozen soil on open 

fields was a principal source of runoff in the 

March 1936 flood near Ithaca, New York (Spaeth 

and Diebold 1938). Frozen soil was only in bare 

fields, not in neighboring woodland or grassland. 

Another study reported about 80 percent of 9 

inches of rain and snowmelt ran off two potato 

fields that had a 14-percent slope. A neighboring 

forested area having 27 percent slope had less 

than 0.5 percent of overland flow (Bennett 1937). 

Apparently, concrete frost occurs only sporadically in the forest. In the Adirondacks, under 

maximum snow accumulation, concrete frost 

about 2 inches deep was present at 30 to 40 

percent of sampling points in sapling stands and 

at 15 percent of those in sawtimber. Frost usually 

occurred chiefly beneath conifer crowns in the 

snow-interception zone (Lull and Rushmore 1961). 

Konda (1955) reported sporadic frost to a depth of 

18 cm under hardwoods in Japan. In a 

hardwood stand in New Hampshire, which had 

numerous mounds and depressions resulting from 

windthrow, Hart and others (1962) noted that 

through most of the winter snow insulated the soil 

and prevented frost formation. The few points 

where concrete frost was observed were on 

mounds. They concluded that any overland flow 

from a mound having concrete frost would be 

absorbed by the unfrozen slopes and depressions 

adjacent to it. 

In New England and the Lake States, many 

other studies have also shown that the frequency 

of concrete frost in the forest is too low to have 

any real effect on overland flow (Hart 1963, Bay 

1958 and 1960, Striffler 1959, and Wray 1959). 

Most of these studies also showed that concrete 

frost occurs more commonly under conifers than 

under hardwoods, and is most prevalent in open 

fields. 

It seems obvious that soil freezing would have 

effects on watershed hydrology not simply 

explained by the concrete frost hypothesis; soil 

water is immobilized, even while migrating 
upward to soil surfaces; a tremendous heat sink 

becomes established which must be dissipated, 

and certainly the pore space in the soil is 

temporarily reduced. 

Thorud and Anderson's (1969) study of the 

forest floor as a heat sink during freezing revealed 

that bare soil froze 55 percent faster than littercovered soil. A 2-inch layer of snow lengthened 

freezing time, but snow and dry pine litter 

together lengthened freezing time 54 percent over 

that required for the same thickness of litter 

alone, and 123 percent compared to snow alone. 

Water in the litter shortened freezing time as 

much as 61 percent. Therefore, we conclude that 

the forest floor and the soil beneath it comprise an 

important sink for energy, and that differences in 

forest floor conditions may cause significant 

differences in hyrologic processes. 

Forestry, Erosion, 

and Water Quality 

Probably the most current interest in hydrologic 

processes arises from their effects on water 

quality (Meier 1975). This section on hydrologic 

processes in relation to forestry must at least 

outline some of the individual water quality 

parameters that forestry can influence. The 

materials are the common particulates (inorganic 

and organic, living and dead), dissolved substances (inorganic and organic), amorphous 

substances, and gases. Radiant energy (transmitted, absorbed, and re-radiated) is also 

involved. These materials and influences are all 

reflected, somewhat inadequately, in such descriptors of water quality as turbidity, pollution, 

contamination, eutrophication, aeration, and 

water temperature. Since the hydrologic system is 

never in equilibrium, all measurements of its 

components present formidable sampling problems -and would do so even if we knew what to 

measure. We know how to measure erosion and 

its sedimentation products fairly well. We discuss 

erosion and its relation to water quality in detail 

because erosion is reported to cause 80 percent of 

the deterioration of water quality because 

products of erosion interact strongly with other 

components, and because erosion is directly 

affected by forest management. 

Erosion and Sedimentation 

The term "sedimentation," as used here, 

consists of three basic processes: erosion, 

sediment transport, and deposition. Erosion is the 

detachment and initial spatial displacement of 

soil, rock, or organic matter by whatever agent 

and in whatever state. Sediment transport is the 

movement of erosion products after initial 

displacement, and here includes movement of 

particles into the interstices of soil or rock. 

Deposition is the temporary or permanent halting 

of the movement of transported products of 

erosion. 

Some characteristics of the forest system that 

affect erosion and sedimentation are unique 

among land types. These include the hydrologic 

properties of the soil mass, the types of terrain 

that the soil mass often occupies, the erosional 

processes and how they occur, and the high 

sensitivity of each process to change. Surface soil 

layers generally have high capacities for infiltration and percolation. Forest soils sometimes 

occupy slopes steeper than the natural angle of 

repose for the geologic material, for the soils are 

anchored by the tree roots. These steep slopes 

imply an erosional process of channel downcutting over long periods, and mass creep and 

occasional mass sliding from lower slopes into the 

channel (Anderson 1967a). 

Surface erosion of forest sites usually follows 

intense rainstorms that follow baring of the soil by 

logging, fire, overgrazing, mass movement, or 

other causes. Landslides and mudflows may be 

started or accelerated by land use, but usually 

they too are associated with heavy rains and 

slide-prone conditions either in the soil mass or at 

the contact of the soil with the underlying rock. 

However, mass movements by soil creep and 

ocassionally by mudflows or landslides are 

pervasive natural processes that occur even in the 

undisturbed forest. 

The three hydrologic processes principally 

initiating erosion and sedimentation are raindrop 

splash, overland flow, and streamflow scour. 

Interception may increase splash in those unsual 

situations where mineral soil has been exposed 

beneath the canopy by burning or trampling, for 

raindrops intercepted by a high canopy and 

dripping from it have greater mass and kinetic 

energy than ordinary rainfall (Tsukamoto 19660) 

and therefore greater potential for causing splash 

erosion. 

Infiltration capacity of forest soils is usually 

high. Surface erosion and transport of soil are 

eliminated when and where infiltration capacity 

equals or exceeds rainfall, snowmelt, and lateral 

overland flow additions. However, Ellison (1949) 
showed how a bare, very permeable soil having a 

high infiltration capacity can be practically 

waterproofed by the splash erosion from 20 

minutes of rainfall. But high infiltration capacities 

can have an undesirable effect. In some localities, 

high infiltration builds up soil water which locally 

destroys cohesion of the soil mass, augments soil 

creep into channels, or causes mass slope 

movement into them; or it may cause local soil 

saturation and growth of channels by solifluction 

(mudflows). However, a recent intensive study of 

slope stability in coastal Oregon (Harr and Yee 

1975) showed that saturated soil was rarely found, 

and further that natural infiltrated and percolating water did not affect the soil aggregation that 

was essential to slope stability. Landslide 

processes are discussed under Timber HarvestLandslides. 

The surface of upland forests, where mineral 

soil is fully protected by a cover of litter and 

humus, contributes little or no sediment to 

streams. In these forests, erosion occurs almost 

entirely within the major and minor stream 

channels; local solifluction and. creep move soil to 

the channel, and the cutting and transporting 

power of streamflow detaches particles from the 

banks and carries them downstream. The channel 

then is in dynamic equilibrium with the quantity 

and frequency of streamflow, which control the 

length, width, and carrying capacity of the 

channel. Hansen (1970) reported a 530 percent 

increase in the volume of suspended sediment in a 

26-mile reach of a Michigan stream, largely as a 

result of channel bank erosion. When infrequent 

high flows occur, they overtax the channel and the 

flow starts to widen and lengthen it. Thus in any 

stream, sediment must be expected in times of 

extremely high flow. Extreme high flows may not 

only produce high yields of sediment, but may 

create unstable channel banks; so the watershed 

is more vulnerable to erosion for some time to 

come (Anderson 1970b, 1972). 

Where areas of the forest floor have been 

disturbed by logging, grazing, or burning, 

infiltration is reduced by the compactive effect of 

moving equipment, trampling animals, or beating 

raindrops, and overland flow; soil erosion can 

result. Loss of soil then becomes a function of soil 

erodibility, length and steepness of slope, and the 

intensity of storm rainfall. 

One index of the intensity of storm rainfall is 

the rainfall erosion index (the product of total 

storm energy in foot-tons per acre-inch and the 

maximum 30-minute intensity, divided by 100). 

This index differs widely from region to region. 

Average annual indexes from available data range 

from 75 to 200 for the Northeast, 200 to 600 for the 

Southeast, and 50 to 250 for the North Central 

States (Wischmeier and Smith 1965). In the West 

other indexes of erosion are more useful, such as 

volume and peak streamflow and the frequency of 

rainfalls versus snowstorms. These have been 

shown to be related to sediment production from 

forested watersheds, and hence to the erosion 

potential of forest sites (Anderson 1954, Wallis 

and Anderson 1965, Anderson 197%). 

After protective litter and humus have been 

removed, comparative soil erodibility controls 

erosion. Comparative erodibility has been studied 

particularly in California, Hawaii, and the Pacific 

Northwest (Anderson 1954, Anderson and Wallis 

1965, Yamamoto and Anderson 1967). In California, for example, soil erodibility varied by a 

factor of eight among major soil types. Soils under 

Douglas-fir stands in eastern Washington were 45 

percent more erodible than soils developed from 

similar parent materials in western Washington 

that had twice as much organic matter in the 

surface 19 inches (Balci 1968). In the southern 

Sierra Nevada, Willen (1965) found that granitic 

forest soils at elevations above 6,500 feet were 

potentially about 2.5 times more erodible than 

granite-derived soils below 4,500 feet. In northern 

California's forest-covered mountains, soils de- 

'veloped from acid igneous and schist rock types 

were more erodible than soils from the more basic 

and ultramafic types; and soils developed under 

fir were less erodible than those developed under 

ponderosa pine, brush, or grass (Wallis and 

Willen 1963). Similarly, soils in Hawaii that 

developed under the native ohia were more 

erodible than soils developed under introduced 

tree species (Yamamoto and Anderson 1967). 

Wooldridge (1964) reported that more than 40 

percent of the soil erosion hazard in central 

Washington could be accounted for by variation in 

the content of organic-matter, pH, total porosity, 

and bulk density of the soil. 

Stoniness of watershed soils may strongly affect 

erosion and water quality. Analysis of sediment 

data from watersheds in western Oregon indicated that streams in areas having gravelly soil 

became armored with coarse particles and hence 

had fewer days of turbid flow (Anderson 1975a). 

Results suggest, for example, that watersheds 

having 67 percent stone in their soil had only 
about 23 percent as many days of turbid 

streamflow as soils containing only 17 percent 

stone. 

Self-healing of disturbed areas can accompany 

the development of an erosion pavement (a layer 

of stones protecting the surface); however, this 

may be effective only after considerable damage 

has been done. Self-healing can be interrupted 

and erosion resumed by storms whose intensities 

exceed the infiltration capacities of the disturbed 

areas. 

The dominant erosion processes differ considerably between watersheds, within management 

units, and over time. Mass movements, such as 

landslides, have accelerated erosion in areas 

considered to have recovered from logging 

(Fredriksen 1970). Within watersheds, unstable 

slope and soil combinations have been identified 

(Wallis 1963). The consequences of these 

differences in erosion potential on sediment yield 

and water quality are outlined under regional 

hydrologic characteristics affecting forestry and 

water. Interactions between sediment and other 

characteristics of water quality are discussed 

under each of those characteristics. 

Although sediment is considered to be the most 

important single factor in limiting water quality, 

forest management also affects other factors that 

influence water quality. 

Water Temperature 

The forest influences the temperatures of soil 

water and streamwater by affecting the paths that 

water takes, by shading the ground and the 

stream, and by using energy for evaporative 

cooling. Management that changes any of these 

influences can change water temperature. 

Raising water temperature may have both good 

and bad results; the balance depends on the 

particular stream situation. Warmer temperatures favor food production, which is all too small 

in many trout streams. If temperature of the 

stream is already near the upper threshold 

favorable for trout, opening the forest along the 

stream channel may be detrimental. The best 

trout fishing is in streams whose maximum 

temperatures never exceed 60 to 68' F. Water 

temperature for warm-water fish should not 

exceed 93O F at any time or place (Tarzwell 1960). 

Indirect effects of increased temperature include 

effects on dissolved oxygen. At elevated temperatures decomposition of organic debris in streams 

may deplete oxygen below critical levels for fish 

(Berry 1975). 

Brown (1969) and Edinger and others (1968) 

have recently studied in considerable detail the 

microclimate of water surfaces and the heat 

balance in flowing streams. Brown reported wide 

differences in the amount of heat absorbed by 

flowing streams and stream bottoms. Bedrock 

bottoms absorbed as much as 25 percent of the 

energy, but gravel bottoms apparently were an 

insignificant energy sink. He reported differences 

of as much as 11' in May in temperatures of 

shaded and unshaded streams. Winter exposure 

of streams and their margins may be important to 

water storage. Walter T. Wilson, in a personal 

communication about 1947, attributed the temporary reductions of groundwater contributions to 

streamflow to freezing at stream margins. The 

formation of frazil ice in streams has also been 

related to the rate of cooling; here, too, the 

insulating effect of the forest may play a 

significant ameliorating role. 

On the other hand, the biological productivity of 

streams that are too cold may be increased by 

raising stream temperature through much the 

same techniques as snowmelt is managedcutting shade to the south while leaving trees on 

the northern stream margin to provide back 

radiation. Berry (1975) has modeled the effects of 

streamside clearing length on stream temperature. Biological productivity also can be affected 

by sediment in streamflow, for light penetration 

may be reduced so much as to inhibit growth of 

beneficial microorganisms. 

Water Chemistry 

Dissolved solids, most of which are essential 

nutrients in the forest ecosystem, are another 

element of water quality. In the mature forest the 

nutrient cycle generally approaches a steady 

state, and only small amounts of nutrients are 

discharged in the drainage water. As a result, 

volumes of dissolved solids are usually small in 

streamflow from forested areas and primarily 

reflect the geology of the area (Foggin and Forcier 

1974, Dillon and Kirchner 1975). 

The forest floor and forest soil have remarkable 

absorptivity. This was most notably demonstrated 

in a (1959-61) study at the Central Sierra Snow 

Laboratory of radioactivity associated with atomic 

bomb fallout. Radioactivity was measured in 
incoming precipitation, in the snowpack, and in 

the snowmelt streamflow. In incoming precipitation, radioactivity reached as high as 50 times the 

water quality standard, and it was as high as 10 

times the acceptable standard in the whole 

10-foot-deep snowpack. Radioactivity in the 

streamflow from the snowmelt approached the 

standard of 1000 micromicrocuries per liter on 

only one day; usually it was on three-tenths of the 

standard or less. Public Health officials concluded 

that the forest floor and surface soil had absorbed 

most of the radioactivity. This may help to explain 

the ability of the forest to remove biological 

pollutants (Nikolaenko 1972, 1974) and chemicals 

that are applied in forest treatments. 

Management practices affect the chemical 

quality of water by influencing the type of 

vegetation and rate of growth (thus affecting 

uptake), the amount and rate of deposition on the 

forest floor (as by production of logging slash or 

the removal of forest products), and the rate of 

decomposition of organic matter (by changing the 

exposure, temperature, and moisture content of 

the forest floor). Any treatment that changes the 

volume of streamflow may influence the removal 

of dissolved solids from the system in the 

drainage water, especially if surface soil, which is 

highest in such nutrients as nitrogen, erodes. 

Of all pollutants dissolved in water, nitrogen 

deserves greatest attention in forest management 

(Tarrant 1972). In coastal Oregon, the total 

nitrogen in precipitation throughfall was nearly 

five times greater under the hardwood Ainus 

species than in rainfall not intercepted by forest 

canopy. Nitrogen was three times greater under 

conifers than in nonforested areas. The annual 

addition of nitrogen to the forest floor was as 

much as 100 lbdacre (Tarrant and others 1969); 

so, for approximately 60 inches of precipitation, 

the concentration of nitrogen was about 7 p/m. 

Natural addition of organic materials directly 

into the stream may temporarily degrade water 

quality. Slack and Feltz (1968) showed that water 

quality in a small stream was related to the 

autumn leaf-fall from reparian vegetation over the 

stream channel. Dissolved oxygen and pH 

decreased; water color, specific conductance, 

iron, magnesium, and the bicarbonate ion 

increased as the rate of leaf-fall increased. Stream 

quality improved rapidly after the channel was 

flushed by stormflow. Organic matter in the 

stream has benefits also, because it is a primary 

source in the chain of food production. 

Forest practices that affect nutrients and other 

water quality characteristics are discussed later in 

the section Management for Water Quality. 

Integrating Hydrologic Processes 

How do we assemble the data on processes to 

predict water yield, floods, erosion, and 

sedimentation? 

That depends on how each process relates to 

the objectives and on what technique is appropriate for predicting (Australian Academy of 

Science 1975). The two general classes of 

techniques, simulation and multivariate analysis, 

have somewhat different objectives. Use of both 

techniques has been greatly facilitated by 

developments in computer technology. Simulation 

as applied in hydrology is essentially a bookkeeping technique-individual hydrologic processes act sequentially on such an input as 

precipitation, and the summed results are routed 

to give an estimate of outputs varying with time. 

Notable working models include those by Crawford and Linsley (1964), Riley and others (1968), 

and Dawdy and others (1972). Many variations 

and extensions are constantly being reported. 

Essentially, the simulation technique relies on a 

satisfactory ability to evaluate the operation of 

hydrologic processes in space and time. The 

model can always be modified so that it will 

predict in a particular circumstance, but no 

greater insight into hydrologic processes seems to 

have come from the applications of simulation 

models. 

Recent simulation models that deal with forest 

hydrology output include the Leaf and Alexander 

(1975) model, which integrates research results 

from Colorado into predicted outcomes of 

different cutting patterns. Galbraith (1975) has 

developed a method for predicting increase in 

water yield from timber harvesting for use in 

northern Rocky Mountain forests. In the Pacific 

Northwest, Ryan and others (1974) have reported 

development of an ecosystem model that includes 

forest hydrology outputs. 

Other simulation models aim at evaluation of 

particular management ,practices, such as prescribed burning (Agee 1973), or timber harvest 

(Belter 1975), or water quality (Willis and others 

1975), or particular outputs, as flood peaks 

(Dawdy and others 1972, Fogel and others 1974), 

or even particular processes as soil moisture 

(Zahner 1956). Each modeler has his own version 

of someone else's model, having made necessary 
modifications to fit his own data available or own 

needs for predicting outcomes. Lombardo (1973) 

has concluded that there are no satisfactory 

models for water quality; the modeling by Willis 

and others (1975) seems to have promise in this 

difficult modeling development. 

In contrast to simulation, multivariate analysis 

results have other uses in addition to prediction 

(Wallis and Anderson 1965, Lull and Anderson 

1968). This type of analysis can determine the 

potential of unit areas of forests to produce 

particular water products (Anderson 1975d). It 

may relate a product to a cause having known 

frequency, and it can test the significance on a 

variable's effect on the product. Once the model is 

developed, independent variables may be manipulated to test the consequences of alternative 

possibilities in land management and to select the 

most desirable outcome. 

The first applications were simple; many of 

them dealt with peak flows. Multiple correlations 

and regression were used to relate meteorological, topographic, and other watershed variables to peak discharges of storms, mean annual 

flood peaks, or peak flows of rare large storms. In 

24 states where studies have been made, the 

principal hydrologic factors that are significantly 

correlated with the mean annual flood are 

drainage area, shape of basin, type of soil, and 

area of lakes (Benson 1962a). Annual peak 

discharges in New England were related principally to area of drainage, main-channel slope, and 

storage in lakes and ponds (Benson 1962b). 

Annual peak discharge of floods in Texas and New 

Mexico was related to drainage area, rainfall 

intensity, main-channel slope, storage, mean 

annual precipitation, and altitude (Benson 1963). 

In Northeastern watersheds, Lull and Sopper 

(1967) found that the highest mean daily 

discharges (at 0.1 percent flow durations) were 

related to precipitation intensity, slope, and 

percentage of area in swamps, but were not 

related to percentage of forest-covered area. 

For small watersheds in most of the United 

States east of the 105th meridian, Potter (1961) 

related the maximum annual peak (equaled or 

exceeded on an average of once in 10 years) to 

drainage area, precipitation, topographic indexes, 

and drainage density. In an earlier study Potter 

(1953) had reported similar findings based on 

analysis of 51 watersheds in the AlleghenyCumberland Plateau; he noted that the percentage of area in cropland, pasture, or woodland had 

no effect on the magnitude of the 10-year peak. 

He based this conclusion on his regression of peak 

flows versus area, for many of the largest 

deviations above the regression had 98 percent 

woodland, whereas those below had 50 to 60 

percent cropland (hardly a conclusive technique). 

On the other hand, Reich (1972) found that 

increased percentages of wooded area reduced 

flood magnitudes in Pennsylvania, at least those 

of 2.33-year return period; he concluded that the 

percentage of wooded area is a more important 

determinant that many geomorphic parameters of 

regional flood prediction equations. Peak discharges from watersheds in the Northwest have 

been related to several meteorologic, topographic, geologic, and forest-cover variables. The 

age and stocking of the forest below the snowmelt 

line during a storm were related to rain-snowmelt 

floods; snowmelt floods were related to the area of 

poorly stocked and burned forest (Anderson and 

Hobba 1959). 

We conclude the discussion of classical 

hydrologic processes, their modifiers, and some 

of their applications realizing that, in almost all 

forest situations, the spatial distribution of many 

of these processes may differ greatly from these 

classic models. For example, water moving 

downslope in both saturated and unsaturated flow 

is effective in extending the period when water is 

available for transpiration to the forests on lower 

slopes, adjacent to channels, and at locations with 

shallow or impervious strata (Tsukamoto 1966a). 

Almost all experimental measurements of water 

use from watersheds have indicated greater use 

than would have been predicted from measurements of soil-water depletion and interception. 

Martinec (1975) reported from a study of 

tritium content of subsurface flow that outflow 

from the watershed represented water hitherto in 

subsurface storage for "a number of years." 

Infiltrated water on the watershed was substituted for, perhaps by some pressure wave 

phenomena, (Vischer 1970 quoted by Martinec 

1975). 

Forests through their effect on the distribution 

of falling rain, on distribution of snow, on freezing 

of the soil, and on the production of ice lenses 

within snowpacks, create situations of highly 

varied water percolation, typically under conditions quite difficult to measure quantitatively. It 

will become evident that these spatial and time 

variations of soil moisture have implications not 

only for management for water yield from forest 

but also for control of flood flows and 

sedimentation. 
II - FOREST TREATMENT AND WATER 


The hydrologic response-water yield, floods, 

and water quality-to forest treatment depends 

on the characteristics of the forest, the nature of 

the treatment, and the posttreatment recovery of 

those watershed attributes that affect the hydrology. The forest itself may be characterized by 

such attributes as type, age, and density, or by 

more fundamental measures such as basal area or 

biomass, or measures that attempt to characterize 

the whole forest ecosystem. The treatments 

themselves vary widely, from harvesting, prescribed burning, grazing, and planting, to the 

havoc wrought by insects, diseases, winds and 

wildfires. The extent to which the forest's 

influence is altered depends on the intensity of 

treatment or assault. The greatest effects are 

usually produced by clearcutting, intense 

burning, heavy grazing, intensive planting, 

catastrophic attacks by insects and diseases, and 

blowdown. The size of the area-and the 

proportion of the watershed-subjected to the 

treatment or assault often have primary importance. 

Some effects are influenced too by climate, 

soils, topography, and geology. They differ by 

season of the year, and are influenced not only by 

a specific forest happening but also by what 

occurred before and after it: how long recovery 

takes, the nature of replacement vegetation, and 

so forth. Thus the subject is complex. Presentation here is in terms of qualitative effects on 

hydrologic processes illustrated by some quantitative examples. 

7imb er Harvesting 

Timber harvesting includes severing trees from 

their stump, cutting the bole into sections, and 

removing the timber from the watershed. 

Construction and use of skidtrails and logging 

roads is usually an integral part of the harvesting 

operation, which may also include burning or 

other disposal of the slash. The impact of timber 

harvesting on the water resource depends upon 

the severity of the changes in vegetal cover, the 

exposure and compaction of the mineral soil, and 

the proportion of watershed affected (Megahan 

1972, Stone 1973). It is also influenced by the rate 

at which soil and vegetation recover, either by 

natural reproduction or by the planting of woody 

and herbaceous species. Timber harvesting 

affects the water resource by its influence on the 

fundamental hydrologic processes. 

Interception 

Interception of precipitation by deciduous 

hardwoods is not greatly reduced by forest 

cutting; logging residue (stumps, branches, and 

foliage) and the remaining understory continue to 

intercept moisture. If the area is to remain in the 

forest cover, revegetation within 10 years can 

restore much of the interception. Partial cutting in 

hardwoods has little effect on snow interception. 

In northern Minnesota, for example, maximum 

snow accumulations in four aspen stands thinned 

to 50, 65, 80, and 115 square feet of basal area 

were 4.5, 4.1, 4.2, and 4.3 inches of water 

respectively (Weitzman and Bay 1959). 

On the other hand, interception by conifers may 

amount to as much as 30 percent of annual 

precipitation; therefore, interception by conifers 

may be reduced more by forest cutting than it is in 

hardwoods. Such reduction can substantially 

increase streamflow. Regeneration of conifers is 

not initially as rapid as the resprouting of 

hardwoods. It may take 20 to 40 years in the East 

and 50 years or more in parts of the West for a 

cutover stand to even approach full interception. 

Snow Accumulation 

Snow accumulation is markedly affected by 

timber harvesting; increases in the maximum 

snow accumulation in four western states after 

heavy cutting ranged from 22 to 40 percent (table 

6). Light cuttings increased snow accumulation by 

10 to 17 percent. In Minnesota, percentage 

increases were much larger because snow 

accumulations were small. The greatest absolute 

increases, up to 19 inches in terms of water 

equivalent, have been in the deep snowpacks of 

the central Sierra Nevada of California, where 

both interception and winter snowmelt were 

involved. 

Often excess snow in openings is a redistribution of snow, and it is partly balanced by a 

decrease under the trees (Hoover and Leaf 1967, 

Hoover 1971,1973). Anderson and Gleason (1959) 

reported that one-half of the 13 inches (water 

equivalent) of greater amount of snow found in a 

cut strip was in effect "stolen" from the forest to 
-- 

Table 6-Increase in maximum snow accumulation (water content) after cutting in western conifer 

forest 

Location and 

forest cover Treatment Maximum increase in 

snow accumulation 

Inches Percent 

(1) Fraser Exp. Forest, Uncut: 11,900 fbm 0.0 

Colo. Cut (residual volume): 

Mature lodgepole pine 6,000 fbm .8 1 12 

4,000 1.01 15 

2,000 1.49 21 

0 1.99 29 

Young lodgepole pine Heavy thinning 

(reduction from 4,400 

to 630 trees per acre) 2.3 23 

Light thinning 

(reduction from 4,400 

to 2,000 trees per acre) 1.7 17 

Mature Englemann Removal of 60% of volume 

spruce-subalpine by strip cutting and 

fir group and single-tree 

selection 2.8 22 

(2) Front Range, Rocky Selection cut 

Mountains, Colo. Commercial clearcut 

Ponderosa pine and 

Douglas-fir 

(3) North Central Wyo. Clearcut blocks 

Lodgepole pine 

(4) Willamette Pass, Oreg. Strip-cut, strips 2 chains 

Mountain hemlock wide 

and true fir 

(5) Central Sierra Snow Clearcut 

Laboratory, Calif. East-west strip, 

(NE) 1 tree-height wide 

Red fir Block cutting, 

1tree-height wide 

Selective cutting; crown 

cover reduced from 

90% to 50% 

90% to 35% 

Commercial selection cut 

Wall-and-step forest 

(6) Minnesota Single-tree selection 

Black spruce Shelterwood 

Clearcut strip 

Clearcut patch 

Compiled as follows: (1) Wilm and Dunford 1948, Love and Goodell 1960; (2) Berndt 1961; (3) 

Berndt (1965; (4) Rothacher (1965b; (5) Anderson 1956,1963, Anderson and others 1958, Anderson 

and Gleason 1960; (6) Weitzman and Bay 1959. 

the leeward. On the other hand, the study of snow forest, and this can increase or decrease peak 

in 36 natural openings showed greater amounts in flow, depending on synchronization with melt 

both forest openings and the forest adjacent to elsewhere on a watershed. 

openings than in the continuous forest (Anderson Haupt (1973) reported the role of snow 

and West 1966, Anderson 1967b). Snow in accumulation in relation to wind and surface 

openings melts more rapidly than snow within the exposure near major ridges, and suggested 
cutting forest on the windward side to store snow 

to the lee. 

Surface Detention 

Logging, land clearing, or fire may reduce 

roughness of ground or stream channel and 

thereby increase the speed of flow in saturated 

areas and in channels. Timber harvesting that 

augments accumulation of snow may increase 

detention capacity in the snowpack. Detained 

water may have contradictory effects when the 

snow melts, depending on the timing and the 

location of the snowpack in which the additional 

water was detained. Forests at high elevations, 

cut or uncut, may have sufficient detention 

capacities for rain and slow snowmelt in early 

season. At intermediate elevations, forest cutting 

usually allows the rapid ripening of snowpacks, 

especially on south slopes. Detention storage 

capacity during rain on snow is lost and melt is 

speeded (Anderson and Hobba 1959); exposure of 

snow surfaces in openings may speed melting by 

increasing latent heat exchange from the moist 

atmosphere to the snow (Anderson 1969). At 

lower elevations, the speeding of snowmelt by 

forest removal may help to desynchronize peak 

flows from different parts of the watershed 

(Satterlund and Eschner 1965). 

Other than surface detention in snowpacks, 

timber harvesting may cause small difference in 

detention on the soil surface, as in pondage in 

skidtrails, behind road fills, and in stump 

depressions resulting from whole-tree logging. 

Most of these effects have not been separately 

evaluated. 

Infiltration, Overland Flow, 

Erosion, and Sedimentation 

These four processes are discussed together 

because when infiltration capacity is sufficiently 

reduced, overland flow and erosion usually follow. 

Erosion of soil provides material for sediment in 

the stream, although not all the eroded material 

reaches the stream and some of the sediment 

comes from the channel area rather than from the 

land surface. 

Merely cutting trees does not affect infiltration 

capacities. The generally high rates of infiltration 

characteristic of the forest remain after harvesting 

except where logging activity has exposed the 

mineral soil or caused soil compaction. The 

influence of the organic layers and the forest soil 

structure persists for some years after cutting; 

when regrowth is reasonably prompt, new organic 

contributions are provided to maintain soil 

stability, which prevents degradation. 

Clearcutting mature hardwoods at Coweeta 

(Hoover 1945) produce no overland flow and 

consequently no erosion. Cut trees were left 

where they fell, and a heavy ground cover rapidly 

developed. At the Hubbard Brook Experimental 

Forest, felling the trees and treating with 

herbicide to eliminate ground cover (a treatment 

for research purposes only), increased sedimentation fourfold during the next 2 years, from 8.6 to 

34 tons per square mile per year (Pierce and 

others 1970). Apparently there was no overland 

flow, and the additional sediment came from the 

stream channel. 

Harvesting reduces infiltration capacity to the 

extent that forest soil is exposed and compacted 

by roadbuilding, skidding, and hauling. Careful 

logging may disturb no more than 10 percent of 

the area; overland flow resulting from reduced 

infiltration may then be of little consequence. In 

contrast, careless logging can compact and 

disturb as much as 40 percent of an area, reducing 

infiltration from several inches per hour to a 

fraction of an inch, and generating damaging 

overland flows from high-intensity rainfalls. 

Murai (1975) reported that infiltration in a cutover 

forest that was heavily disturbed was about 1inch 

per hour-only 20 percent of that in the uncut 

forest. 

In some situations, erosion is relatively easy to 

control. Logging on coarse-textured, permeable 

soils in the front range of the Rockies, with careful 

roadbuilding, has produced little sediment (Leaf 

1966). The essential stability, despite heavy 

cutting, of the glaciated soils of New England's 

forested mountains also has long been recognized 

(Cleland 1910). 

Elsewhere the situation can be quite different. 

On clay soils at Coweeta, roads and logging 

produced maximum sediment concentration in 

streams of 7,000 p/m as compared to 80 p/m for 

an undisturbed area. Turbidity from the logged 

area averaged 93 p/m compared with the 4 p/m 

from the check area. Repeated measurements of 

road cross sections showed that in 4 years the 2.3 

miles of road lost 6,850 cubic yards of soil (Hoover 

1952). This impaired water quality of the stream 
that drains an 1,880-acre watershed so severely 

that the timber value was judged to be less than 

the cost of treating the water (Hursh 1951). 

Surveys of eight major basins in southeastern 

states reported that logging activities were 

responsible for more than half of the increases in 

sediment production from forest lands in seven of 

the basins (Dissmeyer 1976). 

In Arizona, logging and road construction 

increased sediment yield from a 248-acre watershed from 3.5 tons annually to 21 tons from only 

two summer storms and 57 tons from two winter 

storms (Rich and others 1961). Before logging, a 

certain 2,500-acre watershed in the Sierra Nevada 

yielded 0.4 ton of sediment per acre per year. The 

first year after a commerical selection cut of 

one-fourth of this watershed, the logged area 

yielded 6.1 tons per acre; in the following year it 

yielded only 1.8 tons (Anderson 1963). Increases 

in concentrations of sediment were associated 

mostly with the high discharge classes: the 

highest 12 percent of the streamflow carried 60 

percent of the sediment. Sedimentation rates 

dropped rapidly after logging. For a high 

discharge class of 55 to 79 ft 3/ s, the rate before 

logging was 20 p/m; during the first, second, and 

third years after logging, the rates averaged 190, 

90, and 45 p/m (Anderson and Richards 1961). 

Logging roads-Logging roads and their unprotected cuts and fills are a primary source of 

sediment from forested watersheds. Movement of 

sediment downslope from a road depends on the 

amount and velocity of runoff, the availability of 

erodible soil, and the obstructions to sediment 

transport (Haupt 1959). Road cuts can produce 

tremendous quantities of sediment, depending 

upon their slope and aspect. 

In south central Idaho, three adjacent watersheds with highly erodible granite-derived soils 

produced sediment yields of 12,400, 8,900, and 89 

tons per square mile in one season following 

construction of logging roads. Watersheds without roads yielded no measured sediment (Copeland 1965). 

A similar relationship was found in the analysis 

of 29 watersheds in western Oregon: an increase 

in the annual timber cut from 0.6 to 1.5 percent 

would increase sediment loads an expected 18 

percent; increasing total road area from 0.1 to 

0.55 percent would increase sediment loads 260 

percent (Anderson 1954). 

In central Idaho, during a six-year study, the 

effects of skyline logging with no roadbuilding 

were compared with those of jammer logging. 

(The jammer has an A-frame with winch and cable 

mounted on a truck; it requires closely spaced 

roads.) Skyline logging with no roads increased 

sediment deposition by only 1.6 times; in 

contrast, jammer-logging with numerous roads, 

which may disturb 25 percent of an area, 

increased deposition by 850 times for the 6 years 

after road construction (Megahan and Kidd 1972, 

Megahan 1975). 

Gradual reduction of road-induced sedimentation has been observed on some watersheds; 

however, Megahan (1975) believes that full 

recovery in central Idaho may not be expected. A 

watershed crossed by a 37-year-old road, 

apparently fully stabilized, still produced twice as 

much sediment as similar but unroaded watersheds. Historically, roads often have been 

upgraded from dirt to surfaced roads, typically 

with major realignment; such upgrading may be 

beneficial in midslope locations, but highly 

detrimental in increasing sedimentation from 

streamside roads (Anderson 1974). Roads in steep 

watersheds show twice as much increase in 

sedimentation as roads in moderately sloping 

watersheds (Anderson 1976). 

In the Douglas-fir region, only one-third of the 

area of a typical road is occupied by the roadbed; 

cut and fill slopes cover the remainder of road 

area (Dunford 1962). Forest roads in the 

Intermountain region have about 8 acres of cuts, 

fills, and ditches for every mile of road (Usher 

1961). In Mississippi, sawtimber harvesting 

disturbed 15 percent of logged areas; 5 percent 

was contributed by roads, 7 percent by skidtrails, 

2 percent by log movement, and 1 percent by 

landings (Dickerson 1968). 

Under some conditions, sediment production 

from logging roads can be both substantial and 

prolonged. After 1.7 miles of road were built on 

6.2 percent of a 250-acre watershed at the H.J. 

Andrews Experimental Forest, the first storm of 

the rainy season produced a turbidity (suspended 

sediment concentration) of 1,780 p/m, 250 times 

the concentration in the undisturbed watershed. 

Sediment concentrations remained high during 

the first 2 months of the rainy season, and during 

the next 2 years they continued at about twice the 

concentration measured before road construction 

(Fredriksen 1965b). 
The degree of disturbance and consequent 

erosion and sedimentation differ widely according 

to the erodibility of soil, the intensity of the timber 

cut, the care used in logging, and the type of 

equipment used. 

There is considerable evidence that careful 

logging minimizes sediment production. Successful erosion prevention or control depends on the 

care and skill used in skidding and hauling the 

timber products and in the construction and 

maintenance of trails and roads used for these 

purposes. Failure to close substandard roads after 

logging-leaving them for recreational or other 

use-can indefinitely prolong erosion and production of sediment. 

Less soil is lost from high-quality roads than 

from less well built roads. At Fernow Experimental Forest, sediment production per unit 

length for a good road (of moderate slope and with 

drainage provided) was only about half that for a 

poor road (with no restriction on grade and no 

drainage provided) (Weitzman and Trimble 1952). 

The greater the use of skidroads, the greater the 

soil loss. Heavily used skidroads at the Fernow 

lost 3.7 inches of soil during skidding; lightly used 

roads lost only 1.0 inch (Trimble and Weitzman 

1953). Of course, both of these rates would 

produce high turbidity if the lost soil reached a 

stream. 

The density and grade of roads may be 

significantly reduced by adequate planning. 

Logger's-choice road system (unplanned) at the 

Fernow Experimental Forest occupied 4.8 to 7.0 

percent of the area and had grades of 14 to 24 

percent; a planned system occupied 2.5 to 4.6 

percent and had grades of only 9 to 15 percent. 

Careful planning reduced the area in skidroads by 

40 percent and eliminated steep grades (Mitchell 

and Trimble 1959). 

Care in constructing road drainage is needed in 

areas where slopes are unstable; Harr and Yee 

(1975) suggest that drainage from culverts can 

destroy soil aggregation necessary for natural 

stability of slopes. 

Another study at the Fernow showed that 

amounts of erosion and sedimentation resulting 

from logging 50-year-old hardwood stands were 

closely related to the severity of soil disturbance, 

which in turn depended principally on the care 

used in laying out and draining skidroads. Logging 

86 percent of the timber volume with no road plan 

and no provisions for drainage resulted in a maximum turbidity of 56,000 p/m; 38 percent of all 

samples had more than 10 p/m. Logging 20 

percent of the timber volume using careful road 

planning and provision for adequate drainage 

produced a maximum of 25 p/m, and only 1 percent of all samples had more than 10 p/m. 

Meanwhile, the unlogged control watershed showed 

a maximum of 15 p/m, but almost all samples 

registered less than 10 p/m (Reinhart and others 

1963). 

This study emphasized how quickly sedimentation 

diminished after logging. Streamflow from the 

most heavily eroded watershed averaged turbidity 

of 490 p/m during logging; within the first year 

after logging this dropped to 38 p/m, and in the 

second year to a negligible amount (Reinhart 

and others 1963). 

A later clearcutting operation on the Fernow 

(Hornbeck 1967), for which skidroads were carefully laid out, drained, and maintained, yielded 

streamflow with a maximum turbidity of 83 p/m, 

with 95 percent of the samples (taken periodically) 

having turbidities between 0 and 10 p/m. This 

study demonstrated again that, with care, these 

forested watersheds can be clearcut and the 

products removed without seriously increasing 

stream turbidity. Hoover (1952) pointed out that 

ordinary logging procedure at Coweeta produced 

more sediment: an average turbidity of 93 p/m 

compared with 4 p/m from an unlogged watershed; maximum turbidities were 7,000 and 80 p/m, 

respectively. 

On an 800-acre timber sale on the Chattahoochee 

National Forest in Georgia, careful logging 

produced an average suspended sediment content 

of 5 p/m as compared to 4 p/m from an unlogged 

watershed (Black and Clark 1958). 

Vogenburger and Curry (1959) reported that 

during 10 years of logging on the Waynesboro, 

North Carolina, 8,000-acre watershed, 50 miles of 

road were built and 13 million board feet of 

timber were harvested-all without damaging the 

water resource. Sediment yields from a carefully 

logged watershed on the Fraser Experimental 

Forest in Colorado increased to about 100 tons per 

square mile the first year after logging; annual 

yields in the next 8 years ranged from 65 tons to 

negligible accumulations. However, over an 8-year 

period, starting with the year of logging, a statistical comparison showed no difference in mean 

annual sediment yields between the logged watershed and two nearby undisturbed watersheds even 

though timber harvesting increased streamflow by 

25 percent (Leaf 1966). In California, good logging 
showed no detectable increases in sediment discharge, independent of effects of road building 

and increased streamflow; for similar watersheds 

poor logging showed increases in sediment discharge of about 19 percent for each percent of 

watershed area so logged (Wallis and Anderson 

1965). Sediment discharge increased also with 

increased total streamflow brought about by such 

activities as road clearing or logging. In northern 

Idaho, Snyder and others (1975) reported that 

clearcut logged and slash burned areas produced 

increases in filterable solids of 4 to 14 times that 

from unlogged areas. A moratorium on logging 

and road construction and a watershed rehabilitation 

program in the upper half of the South Fork of 

the Salmon River in Idaho since 1965 has been 

associated with a decrease in fines in the downstream river channel (Platts and Megahan 1975). 

The area disturbed by logging with several types 

of equipment has been studied (table 7). Since 

these studies were not conducted and reported 

uniformly, strict comparisons cannot be made. 

They do show, however, that tractor logging 

disturbed (either quite severely or of a severity 

not designated) from 3 to 31 percent of the area; 

the various types of cable logging caused similar 

disturbance on only 2 to 16 percent of the area. 

Megahan and Kidd (1972) reported that in Idaho 

substitution of skyline logging for the jammer 

could reduce disturbance by road construction by 

75 percent. In the Pacific Northwest, skyline crane 

logging requires only about one-third the roads 

necessary for high-lead logging (Binkley 1965). 

Skyline crane logging disturbs soil even less than 

high-lead logging (Dyrness 1967b, Ruth 1967). 

The skyline crane yards logs from steep slopes 

with minimum road construction. Its pattern of 

soil disturbance is less conducive to erosion because 

its skidtrails are mostly across rather than up and 

down the slopes. The disturbance it creates is 

shallower and more evenly distributed than that 

created by the high-lead system (Ruth 1967). 

Balloon logging disturbs soil even less than skyline crane logging (Dyrness, cited by Rice and 

others 1972), but logging by helicopter disturbs 

soil the least of all (Binkley, cited by Rice and 

others 1972). 

Landslides-Road construction and tree cutting 

sometimes trigger landslides. Thirty-four of 47 

mass soil movements during the winter of 1964-65 

at the H. J. Andrews Experimental Forest in 

Oregon were found along roads, although only 1.8 

percent of the total area of the forest was in road 

rights-of-way. Movements were attributed to 

backslope, fill, or drainage failure. Along the 1.7 

miles of road, there were 34 individual mass 

movements, totalling 185,000 cubic yards of earth 

(Dyrness 1967a). Wide differences in slide frequency 

were associated with geologic rock types in the 

area (Swanson and Dyrness 1975). 

Croft and Adams (1950) attributed landslides 

in the Wasatch Mountains of Utah to loss of 

mechanical support from root systems cut and 

burned, and to some extent damaged by excessive 

livestock grazing. In southeastern Alaska near 

Ketchikan, the number and acreage of slides 

increased 4% or more times after logging began in 

1953 (11 slides during the 100 or more years 

before logging, 68 slides in 9 years during and 

after logging). Most slides occurred after 1959; the 

6-year lag perhaps reflected the time required for 

root decay. Road construction caused slope failure 

at several locations (Bishop and Stevens 1964). 

Nakano (1971) discussed resistance to uprooting 

as an index of landslide control. He observed that 

planted trees become more effective as they get 

older, but that the effectiveness of roots of tree 

stumps declines with passing time. Trees reach 

half-effectiveness at about age 30 years; stumps 

decline to half-effectiveness in 8 years after logging. 

Soil and rock movement and sedimentation 

during a slide may be spectacular. Fredriksen 

(1963) described one at the H. J. Andrews Experimental Forest, apparently triggered by rain, snowmelt, a road, and a culvert. This slide carried 

streambed gravels equivalent to 10 cubic feet 

(about 0.5 ton) per acre and suspended sediment 

equivalent to 1.1 tons per acre through the channel. 

Three years later a much heavier rain-on-snow 

storm deposited about 3,000 cubic feet per acre of 

gravel, rock, and logs in the stream channel300 times the amount measured in the 1961 

slides. 

In the interim, almost one-third of this watershed had been logged by a high-lead system and 

then the slash was burned. One of two adjacent 

areas on this watershed was an uncut control. On 

the other one, 75 percent of the timber had been 

harvested by a skyline crane (Fredriksen 1965a). 

During the 1960-68 period the area logged by highlead (6 percent was covered by roads) and then 

burned produced 109 times as much sediment 

discharge as the uncut control, and the area 

harvested by skyline crane produced only 3.3 times 

as much sediment as the control (Fredriksen 

1970). Slope failures were involved in this sedi- 
-- 

-- - 

-- 

Table 7-Area disturbed by logging, for various locations, types of cutting, and equipment 

Location and 

forest type Cutting Equipment and percent of 

logged area affected 

(1) New York and Quebec Spruce Commercial clearcutting Skyline crane: skidtrails scattered and not 

continuous; no water concentration 

(2) West Virginia: All types Tractor: Planned skidroads 2.5 to 4.6 

Appalachian hardwoods Unplanned skidroads 4.8 to 7.0 

(3) Illinois: 

Hardwoods I Selective cutting, about 

50% volume 

Tractor: Log lengths 

Tree lengths 

31 

18 

(4) Mississippi: All types, for saw-logs Litter Bare soil 

Southern pine and pulpwood Wheeled tractor 4 13 

Crawler tractor 6 8 

Mule team 6 6 

A-frame, cable 4 8 

(5) Idaho: Tractor: Single tree 3 to 18 

Ponderosa pine single-tree and Group 3 to 13 

group selection 

(6) Washington: Clearcutting Tractor: 26 in skidroads 

Douglas-fir 

- -

(7) Washington: Deep soil Shallow soil 

Ponderosa pine 65% volume Tractor 15.9 6.3 

Douglas-fir 81% volume Skyline crane 3.2 2.2 

(8) Eastern Oregon and 

Washington: Crown density reductions Tractor: 22 (bare) 

Ponderosa pine of 48% to 67% 

(9) Eastern Oregon and Deep soil Shallow soil 

Washington: 54% of board foot volume Tractor 15.0 5.9 

Ponderosa pine Cable 1.9 13.3 

Horse 2.3 9.5 

(10) Oregon Clearcutting Disturbed Compacted 

Douglas-fir, western Tractor 62 27 

hemlock High-lead 40 9 

(1 1) Oregon: Clearcutting High-lead: 16 (bare) 

Sitka spruce, western Skyline crane: 6 (bare) 

hemlock 

(12) Oregon: Clearcutting High-lead: 14.8 (bare) 

Douglas-fir, western Skyline crane: 12.1 (bare) 

hemlock 

(13) California: 40% to 90% volume Tractor: 22 (bare) 

Sugar and ponderosa 

pines, white fir 

Compiled as follows: 

(1) Fobes 1950 (6) Steinbrenner and Gessel 1955 (10) Dyrness 1963' 

(2) Mitchell and Trimble 1959 (7) Wooldridge 1960 (11) Ruth 1967 

(3) Herrick and Deitschman 1956 (8) Garrison and Rummell1950; 1951 (12) Dyrness 1967b 

(4) Dickerson 1968 (9) Garrison and Rummell 1950; 1951 (13) Fowells and Schubert 1951 
mentation. The first slide originated from soil 

spilled over the hillside below a road being constructed. Thirty-two other landslides occurred 

in the patch-cut watershed during the storm in 

December 1964; all but three were adjacent to 

stream channels. No landslides occurred in the 

uncut control watershed. 

Landslides are not so serious a problem in much 

of the East as in parts of the West. Flaccus (1958) 

concluded that the slides he studied in New Hampshire were not appreciably affected by logging or 

road construction. 

A Logging-Flood-Sediment Interaction-Predieting expected increases in sedimentation after 

logging may be complicated by weather variations. 

Studies have shown that watersheds may produce 

much more sediment in years immediately following a major flood especially when the areal extent 

of major storms coincides with watershed areas 

harvested by improper logging methods, or by 

inadequately designed roads (Anderson 1970b). 

For example, the first year after the December 

1964 flood in north coastal watersheds of California, 

sediment production increased by as much as 33 

tons per acre. Sedimentation the first year after 

this flood was as much as five times the preflood 

amount. Analysis of records from 31 watersheds 

after such major floods showed that the sediment 

increases were associated with topographic differences, the size of the flood in the individual 

watersheds, and the past land use in watersheds; 

these differences also affected the time to recovery 

from the major flood effects on sedimentation. 

The major result of that study (Anderson 1970b) 

was the evidence that poor logging practices, such 

as locating roads adjacent to streams and landings 

in draws, caused increased sediment concentration 

after the floods. Contrasting two watersheds, one 

with the average amount of poor logging (19.2 

acres per square mile or 3 percent of the total area) 

and the other with no logging, the watershed with 

the combination of poor logging and a large flood 

had a 70-percent greater increase in sediment after 

the flood. The increases in sediment discharge 

were greatest on the steepest watersheds and on 

those at higher elevations. Increases in sediment 

discharge lessened each successive year after the 

flood; however, the return to normal conditions 

can be slow. 

There is no question that poor logging increases 

sedimentation by several times the normal. The 

rate of watershed recovery after a combination of 

poor logging and major floods was analyzed by 

the regression of annual sediment yields of some 

northern California watersheds. This analysis 

indicated that 10 additional years would be required 

for recovery of a watershed subjected to poor 

logging over 100 percent of its area and to the 

impact of the 1964 flood (Anderson 1972). 

Evapotranspiration 

Evapotranspiration may be reduced in proportion to the area of the timber stand which is cut. 

The reduction integrates reduced interception, 

reduced transpiration from the canopy, and a 

small increase in evaporation from the more 

exposed forest floor. The reduction occurs principally during the growing season. Clearcutting 

may also increase snow evaporation-in California, 

for instance, from about 0.6 to 2.6 inches, 

depending on exposure (West 1962). 

Evapotranspiration is rarely measured directly. 

Aerodynamic or mass and energy budget techniques have not been widely used in evaluating 

forest harvest effects on evapotranspiration, chiefly 

because of the sampling problems involved. Our 

information on how timber harvesting influences 

it is gained mostly from the measurement of 

changes in soil-water storage and streamflow. 

Soil-Water Storage 

Both storage capacity, at least to a slight extent, 

and storage opportunity can be reduced by cutting 

trees. Capacity is reduced proportionately as soil 

organic matter and accumulations of forest humus 

are reduced. Where regrowth is rapid, as noted, 

this can be only a minor effect. Storage capacity 

and opportunity are also reduced where the forest 

floor is transformed to roadbed or skidtrail; 

usually this is only a small percentage of the 

harvested area. 

However, in the whole logged area, the opportunity for storage may be greatly reduced during 

the growing season and for some time after it. 

For example, Ziemer (1964) found that in early 

September, when moisture depletion is maximum 

in red fir on the western slopes of the Sierra 

Nevada, forest openings 1 year old had 6.9 inches 

less storage opportunity per 4 feet of soil than the 

surrounding forest. With regrowth the difference 

rapidly diminished: 2.9 inches at 5 years, 1.2 

inches at 10 years, and negligible differences at 
16 years. Reduction of storage opportunity, of 

course, is water "available for streamflow" in the 

succeeding year (Wilm and Dunford 1948). 

Shallow soils undergo little change in soil-water 

storage opportunity, because regrowth or a 

replacement ground cover dries the soil readily, 

using about as much water as the original forest 

cover did. 

Duration of the effect of clearcutting is related 

to soil depth. Seven years after commercial clearcutting of a shallow-soil watershed at the Fernow 

Experimental Forest, 78 percent of the original 

increase in streamflow had disappeared. On a 

watershed at Coweeta with a much deeper soil, 

20 years was required to achieve a similar reduction 

after clearcutting (Lull and Reinhart 1967). 

In snow regimes, the duration of reductions of 

evapotranspiration following timber harvest 

depends on the aerodynamic placement of snow in 

relation to the opportunity for soil moisture 

storage (Anderson 1970a, Hoover 1973). 

In upland forests, three measurements may 

enable estimation of actual evapotranspiration 

and indicate the possiblity of increasing strearnflow 

by forest cutting: soil-water measurements at the 

beginning of the growing season when the soil is 

wet and at the end of the season when it is dry, 

plus a record of summer rainfall. (In areas where 

overland flow occurs or where the soil may be 

fully recharged by summer rains, estimating is 

more complicated.) In Utah, for instance, 

measurements of summer losses of soil water 

showed that mature aspen stands used 0.5 to 4.5 

inches more water from the upper 6 feet of soil 

than first-year sprouts of cut aspens (Tew 1967). 

These differences diminished rapidly in succeeding 

years as sprout stands matured. Mature Gambel 

oak utilized 1/4 to 1 inch more soil moisture 

than 1 -year-old sprouts. (Tew 1969). Clearcutting 

oak and aspen can prolong savings only if subsequent sprouting is prevented. Interclonal root 

connections also may reduce the effectiveness of 

small cleared areas of aspen (Tew and others 1969). 

Clearcutting of lodgepole pine in the Uinta Mountains of Utah resulted in 4 inches more water 

left in the soil at the end of summer as compared 

with uncut stands (Johnston 1975). 

In California, fall soil-water deficits ranging 

from 3 to 17 inches on natural forest sites may 

be reduced to 1 to 8% inches after logging or 

brush removal (Anderson 1969). 

Soil-water and supplemental measurements in a 

red fir forest in California suggest water losses of 

24 inches on unlogged forest, and first-year losses 

of 12, 15, and 18 inches for strip, block, and 

selection cuts, respectively, or savings of 12, 9, 

and 6 inches (Anderson 1969). 

Thinning can reduce use of soil water by 1 to 3 

inches. In Oregon, thinned stands of ponderosa 

pine saplings used 1 to 2 inches less water 

during the growing season than untreated stands 

(Barrett and Youngberg 1%5). Helvey (1975) found 

that heavy thinning of 70-year old ponderosa pine 

in central Oregon reduced summer soil moisture 

depletion by from 2.4 to 4.5 inches, but only 

during the first three years after treatment. 

In the fall of three successive years, a Minnesota 

red pine stand, thinned to 60 square feet of basal 

area, had 1.8, 0.5, and 3.2 inches more soil 

water than an unthinned stand with 140 square 

feet (Bay and Boelter 1963). These studies indicate 

that forests use less soil water after cutting than 

before, so more water is available for streamflow. 

However, these are index values only. Hydrologic 

processes are too complicated to permit translation 

of differences in soil moisture and other separate 

processes directly into increases in streamflow. 

Quantity of Streamflow 

Increases in streamflow after various intensities 

of cutting have been demonstrated in many parts 

of the country (table 8). Treatments other than 

timber cutting are also shown in the table for 

coniparison. Considering first-year increases only, 

the heavier the cut, the greater the increase in flow. 

Thus, maximum first-year increases in streamflow 

following clearcutting, partial clearcutting, and 

selection cutting are about 18, 8, and 4 inches, 

respectively. Where average annual precipitation 

is 48 to 90 inches, first-year increases following 

clearcutting ranged from 5 to 18 inches; with 21 

to 28 inches precipitation, increases were 1 to 3 

inches; where precipitation was 19 inches, no increase was reported. 

In Arizona removing mixed conifer forest vegetation has increased water yields approximately in 

proportion to the percent of the area in cleared 

openings and in proportion to the amount of 

precipitation during a year (Rich and Thompson 

1974). "Removal of moist-site forest vegetationDouglas-fir and white fir-from 80 acres of a 

248-acre watershed increased water yields 45 percent. Clearing an additional 100 acres of dry-site 

forest vegetation-dominantly ponderosa pinefurther increased water yields. Compared to 

original conditions, increases varied from 81 percent at 1-inch yield from the control watershed 
to 109 percent at 7-inch yield from the control. 

Clearcutting 83 percent of a 318-acre watershed 

resulted in water yield increases varying from 81 

percent at 1-inch yield from the control watershed 

to 140 percent at 7 inches from the control. 

Clearcutting one-sixth of a 900-acre watershed, 

where the remaining five-sixths of the watershed 

was placed in the best growing condition possible, 

increased water yield about 29 percent. In contrast, 

annual water yields following the individual tree 

selection harvest on South Fork of Workman Creek 

were not significantly changed by the treatment. 

A riparian cut of alder and big-tooth maple 

adjacent to streams and seeps that removed 0.6 

percent of the total basal area of all trees on the 

248-acre watershed did not significantly increase 

water yields." 

Baker (1975) reported that winter streamflow 

from ponderosa pine forest areas in Arizona was 

increased most by completely clearing a watershed. All residual slash was piled in windrows, 

which were oriented to trap and shade snow. 

Increase in runoff has averaged 1.8 inches per 

year, a 33 percent increase over an 8-year period. 

The second largest response resulted from the 

removal of 75 percent of the timber basal area by 

thinning. Here also, the residual slash was piled 

into windrows. The average increase in runoff 

was 1.3 inches per year, or 19 percent for a 5-year 

period. Another watershed was treated by removing 32 percent of its timber in uniform, downslope 

strips. This treatment yielded a 1.0-inch per year 

increase in runoff, or a 16 percent increase over 

a 6-year period. Streamflow varied directly with 

amount of winter precipitation, but was reduced 

in amount proportional to both the insolation 

received (south versus north slopes) and the 

residual timber volume after cutting (H. E. Brown 

and others 1974). 

Duration of Increased Streamflow-This depends 

on the magnitude of the initial increase, the type 

and intensity of cut, and the rapidity of regrowth. 

In the southeast, at Coweeta, after a clearcutting 

that increased flow 14 inches the first year, 

regrowth dropped the increase to 8 inches the 5th 

year, to 6 inches the 10th year, and to an estimated 

1 inch at year 35 (Kovner 1957). A recutting of 

this watershed duplicated the 14-inch increase the 

first year, but the rate of increase dropped much 

faster, reaching 4 inches after only 5 years.' In the 

' Unpublished report, Southeast. Forest Exp. Stn., Asheville, 

North Carolina. 

northeast, after 10 years there was only an estimated 

0.5-inch increase on the Fernow watershed, where 

the first-year increase had been 5.1 inches (Lull 

and Reinhart 1967), and the 2.5-inch increase 

from a selection cutting was reduced to a negligible 

quantity in 3 years. Selection cuttings and thinnings 

have only transient influences on water yield 

because roots and canopies rapidly extend into 

occupied spaces. 

In contrast, effects of treatment may persist 

longer in those western forests where regrowth is 

slow and increased streamflow is derived largely 

from differential snow accumulation. For example, 

2- to 4-inch increases in flow after a 39-percent 

strip cutting of lodgepole pine in Colorado have 

persisted for 17 years and promise to persist 

considerably longer (Leaf 1975b). In an earlier 

study the ratio of increase in snow storage in cut 

plots to that in uncut plots remained virtually 

unchanged over a 24-year period (Hoover and Leaf 

1967). 

Minimum Selection Cuts-The minimum selection cut that will produce a significant increase 

of water yield in humid regions has been estimated 

at 20 percent of the basal area of a well stocked 

stand (Douglass 1967). Clearcutting 20 percent of 

a watershed would also increase water yield significantly. Annual cutting of smaller portions, as is 

done in sustained yield programs, may or may not 

increase water yield detectably. Berndt and Swank 

(1970) noted a significant increase in streamflow 

from a small forested basin in central Oregon 

following increased timber cutting. The criteria of 

"significance" are, of course, strictly from a 

statistical point of view. Once a physical increase 

is shown, statistical significance is not necessary 

criterion-if a 20-percent clearcut increases 

streamflow by a "significant" 2 inches, a 10-percent 

clearcut's 1-inch increase is equally as physically 

significant. 

The greatest percentage increases (table 8) were 

registered in western studies, where runoff was normally low. The comparatively small increases resulting from cutting riparian areas are partly due to the 

small proportion of the total watershed that was 

treated. 

The effects of different kinds of cutting on any 

one watershed, in connection with multiple-use 

programs, have received little study. A 356-acre 

demonstration pilot watershed developed at 

Coweeta includes programs for timber harvest, 

water yield, and recreational use. Clearcutting 

(for regeneration) 180 acres of poor oak-hickory 

stands, plus improvement and understory cuts in 
Table 8-Increases in water yield following forest cutting, by forest type, geographic location, and type of cutting 

of area Water yield increases by years after treatment 

Forest or basal I 
 area area (b) 

(acres) removed 

-Inches - Inches -Percent - (1) Mixed Hardwoods, Western North Carolina 

Clearcut 100 Yes 14.4 10.9 10.9 9.8 7.9 66 46 29 26 

Clearcut 100 NO 16.8 13.0 11.7 11.4 11.2 65 - - -

Clearcut 100 NO 5.0 3.7 2.3 4.4 3.1 - - - -

Clearcut 5 0 Yes 7.8 6.1 5.1 4.4 3.9 - - - -

Selection cut 22b Yes 3.9 2.2 2.8 1.1 1.5 6 5 5 3 

Selection cut 30b Yes Averaged 0.98 per year 

Selection cut 35b Yes Averaged 2.17 per year 

Selection cut 27b Yes Nonsignificant 

Riparian cut 12 Yes Nonsignificant 

(2) Northern Hardwoods, Central New Hampshire 

35 Cleared 100 No 13.5 10.8 9.4 40 29 19 

(3) Mixed Hardwoods, Northern West Virginia 

30 Cleared 100 No 10.3 -

23 Clearcut 100 Yes 5.1 3.4 3.5 0.6 2.2 19 16 - -

(except (83b) 

for culls) 

30 Clearcut 50 No 6.1 5.8 - -

26 Selection cut 36 Yes 2.5 1.4 0.3 1.2 -0.2 10 5 1 4 

30 Selection cut 22 Yes 0.7 0.1 -0.7 -1.6 0.7 2 0 - -

25 Selection cut 14 Yes 0.3 1.3 0.3 0.3 0.0 1 5 1 1 

(4) Oak; Type, Central Pennsylvania 

13 Clearcut 20 No 2.7 

(5) Douglas-fir, Western Oregon 

57 Clearcut 100 Yes 18.2 18.0 36 33 

57 Clearcut 30 Yes 5.9 6.4 5.9 11.7 8.9 16 14 19 38 

(6) Aspen and Conifers, Colorado 

6.1 Clearcut 100 Yes 1.4 1.9 1.0 0.8 0.5 19 27 16 12 

(7) Lodgepole Pine and Spruce-Fir, Colorado 

11 Clearcut 40 Yes 3.3 5.2 3.7 4.6 5.4 32 35 43 63 

(8) Mixed Conifers, Arizona 

3.2 Clearcut 16 Yes 1.2 16 

3.4 Selection cut 32 Yes 0.5 2.0 1.6 1.9 1.2 56 45 - -

3.4 Selection cut 45 Yes Nonsignificant 

(9) Utah Juniper, Central Arizona 

0.9 Cabled, burned, 100 Yes Nonsignificant 

seeded to grass 
5 

Table 8-Increases in water yield following forest cutting, by forest type, geographic location, and type of cutting 

1 I Percent I 

Water yield increases by years after treatment 

Forest Mean annual I I I :f;:::

area precip- stream area (b) 

(acres) itation flow Treatment removed Regrowth 1 2 3 4 5 1 2 3 4 -Inches - Inches - Percent -

(10) Chaparral, Central Arizona 

95 26 2.2 Herbicide 90 Yes 3.4 3.0 2.6 9.8 14.2 111 292 589 451 235 

46 26 2.2 Herbicide 40 Yes 3.0 0.9 1.8 299 517 223 

(grass) 

(11) Oak-Woodland, Central California 

12 25 4.1 Chemical kill 100 Yes 4.0 7.9 4.0 25 65 300 

(grass) 

(12) Chaparral with Woodland along Streams, Southern California 

875 26 2.5 Riparian cut 24 Yes 0.4 -

(13) Ponderosa pine, Beaver Creek, Arizona 

Difference between predicted and 

Mean Percent of actual streamflow by years 

Watershed no. winter area treated or after treatment 

and year stream- basal area (b) 

treated flow ~reatrnent removed 1 2 3 4 5 6 Mean difference 

-Inches - Inches Percent 

12, 1967 6.04 Clearcut 100 3.79 0.92 1.81 1.47 1.39 3.29 2.00 35 

9,1968 6.70 Clearcut in uniform 32 1.98 .61 .34 .84 1.74 1.10 16 

strips 

17,1969 7.63 Thinning 75 .85 1.45 1.51 2.93 1.68 222 

14,1970 4.71 Clearcut in irregular 50 .71 .70 1.61 1.01 2 1 

strips, thinning 

bet. strips 

16,1972 5.45 As above 65 5.60 5.60 103 

'Blank = no data available; dash = no percent given in source reference. 

Compiled as follows: 

(1) Dunford and Fletcher 1947, Johnson and Kovner, 1954, (6) Bates and Henry 1928, Reinhart and others 1963 

Hewlett and Hibbert 1961, Hibbert 1967 (7) GoodeU 1958, Martinelli 1964 

(2) Hornbeck and others 1970; Pierce and others 1970 (8) Rich 1968, U.S. Dep. Agric. Forest Serv. 1964a 

(3) Reinhart and Trimble 1962, Reinhart and others 1963, (9) Brown 1965 

Patric and Reinhart 1971, files of Northeastern (10) Hibbert 1971 

Forest Exp. Stn. (11) Lewis 1968 

(4) Lynch and Sopper 1970 (12) Rowe 1963 

(5) Rothacher 1970 (13) H. E. Brown and others 1974 
92 acres of a cove type to increase water yield, 

increased streamflow the first year by 10 percent 

(6.2 inches) (Hewlett and Douglass 1968). 

Streamflow Timing-The time of the year when 

streamflow increases following timber harvest 

has been less dealt with experimentally than total 

annual increases, for they have an added dimension 

of variability and hence are more difficult to 

demonstrate to be statistically significant. Examples 

of timing of streamflow must suffice. 

At Fernow, clearcutting two watersheds in 

hardwood forest increased the low flow in June 

through October by about 1/2 to 1 inch per month 

(Kochenderfer and Aubertin 1975). Flow from 

November through May was less than or about 

equal to flow from the uncut watershed. Before 

the cutting, streamflow had dried up periodically; 

after treatment, flow remained above 0.3 csm 

(Patric and Reinhart 1971). 

At Coweeta, increases in streamflow during the 

7 years when one watershed was kept clearcut 

started to increase (compared with the control) in 

June, with a 0.2-inch increase, reached about 1-inch 

increases in the months of August through.October, 

and increased in November and December to 1.5 

inches per month; then the increases were less, 

until no appreciable increases were noted during 

April and May. Increases during the 4 driest 

months, August through November, totalled 4.42 

inches, double the normal flow and equivalent to 

about one-half of the total average annual increase 

from the clearcutting of 8.67 inches (Douglass 

and Swank 1975). 

At Fraser, Colorado, nearly all of the increased 

flow of 3.5 inches, associated with the 39-percent 

strip cutting, came in May and early June, with 

some deficit in flow in late June, about equal to 

the excess in early June. Recession flows during 

the July through September period were about 

equal in the cut and the control watersheds (Leaf 

1975b). 

At the Central Sierra Snow Laboratory, a commercial selection cut increased streamflow by 7 

inches; about half of that increase was in June 

(Anderson 1963). 

At the H. J. Andrews Experimental Forest, 80 

percent of the 18-inch increase in streamflow 

resulting from a clearcut harvest occurred in the 

wet October to March season, but even in the 

driest month, September 1967, the increase was 

0.15 inch, a 150-percent increase over that from 

the uncut condition. This increase is important, 

for it supplies an extra 87,000 gallons per day 

per square mile of clearcut watershed. Threemonth increases averaged 0.8 inch in July to 

September and 3.6 inches in April through June 

(Rothacher 1970). 

In all areas the streamflow following forest 

harvesting increased in seasons when augmented 

water supply was most needed. 

Peak Flows 

and Stormf low Volumes 

Peak flows result from the simultaneous arrival 

of water and waterborne debris from many sources. 

The effect of timber cutting on small watersheds 

indicates its effect on floods in general. The first 

eastern study of effects of clearcutting on watersheds was started in 1941 at Coweeta Hydrologic 

Laboratory. A 33-acre watershed was clearcut; 

trees were left where they fell, and sprouts were 

cut annually. Annual streamflow increased by an 

average of about 11 inches, but maximum peak 

discharges did not increase (Hoover 1945, Hewlett 

and Hibbert 1961). 

More recently at Coweeta, after a 108-acre 

mature hardwood forest on a high-elevation 

watershed was clearcut, peak flows increased by 

an average of 9 percent. Volume of stormflow 

from all major storms increased by an average of 

11 percent, or 0.23 inch at the mean storm 

runoff of 2.1 inches. Larger storms produced 

greater effects: a 7-day flood sequence increased 

the volume of storm runoff by 22 percent but 

amounted to less than 1 inch of direct runoff. 

No overland flow was observed (Hewlett and 

Helvey 1970). 

A study of commercial logging on watersheds in 

West Virginia showed that the effects on storm 

peaks depended on the season (Reinhart and 

others 1963). In this study all timber of commercial 

value (86 percent of the total volume) was removed 

from a hardwood-forested watershed. Instantaneous 

peaks (all far less than flood magnitude) during 

the growing season increased by an average of 21 

percent; in the dormant season they were apparently 

reduced by 4 percent. In a clearcut watershed 

storm-period discharges were more than doubled 

in the growing season, and snowmelt flows were 

reduced. In Japan, clearcutting a 6-acre watershed 

increased peak runoff from heavy rains about 20 

percent (Maruyama and Inose 1952). No overland 

flow was observed in either of these studies. The 

Japanese, Fernow, and Coweeta studies indicate 
that timber can be cut heavily without causing 

watershed deterioration that results in overland 

flow, although some peak flows increase. 

In a study at the Hubbard Brook Experimental 

Forest in New Hampshire, an unusual treatment 

-removal of both forest and ground cover and 

prevention of regrowth-was applied. Summer 

peak flows increased considerably. For the six 

highest peak flows during June through September, 1966 through 1969, in the untreated control 

watershed, the peaks for a 39-acre denuded 

watershed averaged double the expected 49 

ftY s/mi2, with the increases for the individual 

events ranging from -19 to 250 percent. Most of 

this variation was due to differences in available 

storage for soil water; infiltration, apparently, 

was not a limiting factor. Changes in dormant 

season high flows not involving snowmelt were 

usually negligible; this indicated the similarity in 

soil water regimens of the treated and untreated 

watersheds in this season (Pierce and others 1970, 

Hornbeck 1973). 

Clearcutting can either decrease or increase 

rates of flow when snowmelt is involved. 

Clearcutting a small watershed at Hubbard Brook 

increased peak flows early in the snowmelt season 

by as much as 35 percent (from 59 to 79 

ftY s/mi2 ) and decreased them as much as 66 

percent (from 34 to 12 ftY s/mi2 ) later in the 

season (Hornbeck and Pierce 1969). 

Western situations are complex, and research 

results reflect this. First, fewer data are available 

from western experimental watersheds (excluding 

the Southwestern brushland region); moreover, 

for much of the region the source of floods is rain 

on snow or snowmelt rather than rainfall alone. At 

the H.J. Andrews Experimental Forest in central 

Oregon, along the western slope of the Cascades, 

no effect of clearcutting one-third of a 250-acre 

watershed was at first apparent on maximum 

flows because rainfall came mostly in lowintensity winter storms of considerable duration 

(Rothacher 1965a). A later report (Rothacher 

1971) presents data showing that increases in 

storm peak flows in the clearcut watershed 

depended on the amount of rainfall during the 30 

days before the storm. In the 1965-69 period, the 

peaks for 84 percent of the storms were greater in 

the clearcut watershed than in the uncut control, 

and were generally greater when the rainfall in 

the preceding 30 days had been less than 22 

inches. Ninety percent of the 73 storms in the 

1965-69 period occurred when antecedent rainfall 

had been less than 22 inches, but the highest 

peaks generally occurred when antecedent conditions had been wet. Peaks showed little or no 

increase after 22 inches or more of antecedent 

rainfall. The record shows the damping influence 

of the forest on peak flows from storms. Other 

clearcuttings in Oregon (Krygier and Harr 1972) 

increased peaks from fall storms by 90 percent 

and from winter storms by 28 percent. 

At Fraser, Colorado, harvesting gave mixed 

results: cutting 39 percent of a lodgpole 

pine-spruce-fir stand in strips 1,2,3, and 6 chains 

wide increased peak discharge from snowmelt by 

50 percent the first year; discharge the next year 

was 23 percent less than had been expected, and 

the third year it was 45 percent greater than had 

been predicted (Goodell 1958). For this high 

Rocky Mountain area, maximum peaks are less 

than 22 ft Y s/mi2 . Lesser cuts have lesser effects. At Coweeta, 

cutting a dense laurel-rhododendron understory 

and riparian (streamside) vegetation did not 

increase maximum peak discharges; and there 

were no overland flows (Johnson and Kovner 

1954). At the Fernow, selection cuts that removed 

20 to 59 percent of the original stand produced no 

perceptible effect on peak flows (Reinhart and 

others 1963). 

Studies of the effects that various treatments 

have on small watersheds under varied conditions 

hardly ever tested the effects of rare events 

associated with large floods-large areas of 

frozen soil, snowmelt augmenting rain runoff, or 

large floods carrying debris. Furthermore the 

treatments usually applied do not drastically 

change the soils. Reinhart (1964b) pointed out 

that distinction should be made betweeen 

clearcutting steep lands and converting them to 

pasture or crops, and clearcutting gentle slopes 

without seriously compacting the soil and 

permitting regrowth. As long as the forest floor 

remains intact, most of the beneficial hydrologic 

effects of the forest may continue to be present. 

Peak flows for several whole large watersheds 

in Oregon were considerably changed (Anderson 

1952). Where watersheds had been logged and 

then burned and where 45 percent of the area was 

left unstocked or poorly stocked, peak flows 

increased by more than 30 percent. 

Anderson and Hobba's (1959) analysis of forest 

cutting and peak flows on 54 watersheds in the 

Northwest approached the forest-flood relationship broadly. From data on watershed differing in 
size, geology, topography, and land use, they 

developed equations for predicting peak discharges based on climatic and watershed variables; they then related deviations of predicted 

from actual discharges to difference in forest age 

and stocking. In those watersheds the standard 

cutting practice had been to clearcut large blocks 

and then broadcast-burn the slash. Anderson and 

Hobba predicted that clearcutting 1square mile of 

Douglas-fir under the practice then current would 

increase the flood peak of rainstorms on ripe snow 

from a watershed by 103 ft3/ s. 

The results of their analysis indicate that forest 

cutting does not drastically affect major floods 

from large basins if sustained-yield management 

is properly applied and if the logged area is 

promptly and fully restocked. If, for instance, 1 

percent of a watershed were cut over each year, 

the increase in peaks would average about 9 

ft3/s/mi2 . This would be only a 6 percent 

increase in the 100-year flood, but more than 

20-percent increase in the mean annual flood. On 

the other hand, large areas in the region studied 

have failed to restock after fire or logging. 

Further, some watershed channels might be 

unstable under a 20-percent increase in annual 

flood flow. 

An analysis of snowmelt floods on watersheds 

on the east side of the Cascade Mountains showed 

that peak flows would be expected to increase by 

about 11 percent when one-half of a watershed 

was burned or poorly stocked; but logging or 

burning half of the watershed would be an 

extreme case (Anderson and Hobba 1959). 

Water Temperature 

Clearcutting near streams sometimes raises the 

water temperature sufficiently to reduce fish 

populations. One obvious remedy is to leave trees 

or shrubs along the channels, where they will 

shade streamflow (Brown and Krygier 1967). In 

West Virginia, Reinhart and others (1963) found 

that clearcutting raised maximum temperatures 

by an average of 8OF during the growing season. 

Temperatures exceeded 7S0F several times; these 

temperatures would probably harm most resident 

trout and salmon (Lantz 1971a). In western 

Oregon, daily temperatures rose 2' in March and 

as much as 14' in September; from August 1 to 15 

the mean high temperature was above 70Â°F On 

the H.J. Andrews Experimental Forest one clear 

day in May, the midday temperature of water 

flowing for 1 hour through an exposed channel 

1,300 feet long increased by 16OF (Brown and 

Krygier 1967). 

Widespread checks of similar logged and 

unlogged drainages in Oregon have shown 

temperatures to be as much as lo0 higher in 

logged areas where riparian vegetation was 

completely removed (Chapman 1962). Two years 

after complete clearing of a Douglas-fir forest in 

the Alsea Watershed, the stream temperature 

reached a high of 8SÂ°F-28 higher than on the 

unlogged control (Krygier and others 1971). On a 

patch-cut watershed with a buffer strip along the 

main stream, the maximum temperature was 

61.SÂ°F 

Exposure of the stream surface to direct solar 

radiation is the principal cause of increased water 

temperature (Brown and Krygier 1967). Undeistory vegetation that survives clearcutting may 

provide considerable protection. For example, at 

the H.J. Andrews Experimental. Forest, dearcutting along increased maximum water temperature 4OF, but the slash burning that followed 

removed old protective stream cover; then the 

mean monthly maximum water temperature for 

June, July, and August increased by 12' to 14OF 

(Levno and Rothacher 1969). 

Water temperature may be lowered as a stream 

flows from an exposed area into a protected one. 

For instance, routing an open, exposed trout 

stream in Wisconsin through the shade of a willow 

grove reduced later afternoon summer water 

temperatures by lo0 to 11' F (Stoeckeler and 

Voskuil 1960). In one study of a patch-cut logging 

area in Oregon, water from the logged portion 

cooled as it passed through shaded areas 

downstream or was diluted by cooler water from 

uncut watersheds (Levno and Rothacher 1969). 

However, in a large-scale test in the Umpqua 

Basin, also in Oregon, local shading of the stream 

apparently did not significantly lower the temperature of water that had been warmed by exposure 

in a logged-over area upstream; the investigators 

concluded that the chief cooling effects were from 

inflow of groundwater (Brown and others 1971). 

Shading upstream tributary streams is important. 

Certain forest effects on radiation and subsurface flow account for significant differences 

observed between large streams and small ones. 

On reaches of large streams that are oriented east 

and west, for example, longwave radiation from 

trees on the north side may well heat the water in 

summer, when the sun is high. Removing these 
trees would both reduce this heating and release 

cooling groundwater in summer; (it might 

possibly increase warming groundwater flow in 

winter). Clearly, tree cutting alongside streams 

should not be prohibited on the basis of stream 

shading alone. The degree of shade desired may 

depend on the effects of the resultant stream 

temperature on water chemistry. 

Water Chemistry 

Timber felling and repeated herbicide treatment completely denuded a forest ecosystem on a 

New Hampshire watershed that had podzol soils 

derived from glacial tills. This treatment increased cation loss by 3 to 20 times; nitrate 

concentration in the streamwater increased from 

about lp/m to 58 p/m (Bormann and others 

1968). As this study continued, nitrate concentrations of as much as 80 p/m were noted, with an 

overall increase of about fiftyfold for the 3-year 

period 1967 through 1969 (Pierce and others 

1970). This nitrate concentration produced a 

noticeable algal growth in the stream. Later, 

Pierce and others (1972) reported on the effect of 

timber harvesting, also in New Hampshire. From 

one clearcut area, the highest nutrient concentrations were only one-third to one-half the levels 

reached in the denuded watershed. "For the first 4 

years of the strip-cut harvest, stream water 

concentrations increased by more than 7 mg/1 for nitrate, 0.9 mg/1 for calcium, and 0.3 mg/1 for potassium. Sulfate concentrations declined by as much as 

1.5 mg/l. In contrast, block clearcutting caused 

maximum increases of 23 mg/1 for nitrate, 3 mg/1 for 

calcium, and 1 mg/1 for potassium, and an apparent 

decrease of 2 mg/1 for sulfate." (Hornbeck and others 

1975). 

Other studies have shown lesser effects of 

watershed disturbance on nutrient discharges in 

streamflow. Aubertin and Patric (1974) found 

only a slight increase in dissolved solids during 

the 2 years following the clearcutting of a 

hardwood forest watershed in West Virginia; the 

maximum concentration of nitrate-nitrogen measured was 1.4 p/m. 

From their studies of mineral balances for 

various disturbed and undisturbed watersheds, 

Swank and Elwood (1971) concluded that the 

rather drastic alterations of the forest ecosystem 

at Coweeta Hydrologic Laboratory had apparently 

not resulted in large, accelerated cation losses to 

drainage waters. However, they did not measure 

mineral presence on watersheds immediately 

after tree cutting or other disturbances. They 

reported that 10 years after a commercial logging, 

nitrate-nitrogen in streamflow increased by 1.9 

pounds per acre per year. This is less than the 3 

pounds normally added from rainfall (Swank and 

Douglas 1975). While forests were in various 

stages of natural revegetation following cutting, 

increased nitrate-nitrogen content in the streamflow was evident for at least 10 years after cutting, 

but appeared to return to "baseline levels" 20 

years after the cutting. In a study in Minnesota, 

Verry (1972) reported no change in the composition of streamwater after clearcutting of aspen. 

Fredriksen (1971) measured the loss of nutrients after timber harvesting and broadcast slash 

burning in old-growth Douglas-fir on the H.J. 

Andrews Experimental Forest.. Nutrient cation 

discharge was 1.6 to 3.0 times that from an 

undisturbed watershed; annual nitrogen loss 

averaged 4.6 pounds per acre compared to 0.16 

pound per acre from the undisturbed watershed; 

but average monthly concentrations never exceeded 0.4 p/m. 

Hart and DeByle (1975) studied subsurface 

water chemistry under different slash treatments 

after clearcutting of a stand of 175-year old 

lodgepole pine. Except for a flush of nutrients 

soon after slash burning, they found no apparent 

differences in the soil solution under four slash 

disposal systems. 

Brown's review (1972) of logging and water 

quality concluded that nutrient losses from 

Northwest forests after clearcutting were a minor 

short-term problem for both the terrestrial and 

aquatic systems. Gibbons and Salo (1973) have 

published an annotated bibliography of 278 

publications related to the effects of logging on 

fish populations in the Western United States and 

Canada. 

Summary 

Timber harvesting increases water yield primarily by reducing evapotranspiration. The 

potential for increased yield is greater where 

precipitation is higher. Where rainfall and 

seasonal evapotranspiration are important, the 

situation is different from those involving snowfall 

and changes in snow interception, distribution, 

and melt rate. 

In areas where snow is not important, the 

increase in water yield the first year after cutting 
appears to be proportional to the percentage of 

basal area cut, and the water yield increases 

mainly during and immediately after the growing 

season. Increases diminish as the forest regrows; 

they may continue for 10 years or less where 

regrowth is rapid and soils relatively shallow. 

Where regrowth is slow or where soils are deep, 

increases may persist much longer. 

Water yield increases from timber harvesting in 

snowpack areas occurs mostly in the spring or 

early summer period of snowmelt discharge; the 

increases following harvesting persist longest 

where vegetation recovery is slow. 

The effect of timber harvesting on floods varies. 

Several factors limit increases in flood peaks and 

flood runoff even after clearcutting, the harvest 

method with the greatest impact. Timber harvesting does not generate overland flow except where 

it disturbs the forest floor. Overland flow from 

logging roads and other disturbed areas is partly 

absorbed by infiltration into adjacent areas, 

especially where logging operations are well 

planned and executed. The effect of cutting on 

flows is diminished, especially in regions where 

precipitation is ample and well-distributed, as 

regrowth reestablishes interception and soilwater retention opportunity. Under sustainedyield management or where forest holdings are 

many and small, only a small proportion of any 

sizable drainage is likely to be cut over at one 

time. 

The fact remains that clearcutting can increase 

flood flows, especially when soil disturbance is 

widespread, where regrowth is slow or covers 

only part of the area, or when snowmelt 

contributes a sizable portion. 

Several conditions accentuate the problem in 

the West as compared to the East: These include 

slow regrowth in many areas because of low 

rainfall, especially in the growing season; greater 

volumes of timber and bigger logs in other areas, 

resulting in the need for bigger equipment and 

greater soil disturbance; and the practice in many 

areas of burning debris after logging. 

Timber harvesting and its associated roads can, 

have, and often still do cause serious erosion and 

sedimentation. The amount of damage on site, in 

local streams and downstream, varies widely with 

topography, climate, soils, and the amount of soil 

disturbance, which depends on such things as 

care in logging, intensity of cut, and the 

equipment used. For many areas, responsible 

logging can keep damages within bounds, but 

better practices than those applied in many areas 

in the past will be required. 

In some steep, fragile areas, conventional 

logging may not be possible without intolerable 

damage. Use of the skyline crane, or of balloon or 

helicopter logging (assuming their use is demonstrated to be practicable) may make timber 

harvesting feasible in these areas. Even with such 

techniques the susceptibility of stream banks to 

scour and sliding induced by increased streamflow following timber harvesting will need to be 

appraised. 

For many of the same reasons we discussed 

with respect to timber harvesting and floods, the 

effect of timber harvesting on erosion, including 

its effect on water quality, is generally a greater 

problem in much of the West than it is in the East. 

Timber harvesting sometimes increases stream 

water temperatures to the detriment of cold-water 

fish. Stream temperatures can be kept cool by 

preserving all or part of the vegetation shading 

the stream channel. Increased water temperatures may sometimes stimulate a favorable 

production in the food chain. 

Research to date indicates that clearcutting 

does not increase volumes of dissolved solids 

enough to lower water quality below drinking 

water standards. However, nitrogen discharge 

may frequently, though temporarily, exceed the 

concentrations necessary to increase the growth 

of algae. It has been reported that less than 0.5 

p/m of nitrogen may cause such growth (Tarrant 

1972). Of the studies so far conducted, only those 

on podzol soils in New Hampshire indicate that 

clearcutting may diminish the nutrient capital of 

the soil. Partial cuts, of course, have less effect. 

Further research on this problem is needed and is 

in progress at most forest experiment stations and 

at several universities. 

Regeneration and Tree Planting 

Forest regeneration and subsequent growth 

increase interception and, particularly, transpiration. Whether regeneration increases infiltration 

capacity depends on the soil's initial capacity. 

Water yield, peak flow, erosion, and sedimentation will gradually be reduced as trees grow in 

height and density. 

Interception 

The growth of conifer plantations over a period 

of years may substantially reduce water yield by 
increasing interception (Swank and Douglass 

1974). Take, for example, an annual rainfall of 41 

inches consisting of ten 1-inch storms, thirty 

0.5-inch, and eighty 0.2-inch. According to 

Helvey's (1967) equations, a 10-year-old eastern 

white pine stand would intercept 8.3 inches of 

water, a 35-year-old stand would intercept 9.9 

inches, and a 60-year-old stand would intercept 

13.1 inches-a reduction of water available for 

annual streamflow amounting to 4.8 inches at the 

end of a 60-year period. The oldest pine stand 

intercepts twice as much as the youngest, and 

twice as much as mature hardwood stands. From 

a single flood-producing 2-inch storm, for 

example, a 10-year-old white pine stand could 

intercept about 0.17 inch, a 35-year-old stand, 

0.23, and a 60-year-old stand, 0.34 inch (Helvey 

1967). 

Infiltration, Overland Flow, 

Erosion, and Sedimentation 

Increased rates of infiltration and diminished 

overland flow make more water available for 

evapotranspiration so less for streamflow. This 

change normally reduces both water yield and 

storm discharges. In the East, this effect is most 

pronounced in the growing season, when streamflow is much less than in the cooler months. 

Infiltration, overland flow, and ,to some extent, 

surface detention change as a plantation matures. 

The significance of the change depends on the 

surface cover and infiltration capacity at the time 

of planting. Planting a bare, eroding site may 

increase infiltration in 10 years to the point where 

overland flow and erosion practically cease (Ursic 

and Dendy 1965). On the other hand, mechanical 

site preparation in some areas of the South is 

reported to cause severely accelerated erosion 

(Dissmeyer 1976). 

Old fields may support enough invading 

vegetation to stabilize soil without trees. In West 

Virginia, measurements of streamwater quality 

showed that farmlands, abandoned for two 

decades, have healed naturally so the areas 

produce only slightly higher turbidities than 

undisturbed forest land (Hornbeck and Troendle 

1969). 

In Tennessee, planting about one-third of the 

severely eroded 1,715-acre White Hollow watershed, mostly to pine, and permitting natural 

regrowth on the rest of the watershed reduced the 

sediment load following the average storm from 

7.3 tons in 1935-36 to 0.3 ton in 1954-55, a 

reduction of 96 percent. The reduction each year 

averaged about 15 percent of the previous year's 

sediment load (Tennessee Valley Authority 1961). 

Planting two-thirds of the Pine Tree Branch 

watershed in Tennessee reduced the sediment 

load from 24.3 tons per acre in 1942-45 to 7.6 in 

1946-50, to 2.2 in 1951-55, and to 1.1 in 1956-60, 

an overall reduction of 95 percent (Tennessee 

Valley Authority 1962). In both of these watersheds, installation of check dams and other 

erosion-control measures was responsible for an 

undetermined portion of the improvement. 

Planting loblolly pine in northern Mississippi 

sharply reduced sedimentation. Annual rates of 

erosion loss on four different types of planting 

sites were: 

Land Use: -

Mean Range

Tons/A cre Tons/A cre 

Pine plantation (22 yrs old) 0.02 0.00 to 0.08 

Mature pine and hardwoods 0.02 0.01 to 0.04 

Abandoned fields 0.13 0.01 to 0.54 

Cultivated lands 21.75 3.28 to43.06 

The pines had been planted on abandoned fields 

where erosion had removed an estimated 2 feet of 

the surface and had cut gullies 5 feet below the 

level of the remaining soil (Ursic and Dendy 

1965). The planting has reduced erosion to near 

the geologic norm for forests in the area. 

Six years after trees were planted on eroded 

cropland at Coshocton, Ohio, they established a 

nearly complete ground cover, sheet erosion 

practically ceased, and small gullies were 

stabilized (Harrold 1961). 

Soil-Water Storage 

Major increases in detention storage may also 

follow forest establishment and growth. For 

instance, on an experimental watershed at 

Coshocton, Ohio, the volume of noncapillary pore 

space in the surface 7 inches of three types of soil 

under three kinds of cover was as follows (Harrold 

and others 1962): 

Hardwood 

Idle land Pine cover cover --------------Percent (by volume)------------ 

Soil type: 

Keene silt loam 11.4 14.7 16.5 

Muskingum silt 

loam over: 

Sandstone 

and shale 14.9 23.4 23.1 

Sandstone 21.3 25.2 24.4 
Thus the two forest stands had from 15 to 55 

percent more detention storage space than the 

idle land. 

Reforestation of old fields, however, may not 

quickly restore detention storage everywhere. In 

South Carolina's Piedmont, Hoover (1950) found 

detention storage of 4 inches in the upper 24 

inches of undisturbed hardwood forest soil, 

whereas under a pine stand 25 to 30 years old with 

a sandy plow horizon, detention storage was 1.2 

inches; detention storage totaled 17 and 5 percent 

by volume, respectively. 

Evapotranspiration and Streamflow 

Evapotranspiration increases as regeneration 

develops. After two clearcut watersheds at 

Coweeta were planted to white pine, streamflow 

steadily decreased (and evapotranspiration -

including evaporation of intercepted water - increased). The cleared plantations averaged 2.5 and 9 

inches more water yield, respectively, the first 6 years 

after planting; but once the crown began to close the 

rate of increase declined to 1 to 

2 inches per year, until at age 10 years the first 

watershed had 3.7 inches less yield, and at the 

age of 11 years the second had 1.3 inches less 

(Swank and Miner 1968). At age 15 years both 

watersheds had about 7.9 inches less streamflow 

than had been predicted if the watersheds had 

remained in hardwoods (Swank and Douglass 

1974). 

Streamflow from a 491-square-mile watershed 

in the Adirondacks decreased 7.7 inches (or 

evapotranspiration increased) over a period of 39 

years, as the forest density and crown cover of 

conifers increased (Eschner and Satterlund 1966). 

The amount of reduction in yield must 

obviously depend on the proportion of the 

watershed planted. If we extrapolate the decreases in water yield [table 91 for partial 

plantings in Ohio, western Tennessee, and New 

York to those for complete planting, the reduction 

would range from about 6 to 9 inches for four of 

the five examples, and to 19 inches for the New 

York watershed where 35 percent of the area was 

planted. The decrease in New York may have 

been greatest because snow was an important 

meteorological factor there. 

Peak Flows 

Increases in interception, infiltration, and 

opportunity for soil-water storage concurrent with 

plantation growth may sharply reduce peak 

discharges. This reduction varies with the type of 

cover before conversion, and the proportion of the 

watershed planted; reductions differ also between 

seasons of the year. The results of four studies 

appear in table 10. The reduction in peaks of 16 to 

66 percent in the New York study was attributed 

to the lower melt rate of snow shaded by the 

conifers in winter; some of this reduction, 

however, could have resulted from greater 

retention of soil-moisture provided by increased 

transpiration during the preceding growing 

season. 

Planting the Tennessee watersheds reduced 

summer peaks by amounts ranging from 62 to 92 

percent. The much greater reduction in winter 

peaks on the Pine Tree Watershed, compared to 

those on White Hollow, may be due to the 

relatively greater area planted and to the smaller 

area of the watershed. 

A planted forest appears to be more effective in 

reducing peak flows than a cutover forest is in 

increasing water yield. This apparent difference 

probably arises from the establishment of forest 

floor and improved soil conditions in the new 

plantation, whereas merely cutting the forest 

trees does not, by itself, usually destroy the forest 

floor or the hydrologic attributes of the soil. Then 

too, the cut forest often recovers to some form of 

vegetation before the soil hydrologic attributes 

deteriorate sufficiently to affect most floodproducing events. 

Planting trees, especially conifers, effectively 

reduces peak flows. Planted land is likely to receive 

better protection from fire and grazing than idle 

land-protection that will maintain flood-control 

benefits. 

Above-normal temperatures in the spring 

occasionally cause abnormally rapid melting of 

snow accumulated under plantations; and the 

greater the depth of snow in the forest, the more 

it may add to above-normal peak flows. Such 

flows are most damaging when they are well 

synchronized, which means that heavy flows from 

all parts of the watershed arrive downstream at 

the same time. Such watersheds require desynchronization of peak flows; this is provided by 

the juxtaposition of open and forested lands such 

as now exists in the northern Allegheny Plateau of 

New York (Satterlund and Eschner 1965); a 

mixture of conifer and hardwood areas may also 

desynchronize potentially destructive peak flows. 

In forest regeneration and tree planting, site 

preparation may include measures that lay bare 
Table 9-Effects of reforestation on water yield from varied conversion plantings in Ohio, Tennessee, New York, and North 

Carolina 

I I~retreatmentmean annual . . .I I 

Forest cover in Location before planting Precip- Stream- Conversion planting by water yield extent and type itation flow for given year 

I -Inches - Inches 

(1) Ohio 30% hardwoods 38 12 71%, pine 5.3 ( 9 yr) 

(2) Western Tennessee 23% hardwoods 5 0 10 65%, mostly pine 3 to 6 (16 yr) 

(3) Central N.Y. 1. Mixed hardwoods 38 2 1 47%, conifers 4.2 (24 yr) 

(3 watersheds) 2. do. 41 24 58%, conifers 6.8 (23 yr) 

3. do. 4 1 25 58%, conifer's 5.1 (23 yr) 

(4) Western Tennessee 65% mixed hard- 4 7 18 34%, mostly pine 0 

woods and pine 

(5) Chenango River Abandoned farm- 45 25 7%, conifer plantations 1.0 (42 yr) 

Basin, New York land (10% second growth 

hardwoods) 

(6) Western Hardwoods: 

North Carolina Watershed 1 68 3 1 loo%, white pine 5.6 (10 yr) 

Watershed 17 76 27 loo%, white pine 10.9 (1 1 yr) 

Compiled as follows: (1) Harrold and others 1962; (2) TVA 1962; (3) Schneider and Ayer 1961; (4) TVA 1961; (5) Muller 

1966; (6) Swank and Miner 1968. 

the mineral soil to improve the seedbed for 

natural seedfall; it could include also any methods 

for removal of vegetation that would compete 

with the trees being planted. These practices may 

promote erosion and sedimentation and therefore 

must be used with care. Wherever dense stands of 

brush have been removed, increased streamflow 

must be expected until vegetation is reestablished 

and develops. 

Summary 

Regeneration of forest stands, either by natural 

seeding or by planting trees after timber harvest, 

reverses the effect of harvesting. Water yield, 

stormflow, erosion, and sedimentation are likely 

to be reduced. The rate of this reduction depends 

upon the rate of growth of new herbaceous and 

woody vegetation, which is influenced by climate, 

the success of regeneration measures, and other 

factors. 

Planting of previously unforested areas can 

have a much greater effect than reforestation; 

the difference in effects depends largely on the 

extent to which the prior cover protected the site 

and utilized available water in evapotranspiration. 

Type Conversions 

Conversion from one vegetation type to another 

may be advocated for a variety of reasons, 

including greater timber production or' increased 

water yield. Conversion may have important 

hydrologic effects, but firm data are scarce for 

many of the different possible conversions. 

Most tree planting in the East has been conifers, 

even where hardwoods were the original cover. 

Studies in Michigan and North Carolina showed 

that conifers use more water than hardwoods. 

In northern Michigan the annual yield of water 

from a jack pine plantation was 2.6 inches less, 

and red pine with an oak overstory 3.0 inches 

less than the yield from a deciduous stand (Urie 

1966, 1967). At Coweeta two watersheds replanted 

to white pine yielded about 7.9 inches less water 

after 15 years than the original hardwood forest. 

Most of this reduction occurred during dormant 

seasons, but some occurred in each month (Swank 

and Douglass 1974). However, streamflow increased 

during the first 6 years by an average of 2.5 inches; 
Table 10-Effects of reforestation on peak flows from selected experimental watersheds 

I Watershed condition 

Watershed location Area Effect on peak flows 

Before treatment After treatment 

(1) Shackham Brook area 25% deciduous 27% deciduous From 1939 to 1957 peak flows 

Near Truxton. N.Y. 1% coniferous 57% coniferous were reduced by 41% 

74% pasture and crops 16% pasture and crops ranging from 66% in 

November to 16% in April. 

(2) White Hollow Watershed 66% poorly stocked 100% mixed hardwood From 1935-36 to 1942-49, 

Mason Co., Tenn. mixed and pine summer peak discharges 

hardwood and pine were reduced from 73% 

4% cultivated to 95%, dependent on 

4% cultivated initial soil wetness 

26% abandoned land and rainfall intensity. 

Winter peaks were 

reduced from 0% to 28%, 

depending on amount 

surface runoff. 

(3) Pine Tree Branch 23% deciduous 33% deciduous From 1941-45 to 195 1-60, 

Watershed, 16% cultivated 65% coniferous summer peaks were 

Henderson Co., Tenn. 19% pasture 2% miscellaneous reduced 92% to 97%, 

50% idle winter peaks 71% to 

2% miscellaneous 92%, depending on 

rainfall intensity 

and soil wetness. 

-

(4) Watershed 172 29% woodland 43% natural woodland From 1938 to 1957, 

Coshocton. Ohio 51% pasture 57% forest plantation average growing season 

20% idle (pine and locust) peaks were reduced 

by 59%;dormant season 

peaks were reduced by 

69%. (Mean peaks 

were 35 and 46 ft3 /s/mi2 

in growing and dormant 

seasons, respectively.) 

No effect was found 

on peaks from extreme 

storm occurrences (data 

were insufficient for 

rigorous analysis). 

Compiled as follows: (1) Schneider and Ayer 1961; (2) TVA 1961; (3) TVA 1962; (4) Harrold and others 1962. 

so 15-year average reduction was about 1.7 inches may be chiefly a matter of rooting depth, since 

per year. Under intensive management, including the shallower rooting grass transpires less moisture 

periodic thinnings, intermediate harvests, and than trees. Other possible differences in water use 

final cutting, the water yield will be partly restored between grass and forest are the lower height and 

and the value of pine products may justify conifer smoother surface of the grass, which reduce both 

planting, even if it causes some water loss. energy absorption and vapor exchange. The shorter 

Brushland has been converted to grassland growing season of grass also influences its use of 

range in California to increase water yield and water. When precipitation is adequate to charge 

forage production. Differences in water yield the soil mantle, the potential annual increases 
from conversion of chaparral to grassland range 

can amount to 1.2 inches for a 3-foot soil, 3 inches 

for a 6-foot, and 6 inches for a 9-foot soil 

(Bentley 1967). Rowe and Reimann (1961) showed 

that increases occurred only in years when rainfall 

exceeded 25 inches and only when deep rooted 

weedy herbs were not present. Root depth was 

the key to difference in water use between trees 

and grass in western Colorado. Quaking aspen 

used 19 inches of water, spruce 15, and grass 9 

inches during the growing season. Use of moisture 

by grass was confined almost entirely to the upper 

4 feet of the 8-foot-deep soil (Brown and Thompson 1965). 

In Arizona, conversion of brush to grass increased 

streamflow from small watersheds by one-third so 

that present annual water yield is as much as 5 

inches depending on soil depth and amount of 

precipitation (Ingebo and Hibbert 1974). In another 

Arizona study (Longstreth and Patten 1975), conversion from chaparral to grass increased water 

discharge by four times, but, except for nitrogen, 

ion concentrations were similar with and without 

conversion; nitrate reached 4 mg/liter under grass, 

but was rarely detectable under the deep-rooted 

chaparral. 

Potential increases in water yield diminish as 

regrowth increases. Bulldozing woodland brush at 

high elevation in California saved 4 to 5 inches of 

soil moisture the first year for soils 4 feet deep; by 

the fifth year no saving occurred because of use by 

brush sprouts (Anderson 1963). A further benefit 

was delay in snowmelt; in the bulldozed area the 

melt in the April 1 - May 10 period was 3 inches 

less than it had been prior to brush treatment. 

When the forest becomes established in this area 

it promises 7 inches of delayed snowmelt compared 

with the brushfield. 

Grassland converted from steep forest and 

brushland is a principal source of increased suspended sediment in the streams of northern California (Wallis and Anderson 1965). Conversion to 

grass of 15 percent of the steep forest lands was 

followed by a 4.7-fold increase in sediment discharge. Erosion the first year after a controlled 

burn in Los Padres National Forest produced 3 

tons of sediment per acre from steep slopes; runoff water contained only traces of nitrogen, but 

13 lbs/ac was lost in sediment (DeBano and Conrad 1976). Areas proposed for conversion to grass 

cover should never include steep slopes or shallow 

or infertile soils liable to soil erosion or slippage. 

Mass slope instability under grass on steep 

slopes is a major problem (Rice and others 1969, 

Rice and Krammes 1971). On the San Dimas 

Experimental Forest, areas of burned brush converted to grass had 8-fold increases in landslides 

and sediment production (Rice and Foggin 1971). 

Similar consequences were noted in a northern 

California study.I0. Surveys have shown that 25 to 

30 percent of the chaparral area in southern California and Arizona can be classed as potentially 

productive for forage (U. S. Senate Sel. Comm. 

Natl. Water Resour. 1960b). However, these 

estimates were made without benefit of recent 

research results, either on methods of conversion 

or on the consequences of conversion to grass. 

At Coweeta, a 22-acre forested watershed was 

clearcut, fertilized, limed, and seeded to grassKentucky 31 fescue. The first-year water yield was 

0.67 inch less than the yield from the original 

forest. After a decline in reserves of fertilizer and 

in the production of dry matter, water yield 

increased until by the fourth and fifth years it 

was averaging about 5.8 inches more than yield 

from the original forest, an 18-percent increase. In 

the sixth year the area was refertilized; the grass 

responded vigorously, and the increase in water 

yield dropped to near zero (Hilmon and Douglass 

1968). Thus grass may present a water-saving 

alternative in forest areas that have suitable soils 

and topography. Murai (1975) noted possible 

adverse results of conversion from forest cover to 

grass. He reported that whereas natural grassland had an infiltration capacity of 40 to 70 

percent of forest land, a forested area converted 

to grass cover had infiltration capacity of only 

20 to 25 percent of its capacity when in forest. 

Contemplated conversion of forest land to grass 

should be considered with due respect to the 

possible adverse hydrologic consequences. 

The conversion of forest to agricultural or 

urban use causes major hydrologic changes, but 

the problems created are in agricultural and 

urban hydrology rather than forest hydrology, 

and therefore are not discussed here. However, 

where such conversions are being made, the 

hydrologic and other benefits of keeping some 

portion of the area in forest cover, and properly 

protecting and managing it, should not be overlooked. 

lo Burgy, R. H., and 2. G. Parazifirou. 1971. Effect of vegetation management on slope stability. (Unpublished report on 

file, Dep. Water Sci., Univ. Calif., Davis.) 
Fertilizers, Herbicides, 

and Insecticides 

Intensive forest management may include the 

use of fertilizers, herbicides, and insecticides. 

These materials can contaminate streamflow and 

groundwater, but proper control of treatments 

can substantially reduce this threat to watershed 

values. The future role of chemicals in forestry 

has been discussed by Tarrant and others (1973). 

They predicted that selective, less persistent 

chemicals will continue to be used in forest 

management, but they state that chemical applications basically are treating symptoms of unhealthy ecological conditions. 

Fertilizers 

Fertilizing forest to increase growth has become 

accepted practice in some parts of the country. 

More forested areas have been fertilized in the 

Southeast and Pacific Northwest than elsewhere. 

In the Pacific Northwest about 300,000 acres of 

forest land are fertilized annually (Moore 1974). 

Fertilizers may be used commonly in the future, 

but their effect on water quality must be considered; 

a few studies have already been conducted. 

Heikurainen and Paivanen (1970) reported the 

effects of forest thinning, clearcutting, and fertilizing on the hydrology of drained peatland in Finland. 

The groundwater table rose as much as 6 inches in 

summer after the heaviest cutting. Fertilizing, 

with associated growth stimulation, lowered the 

groundwater table by 2 to 3 inches, and there was 

an associated decrease of 24 to 28 percent in 

outflow. Moore (1975) fertilized a 169-acre forested 

watershed with 426 pounds of urea (200 pounds 

nitrogen) per acre and found little effect on water 

quality. Only one-half pound per acre was discharged in streamwater the first year; maximum 

concentrations found in the streamwater were 1.4 

p/m of urea and less than 0.2 p/m for nitratenitrogen. Aubertin and others (1973) applied 500 

pounds of urea (235 pounds nitrogen) per acre in 

May to a 74-acre forested watershed in West 

Virginia. In the year following fertilization, nitrogen 

in the streamflow was increased only about 18 

percent. Ammonium-nitrogen concentration was 

usually below 1 p/m and always below 2 p/m. 

Nitrate-nitrogen concentrations remained relatively 

low (below about 5 p/m) through most of the 

summer but rose as streamfbw increased in the 

fall and reached 14 p/m during one storm period 

in September. Bengston's excellent review of forest 

fertilizing (1972) includes a discussion of its 

impacts on the environment. 

On forested watersheds where overland flows 

are minimal, fertilizing is not likely to affect 

water quality adversely if direct application to 

streams is avoided and if application is restricted 

during spring snowmelt and heavy storms (Moore 

1974). However, because different fertilizer 

materials are being applied at various rates during 

the current development of fertilization practices, 

streamwater should be monitored as a safeguard. 

Herbicides 

The risk of contamination from herbicides is a 

legitimate cause for concern. However, in many 

management situations their careful use has prevented problems. For instance, hand spraying 

streamside vegetation in New Jersey, Pennsylvania, 

and California, and basal spraying, stump treatment, and foliage spraying in West Virginia did 

not contaminate flow downstream (Krammes and 

Willets 1964, Lull and Reinhart 1967). However, 

after the experimental application of fenuron to 

part of a chaparral watershed in Arizona, relatively 

low concentrations of the herbicide persisted in 

the stream water for 2 full years (Davis and 

Ingebo 1970). After helicopter spraying in Oregon 

some herbicide was found in all streams in the 

sprayed area. This kind of contamination can be 

held to a minimum by avoiding direct application 

to large, slow-moving streams and marshy areas 

(Oreg. State Dep. Agric. 1967). The drift of 

herbicides during aerial spraying over western 

watersheds has caused major concern. 

After considering the toxicity of the herbicide 

2,4,5-T to animals, its biological degradation in 

the soil, and its incidence in streams after spraying, 

Montgomery and Norris (1970) concluded: "The 

hazard of 2,4,5-T in the forest environment is 

low when used according to tested procedures." 

Herbicides applied as aerosols are likely to drift; 

so this method of application is no longer recommended. Herbicides can be used to control vegetation but should be used only where known to 

be safe. Research may answer questions about 

safety that are now causing concern. Kunkle (1974) 

published some guides for proper use of herbicides 

and insecticides. 

Insecticides 

Insecticides also are used as tools in forest 

management. They pose a greater potential hazard 
to wildlife and man than herbicides. Present 

policy emphasizes minimal use of insecticides, the 

use of less persistent ones, substitution of biological 

controls wherever possible, and evaluation of 

environmental effects before insecticides are 

applied. 

Fire 

Burning the forest can increase both water yield 

and stormflow discharge. The amount of increase 

depends on the intensity, severity, and frequency 

of burning and the proportion of the watershed 

burned. Where much of the foliage is destroyed, 

interception and evapotranspiration are reduced; 

where the organic layers of the forest floor are 

consumed and mineral soil exposed, infiltration 

and soil-water storage capacities can be reduced. 

Fire may have greater effect on peak flows and 

erosion than harvesting, because it destroys the 

protective influence of the forest floor on a watershed that is completely burned. 

Fires range from the intense conflagration that 

consumes everything in its path to the light surface 

fire that consumes only recently deposited, undecomposed leaf litter on the forest floor, and the 

range in effects of fire is just as great. Crown fires 

are generally more destructive than surface fires, 

but under some conditions a severe surface fire 

can kill all the trees and understory vegetation. 

The duration of fire effects ranges from a very 

short period to many decades, depending on the 

extent of the fire itself and the rate of recovery, 

which is influenced by both natural conditions and 

remedial measures applied by man. 

Occasional fire has always been a natural occurrence in many forests; many present-day forest 

types owe their origin and perpetuation to fire. 

Thus what we call normal hydrologic behavior of 

many forested watersheds already incorporates 

some effects of fire. 

Forests in the United States experienced a long 

period when fire frequency was greatly increased 

by actions of man. To some extent this is still true, 

but current prevention and control efforts generally 

keep fire from having the serious impact on forests 

that it had before settlement. When fires are less 

frequent, they are likely to be more severe because 

of the larger accumulation of fuel on the forest 

floor. 

Forest areas are sometimes burned over to 

attain timber management or other objectives. 

These burns, called prescribed burns, are generally 

made during periods when burning conditions 

are moderate so that the impact on the forest floor 

and understory vegetation is less severe than the 

effects of large wildfires. No one has yet accurately 

determined or clearly documented (1) what forest 

types and soil conditions, (2) what sequences of 

weather conditions, or (3) what frequency of 

controlled burns will achieve the usual management objectives without also having adverse effects 

on watershed values and watershed protection. 

The needed evaluation is complicated by the 

sporadic nature of conflagrations, the infrequency 

of major storms, and the wide variation of watershed recovery potential after fires. 

Recovery from fires, usually surface fires, may 

be rapid in the East-typically within a few years; 

regrowth after severe burning can be very slowrequiring decades in some forests. 

Interception 

Forest fires usually are classed as surface or 

ground type, or as crown fires; both types may kill 

trees. Severe fire may drastically reduce interception, even more than a timber harvest. As 

fire consumes or kills the principal intercepting 

surface, it can reduce summertime interception by 

hardwoods and conifers, respectively, from about 

10 and 20 percent of rainfall to less than 5 percent. Most surface fires have little or no effect on 

canopy interception, but in Hawaii, a 17-percent 

increase in stormflow after the burning of fern 

cover from a watershed was associated with a 

reduction in "storage that was readily available 

for evaporation, such as interception storage." 

Infiltration and percolation were unaffected by 

the burn (Anderson and others 1966). 

The maximum reductions in interception following surface fires are suggested by the amount of 

storage water in the litter of forest floors, discussed 

in the section on evaporation. 

Infiltration, Overland Flow, 

Erosion, and Sedimentation 

Infiltration, surface detention, and overland 

flow may or may not be affected by fire. In the 

humid East, fires severe enough to cause serious 

damage are rare under present forest protection. 

In the past, severe fires have reduced some surface 

areas, especially at higher elevations, to almost 

barren rock. In the drier West, the effect of fire is 

greater than in the East. The slow recovery of 

vegetation after fire at high elevations there results 

in greater accumulation of snow and more rapid 

melting, both of which add to hazards of spring 
flooding. Hot summer fires in the West can reduce 

the forest floor to ashes and thus set the stage for 

higher peak flows and greater water yield as overland flow. 

The first year after a wildfire burned over three 

experimental watersheds in Washington, maximum 

streamflows were double the rate of flows before 

the fire, and debris flows in the same area were 

from 10 to 28 times as great as they were before 

the fire (Klock and Helvey 1976). In northern 

Montana, plot studies of runoff and erosion after 

broadcast burning following logging of mixed 

conifer stands recorded that runoff from snowrnelt 

increased and remained high for four years after 

the burning, but erosion dropped back to normal 

volumes by the third year (DeByle and Packer 

1972). Nutrients were lost in runoff only during 

the first year after the burning. Cole and others 

(1973) found losses from leaching were three to 

four times higher in slash-burned areas than in 

clearcut areas that were not burned. 

Three studies of the effects of repeated burning 

on rates of infiltration in plots in the Ozark 

Mountains in Missouri showed that rates of 

infiltration into unburned surfaces were from 

about 60 to 800 percent higher than into soils of 

burned plots (Arend 1941; Auten 1934; Paulsell 

1957). 

Other research has shown less notable differences. 

Burns (1952) found that moderate burning on 

sandy soil in the pine barrens of New Jersey had 

little effect on infiltration; it increased the time 

required for 1 liter of water to infiltrate from 140 

to 150 seconds. Hodgkins (1957) found no significant difference in infiltration rates between burned 

and unburned areas in loblolly-shortleaf pine stands 

in Alabama. 

In northern Idaho, under an unburned stand of 

western hemlock with a duff layer about 2 inches 

deep, the infiltration rates exceeded the rates of 

applied rainfall, 3.5 to 5.2 inches per hour. In a 

stand broadcast-burned 17 years earlier, which 

had a thin and discontinuous layer of duff, the 

infiltration capacity was 2.8 inches per hour. 

However, this rate was exceeded only occasionally 

by natural rainfall (Holland 1953). In the Pacific 

Northwest, where thousands of acres of logging 

slash are burned annually for fire protection, 

slash burning has little effect on the hydrologic 

properties of the soil; its major impact is limited 

to severely burned spots that occupy only 3 to 8 

percent of the total area (Tarrant 1956, Dyrness 

1963). In the Idaho granitic batholith wildfire 

and slash-burned area reburns have been major 

problems (Megahan and Molitor 1975). Present 

policies designed to abate air pollution are leading 

to revision of slash-burning practices. 

Burning affects overland flows very differently 

on different cover types. In the northern California 

brush zone, there was no consistent difference 

in runoff from sparsely covered chamise plots 

before and after burning; but runoff increased by 

a factor of 1.35 to 14.8 after burning of manzanita, 

oak, and shrub oak types (Anderson 1949a). 

The effects of fires on both runoff and erosion 

depend on their frequency. Frequent fires can 

remove most of the protective cover, and thereby 

increase the potential for overland flow. In North 

Carolina, overland flow from a woodland plot 

burned twice a year for 9 years increased rapidly 

at first (Copley and others 1944). After 5 years' 

burnings, the annual runoff from the burned plot 

levelled off at an average of about 8 inches, 

equivalent to 22 percent of the rainfall (compared 

to less than 0.01 inch from the unburned control 

plot). The woodland plot burned twice annually 

lost 0.01 ton of soil per acre the first year, and 

0.03 the next year; by the fifth year the loss was 

3.90 tons; the next 4 years the loss averaged 

about 5 tons per acre-a substantial amount, 

but only about one-fifth the loss from plots 

where cotton and corn were growing. The unburned 

plot consistently lost only 0.01 ton per acre per year. 

In the loessial upland of Mississippi, Meginnis 

(1935) found that for 103 rainstorms annual burning of a scrub oak forest resulted in overland flow 

from 54 storms, compared to 32 from a mature 

oak forest unburned for at least 7 years. In the 2-

year study, less than 1 percent of the rainfall 

appeared as runoff in the mature oak plot, whereas 

the scrub oak plot produced 8 percent. Erosion 

from a scrub oak plot, typical of areas subject to 

severe cutting and annual fires, amounted to 0.33 

ton per acre per year as compared to 0.02 ton 

from a mature oak forest. Conditions under the 

scrub oak were somewhat better than those in the 

North Carolina study; small quantities of litter 

were present but the mineral soil was exposed in 

many places (Meginnis 1935). 

The development of a nonwettable layer of soil 

a little below the surface following fire is being 

intensively studied in California and elsewhere, 

and is discussed below in the section on southern 

California and Arizona chaparral. The extent to 

which this phenomenon occurs in the rest of the 

United States is not known; it probably occurs 

elsewhere (Bond 1968, DeBano 1969, Meeuwig 

1971, Scholl 1971) but almost certainly with less 
noticeable consequences than in the chaparral, 

where the effect of fire on floods is evident. 

However, this nonwettability of soil may promote 

overland flow in any area that has the combination 

of periodically repeated fires, coarse-textured soils, 

and high intensity rainstorms. 

The effects of forest wildfire and prescribed 

burning on erosion and sedimentation depend on 

the severity of the burn, the erodibility of the soil, 

the potential for recovery of the vegetation, and 

the kind of storms that follow the fire. In humid 

forest regions, occasional wildfire and infrequent 

prescribed burning do not produce overland flow 

and hence do not cause erosion. Thus summer 

prescribed fires in Georgia's lower Piedmont, 

which killed 86 percent of the understory 

hardwood stems and provided for successful 

regeneration of pine, had negligible effect on soil 

movement. "Almost all of the decomposed litter 

was left to protect the soil; even some of the 

partially decomposed litter remained unburned. 

The top layer of mineral soil also has organic 

matter incorporated in it and is receptive to 

rainfall absorption" (Brender and Cooper 1968). 

Studies of prescribed burning on much drier 

ponderosa pine sites in California and Arizona 

showed no noticeable effect on overland flow and 

erosion. In both studies a sufficient layer of 

organic material remained after the fire to protect 

the soil (Biswell and Schultz 1957, Cooper 1961). 

The bulldozer trails created in controlling the 

burns contained some overland flow. In a 

mixed-conifer forest, prescribed burning increased both surface runoff and erosion (Agee 

1973). In another study in Arizona, erosion 

occured only where less than 60 percent litter 

cover remained after burning (Pase and 

Lindenmuth 1971). 

Massive wildfires in western forest regions 

have accelerated both erosion and sedimentation. 

In northern California watersheds, a 10-year 

average of 34 acres per square mile of wildfire 

increased sediment discharge 2.3 times (Wallis 

and Anderson 1965). Seventeen years after the 

Tillamook Burn in the Wilson River Watershed of 

Oregon, the annual rate of sediment discharge 

was 500 tons per square mile, five to eight times 

that of nearby unburned forested watersheds 

having similar geology (Anderson 1954). 

Similarly, presence of brushfields at high 

elevations in the Sierra Nevada in California has 

been attributed to the spread of autumnal fires 

set by sheepmen to "green up" the next season's 

growth. Recent analysis shows those brushfields 

produce 55 percent more sediment (measured as 

deposition in reservoirs) than coniferous forest 

stands (Anderson 1974). In southern California 

too, "old fires," fires that had burned 15 to 60 

years earlier, were still accelerating reservoir 

deposition. During the March 1, 1938 flood, 

thrice-burned areas had sediment rates four times 

those of areas that had no old fires (Anderson and 

Trobitz 1949). 

When trees, ground vegetation, and forest floor 

are completely destroyed by fire, high-intensity 

rainfall usually produces great quantities of 

sediment. On the 242-acre Dog Valley experimental watershed established on such a burn on 

the east side of the Sierra Nevada near Reno, 

Nevada, a single storm produced 16,100 cubic feet 

of sediment, or about 2,500 tons per square mile. 

Nearby unburned areas produced scarcely a trace 

of sediment (Copeland 1965). During the same 

year, only low-intensity rain and snow fell in 

another part of the burn; maximum sediment 

concentration in the streamflow did not exceed 78 

p/m (Anderson 1962a). 

Substantial erosion followed an intense fire on 

60 acres of a 318-acre watershed in the South Fork 

of Workman's Creek in Arizona. The fire 

consumed litter and ground vegetation and killed 

all but a few ponderosa pine; it was followed by a 

3.8-inch rain, one of the heaviest on record in that 

area. The burn was confined to the flattest slopes; 

unburned vegetation trapped and held half of the 

sediment, and tree growth and rocks prevented 

gully formation. In spite of these favorable 

conditions, sedimentation was about 1 acre-foot, 

equivalent to about 33 tons per acre of burn (Rich 

1962). 

Hot fires are not always followed by great yields 

of sediment. Soil type, revegetation, topography, 

and meteorological events may nullify fire effects 

on erosion. Erosion indicators on a fire-denuded 

area of the Douglas-fir region show that the 

exposed "shot-loam" soil maintained sufficient 

infiltration capacity to prevent most overland 

flow; growth of vegetation during the first year 

after the fire provided additional effective control 

(Sartz 1953). 

Soil-Water Storage 

Fire reduces the capacity for soil-water storage 

when humus layers and organic material in the 

mineral layers are burned, or when soil exposure 

augments the oxidation of organic matter. In the 
surface 2 inches of soil, severe surface fires can 

reduce the capacity about 1/4 inch (Dyrness and 

others 1957). When an overlying 2-inch layer of 

humus has been destroyed, the total reduction of 

water storage capacity would be about 1 inch. 

Obviously crown fires drastically reduce evapotranspiration and opportunity for soil-water 

storage; the result is similar to that of cutting the 

forest. 

Evapotranspiration 

A light ground fire may have little or no effect 

on evapotranspiration; a hot crown fire may have 

an effect equal to or greater than clearcutting, for 

it may destroy the forest floor, the tree canopy, or 

both. A reduction of interception and transpiration may be partly offset by increased evaporation 

from the forest floor, particularly if seasonal 

rainfall comes as many low-rainfall storms. 

Quantity of Streamflow 

Fire-prone brushland in California and Arizona 

can be a source of increased streamflow. For 

example, burning the Fish Creek Watershed in 

southern California killed almost all of the 

chaparral, and annual streamflow increased by 

2.5 inches the first year after the fire. The 

increase declined to 0.7 inch by the sixth year, for 

an average increase of 29 percent for the 6-year 

period (Hoyt and Troxell 1934). In the Santa Ynez 

watershed, however, where sediment was eliminated from the total volume of water and 

sediment, a major fire did not increase total 

annual flow (Anderson 1955). The burning of a 

woodland-brush experimental watershed in Arizona sharply increased water yield: over a 

36-month period before the fire, accumulated 

precipitation of 70 inches had produced 3 inches 

of flow; in 21 months after the fire, 50 inches of 

precipitation produced 16 inches of flow (Price 

1962). 

The Tillamook Burn in 1933 in Oregon (partly 

reburned in 1939 and 1945) increased the total 

annual water yield of the Trask and Wilson River 

watersheds (143 and 159 mi2, respectively) by 9 

percent (8 inches) and July-through-September 

flow by 16 to 20 percent (0.5 to 0.7 inch) for the 

first 16 years after the 1933 fire (Anderson 1975b). 

In 1970 fire killed virtually 100 percent of the 

surface vegetation on the Entiat Experimental 

Forest in north-central Washington. Helvey (1972) 

reported increases in streamflow the first year 

after the fire that averaged 3.5 inches for three 

watersheds of about 2 mi2 each; increases came 

mostly during spring snowmelt and during the 

summer months. Debris flow was not measured, 

but more than 3,000 yd3 mi2 was deposited at 

the mouths of the watershed; this included some 

boulders as large as 6 ft in diameter (Helvey 1973). 

Stream chemistry was only moderately affected. 

Nitrate-nitrogen was increased by a factor of 

eight, but averaged only 0.04 p/m, whereas 

cations actually decreased because of dilution by 

the increased streamflow (Tiedemann 1973). 

Peak Flows 

The Tillamook Burn also increased annual peak 

flows from the Trask and Wilson River watersheds. Their annual peak discharge increased 

about 45 percent the first year after the burn, 

compared to the adjacent slightly burned Siletz 

watershed (200 square miles in area). The 

increase declined to 10 percent by the seventh and 

eighth years after the burn with no apparent 

increase thereafter (Anderson 1976b). 

A crown fire on the 318-acre South Fork 

watershed in Arizona killed all but a few of the 

pine and Douglas-fir trees and consumed litter 

and ground vegetation. Predicted peaks for an 

unburned condition and actual peaks after the 

burn for the four highest flows during the first 

summer were: 

Predicted Actual 

ft'/s ft3/s 


8 78 

2 19 

3 16 


1 21 

Peak flows increased 5 to 15 times, and they 

continued high through the second summer. 

Winter peaks did not exceed preburn height (Rich 

1962). 

Snowmelt flood peaks may be increased by 

burning the shade-producing trees. We have 

already noted that burning over half of a 

watershed on the east side of the Cascade and 

Blue Mountains areas in Oregon and Washington 

may increase peaks by about 11 percent 

(Anderson and Hobba 1959). Both deliberate 

broadcast burning and frequent wildfire in 

logged-over areas may have contributed to the 
increases from rain-on-snow floods reported. In 

Idaho, after 18 percent of the Clearwater drainage 

was burned in 1919, spring flood peaks were 11 

percent greater and the average peak flow came 

14 days earlier. The Columbia River flood in the 

spring of 1948 may have been due partly to the 

large areas of burned-over forest in the headwaters. At the time 31 National Forests occupied 

about one-third of the basin; more than 5 million 

acres of them had burned, 11 percent of their total 

area; many of these lands had recently burned 

over two or three times (U.S. Dep. Agric., For. 

Serv. 1950). 

The classic test of the effect of burning on 

snowmelt peak discharges was conducted at 

Wagon Wheel Gap in Colorado some 50 years 

ago. There the forest cover was cut and burned on 

one watershed and left untouched in a paired 

basin. Peak flows from the treated basin 

decreased by as much as 50 percent the first two 

years after the treatment, and were lessened each 

year by the recovering vegetation until by the 

seventh or eighth year there was little difference 

in the peaks from the burned and untreated 

watersheds (Bailey 1948). 

Prescribed burning has been common practice 

in the Atlantic Coastal Plain for many years. It is 

applied to reduce brownspot infection of longleaf 

pine seedlings, competition from hardwoods, or 

fire hazard. Burning may be repeated every 3 to 

10 years. There has been no evidence that this 

practice results in any great increase in peak 

flows. 

A substantial reduction in the area burned by 

wildfires has diminished the hydrologic impact of 

fire. From 1931 until 1936, an average of 42 

million acres of forest land burned annually; from 

1961 to 1966, the average was one-tenth as much, 

4.3 million acres (U.S. Dep. Agric., For. Serv. 

1967a), or about 0.4 percent of the total forest 

area. 

Summary 

The effects of fire on forest-produced water 

differ. Light, surface prescribed burns or wildfires 

have little impact. Wildfire that consumes the 

forest floor and kills the trees and other 

vegetation over a large area has major impact on 

stormflows, erosion, sedimentation, and the 

quantity of streamflow. Duration of effects' is 

strongly influenced by the rate of revegetation. 

For the country as a whole, the current level of 

fire protection has greatly reduced the hydrologic 

importance of fire from what it was several 

decades ago. Where severe, widespread wildfire 

still occurs, as in some areas of the West, fire is 

still a serious threat to watersheds. 

Grazing 

Grazing is an annual harvest. Whether its 

effects become cumulative and reach hydrologic 

significance depends upon the intensity of 

grazing, the season of use, and the sensitivity of 

the land. The most recent survey of the extent and 

importance of forest grazing was made by the 

U.S. Forest Service (U.S. Dep. Agric., For. Serv., 

For.-Range Task Force 1972). This survey 

estimated that in 1970 about half (85 million 

acres) of the western forest, and about four-tenths 

(161 million acres) of the eastern forest were 

grazed. This study reported exploitative grazing 

(as opposed to acceptable management) on less 

than 4 percent (3 million acres) of the area grazed 

in the western forest, and on 45 percent (72 

million acres) of the area grazed in the eastern 

forest. In Colorado Basin, reduced livestock 

numbers, improved range management, and 

erosion control have effectively reduced sedimentation; Hadley (1974) attributed the 50-percent 

reduction of suspended sediment load carried by 

the Colorado River to such management. 

The grazing of forested watersheds has been 

the subject of much heated controversy for many 

years. Some quantitative effects on hydrologic 

processes have been reported. 

Interception and Evapotranspiration 

The consumption of foliage by animals in the 

forest is rarely severe enough to reduce interception significantly or to curtail evapotranspiration; 

grazing of ordinary pasture land may have greater 

effect on these processes. Continued heavy 

grazing can eventually kill or reduce the vigor of 

trees; either effect will decrease both interception 

and evapotranspiration. 

Infiltration, Overland Flow, Erosion, 

Sedimentation, and Peak Flow 

Woodland grazing may sharply reduce infiltration and increase overland flow by soil compaction. Stoeckeler (1959) measured the following 
infiltration capacities in ungrazed and grazed oak 

and conifer stands in Wisconsin: 

Infiltration 

capacity 

(in/h) 

Cover: 

Ungrazed native oak 

Grazed native oak 

Ungrazed Scotch pine 

Grazed Scotch pine 

The effect of grazing on infiltration may be 

much less under other conditions. In some 

western conifer types, grazing is localized in 

forest openings and meadows; in such areas 

infiltration capacities may not be affected in any 

widespread, continuous manner. On the Manitou 

Experimental Forest, for instance, infiltration 

rates "were always high" under litter-covered 

soil beneath a canopy of ponderosa pine; they 

averaged 22 percent higher than rates under 

open-grown pine with a grass understory, and 39 

percent greater than on grassland (Dortignac and 

Love 1961). No erosion was apparent under closed 

canopies that had a ground cover of tree litter. 

Lower infiltration rates and greater potential for 

both grazing and erosion were usual in open 

forest with a ground cover of herbaceous 

vegetation and pine litter, and in open glassland 

parks that supported herbaceous vegetation. 

About 8-1/2 percent of the rainfall in eight 

intense storms appeared as overland flow on a 

grazed watershed near Lacrosse, Wisconsin. 

Overland flow occurred only twice on an ungrazed 

area, and then in insignificant quantities (Hays 

and Atkinson 1939). A later study at the Coulee 

Experimental Forest, also near LaCross, showed 

that only 3 percent of the precipitation from five 

major storms appeared as overland flow from a 

heavily grazed woodland. Ungrazed forested 

watersheds produced no measurable amounts. 

Peak flow from the grazed area was 0.12 inch per 

hour or 77 ftY s/mi2 . Maximum sediment 

concentrations were 55,900 p/m from the grazed, 

and 100 p/m from the ungrazed area (Sartz 1976). 

Another grazed hardwood watershed in Wisconsin lost soil at the rate of 0.1 ton per acre per 

year, perhaps four times the rate from ungrazed 

woodland but considerably less than from 

cropland (Hays and others 1949). 

In a more intensive study at Coweeta a 145-acre 

forested watershed was grazed from May to 

September for 9 years by an average of six head of 

cattle. By the end of the first growing season, 

practically all herbaceous forage and much of the 

hardwood understory had been consumed, and 

supplementary feeding was necessary. For a 

number of years there was little apparent effect 

on runoff, but by the end of the eighth grazing 

season, overland flow moved directly into the 

stream and the frequency and magnitude of peak 

flows increased immediately and sharply. Before 

grazing, 2 inches of rainfall (between beginning of 

flow and peak flow) produced a discharge of about 

18 ft3/s/mi2; after 9 years of grazing the peak 

was 32 ft3/s/mi2. Comparable values were 32 and 

120 ft3/s/mi2 for a 4-inch rainfall (Johnson 1952). 

This grazing treatment hardly affected sediment 

yield until overland flow finally made its way 

to the channel in the ninth year of grazing. 

Shortly thereafter the maximum turbidity in one 

storm was 108 p/m as compared to 30 p/m from 

an adjacent ungrazed forested watershed (Johnson 1952). Hursh (1951) attributed to the delay to 

the accumulation of forest-litter plugs along 

natural drainage lines; eventually the surface 

water increased enough to carry away the plugs 

and develop uninterrupted channels to the main 

stream. 

Dissmeyer (1976) reported that overgrazing in a 

large river basin in the South caused 92 percent of 

the estimated accelerated erosion. In the Boise 

River Basin in Idaho, Rennar (1936) reported that 

in timber types overgrazing had been responsible 

for much of the watershed erosion damage. 

Summary 

Properly managed forest grazing has little 

adverse effect on surface hydrology or erosion. 

Overgrazing reduces infiltration and increases 

overland flow. Voluminous evidence shows that 

overgrazing increases erosion greatly. Unless it is 

heavy enough to eliminate much of the forest, 

grazing has only slight effect on the quantity of 

streamflow; it can have much greater effects on 

stormflow volumes and peaks, erosion, and water 

quality. 

Forest-Land 

Disposal of Waste 

The disposal of municipal and industrial wastes 

may someday be an important use of forest land 

(Sopper and Kardos 1973), and, depending upon 
circumstances or emphasis, the fertilizing of 

timber crops with wastes may become an 

accepted forest practice (Gagnon 1973). The areas 

of forest land used for disposal of waste can 

satisfy an important need, especially for disposal 

of sewage from rural communities, even though 

such use will require only a very small proportion 

of all forest land. Waste disposal can have 

significant hydrologic consequences. Use of 

wastes on the land, under careful control and 

management, can (1) dispose of the waste, (2) 

renovate and recycle water, (3) recycle nutrients 

to increase forest or understory vegetation 

production, and (4) in some areas serve to create 

"green belts" for forest fire hazard reduction. 

Seabrook Farms pioneered sprinkler irrigation 

of woodland in the sandy coastal plain of New 

Jersey in 1949 (Thornthwaite 1951). They 

discovered early the advantages of using woodland for waste disposal: with an open-field spray, 

2 inches of water a day saturated the soil to plow 

depth and started overland flow; in contrast, 

when more than 150 inches of water was applied 

over a 10-day period to a wooded area only 400 

feet away, there was no noticeable saturation. 

Although about 400 to 600 inches of water was 

applied annually for 19 years, there has been no 

overland flow. The trees did not survive, but the 

protective forest floor, augmented by organic 

debris in the waste water, maintained a high 

infiltration rate. 

In areas where infiltration capacity is low, 

polluted water has been purified by slow overland 

flow downhill through forest litter, humus, and 

ground vegetation. Suspended and dissolved 

solids are filtered out and converted into humus 

(Mather and Parmelee 1963). 

Effluent from sewage treatment has been 

successfully sprayed in woodland at the 

Pennsylvania State University at intensities of 1to 

4 inches depth per week. Water samples collected 

at the 12-inch soil depth under a red pine 

plantation showed a 95- to 98-percent reduction in 

concentration of alkyl benzene sulfonate, a 

constituent of detergents, and reductions of 68 to 

88 percent in nitrate N, organic N, K, Ca, and Mg. 

The average concentrations of all constituents in 

the percolate at 12 inches were considerably less 

than the allowable limits set for drinking water by 

the U.S. Public Health Service. With a 2-inch 

weekly irrigation rate from April 8 to November 

18, the total weight of constituents applied was 

equivalent to 2,500 pound per acre of 10-10-10 

(NPK) fertilizer (Parizek and others 1967). After 

nine years of irrigation with treated municipal 

wastes, no detrimental effects on the forest soil 

were observed (Richenderfer and others 1975). 

Sprinkler systems are now employed extensively in disposal of waste water. By 1957, 250 

systems were operated by food processing plants 

and 18 operated by pulp and paper mills. In 

1972, 75 installations in Pennsylvania were 

spraying municipal wastewater on the land and another 10 to 15 were in planning and design stages 

(Rhindress 1973). 

Waste water and sludge may prove to be useful 

in reclaiming surface mines (Lejcher and Kunkle 

1973). Results of recent tests (Sopper 1975) 

indicate the revegetation of anthracite coal refuse 

is possible through the application of treated 

municipal wastewater and liquid digested sludge. 

The feasibility of using wastewater to irrigate 

greenbelts for the reduction of wildfire hazard in 

California chaparral is being studied (Youngner 

and others 1973). Irrigation at rates of 1.75 

idweek or more maintained moisture content of 

Ceanothus at levels above 70 percent, where they 

are not readily flammable. 

Much research and development must be 

completed before the application of wastes to 

forest land can become widespread or routine. 

Evans (1973) has suggested 19 research needs; 

these include economic and social consideration; 

techniques for handling waste materials; pollution 

effects on land, groundwater, and streams; 

effects on animal and plant populations, including 

crops; infiltration and storage capacities of 

different soils; cold weather problems; and the 

need for better systems for monitoring soil and 

water and adequate standards and guidelines for 

resultant water quality. 

Insects, Diseases, and Weather 

A tree killed by insects, disease, or windthrow 

affects the hydrologic cycle much the same as if it 

had been cut down;'interception and evapotranspiration are reduced or stopped but infiltration 

usually is not affected. The hydrologic changes 

differ in detail, and, of course, there is none of the 

machine-caused site disturbance that usually 

accompanies timber harvesting. 

Insects kill more trees than any other agent; 

weather (wind, ice and snow, lightning, and 

drought), and disease kill markedly fewer trees. 
The estimated mortality for 1952 was (U.S. Dep. 

Agric., For. Serv., 1958): 

Growing stock Live sawtimber 

Millionft3 Millionfbm 

Cause: 

Insects 1,000 5,041 

Weather 843 3,387 

Disease 773 2,242 

2,616 10,670 

A reassessment in 1970 (U.S. Dep. Agric., For. 

Serv., 1975) was that natural mortality of 

sawtimber amounted to 15.3 billion board feet 

annually. If confined to one area, these losses 

would be equivalent to more than 2 million acres 

of forest destroyed, and their effect on streamflow 

would be enormous, as indicated by the individual 

effects of fire, insects, and blowdown on 

streamflow amounts and floods. 

These damages are scattered throughout the 

forest land of the country. Mortality in any given 

affected area is usually caused by a single disease 

or is confined to a single insect-ridden species, 

and not all individuals of that species succumb. 

These conditions modify the impact so that it 

probably is comparable to or less than the total 

effect from selection cuttings. This would be true 

particularly for mixed hardwood stands in the 

East or mixed conifer stands in the West. 

Although chestnut blight reduced the production 

capacity of the hardwood forest north of Maryland 

by 15 to 50 percent (Boyce 1938), it occurred in 

mixed stands and was a progressive disease, 

requiring 1to 10 years to kill a tree. Streamflow 

would be barely affected if surrounding trees 

continued their growth and maintained evapotranspiration rates. Sometimes the effect of 

damage caused by a single insect species or 

disease can be singled out and measured, as it 

was when beetles killed most of the spruce and 

pine on the 762-square-mile White River drainage 

in Colorado. Love's analysis (1955) indicated an 

annual increase in streamflow of about 2 inches in 

the 1947-51 period following the kill. Total 

increase in two large river basins for the 25-year 

period 1941 through 1965 was 22 and 14 percent, 

or 37 and 30 inches (Bethlahmy 1974). Peak flows 

were 27 percent higher in the west-flowing White 

River, but only 4 percent higher in the 

north-flowing Yampa River. 

Catastrophic winds, massive earthslides, and 

snow avalanches that fell trees over large areas 

may have greater effects on water than attacks by 

insects, especially the effects on water quality 

caused by erosion and sedimentation. The 1938 

hurricane in New England destroyed about half 

the merchantable timber in a swath 80 miles wide 

extending from Rhode Island and eastern 

Connecticut to the White Mountains (Barrett 

1962). That storm doubtless increased water yield 

(Patric 1974). Eschner and Satterlund (1966) 

showed how extensive blowdown in the Adirondacks from a storm in 1950 interrupted a 39-year 

trend in which the annual water yield from a 

protected watershed had gradually declined by 

about 7.7 inches. The*blowdown and continuing 

mortality of storm-weakened trees during the next 

several years increased water yield to near the 

original level. 

The effects on erosion and erosion-induced 

turbidity of streamflow are generally minimal; 

water temperature may be locally affected, and 

water chemistry may be altered temporarily by 

leaf fall and accumulation of debris in channels. 

The total effect of forest damage by insects, 

diseases, and weather is usually incorporated into 

what we accept as normal variability of streamflow. 

Minimum-Treatment 

Management 

In land-use planning, the point is frequently 

made that one possible alternative is to apply no 

management at all. This practice of leaving lands 

in their natural state is being applied to more than 

11 million acres of officially designated Wilderness Areas, more than 4 million acres of Primitive 

Area managed as wild lands, and to many other 

areas. What are the effects on water of such 

minimum-treatment management? 

If complete protection were possible, the trend 

in forest succession would be toward the climax 

type, which probably occupies the site more 

completely than any other. Under this condition, 

on-site use of water would be at or near the 

maximum, and erosion and sedimentation would 

be at a low level in most areas. 

Even though protected from disturbance by 

man, the forest cover may be partly or completely 

destroyed by fire, insects, or wind, and the water 

regime may be affected in ways that have already 

been discussed. The effects of fire and insect 

attack may be greater than in the managed forest 

because of the absence of directed prevention and 

control measures, planting, or other activity for 

site rehabilitation. 
I - SPECIAL 

Unusual conditions in some areas in the United 

States present special forest-water problems. 

Though the hydrologic processes already discussed apply in these situations too, we believe 

special attention to them is merited. The following 

four situational problems deserve brief special 

attention: 

1. Southern California and Arizona chaparral 

-an extreme fire-flood-erosion situation 

2. Wetland Forests - extreme water 

abundance 

3. Phreatophytes -extreme water use 

4. Surface Mining -extreme site disturbance 

Southern California 

and Arizona Chaparral 

Of the 759 million acres of forest land in the 

United States, about one-third is classed as 

noncommercial because it does not yield wood 

products. About 101 million acres of this land is in 

the West. Most of this forest has the same 

relation to floods, erosion, and sedimentation as 

the commercial forest does, but about 16 million 

acres of it behave quite differently. Forests on this 

land burn readily and completely and thereby set 

the stage for disastrous floods that usually 

produce huge volumes of sediment. This is the 

chaparral area of southern California and Arizona, 

the country's most inflammable forest and, per 

unit area, the greatest source of forest-flood 

damage. In some areas, even unburned chaparral 

cannot stabilize the soil that supports it. These 

conditions also exist in varying degrees along the 

central coast of California and in a belt around the 

great valleys. 

Of the two areas, California's chaparral 

presents the greater problem. Its 17 million acres 

of chaparral and associated types have a 

Mediterranean climate-dry, hot summers and 

mild, wet winters. Annual precipitation averages 

about 27 inches but ranges from 12 to 48 inches. 

Nearly three-fourths of the rain comes during 

December through March; there is almost none 

during the summer. Some of the highest rainfall 

intensities and amounts in the United States have 

been recorded in this area: 1.02 inches in 1 

minute, 11 inches in 7.3 hours, 26 inches in 24 

hours, and 43 inches in 3 days (Anderson 1964). 

Much of the problem of the chaparral area is 

caused by its location. Chaparral occupies roughly 

70 percent of the mountain ranges fronting the 

southern third of California's coast. Below it are 

300 square miles of valuable properties: homes, 

orchards, towns, cities, highways, railroads, and 

industries. 

Flood damage can be immense. In the 1938 

flood in the Los Angeles area, 87 lives were lost, 

and property damage was estimated at $79 

million. Potential average annual damage there 

had been estimated at $34 million (U.S. Senate 

Sel. Comm. Natl. Water Resour. 1960a). The 

Flood Control Acts of 1936 and 1945 authorized 

federal flood control expenditures totalling more 

than $400 million (Hoyt and Langbein 1955). By 

1969, about $1 billion had been spent on flood 

control structures in the Los Angeles area (Wood 

1970). Damage following fires and expenditures 

for flood control attest to serious and closely 

related problems of fire and flood control. 

Fire-Flood-Erosion 

Fires followed by the January-February storms 

in 1969 were responsible for 47 flood deaths 

(Calif. Dep. Water Resources 1970). Rice and 

Foggin (1971) and Scott (1971) described the 

sedimentation consequences of the storm. More 

than 200,000 cubic yards per square mile of 

watershed was measured in individual debris 

basins (Scott 1971). 

Colman (1953a) described three other fireflood-erosion sequences. On New Year's Day in 

1934. less than 2 months after fire burned 7 

square miles of chaparral in the mountains above 

the cities of Montrose and La Cresenta, a severe 

storm struck. The flood that followed killed 30 

persons, devastated several towns, and caused $5 

million damage; unburned watersheds nearby 

produced only normally high streamflow. 

In July 1945 an airplane crashed into the 

chaparral of the upper Santa Ana River watershed, and started a 4,000-acre fire. Although this 

burn covered only 1125th of the watershed, 

thunderstorms that autumn caused mud and rock 

flows that interrupted the operation of three 

hydroelectric plants and disrupted irrigation 

schedules on 10,000 acres of citrus orchards. 

In 1950, the fire-flood-erosion sequence was 

most convincingly demonstrated. A fire on July 4 

in the hills 4 miles north of Yucaipa, California 

burned about 630 acres of chaparral. Two days 

later a severe thunderstorm struck the burn and 

areas surrounding it; mud and boulders poured 

from the burned area in quantities that blocked 
roads and incurred several thousands dollars' 

worth of damage. There were no flood flows or 

erosion on adjacent unburned drainages (Colman 

1953b). 

Such damaging fire-flood sequences had led to 

record expenditures for fire control. The average 

annual per-acre costs in the chaparral zone are 

several times the national average (Davis 1959). 

Streamflow records from experimental watersheds in the San Dimas Experimental Forest 

before and after fires give some indication of 

fire's effect. After a fire in 1938, two storms from 

an unburned watershed produced peaks of 7 and 

17 ft3/s/mi2; a watershed only 3 percent burned 

had peaks of 12 and 20 ft3/s/mi2; and one 26- 

percent burned had peaks of 26 and 55 ft3/s/mi2. 

After the 1953 burn, a heavy storm on an unburned watershed caused a peak of 5 ft3/s/mi2; 

on one 3-percent burned, a peak of 20 ft3/s/mi2; 

and on one 32-percent burned, a peak of 429 

ft3/s/mi2. With wet soil conditions and smaller 

storms, peaks from burned watersheds were 1.2 to 

15.6 times greater than peaks had been when the 

watersheds were unburned (U.S. Dep. Agric., 

For. Serv., San Dimas Exp. For. 1954). 

The 1960 fire at San Dimas produced even 

greater differences. For two of the larger watersheds, 740 and 875 acres, peak flows from a 

4-inch storm before the fire were 0.76 and 4.4 

ft3/s/mi2, respectively; a similar storm after the 

fire gave comparable peaks of 660 and 880 

ft3/s/mi2 (Krammes and Rice 1963). Statistical 

relations between flood peaks and sedimentation 

and forest fires, and the recovery of vegetation 

after fires, have provided a basis for intensified 

fire protection (Anderson 19490). 

Tremendous discharges from freshly burned 

areas may be due partly to fire-derived nonwettable layers of soil. These layers are formed when 

large soil temperature gradients cause vapor and 

gases containing hydrophobic substances to move 

downward from the surface organic matter into 

the surface soil. There they condense on soil 

particles and inhibit infiltration. The depth and 

thickness of the water repellent layer depend on 

the intensity of the fire and the amount of 

vegetation and litter consumed (DeBano and Rice 

1973). Soil texture also seems to be a factor; clay 

soils are less susceptible than sandy soils 

(DeBano 1969). Similar repellency has been 

reported for soils under both natural and burned 

chaparral in Arizona (Scholl 1975). Small-scale 

research tests indicate that chemical wetting 

agents may be useful in reducing overland flow 

and erosion from nonwettable soils, but recommendations cannot be made yet for general 

application (Krammes and DeBano 1967). A 

large-scale test failed to reduce overland flow and 

erosion during the 1969 flood (Rice and Osbom 

1970). 

Water repellency of soils developed by fire may 

prove an advantage in reforestation of bums. 

DeBano and Rice (1973) have suggested that if 

stock is planted in contour furrows, the extra 

runoff from the inter-furrow repellent areas will 

be trapped in the furrows and provide moisture to 

nurture the new seedlings. It would seem also 

that alternate furrows for trees and dense contour 

seeding, such as rows of barley or mustard, would 

accomplish both immediate erosion control and 

reforestation. 

Erosion Without Fire 

Along the Los Angeles front of the San Gabriel 

Mountains in southern California, watersheds 

long unburned steadily contribute sediment to 

stream channels. On south-facing slopes of 90 

percent in the Los Angeles River watershed, that 

have a cover density of 65 percent, debris moves 

into the channel at an average annual rate of 3.56 

tons per acre. A little more than half of this is 

deposited during the dry season; many of the 

slopes lie at angles steeper than the natural 

repose for dry material. "A breeze that shook the 

brush was enough to start a minor slide. . ." 

During the rainy season most deposition occurred 

after soil-moisture storage opportunity was 

satisfied. Debris movements from north-facing 

slopes of 70 percent and from north- and 

south-facing slopes of 55 to 60 percent averaged 

from 0.2 to 0.72 tons per acre per year (Anderson 

and others 1959). 

Highly erodible road slopes in southern 

California also pose problems. Erosion from road 

fills has averaged from 6 to 10 times that from 

adjacent nonroad areas (Anderson and Wallis 

1965). Special erosion-prevention procedures 

must be used (Kraebel 1936). On the Angeles 

National Forest they include reducing volumes of 

cuts and fills by using retaining walls and 

cribbing, reducing design speeds to meet 

minimum traffic needs, fitting road alignment to 

topography, keeping road gradients to a minimum, and contour-trenching, staking, and seeding of fill slopes (Usher 1961). 
The methods for stabilizing road-fill suggested 

by Kraebel (1936) were used on the road to the 

Palomar Mountain Observatory in southern 

California (Juhren 1949). The road-fill treatments 

consisted of contour wattling (bundles of brush 6 

to 7 feet long and 4 to 6 inches in diameter placed 

end to end in contour trenches) together with 

seeding of barley or ryegrass, using wheat straw 

between rows, and planting willows, mulefat, 

trees, and shrubs. In the 1938 flood, erosion from 

unprotected slopes was as much as 680 cubic 

yards per acre, equivalent to 5 inches' depth over 

the area. The only fills that did not erode were 

those treated. Since many of these improved 

methods also reduce costs of road maintenance, 

there is hope for prevention of major increases in 

sediment discharge from large road construction 

projects. 

Erosion After Fire 

Sedimentation accounts for much of the 

fire-flood-erosion problem in the chaparral of 

southern California. During the summer following 

the Woodwardia fire in October 1959, dry creep 

from steep slopes increased by 4 to 17 times. 

Erosion directly related to the fire ranged from 2.2 

to 24.7 tons per acre the first year; south-facing 

slopes yielded the most debris-10 times the 

preburn rate. About 89 percent of the eroded 

material came from surface sloughing during the 

dry season (Krammes 1960). 

Increases in rainfall erosion were even greater 

in another area. After the January 1954 storm on 

the December 1953 burn at the San Dimas Experimental Forest, an average of more than 0.6 inch 

of ash, soil, gravel, and decomposed rock was 

removed from side slopes by sheet and rill erosion. 

In addition, the material from channel erosion 

gave an estimated erosion rate of 55,500 yd3/mi2 

of burned area. The normal erosion rate for that 

drainage is about 2,000 yd3/mi2 per year (U.S. 

Dep. Agric., For. Serv., San Dimas Exp. For. 

1954). These values are not exceptional for this 

part of the country. Forty-one watersheds in 

southern California, from 1 to 1,465 square miles 

in area, produced annual averages of 600 to 9,770 

cubic yards of sedimentation per square mile. 

After one-fourth of the watershed was burned, 

estimated production from a 100-year flood was 

9,900 to 113,000 cubic yards (Anderson 1949b). 

Maximum yearly sedimentation of 71 debris basins 

guarding the San Gabriel Mountain front has 

ranged from 3,500 to more than 200,000 yd3/mi2 

(Los Angeles County 1970). 

Control &d Rehabilitation 

Flood and erosion control require prevention or 

control of wildfire. Land managers agree that this 

requires construction of firebreaks and some 

managers recommend reduction of fuel by 

converting chaparral covered land to grassland 

wherever feasible. This conversion, however, may 

reduce the opportunity for soil-water storage. 

Conversion from chaparral to grass cover at San 

Dimas increased the average daily evapotranspiration rates during the rainy season from 0.048 to 

0.059 inch, an average annual increase of about 2 

inches. Most of it occurred from January to April 

when scrub oak growth was slow and annual grass 

growth relatively rapid. Evapotranspiration from 

grass practically ceased when the grass matured 

in early summer, having used all available water 

to a depth of 2 112 feet and created some water 

storage opportunity to depths of about 7 feet. 

During summer evapotranspiration losses were 

far greater from the chaparral (0.073 compared to 

0.034 inches per day) and continued until all 

available moisture in the 12-foot soil depth had 

been utilized (Rowe and Reimann 1961). The 

soil-water storage opportunity on deep soils under 

chaparral is almost always more effective for flood 

control. During the January to April rainy season, 

the somewhat greater soil-water deficits built up 

by the greater evapotranspiration under grass are 

quickly satisfied in any flood-producing storm. 

The soil slippage problem in steep grassland is 

discussed later in this section. 

Burned-over watersheds have such high damage potential that they must be rehabilitated 

immediately. Annual ryegrass, broadcast seeded, 

can provide a quick ground cover that persists 

for a few years but does little to moderate 

damages from peak flows. Wheatgrasses (longlived, drought-tolerant bunchgrasses) have performed well in tests. They mature somewhat later 

in the spring or summer than many other grasses 

-an important consideration in planting for fire 

control and for a fuel-break cover (Bentley 1967). 

The treatments following the 1960 fire at the 

San Dimas Experimental Forest are a good 

example of erosion control (Rice and others 1965). 

Tested were broadcast seeding annual and 

perennial grasses, bulldozing wide contour 

trenches (Bailey and Croft 1937), building check 
dams in channels, and planting barley in contour 

furrows. The total debris produced during the 

first year after each of four treatments was: 

Treatment: Yd3acre 

None 29 

Contour trenches 14 

Channel check dams 17 

Contour planting 10 

The check dams filled quickly to their design 

capacity during the first two storms. Contour 

trenches, although large, could not be spaced 

closely enough to provide adequate storage for 

runoff volumes from large storms. Planting barley 

on the contour was the most successful treatment: 

seeded at the rate of 150 pounds per acre and 

fertilized, it prevented appreciable overland flow, 

but the treatment deteriorated rapidly 2 years 

after sowing (Krammes and Rice 1963). Standard 

rates of grass seeding, because of steep slopes 

and surface instability, accomplished little for it 

did not produce a total vegetative cover significantly greater than that on unseeded controls. A 

high-density (20 lbdacre) sowing of a mixture of 

annual grasses did reduce erosion by 16 percent. 

The average cost of helicopter sowing on large 

areas is about $1 per acre plus cost of seed 

(about $4 per acre for high-density annual mixed 

and $13 for perennial). The cost of barley in 

contour rows is about $140 per acre. This measure 

must obviously be restricted to critical erosion 

areas (Corbett and Green 1965). 

Soil slippage in brushland converted to grassland following a forest fire had produced 3 to 7 

times as much erosion by two large storms as 

occurred in naturally recovering brushland (Rice 

and Foggin 1971). 

Removing flood debris and seeding of watersheds as an erosion control measure following a 

fire can cost more than fire suppression. For the 

1960 fire at San Dimas, the fire suppression cost 

(Federal only) was $800,000, whereas cleanup and 

erosion control cost $917,000. In the first 2 years 

after the fire, debris production amounted to 

24,000 cubic yards per square mile. During the 

same period, 33 unburned watersheds in the 

surrounding San Gabriel Mountains produced 

6,000 cubic yards per square mile, while 16 

partially or completely burned ones produced 

40,000 cubic yards per square mile (Rice 1963). 

To prevent erosion from unburned watersheds 

in southern California, various reinforcements of 

existing vegetation are recommended. To reduce 

sliding from upper slopes, species should be 

found that will convert the original singlestemmed vegetation to a multi-stemmed but 

deep-rooted cover. On slopes that exceed the 

angle of repose, the soil mantle can be tied to the 

underlying rock by additional vegetation without 

reducing the effectiveness of the existing deeprooted brush. To prevent gullying of colluvial 

deposits, overland flow should be spread by 

mechanical means or by planting multi-stemmed 

vegetation; widely-spaced, single-stemmed vegetation is relatively ineffective (Hellmers and 

Anderson 1955). 

No rehabilitation measure yet devised gives 

immediate protection comparable to unburned 

chaparral. Debris basins or other protective 

devices are often needed to reduce damage after 

fire. 

Arizona Chaparral 

Arizona has about 4 million acres of chaparral, 

varying from dense stands to open, desert-like 

scrub. Annual precipitation on this area is 

somewhat less than that on the California 

chaparral; it ranges from 16 to 25 inches. Most of 

it comes as winter rainfall; but in contrast to 

California, summer storms account for about 

one-third of the total annual precipitation and 

those storms can cause flooding and erosion. 

The Arizona chaparral, like its California 

counterpart, can be completely consumed by fire. 

Peak flows and sediment production increase 

immediately. After an intense fire, one of the 

3-Bar Experimental Watersheds produced 40,000 

tons of sediment per square mile over a 6-month 

period; unburned watersheds produced from 

negligible amounts of sediment over periods of 2 

to 3 years to as much as 500 cubic yards of 

sediment per square mile from two storms of 1 to 

2 inches (Glendening 1959). With 70 inches of 

accumulated precipitation, accumulated sediment 

was about 200 tons per square mile in the 36 

months before the fire; in the next 21 months after 

the fire, accumulated sediment increased 100-fold 

to 22,000 tons per square mile with 50 inches of 

precipitation (Price 1962). Within 3 years after the 

fire, the severe flooding and sedimentation on the 

3-Bar Experimental Watershed was controlled to 

near prefire levels by the vigorous growth of 

introduced lovegrasses plus some fifty species of 

native herbaceous cover (Pase and Ingebo 1965). 

Conversion of brush to grass may interrupt the 

erosion cycle associated with wildfire as well as 
produce one-third to 5 inches more streamflow 

(Hibbert and others 1974). T.C. Brown and others 

(1974) estimated that it might be economically 

feasible to convert about 300,000 acres of National 

Forest land in the Salt-Verde Basin of Arizona to 

useful species of grass. 

Because of the lesser concentration of population below chaparral watersheds of Arizona than 

in southern California, flood damage from 

Arizona Chaparral watersheds is less spectacular 

but still locally important. 

Wetland Forests 

Wetland forests generally reflect a dominant 

influence of an abundant supply of water 

seasonally or otherwise (Bay and Klawitter 1963). 

They cover nearly 37 million acres in the southern 

and southeastern United States, bordering the 

Atlantic and Gulf coasts and in the lower 

Mississippi Valley. In the Lake States also, large 

areas of wetlands are in bogs. Present management there is directed largely to obtain regeneration of forests following harvest (Boelter 1974). 

Water management is being practiced on more 

than 2 million acres of wetland forest in the 

southeastern United States (Klawitter 1972). 

Although most of this management has increased 

timber productivity of the land, it may have 

various hydrologic consequences as well. The 

primary objective of water management designed 

to fulfill productivity objectives is to hold 

sufficient water on some parts of the land to 

obtain maximum forest growth but in other places 

to remove surplus water in an orderly manner. 

. Surplus water in headwater bays and wet flat 

lands is not waste water, for such water is used to 

recharge swamps in bottom land soils; to maintain 

water fowl, aquatic, and estuary habitats; and to 

provide buffer against salt water intrusion. To 

accomplish these objectives, a water management 

system must be designed to meet both on-site and 

the downstream objectives. The design will vary 

depending on the type of wetland involved. 

Klawitter (1972) has summarized management 

objectives and techniques for four types of 

wetlands: wet flats, bays, swamps and upland 

ponds, and bottomlands. 

Wet Flats 

Wet flats are upland sites located on broad, 

level to nearly level +erstream areas of the 

lower coastal plain a. 'twood section. Most 

efforts in water management are now concentrated on the 4 million acres of wet flats that 

support pine. One current procedure is to remove 

surface water and lower the ground water enough 

by means of surface ditches to increase the 

trafficability for heavy equipment and thereby 

facilitate road construction and timber harvest. 

For estimating the effects of drainage on flood 

flows, Klawitter (1972) suggested that the 

maximum 24-hour average flow rates can be 

computed by using the Cyprus Creek formula 

(Stephens and Mills 1965). He applied this 

formula to southeastern wetland areas, and 

arrived at a water removal rate of 1 inch in 24 

hours (this is equivalent to 27 ft3/sec/mi2 of 

drained area). 

Bays 

Bays, or upland bogs, cover approximately 3 

million acres of wet forest land in the coastal 

plain. Although they can be found throughout the 

Southeast, they are mostly in eastern North 

Carolina or in the northern part of the flatwoods 

section. Coastal plain bays typically produce 

relatively little timber, water, forage, and 

wildlife. Because of fertility problems, Ralston 

(1965) concluded that not enough is known at this 

time about the hydro-chemical processes of 

infertile bay soils to recommend suitable measures to improve forest growth. Numerous stumps 

have been uncovered where roads or ditches are 

constructed in this wetland type; this indicates 

that major vegetation changes have taken place in 

these areas. Trousdell and Hoover (1955) reported 

that logging caused water levels to rise enough to 

endanger regeneration and seriously hamper 

projected future logging operations. Hydrologic 

consequences of such changes in the vegetation 

have not been evaluated. 

Swamps and Upland Ponds 

Swamps occupy the lowest location along the 

sluggish streams and rivers in the coastal plain 

and in the broad depressions in the heads of 

streams. Occasionally, maritime terraces or sand 

ridges formed by the sea block areas of low-lying 

land; these terraces form large swamps like the 

Dismal Swamp in Virginia, and the Okefenokee 

Swamp in Georgia and Florida. Upland ponds 

occupy small depressions in bays, wet flats, or 

piney woods and are managed in conjunction with 

them. They are frequently as wet as swamps, but 
depend on overland flow and seepage from 

surrounding uplands for their water supply. 

Swamp vegetation is well adapted to the wet 

environment: such species as bald Cyprus and 

water tupelo grow best on these sites. 

Removal of surface water from swamps can kill 

older trees and also destroy waterfowl habitat, 

sanctuaries and escape for deer, and conditions 

suitable for other wildlife. These values can be 

enhanced by such methods as installing dikes and 

control structures at well chosen locations to 

control the water levels in swamps. Hydrologic 

consequences of such management have been 

little studied; however, the characteristics of 

increased pondage and retention of flood waters 

would indicate a reduction of flood runoff. 

Bottomlands 

Bottomlands provide the extra channel capacity 

required to carry stormflow to the sea. Small 

streams seldom support a width of more than a 

few hundred feet, whereas major rivers are 

frequently separated from adjacent uplands by 

several miles of bottomlands. Productivity in such 

bottomlands is high for both timber and wildlife 

because of the excellent inherent fertility and 

abundance of moisture in bottomland forest. 

Uncontrolled drainage adversely affects stand 

composition, tree growth, and regenerative 

potential of these lands. Consequently, current 

water management consists of a kind of flood 

irrigation-increasing the water available for 

plant growth by impoundment-construction of 

low dikes and dams in flats and shallow 

drainageways (Schlaudt 1962, Broadfoot 1964, 

1967). Again, the hydrologic consequences have 

not been well studied; however, some additional 

use of water would be expected and some 

detention benefits of the temporary pondage 

would reduce flood peaks and prolong water 

yields in downstream areas. Shallow-water impoundments in bottomlands may attract waterfowl and hence have benefits additional to those 

of growth and water control. Klawitter (1972) 

concluded that water management is a means of 

improving the productivity of millions of acres of 

wetland forest for wildlife, timber, forage, and 

water in the southeastern United States. Hydrologic consequences and opportunities associated 

with the detailed management techniques and 

wetland conditions need further study. 

Phreatophytes 

Phreatophytes are trees and shrubs that thrust 

their roots down to the groundwater under and 

adjacent to stream channels. Most phreatophytes 

grow below the forest zone, in desert or plains 

rather than in a forest environment; for that 

reason, discussion here is brief. According to one 

estimate, phreatophytes consume about 25 

million acre-feet of water per year in arid and 

semiarid areas of the West; this is equivalent to 

about twice the average annual flow of the 

Colorado River at Lees Ferry, Arizona (Babcock 

1968). 

On a per-acre basis, phreatophytes consume an 

estimated 4 to 9 acre-feet of water. How much of 

this can be "saved" by cutting saltceders, 

arrowweed, and cottonwood (three chief water 

users) and how much of the "saving" can be 

converted to more beneficial use are questions 

research has not yet answered. In some places 

this vegetation has enhanced values for recreation 

and wildlife that have exceeded the estimated 

value of water that would be saved by removing it. 

Horton and Campbell (1974) have summarized 

some of the possibilities and limitations for 

management of phreatophytes, and Horton (1973) 

published a comprehensive abstract bibliography 

of research related to management of phreatophytes and other riparian vegetation. 

Robinson (1967) reported that annual savings in 

areas of dense growth may amount to 2 to 3 feet of 

water. The depth of the water table may determine 

the ultimate management of these areas. If the 

depth is 4 feet or less, cleared areas can be sown to 

grass. If it is more than 4 feet, replacement of 

vegetation is more difficult; fanning with irrigation 

presents no problem, but elsewhere the cleared 

areas invite wind erosion (Horton 1966). 

Rowe reported (1963) that during the first dry 

season following clearing of streamside vegetation 

along a channel in the San Dimas Experimental 

Forest, the clearing saved the equivalent of 14 

inches depth of water per acre cleared (Rowe 1963); 

moreover, streamflow increased chiefly in summer 

and at the beginning of the soil-wetting period in 

subsequent seasons, when flow usually was lowest 

and water was most needed. 

In the largest phreatophyte control program yet 

attempted, one area of 5,300 acres in the Rio 

Grande Valley was cleared of vegetation (principally 

saltcedar and mesquite); this saved an estimated 

14,000 acre-feet of water annually. In current 
projects, thousands of acres are being cleared in 

New Mexico, Arizona, and Texas. 

Until recently phreatophytes were almost universally regarded merely as wasters of water. Now 

their place in the environment is coming to be 

recognized, and multiple-use planners are assessing 

the benefits of phreatophytes to fish, wildlife, 

and aesthetics. For example, Bristow (1968) has 

estimated that the hunting of whitewing doves on 

1 acre of phreatophytes in Arizona can add about 

$880 per year to the economy of the state. 

Surface Mining 

Surface mining, chiefly of coal, has increased 

steadily since Word War 11. Until 1965 an estimated 

3.2 million acres of land, much of it forest, had 

been disturbed by surface mining in the United 

States; an estimated 150,000 acres was disturbed 

in 1964, and the rate has been increasing since then 

(U.S. Dep. Inter. 1967). In the West alone more 

than 21 million acres of commercial quality coal 

and phosphate areas may be subject to surface 

mining (Copeland and Packer 1972). 

Cutting the forest and disturbing the soil in surface mining has much the same effect on water as 

other activities already described, but the disturbance is greater-truly extreme-and the effects greater. Surface mining sometimes exposes 

types of rock that have a high potential for polluting the water in streams and impoundments with 

acid and other deleterious chemicals. 

Reclamation of surface-mined areas has proved 

extremely difficult. For this reason surface mining 

has been and continues to be the subject of much 

controversy and legislation. Reclamation involves 

both engineering-including the proper placement and grading of spoils, provisions for drainage, and sometimes impoundments for trapping 

sediment-and establishing vegetation. It is being 

increasingly recognized that, for successful reclamation, the mining operation must be planned 

and conducted from the beginning with adequate 

consideration for reclamation requirements. 

Mined areas are often difficult to plant or 

replant. Fertilizing (usually with nitrogen and 

phosphorous), liming, and irrigation may be required. Sometimes followup treatments are necessary after initial establishment to insure adequate 

continued growth. 

Where forested areas are mined, the reclamation 

objective is usually to reestablish forest cover. 

Forestry has a dual role: (a) establishing trees and 

shrubs to stabilize the site, control erosion, and 

improve aesthetics, and (b) returning the land to 

productive use: timber growing, game habitat, 

recreational use, or some combination of these 

uses. 

Reclamation research was begun in the 1930's 

by the U.S. Forest Service in the Central States 

(Limstrom 1960); now several universities and 

other Federal and State agencies are also studying 

the problem. Practical methods for planting trees 

in the East and Midwest have been developed and 

guides have been published (Paton and others 

1970, Davis 1971). 

Increasing attention has been given recently to 

research on the formidable hydrologic problems 

that follow strip mining (Curtis 197la, 1971b, 

1972a. 1972b). Maximum sediment concentrations 

from three watersheds in Appalachia increased 

from 150 p/m to 46,400, 26,900, and 9,600 p/m, 

respectively, after these watersheds were strip 

mined. Peak flows increased by a factor of 3 to 5 

after surface mining. On the other hand, water 

quality from restored strip mine areas in pinyonjuniper land in Arizona was well within EPA 

criteria; content of nitrate nitrogen in water was 

less than from the unmined control watershed 

(Verma and others 1975). 

Most surface mining in the United States has 

been done in the East, but it is proposed for 

producing coal and other minerals in many states 

in the West (Copeland and Packer 1972). Revegetation, with trees or other vegetation, is 

difficult under the relatively harsh soil and climatic 

conditions widespread in the West. 

A large volume of literature on reclamation is 

accumulating (Frawley 1971, Hutnik and Davis 

1973, Cook and others 1974, Johnston 1975). 

Specific techniques for reclamation have been 

developed to overcome problems of lack of nutrition, adverse microclimate, inadequate water, and 

erosion inhibiting establishment of plants. Water 

supply for establishment has been provided by 

using water harvesting techniques of laying impervious strips between planting~ with wax or 

polyethelene or by irrigation (Aldon 1975). Shaping 

the soil surface so as to trap snow to augment the 

water supply has been suggested (Tabler 1975). 

Use of artificial barriers to stabilize the surface on 

steep or highly erodible slopes has been found 

effective (Heede 1975). Much testing has been 

done to identify plants suitable for use at specific 

sites (Cook and others 1974), including use of 

legumes to improve fertility (Vogel 1973). 
IV - POTENTIALS 

The potentials for management and the pressures 

for improved management differ widely nationwide. In 1962 the U.S. Department of Agriculture 

estimated that more than 220 million acres of 

forest and other woodland in the continental 

United States needed better management to improve conservation of both soil and water (U.S. 

Dep. Agric. 1962). Here we first discuss potentials 

for management in general terms and then focus 

upon six separate extensive regions, each of which 

has its distinctive forest-climate relationship. 

Our prime concern here is forest management 

with respect to water: increasing water yield, 

enhancing the forest's flood control function, 

increasing its prevention of erosion, and expanding 

its protection of water quality. The multiple-use 

manager must, of course, use data relating to all 

phases of resource use in developing strategy for 

effective management of the forest. 

For specific local forested areas, such as those 

that directly supply municipal water systems, 

watershed management considerations may be 

paramount. On other forested areas, watershed 

management may receive relatively less emphasis 

than management to promote or provide other 

goods and services; these differing relative emphases 

result from social as well as resource considerations. 

Conflicting Objectives 

While acknowledging the importance of forestry 

in helping to solve problems of water yield, floods, 

and water quality, we must emphasize that forestry 

provides no cure-all; some management objectives 

are hydrologically incompatible with others. No 

single method of managing forested watersheds 

can improve all aspects of water yield and control. 

If we want more water, we may sometimes get it 

when we do not want it, and we may have to 

make special provisions to keep that extra water 

from damaging property. If we want water yield 

delayed for summer irrigation, the delay may 

sometimes reduce production of waterpower in 

winter or spring. The purest water generally comes 

from the least used forest. The objective of flood 

control is not compatible with achieving the 

greatest water yield. In some places the conflict 

over objectives is critical; in others, trivial. 

Forest management for water production and 

control must be coordinated with other water 

management practices, such as construction and 

FOR MANAGEMENT 

operation of reservoirs and filter plants, weather 

modification, and water harvesting. 

Financial incentives often are the deciding factor 

in determining individual land owners' objectives 

and whether they practice watershed management. 

In the words of Marion Clawson (1972), "Unless 

or until some means can be devised whereby forest 

managers can gain financially from watershed 

management, very few programs aimed at increasing the supply or improving the quality of 

water from forested watersheds will be undertaken" 

-at least on most private lands. However, public 

opinion and legal restraints are beginning to exert 

strong influence on water management of forest 

lands (Meier 1975). 

Management for Water Yield 

Forests cover about one-third of the conterminous 

United States and mark the areas of greatest 

precipitation and streamflow (fig. 1). These 650 

million acres of forest receive about one-half of 

the country's total precipitation and yield about 

three-quarters of its total streamflow. On a unit 

area basis, forest land receives about twice as 

much precipitation annually as other land, 45 

inches versus 22. Because it receives more water, 

the forest consumes more water than other areas, 

25 inches versus 19. More of the precipitation 

becomes streamflow-20 inches, or 44 percent, 

from the forest; 3 inches, or 15 percent, from other 

lands (Wooldridge and Gessel 1966). Forest regions 

of the United States coincide closely with areas 

where average annual precipitation exceeds 20 

inches and average annual streamflow exceeds 5 

inches. Forests and streamflow are highly correlated, 

particularly in the West. In the Columbia-North 

Pacific, California, Great Basin, and Upper and 

Lower Colorado Regions, more than 90 percent of 

the streamflow originates in high altitude watersheds that are largely forested and are predominantly 

in National Forests (Water Resources Council 1968). 

Water shortages occur locally throughout the 

country but are more serious in the West. For 

example, in four of the six western forest regions, 

the Water Resources Research Council (1968) 

rated water shortage a major problem; in seven of 

eight regions in the East, it was rated a minor 

problem. 

By the year 2020, the annual demand for water 

produced in forested regions is expected to increase 
by 30 million acre-feet in the East and by 39 million 

acre-feet in the West, according to projections by 

the Water Resources Council (1968) for water 

source regions that contain most of the forest 

area. 

These demands for water may be met in varied 

ways (National Academy of Sciences 1971). New 

sources of water may be made available by such 

familiar techniques as cloud seeding and desalting 

of saline water; less well developed, such as augmenting fog drip, creation of artificial ice fields, 

and deliberate snow avalanching, also have possibilities. Part of the demand for more water may be 

met by conserving existing sources of water. This 

may be accomplished by vegetation management, 

reduction of evaporation from soil water and 

snow surfaces, and by restoration of water quality 

by reclaiming wastewater. Further, some water 

can be made more useful by being transported 

from areas having excess supply to areas of deficit 

or by using water where it supplements existing 

supply. Consideration and comparison of the 

alternatives strongly suggests that the forest may 

often be a productive and economical source of 

more water. But since some increases may produce 

floods, care must be exercised to insure that increases in water yield are useful rather than 

damaging. 

Management for Maximum Water Yield 

Research has shown that water yield from 

forested areas increases as evaporative losses are 

reduced; therefore, the maximum possible increases 

from forest cutting are obtainable by some form 

of clearcutting. First-year increases following 

clearcutting range from 1 to about 18 area-inches 

throughout the country. How long the increases in 

water yield persist depends on the rate of regrowth, 

which differs widely among regions and vegetation 

types. 

Most of the increases in water yield that have 

been measured have been on small experimental 

watersheds surrounded by large forested areas 

(table 8). In effect, small watersheds are holes cut 

into the forest canopy. This means that the microclimate on the clearcut areas is not the same as 

that on fully open areas. The results of clearcutting an area large enough to function as a 

completely open area have not been completely 

evaluated. Some large-scale effects appear to be 

similar to those on the experimental watersheds. 

The increased runoff from the 300-square-mile 

Tillarnook Burn is like the result of the cleal-cutting 

on the H. J. Andrews Experimental Forest. In the 

East, the decrease in streamflow associated with 

regrowth on the Sacandaga Watershed is in accord 

with results at Hubbard Brook. Clearcutting of 

large areas is unlikely; however, the hydrologic 

consequences of management of large open areas 

may be of interest, for some such area may be 

considered for restoration of the forest. 

Water-Yield Increase 

Resulting from Multiple Use 

The possibilities of managing the forest simultaneously for timber, water, wildlife habitat, and 

other uses have achieved greater importance in 

recent years following managerial and legislative 

recognition of the multiple-use potential of forest 

lands. To some degree we can now have timber 

harvest, or other use, and more water, too. To 

some degree we have had both in the past. 

Although increases in water yield resulting from 

past forest cutting were usually not evaluated, 

they must have been substantial. In about 100 

years, the area of commercial forest in the United 

States was reduced from 828 to 484 million acres. 

Ninety-two percent of this reduction, 316 million 

acres, was in the East; it cleared 42 percent of the 

land in 29 states. Now about 2 percent of the total 

timber is cut annually. 

Although we can expect more attention to water 

in multiple-use management of public lands in 

both East and West, the withdrawal of lands for 

wilderness, parks, scenic rivers, and other such 

special uses will reduce the possibilities for water 

management as well as timber harvest. 

Management for water yield may deserve major 

emphasis in snowpack zones, for their yields are 

high, and they have potentials for affecting the 

amount, timing, and duration of yield. A snowpack zone is any area that receives 60 inches or 

more of snowfall annually. The snowpack zone is 

an important source of streamflow in both the 

Northeast and the West, but the potential for 

management to increase water yield is much less 

in the Northeast. These include parts of Maine, 

Vermont, New Hampshire, New York, northern 

Michigan, and high elevations in the 11 Western 

States-a total of about 240 million square miles, 

most of which is forested. The snowpack zone 

comprises a little more than one-third of the 

nation's total forest area. In New England and 

New York, streamflow in April and May, the prin- 
cipal snowmelt months, constitutes 35 to 50 percent of the annual yield (Lull and Pierce 1960). In 

the Colorado Rockies above 9,000 feet, probably 

about 90 percent of the annual water yield originates 

from snow (Goodell 1966). The snowpack zone in 

California, 12 percent of that state's land area, 

furnishes an estimated 51 percent of its strearnflow (Colman 1955). 

Noncommercial timber lands both above and 

below the commercial forest zone, mostly in the 

West, can also provide sizable and widely distributed areas suitable for water-yield management. 

Generally these lands are in regions where annual 

precipitation exceeds 18 inches. Research has indicated that the National Forests, under multipleuse programs, can produce an increase in water 

yield of 9 million acre-feet annually (U.S. Dep. 

Agric., For. Serv. 1967b). This increase is said to 

be compatible with sustained-yield timber management. About 7 million acre-feet of the total would 

be derived from the commercial forest, about 1 

million from phreatophyte clearing, and the 

remainder from chaparral and other areas. These 

estimates are for total potential; considering the 

time required to start such a program, a more 

practical estimate of what could be achieved in the 

next 50 years is 3.7 million acre-feet. New techniques could increase yield and speed up applications of management for increased water yield. 

These increases in water yield possible under 

multiple-use management are attainable by clearcutting in suitably designed patterns, encouraging 

growth of hardwoods rather than conifers, and 

prohibiting tree planting in riparian areas. Smaller 

and shorter-lived increases can sometimes be 

attained by selection and other timber cutting 

practices. Only effects on water yield are considered 

here. However, steadily increasing demands for 

water, timber, and other forest products will 

inevitably require emphasis on their simultaneous 

production. Within any area of management, 

these uses may well be reconciled by economic 

analyses like those suggested by Gregory (1955), 

Black (1963), and Brown and others (1974). The 

proper combination of timber and water production occurs at the point of greatest possible 

difference between total cost and total revenue. 

Restraints designed to prevent undesirable effects 

on the environment will be increasingly imposed. 

Cost of Increasing Water Yield 

The costs for increasing water yield under 

multiple-use management are only a fraction of 

total costs for maximum yield (table 11); they 

result from required special cutting practices that 

restrict the volume harvested and require cutting 

patterns that may add to logging costs. The 

estimated cost of $25 per acre-foot for maximum 

yield is equivalent to 8 cents per 1,000 gallons. 

The cost of water obtained by increasing forest 

water-yield is about one-fourth to one-half the 

cost of that obtained by any other current method 

except cloud seeding, a method not yet fully 

researched for its effects over large areas. 

Table 11-Costs of additional water obtained by alternative 

methods 

Method and Cost per 

location acre-foot 

Dollars 

(1) Forest management by multiple use: 

Western National Forests 1.44 

Commercial forest, 

United States 0.89 to 3.17 

(2) Maximum water yield 

Femow Exp. Forest, W. Va. 20 to 30 

(3) Salt water conversion 

Various locations 80 to 160 

(4) Water transmission 

From N. California to New 

Mexico to Los Angeles 45 to 65 

(5) Harvesting water from asphalt basin 

Arizona and New Mexico 80 to 160 

(6) Cloud seeding 

California 0.40 to 4 

I 

Compiled as follows: (1) U.S. Dep. Agric., Forest Serv. 

1967b (estimates by Irvin C. Reigner, Ralph C. Maloney, and 

E. G. Dunford, Aug. 2, 1969, on file, Forest Serv., U.S. Dep. 

Agric., Washington, D.C.); (2) Lull and Reinhart 1967; (3) 

Kohout 1969; (4) Patric 1959; (5) Black and Popkin 1967; 

(6) Kriege 1969. 

Insome locations water yield can be substantially 

increased by forest management designed primarily 

to produce maximum yields of high quality water. 

This would cost less than other methods that are 

sometimes deemed practical. Forest watershed 

management deserves to be considered as an alternative or an adjunct to other methods. It is more 

flexible than most alternatives; it can be deferred 

until the time of maximum need; it can be applied 

to meet even small local needs; and to some extent 

it is reversible and can be abandoned without 

difficulty. The value of yield increases through 

watershed management may, however, depend on 

available reservoir storage (Hoover 1969). Forest 

management may be practiced to increase the 

effectiveness of water production by cloud seeding. 
Leaf (1975a) has estimated, for example, that 

the combination of converting 40 percent of a 

forest area in central Colorado into openings 

5-to-8 tree heights across, plus augmentation of 

snowfall by 15 percent (by cloud seeding), would 

double water yield from the treated area. 

Management for 

Flood Reduction 

Floods are among the most damaging of all 

catastrophies. The Water Resources Council (1968) 

estimate of potential annual damage (in the absence 

of protective measures) in the United States was 

$1.7 billion; by 2020 it will be $5 billion. 

Flood damages steadily increase. In 1957, the 

dollar loss was double that of 1936 despite the 

expenditure during the 1936-57 period of $4 

billion in flood prevention activities. Bernstein 

(1974) reported that a 1973 appraisal gave an estimated $7 billion having been spent for flood control since 1936; yet annual flood losses are about 

$1.25 billion and are continuing to increase. Increasing losses have been charged to more frequent 

flooding, the rise in property values, and the 

greater occupancy of flood-prone lands. 

Forests, which occupy the major area of upland 

watersheds, are directly associated with flood 

damage in tributary streams. Estimates of the 

proportion of total flood damage that is incurred 

in upland watersheds have ranged from 40 percent 

(U.S. Senate Sel. Comm. Natl. Water Resour. 

1960a) to 56 percent (Ford and others 1955). 

Forest-flood relations in the East have been 

discussed in detail by Lull and Reinhart (1972). 

Floods resulting from late summer or fall hurricane 

rains strike the East. The most damaging storms 

in the Northeast were in 1955 and 1972. There 

were two hurricanes in 1955; rainfall from Hurricane Connie saturated the soil, priming it for the 

next week's onslaught of Hurricane Diane, which 

deposited record rainfall in eastern Pennsylvania, 

New York, and southern New England. In 1972, 

Hurricane Agnes became stationary over Pennsylvania. It deposited as much as 18 inches of rainfall during the period of June 20 through June 25, 

and caused the biggest flood ever recorded on the 

Susquehanna River (Pennsylvania State University 

1972). Hurricane Camille in August 1969, which 

deposited 28 inches of rain in 8 hours, was most 

damaging in Virginia (Williams and Guy 1973). 

In the East, floods from snowmelt alone are 

rare, but they occasionally occur. The flood in 

April 1928 in the deep snow country of the western 

Adirondacks was caused solely by the delayed 

thaw of a heavy snow cover (Hoyt and Langbein 

1955). 

In the forested West, precipitation is generally 

low in summer and high in winter. Exceptions 

are the frequent short-duration high-intensity 

summer rainstorms along the front ranges of the 

Rockies and on the Intermountain Plateau; occasionally there are similar storms over most of the 

mountainous West that produce damaging flows. 

In the far West, snowmelt floods occur nearly 

every year in late spring or early summer in some 

major basin draining the Rocky, Sierra Nevada, 

Cascade, or Olympic Mountains. 

In the high rainfall zones of California, western 

Oregon, western Washington, and Idaho, early 

winter storms are the most frequent flood producers. 

Rain on low-lying or shallow snowpack produces 

the greatest floods. Snowmelt floods in the major 

valleys, usually in June, are second in frequency. 

Three types of protective measures can reduce 

flood peaks or prevent increases in them. In order 

of increasing opportunity they are: management 

of existing forest land to reduce floods from rainfall, conversion of open land to forest, and snow 

management. 

Forest Management and Rainfall Floods 

Opportunities for moderating floods lie in 

management of timber, fire, and grazing. 

Timber harvesting affects a large portion of the 

forest at one time or another. Soil disturbance 

from logging typically occurs on 10 to 40 percent 

of the area harvested. Extreme disturbance (77 to 

88 percent of the logged area) may follow tractor 

logging and burning slash of old-growth redwood 

(Boe 1975). Three obvious ways to reduce stormflow are by reducing the disturbed area by choice 

of yarding method (Rice and others 1972), by 

rehabilitating logged areas that produce overland 

flow, and by providing filter strips between bared 

areas and streams. Keeping soil out of the channel 

is discussed below under "Management for Water 

Quality": this helps maintain channel capacity 

and channel bank stability and reduces the bulking 

of stormflows to a minimum. 

Cutting trees reduces evapotranspiration and 

soil-water storage opportunity in season. Hence, 

for prevention of dry-mantle floods management 

of both private and public forests should aim at 

limiting the area of any sizable drainage that is 

subjected to heavy cutting at any one time and do 

whatever is necessary to insure rapid regeneration. 

It is also beneficial to increase the stocking of 
trees in some existing stands to increase evapotranspiration and soil-water storage opportunity. 

The Water Resources Council (1968) has indicated 

needs for timber stand improvement on 9 million 

acres of federally owned land and on 20 million 

acres of non-federally owned land. 

Wildfire burns over about 5 million acres of 

forest in the average year. Reduction of this 

acreage moderates flood damage, at least where 

intense fires are prevented or limited in areas that 

have high flood and sediment potential and slow 

or incomplete recovery of vegetation after fire. 

Fuel management (including burning and other 

measures) is important in prevention of wildfire 

damage. Besides helping to reduce the acreage 

damaged by wildfire, fuel management can reduce 

the impact on those areas where wildfire does 

occur. Conditions differ widely, even within regions 

and sometimes from year to year in the same 

area; however, we have stated some generalizations 

in various sections of discussing differences in 

regional fires and flood frequency. 

Wildfire may occur infrequently on any area, 

but grazing is usually an annual harvest. About 

85 million acres of forest are grazed. Since an 

estimated 20 million acres (about 4 percent of the 

total forest area) is grazed heavily enough to cause 

overland flow, grazing poses local flood problems 

but no widespread danger. Good watershed 

management (and good livestock management, 

too) must determine the safe carrying capacity of 

the forest range and then limit use to that capacity 

by using measures required to effect proper seasonal 

use and distribution of stock. This means eliminating 

grazing in some forest areas. 

Conversion of Open Land to Forest 

Research has amply demonstrated that the conversion of idle, eroding land to forest can sharply 

reduce peak flows over a period of 10 to 20 years. 

The dimensions of the job that needs to be done 

are indicated by the 35 million acres of commercial 

forest land that are less than 10 percent stocked 

and may need to be planted (US. Dep. Agric., 

For. Sen. 1965). A more recent estimate indicates 

that 22 million acres of understocked land need 

reforestation (Water Resources Council 1968). 

Even where these lands pose no massive flood 

threat, their rehabilitation would help to reduce 

flood peaks on tributary streams and would 

alleviate sedimentation problems downstream. 

Snow Management 

If floods from either snowmelt alone or from 

rainfall plus snowmelt originated on forest land, 

they are forest-influenced. The patterns in which 

forest trees are cut or left can influence snow 

distribution, melt rates, and snowpack influences 

on storage and delivery of rain (Anderson 1963, 

1970a, Hoover 1971, 1973, Smith 1974). Although 

most forests probably are not managed primarily 

for flood prevention, the selection of cutting 

patterns and the scheduling of forest cutting 

may well be influenced by flood prevention 

objectives. The options are many, the effectiveness is great, and the objectives complement 

other objectives, such as water quality control. 

Goodell (1959) explained that forest influences 

together with topographic influences can reduce 

flood peaks by desynchronization. Topography has 

the greatest influence on flood peaks. Snow on 

south-facing slopes characteristically melts earlier 

than snow on north slopes. Forest management 

can enhance this desynchronization by increasing 

the variability of melt rates over a large watershed. If, for example, the forest on a southfacing slope is managed to produce wide open 

strips running north and south, snowrnelt should 

be seasonally early. If a north slope has dense 

continuous forest cover, the melt should be comparatively late. Thus, melt water from the south 

slope should be largely discharged before the northslope yield reaches its maximum. Complexity arises 

on large watersheds where consideration must be 

given to the timing of discharges from numerous 

slopes differing in steepness, aspect, and elevation. 

Complexities arise in management for wet years and 

dry (Anderson and West 1966) and in slope exposure 

in areas that have different snow amounts or 

characteristics (Smith 1974, Warren and Ffolliott 

1975). 

Management for 

Maintaining Water Quality 

Recent Federal and State legislation has given 

top priority to management for water quality 

control. Four Congressional acts with five amendments and recent presidential Executive Orders 

constitute the existing status of water quality 

legislation for United States surface waters. A 

particular concern has risen about nonpoint 

sources of deterioration of water quality, such as 

might be associated with forest roadbuilding, 
treatment of logging residue, and preparation 

of sites for planting (Meier 1975). 

Management of the quality of water from forest 

lands must rely on four basic steps: 

1. Appraisal of the present and potential uses 

of water and how those uses would vary with 

different characteristics of water quality. 

2. Appraisal of the present water supply and 

characteristics of its quality, including its natural 

variability. 

3. Appraisal of the changes in quality that can 

be achieved by alternatives in management. 

4. Appraisal of the value to beneficial uses of 

water that could result from alternatives of management. 

Uses of water from forest land may be the 

crucial decision variable in forest land management. A local domestic water supply or local 

fishing requirement may dictate the direction and 

stringency of water quality management. On the 

other hand, the quality of water delivered to a 

downstream reservoir may seem to be equally 

cnlcial to a management decision, but may not be, 

for a filter plant could be installed to produce 

suitable improvement in quality. It has been said 

that "any water of improved purity will find a 

use", but the forest is there to use also (Lantz 

1971b). Let us look at some of the characteristics 

of water quality supply from forests and then at 

the effects of management alternatives on water 

quality characteristics. 

The forest has amazing capacity to buffer 

changes in the water's content of solids, dissolved 

inorganic chemicals, organic compounds, and 

microorganisms. Solid particles eroded from the 

soil surface in local areas may be filtered effectively 

by the forest floor or the forest soil together with 

other absorbed materials. The forest floor and 

forest soil naturally absorb both organic and 

inorganic chemical compounds; this was dramatically demonstrated by spraying massive quantities 

of domestic, industrial and agricultural wastewater 

on forest sites (Sopper and Kardos 1973). 

Nikolayko (1974) has documented the removal of 

microorganisms by the filter effects of the forest. 

But natural forest systems do not necessarily 

produce the best quality of water for all uses: 

organic acids from forest litter may produce 

water high in calcium content in regions underlain with limestone, phenols dissolved from leaf 

fall in streams may produce undesirable odor 

or taste in the water, and water temperatures 

may be kept too cool for greatest production in 

the aquatic environment. Streamside vegetation 

may dry up channels. Local soil and climatic 

accidents such as landslides may produce occasional deterioration in water quality. At the same 

time that we consider maintenance of water quality 

we may consider enhancement. 

The parameters of water quality subject to 

management could be any or all of the more than 

40 listed by the Environmental Protection Agency 

(1972), but the ones currently being monitored 

from forest lands are generally turbidity, suspended 

sediment, pH dissolved oxygen, total dissolved 

solids, and temperature. Other parameters may 

include coliform bacteria, phosphorus, nitrates, 

certain heavy metals, and chlorides. The products 

of erosion contribute directly to several of these 

parameters and have received the most study. 

Erosion and Sedimentation 

It has been estimated that 80 percent of the 

deterioration in water quality is due to suspended 

sediment, mostly from soil erosion. 

Forest cover strongly influences the volume of 

soil erosion and the influx of erosional products 

into streams and lakes. Man's activities in the 

forest often accelerate erosion and sediment 

production; this has long been recognized, and 

much has been written about the problem and 

how to prevent it. 

Surface erosion, gully erosion, mass soil movement, channel erosion, and the transport of eroded 

material all degrade water quality. Suspended 

sediment damages municipal and industrial water 

supplies and also causes problems within the 

forest ecosystem itself. Dirty water degrades 

the aquatic habitat, reduces recreational use and 

enjoyment of the forest, and detracts from its 

visual appeal. 

The magnitude of the problem of erosion control on forest lands depends on several considerations: soil disturbance, topography, and the 

nature of the soils, to name a few; each of these 

varies widely within any given region. 

Basic statistics of the National Inventory of 

Soil and Water Conservation Needs (U.S Dep. 

Agric. 1962) show that about 1 percent, or 4.5 

million acres, of the forest land in the East needs 

treatment to control erosion. Almost half of this 

area is in the Southeast (largely in Alabama, 

Georgia, and Mississippi), and more than one-
quarter is in the Central States (mostly Kentucky 

and Missouri). These estimates indicate that about 

9 percent, or 7.5 million acres, of the forested 

West needs treatment to control erosion. Twothirds of this area is in the mountainous portions 

of Arizona and New Mexico; most of the remaining third is divided about evenly between California 

and Oregon. 

The severity of soil disturbance is often the 

prime factor in soil erosion. It is surely evident 

by now that an undisturbed forest soil promises 

a minimum of erosion. With some exceptions, 

surface erosion, mass movement, or channel 

cutting may be expected whenever mineral soil is 

exposed by logging, fire, or grazing. 

Erosion Control-Logging 

Erosion control begins with planning the road 

system and its drainage. The design of an erosion 

control drainage system requires information 

about the volume of water to be drained, the 

erosion potential of the subsoil, and the duration 

cF use of the system (Engberg 1963). Since as 

much as 90 percent of the sediment produced 

by erosion on timber sale areas comes from 

roads (Packer and Christensen 1964, Megahan 

1975), planning must begin with careful choice 

of logging methods appropriate to the area and 

with careful road location and design (Engberg 

1963, U.S. Environmental Protection Agency 

and others 1975). Logging and skidroad mileage 

can be reduced by logging with skyline systems 

that reduce soil disturbance by about one-half 

of tractor logging. New equipment that can 

traverse roads having steep grades promises to 

make short access to ridgetop roads feasible, 

thereby reducing road erosion. In the future, 

balloon or helicopter logging may reduce soil 

disturbance even more (see the section on Timber 

Harvest and Erosion). 

Slope-length relationships and frequency of 

use should govern road location. For example, 

a 4-percent grade may reduce drainage problems, 

but an 8-percent grade requires only half the 

length of road to reach the same elevation and 

may not tax modern vehicles. The time required 

for travel would also be shorter (Byrne 1963). 

Near the end of the road soil disturbance may 

be reduced by lowering road design standards 

to meet the expected reduction in road use (Banta 

1963). Narrow roads with grades as steep as 20 

percent have been used on low-use, dead-end 

spur ridges in an attempt to stay on the ridgetop 

and avoid the steep, thin-soiled headwalls and 

midslope locations. Side casting of road cut 

material on steep slopes may scour off shallow 

soils; in southwestern Oregon, end hauling to 

waste disposal areas has been proposed as a 

solution to this problem (Dittmer 1971). 

In areas having diverse soils, a map of forest 

soils may be the basis for locating forest roads 

away from erosion-prone areas (Fisher and Bradshaw 1957). Similarly, identification of slideprone areas from soil series and slope classes may 

enable avoidance of these major sources of erosion 

(Wallis 1963). The effects of road location and 

construction standards on sedimentation were 

clearly indicated in a recent study of deposition 

in reservoirs in 48 northern California watersheds. 

Streamside roads produced twice as much sediment as roads located on ridges or slopes; the 

greatest producers of sediment were improved 

secondary roads at streamside. Deposition increased 6.9 times for each mile of road per 

square mile of watershed above a reservoir 

(Anderson 1974). Road location is especially 

important in steep watersheds (Anderson 1976). 

The control of road erosion requires not only 

proper location but cut and fill-slope protection 

and drainage necessary to prevent overland flow 

from developing enough depth and velocity to 

seriously erode the road surface and roadside 

ditches; Drainage must also prevent road runoff 

from reaching the stream channel directly. Surface 

flow has been diverted to roadside filter areas. 

Planting ponderosa pine on road fill slopes has 

effectively reduced surface erosion of fill slopes 

(Megahan 1974). Erosion from road fills and cut 

banks has been reduced by seeding, mulching, 

and fertilizing (Dyrness 1975, Berglund 1976). 

Mulching the surface is particularly important if 

erosion is to be prevented the first year after 

road construction, before vegetation becomes 

fully established. 

But logging is more than roadbuilding. Prospects for maintenance of water quality by prevention of erosion associated with logging 

involves proper choice of a combination of silvicultural method, logging method, slash disposal, 

and post-logging treatments that will keep local 

erosion to a minimum (Rothacher and Lopushinsky 

1974). Secondary effects must be controlled: augmentation of water yield, rapidity of snowmelt, 

and decomposition of forest floor material. Local 

erosion is being controlled chiefly by dispersion 
of forest residues, installing crossdrains in skid 

trails, and seeding bare areas with grass; however, 

the control of channel erosion induced by the 

increased water yield or increased rate of snowmelt is only starting to be recognized and properly 

evaluated. Current evaluations involve selection 

of selectable increases in water yield associated 

with the area and type of cutting patterns (Galbraith 1975); then, the channel's tolerance must 

be appraised separately on the basis of a stability 

rating. If need be, the area to be logged is 

adjusted to meet the yield-stability criteria. One 

appealing prospect is to minimize the impact 

on the initial reach of the channel by making 

widespread, numerous small cuts or resorting 

to single tree selective cutting. 

Part of the total problem of logging is disposal 

of the logging wastes that in steep forest area 

usually end up in stream channels; this poses 

another whole set of water quality problems. 

Organic debris, which may vary from whole 

trees to simple organic compounds, poses varied 

problems to the forest manager. These problems 

vuy from bulking and damming of flood flows 

to producing offensive odor in drinking water. 

The primary problems of water quality involve 

slow mechanical wear of debris in streams, 

dissolved solids affecting stream chemistry, and 

dissolved organic substances affecting water taste 

or odor. Secondary effects of the presence of 

organic debris in streams include such diverse 

things as interacting with sediment in the water, 

causing blocking of streams and scouring of 

streambanks, blocking of culverts, reducing 

stream oxygen, and effects on microorganisms in 

water action on their food chain. Some of these 

latter, in certain amounts, may be beneficial 

(Jackson 1975, Triska and Sedell 1975). 

Presence of organic debris in streams along the 

Pacific coast raises special problems because this 

debris is present in large volumes, partly from 

natural causes and partly as a result of poorly 

planned or poorly managed logging operations 

(Rothacher 1959, Froelich 1971). Burns (1972) 

emphasized the need to keep all timber out of 

streams because decaying slash depletes intergravel oxygen. Low production of salmonids in 

clearcut watersheds of the Olympic Peninsula 

of Washington has been found to be associated 

with the large amount of organic debris in the 

streams (Allee and Smith 1974). 

Froelich's outline (1971) of procedures for 

controlling the gross organic component of debris 

in streams essentially agrees with all other guides 

for eliminating pollutants from streams: the best 

control is simply to keep the pollutant out of the 

stream. Clearing debris out of channels, particularly channels of narrow streams, may actually 

cause more damage than leaving the stream alone 

(Burns 1972). Hewlett and Douglass (1968) found 

that most of the increase in sediment in streams 

on a multiple-use water shed resulted from stream 

"improvement" activity, including clearing. A 

study of 304 stream reaches in the upper Missouri 

River basins following the 1948 flood (Anderson 

and Ingebo (personal observation) ) revealed that 

presence of debris did not reduce stability of first 

order tributary streams, whereas debris in stream 

links of higher order streams frequently caused 

scour of banks by forcing the flow to bypass it. 

Berry (1975) has concluded that reduction of 

oxygen in streams along the Oregon and Washington coast was closely related to length of 

clearcuts and temperature of the streamwater and 

suggests that cutting practices be modified by 

manipulating the length of clearcuts and leaving 

buffer strips instead of removing debris from 

channels. 

Microbiological 

A common index of the microbiological pollution in water is the coliform content. Prospects 

for reducing this index by forest management 

have been published in the Soviet literature. 

Drobikov (1973) reported that whereas streamflow from a clearcut area had (in summer) a 

coli index of 2300 to 9600, under the same conditions the index from selective group cutting was 

only 230 to 2300. Similar prospects for microbiological reductions may occur with choices of 

silvicultural methods in the United States in areas 

that have high summer rainfall. 

Erosion Control-Fire 

Erosion after severe fire is serious, especially 

in areas where low rainfall or repeated burning 

delay natural revegetation. 

An extreme example of effects of fire on 

erosion is in the southern California and Arizona 

chaparral and has been discussed under that 

heading. Planting either herbaceous or woody 

species or both can often prevent some potential 

damage from erosion and sedimentation. The 

reforestation of 255,000 acres of the Tillamook 
Burn in Oregon is an outstanding example of 

successful reforestation. Now, 25 years after the 

start of reforestation of part of the burn, trees 

are 50 feet high-already high enough for a 

commercial thinning (Oreg. Dep. For. 1973). The 

hydrologic consequences of reforestation are 

documented elsewhere in this paper. It is presumed that reductions in sedimentation were 

correlated with the reduced peak flows that 

followed reforestation because concentration of 

sediment in the watershed varies approximately 

with the square of the number of inches of 

streamflow. 

Another technique for reducing the effect of 

wildfires on water quality is to use care in timing 

of post-fire treatments. For a short time, at least, 

the watershed is highly susceptible to other 

disturbance, such as road construction or salvage 

logging. The adverse erosion effects on the 

Tillamook Burn may have resulted from the 

post-burn logging and road building in the area 

described by Bailey and Poulton (1968). Megahan 

AVERAGE ANNUAL STREAMFLOW 

0

-

inches 

0 - I 

mm 

0-25 

EZB -5 25- 127 

m 5-20 27-508 

20 -40 508- 1016 

Over 40 Over 1016 

and Molitor (1975) suggest deferring salvage logging until dead needles dropped from trees can 

provide a ground cover to protect against erosion. 

Regional Characteristics 

and Possibilities: The East 

Regional differences in the relation of the forest 

to water yield, floods, and water quality result 

in different practices and possibilities for improvement. To assess these differences, we have 

divided the country into six major regions, three 

in the East, three in the West. We suggest 

certain practices that are based on research results 

already published and on climatic and streamflow 

data. These recommendations are not definitive; 

the selected regions are too diverse and the 

management objectives for even single watersheds 

too complex to permit statement of more than 

general characteristics and recommendations. 

The three regions in the East and their characteristics are shown in fig. 5 and tables 12 and 13. 

Figure 5-Major forest regions in the Eastern United States, and average annual streamflow. 
-- 

Table 12-Mean annual precipitation, streamflow, and evapotranspiration in selected forest types in the East, 

by geographic regions 

Mean annual.. . Region and forest type Area 

Precipitation Streamflow Evapotranspiration 

Thousand acres Inches 

Northeastern Conifers and Hardwoods 

New England, New York, 

and Pennsylvania: 

White-red-jack pines 

Maple-birch-beech 

Oak-hickory 

Michigan, Wisconsin, 

and Minnesota: 

White-red-jack pines 

Maple-birch-beech 

Oak-hickory 

Aspen 

Central and Southeastern Hardwoods 

Northwestern portion: 

Maple-birch-beech 

Oak-hickory 

Oak-gum-cypress 

Southeastern portion: 

Oak-hickory 25,776 49 

Oak-gum-cypress 25,884 50 

Southeastern Pines 

Southeastern area: 

Loblolly-shortleaf 52,008 49 

Longleaf-slash 25,967 52 

Source: U.S. Senate Select Committee on Water Resources 1960b. 

The East has no areas of perennial water they cannot be ignored in forest watershed 

shortage, but occasional droughts cause severe management, for how we change them can be 

local problems. Other areas have possibilities for important. 

increasing water yield enough to meet mounting . The principal technique for management for 

domestic and industrial demands (Douglas 1974). chemical water quality was emphasized by 

Tarrant (1972): "If you do not want the chemical 

Water Chemistry and Temperature in stream water, don't put it there!"Chemicals 

must be kept out of streams and other water 

Content of dissolved solids and water tempera- bodies, and chemicals should be applied to land 

ture are parameters of water quality; management surfaces only where the possibility of their moveattempts to keep each with certain limits. Dis- ment from land to water is low. The degree to 

solved solids content in streams flowing from which this has been achieved is stated in sections 

forested areas are usually low and reflect mostly discussing applications of chemicals for specific 

the local climate and geology. Stream-water purposes. 

temperature, of course, depends mostly on climate; When timber is harvested, leaving buffer strips 

but forest cover may moderate the effects of of uncut or lightly cut timber is probably the 

climatic extremes. Forest treatment can affect most effective means for preventing undesirable 

both of these characteristics of water quality; increases in streamwater temperature (Brown and 
Table 13-General characteristics of major forested regions in the East 

Characteristic 

(1) Forest area 

(thousand acres) 

Major species 

(2) Rainfall, max. 10-year 

24-hour (inches) 

(3) Freeze-free period, mean 

length (days) 

Snowzone area 

(thousand acres) 

(4) Flood damage: 

Total mean annual 

(million dollars) 

(dollars/acre, all land) 

Upstream mean annual 

(dollars/acre, all land) 

Regional forest type 

Northeastern hardwoods Central-southeastern Southeastern 

and conifers hardwoods pines 

98,504 210,240 85,161 

Maple; oak; beech; Oak, hickory, ash, Shortleaf, loblolly, 

birch; eastern maple, yellow- longleaf, and 

white, red, and poplar, beech slash pine 

jack pine; 

spruce 

Compiled as follows: (1) U.S. Dep. Agric. Forest Serv. 1965; (2) Hershfield 1961; (3) U.S. Dep. Commer. Environ. Data 

Serv. 1968; (4) Water Resour. Council 1968. 

Krygier 1967). Brown and Brazier (1972) describe 

a method of designing buffer strips to provide 

optimum protection for the stream while achieving 

optimum utilization of timber. 

The half of the entire Eastern region that is 

classed as forest yields roughly 500 million 

acre-feet of water per year through surface 

streams alone (Hewlett 1967a). Treating only 10 

percent of this area could increase the yield by 

10 million acre-feet of water annually, enough to 

meet the needs of an additional 50 million people. 

Because they are publicly owned, the 23 million 

acres of Federal and State forest lands that provide 

the highest water yields in the East may someday 

be managed with more emphasis on increasing 

their water yield. 

Northeastern Conifers and Hardwoods 

Precipitation in the Northeast ranges from 24 

inches in Minnesota to 74 inches in New Hampshire's White Mountains (U.S. Dep. Commer., 

Environ. Data Serv. 1968). Snowfall averages 

60 to 100 inches annually in the Lake States, but 

rainfall intensities in this region are the lowest in 

the East. Mean annual streamflow ranges from 5 

inches in northern Minnesota to 20 inches or 

more in much of New England and New York 

(Busby 1966). The estimated mean annual evapotranspiration showed less spread, from about 18 

to 24 inches. 

Water yield-Mean annual precipitation, 

streamflow, and evapotranspiration by major forest 

types in the Northeast are given in table 12 along 

with comparable data for other regions in the 

East. Streamflow is about twice as great in New 

England, New York, and Pennsylvania as it is in 

the Lake States for similar forest types, but 

evapotranspiration is about the same, around 20 

inches. 

Water conservation-Water might be saved 

by not planting trees adjacent to reservoirs, 

where in essence the plantings would become 

riparian vegetation; it has been estimated that 

this could save 1 to 6 inches per year in the 

Northeast. Herbaceous vegetation, which might 

be encouraged to promote soil stability in these 

areas, would consume some of this saving, but 

not all of it (Lull and Reinhart 1967). Where 

esthetically acceptable, cutting trees adjacent to 

reservoirs may save water. 

In humid areas, riparian sites near streams 

may be shaded and cool, with a consequent 
reduction in the potential for evapotranspiration, 

or sufficient water may be available for nearpotential evapotranspiration over the whole watershed. A riparian cut here would have an effect 

no greater-possibly not as great-than a cut 

elsewhere. 

Limited evidence from the East suggests that 

favoring hardwoods rather than planting conifers 

would increase water yield. Savings might amount 

to from 2 to 10 inches per year, or perhaps 

even more. On conifer plantations under intensive 

management (including periodic thinnings and 

intermediate and final harvests), the reduction in 

water yield from pine stands compared with yield 

from hardwood stands would be partially restored. 

If both water and timber values are compared, 

conifer plantations may often be preferable to 

hardwoods. Indeed, private landowners much 

prefer conifer stands because they yield cash 

benefits, but increased water yield brings no such 

benefits. 

Clearcutting hardwoods and providing the 

minimum ground cover necessary for preserving 

mil stability may increase water yield by an 

amount equivalent to about half of the hardwoods' evapotranspiration, an annual increase 

that might range from 8 to 11 inches. Clearcutting under a sustained yield system that encourages immediate regrowth can increase the 

first year's water yield by as much as 4 to 14 

inches. Clearcutting conifers may give as much as 

4 inches' greater yield than cutting hardwoods. 

These increases diminish rapidly and almost completely disappear in about 10 years. Under an 

80-year sawtimber rotation and even-aged management, the net increase in water yield could 

range from 0.5 to 0.7 inch annually. Of course, 

this is in comparison with water yield from a 

forest previously subject to no cutting at all; if 

the previous yield was affected by prior timber 

harvest or other forest removal, this increase 

would be reduced or eliminated. 

If timber is taken from a watershed under a 

cutting system that removes timber uniformly 

over the entire area and creates only very small 

openings, there is some evidence that the increase 

in yield would be no more than about one-third 

of the increase that could be realized from block 

cutting the same volume of timber (Lull and 

Reinhart 1967). 

For the northeastern region, Lull and Reinhart 

(1967) summarized the costc of achieving the 

maximum water yield that is consistent with 

maintaining a protective ground cover by removing fully-stocked, noncommercial stands. These 

costs were $100 to $200 per acre for clearcutting and $10 to $60 per acre for herbicide 

treatments, controlled burning, or bulldozing to 

further control vegetation. Combinations of treatments or retreatments might be necessary to establish and maintain the desired cover. The cost in 

terms of water yield could be an estimated 

10 cents per thousand gallons or $33 per acre-foot. 

Foremost among the potential management 

areas would be the 2 million acres of forest 

land in 14 northeastern States that comprise 

watersheds and reservoir-protection areas under 

the control of more than 750 municipalities, 

private water companies, and State and Federal 

agencies (Corbett 1970). The principal function 

of these areas now is to protect water quality; 

they also provide whatever income can be derived 

from harvesting forest products without reducing 

water quality. 

Peak flows-The occurrence of highest flows 

in early spring rather than in winter is a distinguishing characteristic of the northeastern 

region (Miller and others 1962). The combination 

of spring rainstorms and snowmelt has produced 

record peak flows from New England's forested 

mountains. Peak flows and most of the annual 

yield usually occur together; 13 of the 23 inches 

of annual streamflow from northern New England's watersheds come during the spring months 

(Sopper and Lull 1965). However, occasional 

fall hurricane storms produce the highest local 

peak flows. 

There is little question that stormflow is higher 

from cutover forest land, but mostly during the 

growing season (Lynch and others 1975, Corbett 

and Heilman 1975, Patric 1973). The few possibilities for reducing flood peaks from forested 

areas depend on logging practices that require a 

minimal area of road systems and landings and 

control overland flow from them. Another possibility is the reforestation of 8.5 million acres of 

nonstocked forest land. But where high spring 

temperatures may rapidly melt the snow accumulated under conifer plantations, planting conifers 

may occasionally serve only to increase peak flow 

on these occasions. In such areas, a combination 

of open land (with soil stabilized) and forest 

land may be preferable. Federer and others (1972) 

recently reviewed pertinent research, and concluded 
that the possible effects of snow management on 

floods in the Northeast are small, that regional 

management is impossible because of the many 

ownerships, and that management of forests for 

protection from snowmelt floods need not be 

considered further in this region. According to 

another viewpoint, management should aim to 

preserve the existing diversity of land use, which 

serves to desynchronize peak flows from different 

parts of northeastern watersheds. 

Sedimentation-The minimum sediment concentrations in the country are in the northeastern 

region (Rainwater 1962). Streams draining watersheds that have all types of land use average 280 

p/m or less in most of this area, whereas streams 

in northern Ohio, northern Illinois, and southern 

Wisconsin average values as high as 2,000 p/m. 

Mean concentration is estimated at 390 p/m, 

equivalent at 10 inches of annual streamflow (in 

the Lake States) to 283 tons per square mile, and 

at 25 inches (in New England) to 707 tons per 

square mile. These sediment concentrations are 

far above acceptable standards for water quality; 

hence management of forest land to improve or at 

least not further impair downstream water quality 

is important. 

Erosion on forested lands occurs only on areas 

where soil has been disturbed. Stony soils and the 

formation of erosion pavements in most of the 

region preclude prolonged soil loss. The 10,000- 

square-mile Driftless Area in southwestern 

Wisconsin presents the greatest erosion problem 

because of its highly erodible soils and steep 

topography. 

In all of the Northeast, road design and 

maintenance are crucial to sediment control 

(Kochenderfer 1970). Spacing of cross drains and 

width of protective strips have been determined 

by the steepness of the road. Trimble (1959) 

recommended that maximum grades on truck 

roads or heavily used skidtraiis on municipal 

watersheds should be less than 10 percent, except 

for very short stretches. Such roads can be 

drained adequately by cross drains spaced by this 

rule of thumb: divide 1,000 feet by the percentage 

road grade. With a 5-percent grade the drains 

would be 200 feet apart; with a 10-percent grade, 

they would be 100 feet apart. 

The recommended minimum distance from 

road to stream in the White Mountains of New 

Hampshire is 50 feet plus 4 feet for each percent 

slope to the stream. Thus, on a 20-percent slope 

the road should be located at least 130 feet from 

the stream (Trimble and Sartz 1957). Waterspreading devices below the drainage outlet could 

make narrower strips acceptable. 

The key to maintenance of good water quality in 

the northeastern forests, according to Trimble 

and others (1975), is intelligently regulated roads 

and application of known good logging practices; 

otherwise impairment of forest water quality is 

certain. 

Chemical water quality-The study of nutrient 

discharge after clearcutting in New Hampshire 

showed concentrations of nitrate and some other 

ions in streamwater as high as 26 mg/1; this is the 

highest concentration found after clearcutting 

anywhere in the country (Hornbeck and others 

1975, Pierce and others 1972). In the Fernow 

Experimental Forest, Aubertin and Patric (1974) 

reported that increases in nitrate-nitrogen concentrations in streamflow following cutting 

averaged about 1 mg/1 or less. Increases at 

individual locations had comparable values. 

Similar results were reported by Lynch and others 

(1975) in a study in Pennsylvania. When only a 

small portion of any large drainage in areas like 

these is clearcut at any one time, nutrient 

concentrations do not increase enough to be a 

hazard to drinking water. However, even with this 

precaution, there might be a problem of local 

eutrophication, and probably temporary stream 

and lake eutrophication as well. 

Central-Southeastern Hardwoods 

The Central-Southeastern hardwoods region, 

largest of the six forest regions, extends from the 

95th meridian across the Mississippi and Appalachians into the Coastal Plain. Mean annual 

precipitation is as much as 80 inches in part of the 

Appalachians but only about 36 inches at the 

western edge of the region; corresponding runoff 

for these areas is about 40 and 10 inches, 

respectively. The estimated evapotranspiration 

ranges from about 26 inches in the northern 

portion of the region to about 40 inches in 

northern Louisiana. 

Water yield-For the upland types in this 

region, streamflow averages about 40 percent of 

precipitation; for the oak-gum-cypress type, the 

average is about 30 percent (table 12). 

Clearcutting hardwoods in this region and 

maintaining a soil-stabilizing ground cover can 

increase annual water yield an estimated 8 to 14 

inches in the northwestern portion and 12 to 16 
inches in the southeastern portion; the first year 

after cutting, the yield may be 3 to 4 inches 

greater than this. In the southern Appalachians, 

streamflow increase after cutting is approximately 

twice as great from north-facing as from southfacing watersheds (Douglass and Swank 1975). If 

regeneration is immediate, this yield diminishes 

to a negligible amount through a recession period 

of 10 to 20 years. Again, under even-aged 

management, an 80-year rotation, and cutting a 

portion of each management unit every 10 years, 

the average annual increase in water yield in the 

northwestern portion of the region would be an 

estimated 1.0 to 1.6 inches. Thinnings and 

selection cuttings would increase water yield a 

little but only briefly. 

The possibility of decreasing water yield from 

forests in the Southeast is real, if 20 million acres 

of upland hardwood forests were converted to 

southern shortleaf pines. Douglass (1974) has 

estimated that water yield would be reduced 8 

inches per year, and that even if the pine forests 

were intensively managed they would use more 

~aterthan the present hardwood forest. 

Peak flows-In the North Central area, from 

12 to 24 percent or more of the precipitation goes 

into stormflow, but only 4 to 12 percent in the 

Piedmont and Coastal Plain of the Southeast 

(Woodruff and Hewlett 1969). Winter is the 

principal season of high flows. One possible 

means of flood reduction is reforestation of the 15 

million acres of nonstocked land. The present 

'nonstocked" . classification means that these 

lands do not have silviculturally desirable trees. 

We do not know how much of it has other 

volunteer vegetation that serves some useful 

hydrologic function. 

Sedimentation-The mean annual sedimentation rate for this region, coming from lands in all 

types of use, averages 814 p/m or 944 tons per 

square mile per year for a streamflow of 16 

inches. Streams that drain loessial soils in the 

Mississippi basin have much higher average rates 

-as much as 6,000 p/m-and average rates up 

to 2,000 p/m occur in the Ohio River basin and the 

Piedmont Zone. Streams in the Appalachians and 

the Coastal Plain have low average rates, ranging 

up to about 280 p/m, similar to those in most of 

the Northeast. 

As in other regions, poorly designed and 

located roads are the main cause of deteriorating 

water quality (Douglass and Swank 1975). During 

storms, turbidity is 10 to 20 times greater in a 

clearcut watershed with logger selected roads 

than in an undisturbed watershed. In undisturbed 

watersheds typical storm turbidity ranges from 

20 to 30 p/m. However, in a watershed where 

roads were carefully designed and constructed, 

maximum turbidity increased tenfold (Douglass 

1974). Apparently, in this area it is not enough to 

just declare that roads are adequately located and 

designed. 

The self-healing process characteristic of 

northeastern soils is less prevalent in the 

Southeast; erosion once started on the deeper, 

less stony soils, continues for longer periods. This 

places even greater stress on need for careful 

location, construction, drainage, and maintenance 

of logging and skidding roads and on the 

stabilization of road cuts and fill banks. Tree 

planting has major importance in site rehabilitation and sediment control. 

Three opportunities for improvement in water 

quality in the South through erosion control have 

been suggested. First, reforestation of 15 million 

acres of depleted upland hardwoods should 

reduce erosion. Ursic and Dendy (1965) measured 

five times greater soil losses from these depleted 

hardwood forests than from mature pinehardwood forest. Second, erosion can be reduced 

during mechanical site preparation for forest 

planting, which is a chief source of accelerated 

erosion in the South (McClurkin and Duffy 1975, 

Dissmeyer 1976). Planting a quick growing cover 

crop is one method. Third, erosion can be reduced 

by prevention of overgrazing of the hardwood 

forests, which is another serious source 

(Dissmeyer 1976). 

Reforestation with pine often takes 10 years to 

produce a litter cover sufficient to protect the soil. 

Duffy (1974) combined grass and pine planting; 

by deferring fertilization, he reduced grass 

competition with pine sufficiently to allow pine 

establishment. 

Southeastern Pines 

The southeastern pine region includes portions 

of the Piedmont and most of the Coastal Plain. 

Annual precipitation ranges from 40 inches on the 

western edge to 60 inches along the Gulf Coast. 

Rainfall intensities in this region are the highest 

in the East. The mean annual streamflow ranges 

from about 10 to 30 inches, and evapotranspiration from about 30 to 40 inches. 
Water yield-Mean annual precipitation for 

both major types of pine (loblolly-shortleaf and 

longleaf-slash) averages 50 inches, streamflow 15 

inches, and evapotranspiration 35 inches (table 

12).Hewlett (1972) pointed out that although the 

Coastal Plain areas generally have abundant 

water, the ridge and valley provinces find water in 

rather short supply. 

Clearcutting southern pine may increase annual 

water yield by 16 to 18 inches (about half the 

estimated evapotranspiration) after a protective 

ground cover develops. The maximum increase 

the first year may amount to 19 to 22 inches. 

During regrowth of a forest stand, measurements 

of soil water suggest that increases in yield may 

persist for 15 to 20 years and the immediate 

reduction may not be as sharp as when sprouting 

hardwoods utilize established root systems. We 

have already pointed out that even-aged management (an 80-year rotation with parts cut at 

10-year intervals) can increase the average annual 

water yield by 1.4 to 1.6 inches. Likewise, 

thinnings and selection cutting may be more 

effcdive in increasing water yield in pines than in 

hardwoods (Rogerson 1971). Since pines do not 

sprout from the stump, reoccupation of the site 

may therefore be slower. 

Douglass (1974) pointed out that although 

water quality is emerging as a primary problem in 

the South, water yield management is an 

important part of quality management. 

Peak flows- Winter months (January, 

February, March) and hurricane months (September and October) are periods of highest flows. 

Deep, permeable Coastal Plain sands contain and 

slow the movement of flood-potential rainfalls into 

streamflow. The Piedmont produces more stormflow, but under the undisturbed forest, the deep 

soils also hold flood flows to a minimum. Hewlett 

(1967b) estimated that only 4 percent of the 

precipitation falling in the Sand Hills and Upper 

Coastal Plain of Georgia was yielded as stormflow; in the Piedmont it was 10 percent, and in the 

northwestern Ridge and Valley lands, 15 percent. 

Several studies have shown that peak flows from 

eroding idle land can be reduced drastically 

by establishing deep-rooted vegetation. This 

appears to be the most effective method of 

reducing local flood peaks. 

Sedimentation-The mean annual sedimentation rate (from all lands in all uses) is about 650 

p/m, or 850 tons per square mile for an annual 

streamflow of 18 inches. The Coastal Plain forest 

has few sedimentation problems; its most turbid 

streams average only 280 p/m. The Piedmont is 

the problem area; some streams there average 

2,000 p/m. Logging on Piedmont soils may start 

erosion that can seriously damage both site and 

streamflow. With care, however, pine stands on 

highly erodible soils can be logged without 

causing serious loss of soil. 

Pines are widely used to control erosion. On 

areas that are not eroding very severely, planted 

pines can stabilize the soil, develop a forest floor 

that will facilitate infiltration, and control overland flow in a few years. Where only infertile soils 

remain, or where ground slopes are steep or 

eroding badly, seeding for herbaceous cover or 

mechanical erosion control should accompany or 

precede pine planting. 

Regional Characteristics 

and ~ossibilities: The West 

Western forests range from semiarid to subhumid. In the semiarid West, the demands of 

cities, agriculture, and industry for more water 

from higher-elevation forest areas have generated 

growing interest and some action programs to 

increase water yield by forest cutting. 

Opportunities appear most favorable on about 

15 percent of the area of the 17 states west of the 

100th meridian. This 15 percent includes 116 

million acres of high-elevation forest land, 22 

million acres of chaparral, and 16 million acres of 

phreatophytes. The maximum possible increase 

in yield from forest cutting in the West is 

estimated at 12.5 million acre-feet annually (U. S. 

Senate Select Committee on National Water 

Resources 1960b). If we include the potential 

increase in water yield resulting from clearing of 

phreatophytes, a goal of 25 million more acre-feet 

would not appear unrealistic. 

The full potential would seldom be achieved. 

For example, the potential for the lodgepole pine 

and Englemann spruce-fir types is an estimated 

3.8 million acre-feet. According to one assessment, if these types are managed for sawtimber 

only, with water yields incidental, the increase 

would be 385,000 acre-feet; if managed for 

pulpwood, the increase would be 962,500 acrefeet; or if managed principally for water, cutting 

every 25 years to give an average annual increase 

of 1.5 inches, the average annual increases would 

be 1,925,000 acre-feet (U.S. Senate Sel. Comm. on 

Natl. Water Resour. 1960b). Such increase may 
now be practical because in these timber types the 

pattern of cutting that favors water yield is also 

silviculturally desirable (Leaf and Alexander 

1975). 

National Forests offer the greatest possibilities 

for increasing forest water yield. These forests 

occupy 21 percent of the area of the 11 Western 

States, receive 32 percent of the precipitation, and 

produce more than 50 percent of the total 

streamflow. Their average annual flow is 14 

inches, compared to the 3-1/3 inches from areas 

outside the National Forests. The greatest water 

producer is the snowpack part of the commercial 

forest zone, where precipitation ranges from 20 to 

more than 100 inches annually and much of it 

becomes streamflow. More than a half million 

acres of this zone is cut over annually, providing a 

substantial water increase. 

Even in water-short areas of the West, 

however, management cannot consider water 

yield alone. Floods are also a problem. History 

shows that the cumulative effects of burns and 

reburns on large and small watersheds have 

pxed a constant and widespread flood sedimentation threat. The 100-mile swath across Montana 

and Idaho left by the 1905 fire and subsequent 

reburns is still partly unstocked or understocked; 

the Yacolt fire in Washington and the Tillamook 

fires in Oregon left huge devasted areas. In all of 

western Oregon, logging and burning had left 

only 15 percent of the logged forest "well 

stocked," according to a detailed survey in 1947 

(Anderson 1952). In 1970 the Sky Harbor and 

2,000 other fires, started by a single lightning 

storm, burned more than 200,000 acres in central 

Washington. In view of the known long-term 

effects of fire on western watersheds, we must 

expect hydrologic problems from these recent 

conflagrations (Anderson 1976b). 

Snowmelt and rain-on-snow have produced 

some of the largest floods in the West. 

Availability of snow and the frequency and 

amount of rainfall determine the potential hazard. 

In western Oregon, for instance, the combination 

of the two places the greatest potential hazard at 

elevations between 2,000 and 4,000 feet. This is 

the zone, therefore, where flood protection is 

most needed (Anderson and Hobba 1959). 

Erosion and its consequences in deteriorating 

water quality are management problems throughout the West; logging roads and skidtrails must 

be planned in advance to reduce both length and 

gradient (Silen and Gratkowski 1953, Mitchell and 

Trimble 1959). Planning also includes locating 

cutting areas and landings before logging 

begins. Landings should be so located as to 

minimize yarding across streams (Dunford 1962). 

In the western snow zone, measures to minimize 

sediment production include patch or contour 

stripcutting on steep slopes, leaving strips of 

trees adjacent to the channels of headwater 

streams, keeping road fills away from streams, 

revegetating road cuts and fills, diverting 

road-drainage water away from stream channels, 

keeping landings out of drainages, diverting 

water from skidtrails after their use, and 

removing temporary stream crossings (Anderson 

1966). Sedimentation damage from floods in the 

Pacific Northwest has led to recommendations for 

intensive planning: "To minimize damage to the 

forest transportation system, roads and bridges 

must be planned, designed, constructed, and 

maintained with adequate recognition of soil 

stability problems. . ." (Rothacher and Glazebrook 1968). Specific items include retaining walls 

where necessary to reduce fill embankments, 

grade dips as a safety measure in case culverts or 

ditches become blocked, trash racks to reduce 

culvert plugging, and gabions to minimize bank 

erosion at stream crossings. 

Detailed recommendations for the control of 

sediment from logging roads have been developed for the Intermountain and northern Rocky 

Mountain regions (Packer and Christensen 1964, 

Packer 1967b), for forest and brushland zones in 

California (Kraebel 1936), and for the Douglas-fir 

region of the Pacific Northwest (Society of 

American Foresters 1961, Rothwell 1971, 

Burroughs and others 1973, U.S. Environmental 

Protection Agency and others 1975). 

The three major forested regions in the West 

and their characteristics are shown in fig. 6 and 

tables 14 and 15. 

West Coast Forests 

The West Coast forest region, the smallest of 

the six, features the highest annual rainfall, the 

deepest snowpacks, and the largest trees. The 

coastal mountain ranges receive the entire range 

of annual precipitation, 40 to 150 inches (U.S. 

Dep. Comm. Environ. Data Serv. 1968); most of 

this precipitation comes as rainfall. Eastward, the 

main Cascade Range and the Sierra Nevadas have 

a similar range of precipitation, but most of it 

comes as snow. Rainfall intensities range from 6 
AVERAGE ANNUAL STREAMFLOW 

inches -

mm

Figure 6-Major forest regions in the Western United States, and average annual streamflow. 

Table 14-Mean annual precipitation, streamjlow, evapotranspiration, and potential increase in water yield of selected 

forest types in the West 

Mean annual . . . Potential 

Region and forest type Area increase 

Precipitation Streamflow Evapotran~piration in yield 

Thousand acres Inches 

West Coast 

Mixed conifers 

True fir 

Douglas-fir, hemlock, redwood 

Rocky Mountain 

Lodgepole pine 

Englemann spruce, fir 

White pine, larch, fir 

Aspen 

Ponderosa pine 

Douglas-fir 

Southwestern brushland 

Southern California chaparral 

California woodland, grass 

Arizona chaparral 

Source: U.S. Senate Select Committee on Water Resources 1960b. 
Table 15-General characteristics of major forested regions in the West 

Regional forest type 

Characteristic 

Westcoast forest Rocky Mountain forest Southwestern brushland 

(1) Forest area (thousand acres) 36,446 140,818 52,000 

Major species Douglas-fir, western Ponderosa, lodgepole, Chaparral, pinyon and 

hemlock, red- and western juniper, 

wood, true firs, white pine; phreatophytes 

pines and Douglas-fir; 

spruces true firs; 

spruces; and 

aspen - (2) Rainfall, max. 10-year 

24-hour (inches) 

(3) Freeze-free period, mean 

length (days) 

Snowzone area (thousand 

acres) 

(4) Flood damage: 

Total mean annual 

(million dollars) 

(dollars/acre, all land) 

Upstream mean annual 

(dollars/acre, all land) 

Compiled as follows: (1) U.S. Dep. Agric. For. Sew. 1965; (2) Hershfield 1961; (3) U.S. Dep. Commer. Environ. Data Serv. 

1968; (4)'Water Resour. Counc. 1968 

to 10 inches in 24 hours, at a 10-year frequency 

along the coast, to 2 to 8 inches on the upland 

ranges. The snowpack, a principal source of water 

supply, occupies in season most of the main 

ranges of the Cascades and the Sierra Nevadas. 

In these areas, reservoir storage is a typical way 

of prolonging delivery of water. Reservoirs 

become particularly important in forest management for improvement in water supply. Water 

delayed in delivery from snowpacks can refill 

reservoirs depleted by earlier withdrawal for 

irrigation; water saved by manipulating vegetation or a variety of other techniques can replenish 

reservoirs in dry years or seasons. The basic 

problem is to make sure that the management 

applied is compatible with other land uses, water 

uses, and water control and that the techniques 

are applied where and when they will be the most 

effective. 

Water yield-Mean annual precipitation, 

streamflow, evapotranspiration, and potential 

increase in yield for the western region are given 

in table 14. The potential increase in water yield, 

based on cutting patterns that would increase the 

snowpack yield, is equivalent to about one-fourth 

of the calculated evapotranspiration, or 3 to 6 

inches. Studies of the effects of clearcutting in the 

red fir type in California (Anderson 1969) and the 

Douglas-fir type in Oregon (Rothacher 1970) have 

given estimated annual increases of 12 and 18 

inches, respectively. 

Patch-cutting (with roads) of 30 percent of a 

watershed in the Douglas-fir type in Oregon 

increased water yield about 8.5 inches per year 

over a 5-year period (Rothacher 1970). In the red 

fir type, first-year water savings estimated at 12, 

9, and 6 inches may be derived from strip cuts, 

block cuts, and selective cuts, respectively 

(Anderson 1969). Where the objective is maximum snow accumulation and maximum delayed 

melt, a wall-and-step cutting pattern has evolved. 

To achieve the pattern in the mixed conifer forest 

of the California Sierra Nevada the cut strips 

should be oriented according to topography: 

Generally, these strips should run east-west on 

north and south slopes, northeast-southwest on 

east slopes, and northwest-southeast on west 

slopes. This arrangement maximizes the shade 

during that portion of the day when the sun's rays 

are most nearly normal to the sloping surface. 

Successive strip cutting, proceeding southward, 

would then provide a wall of mature trees for 

shade and would minimize back radiation. The 

width of strips on south slopes steeper than 20 

percent should be about one-half tree height (at 

rotation age). Strips are spaced according to the 
number of cutting cycles in a rotation (Anderson 

1956). A test of this pattern, where the strip was 

located so that residual small trees formed the 

"step," showed a 25-percent increase in snow 

accumulation. Seventy percent of the increase 

persisted well into the melt season (Anderson 

1963). 

Opening the forest in the West has relatively 

long-lived effects on yields of snow and water; 

increases probably last 20 or more years. Savings 

in interception losses may persist to the 

culmination of the leaf surface on regrowth, about 

35 years. 

Others areas subject to management for 

improved water yield include northern California, 

where there is major opportunity for conversion of 

brushlands to productive forests, and where water 

benefits add to the justification. In the highelevation zones of the Sierra Nevada west-side, 

for example, 2 million acres of large brushfields 

could be converted to forest, saving 11 inches of 

water during the conversion process and ultimately improving management of snowmelt 

(Anderson 1963). 

Peak flows-In the coastal range, highest 

flows come during the winter months, a result of 

heavy rainfall on wet-mantle soils. Both the 

magnitude and frequency of floods appear to be 

increasing as timber cutting extends through the 

redwood region (Lee and others 1975). Logging 

various portions of a watershed on a staggered 

schedule may possibly change the times of 

concentration and reduce peaks. Control over the 

location, design, and maintenance of logging 

roads, skidtrails, and landing-along with treatment of these areas after use-is necessary to 

reduce overland flow. 

Three types of floods originate in the snowpack 

zone: from snowmelt, rain on snow, and rain. Rain 

and rain on snow produce the largest floods. The 

effects of management on floods depend on the 

kind of flood and the kind of mangement. By 

altering the timing of water yield, for example, 

management may also reduce peak flows 

(Anderson 1963). 

In the Sierra Nevadas of California, for 

example, periodic snowmelt floods occur as late 

as June. A dense uncut forest may contribute 

about 12 inches less water with a much slower 

melt rate: the snowpack on April 1 may contain 

the equivalent of 50 inches of water, and melting 

may continue until the end of June. Large 

openings, on the other hand, may contain an 

additional 5 to 10 inches of water, and melting 

may be enough more rapid that it will cease early 

in June. The timing of snowmelt in selectively cut 

areas differs between low and high snowpack 

years. Because the degree of snychronization of 

snowmelt from many parts of a watershed 

determines the size of floods, management 

practices that augment or diminish such synchronization will increase or reduce snowmelt 

flood peaks. 

According to Anderson (1966), maximum flood 

protection results from: 

a. Maintaining maximum use of water by 

vegetation 

No cutting, selective cutting, strip-cutting 

on the contour, and other types of cutting, in 

that order, and maintaining deep-rooted 

vegetation on deep soils and adjacent to 

stream channels 

b. Maximizing lengths of water flow paths 

Maintaining surface infiltration and deep 

percolation, preventing soil freezing, and 

draining roads away from stream channels 

c. Maximizing diversity in timing of snowmelt 

Selective cutting on south-facing slopes 

coupled with no cutting or strip-cutting on 

north-facing slopes, and encouraging the 

formation of snowdrifts with natural or 

artificial barriers 

Sedimentation-Sediment concentrations in 

rivers differ greatly over most of this region, 

ranging from 50 to more than 2,000 p/m for 

watersheds that drain both forest and nonforest 

lands. In the northern California brushfields, 

manzanita provides the best soil protection and 

chamise the poorest. In gently sloping areas, soil 

is best protected by removing the brush and 

seeding to grass; erosion rates increase temporarily until the grass is established (Burgy 1958). 

The mean annual turbidity (again averaging for 

all types of land use) is about 54 p/m in western 

Oregon and 470 in northern California. Average 

turbidity ranges from 12 to 220 p/m in Oregon 

and from 8 on the Sierra east-side to 20 on the 

west-side and as high as 2,000 p/m in north 

coastal California. In the redwood Douglas-fir 

forest, excessive disturbance of soils by logging 

can increase sedimentation eightfold. If revegetation is rapid, sediment concentration decreases 

rapidly about 3 years after the logging, but large 

storms may bring back instability and result in 

further high concentrations of sediment 

(Fredriksen 1970, Anderson 1970b). Erosion 
accelerates most on landings, skidtrails, roads, 

and on the landslides that they may trigger. 

Proper location, maintenance, and closure of 

these disturbed areas can reduce sedimentation 

from these sources to a minimum. However, in 

unstable stream channels any sources of augmented streamflow-independently of control of 

erosion at such sources-may be expected to 

increase sedimentation (Anderson 1975~). 

In the Northwest, combination of 25-percent 

patch cut with slash burning in a watershed with 

logging roads showed a 6-year average sediment 

concentration 48 times that on an undisturbed 

watershed, whereas a complete clearcut without 

roads had only about a 5-fold increase. Six-year 

average concentrations of sediment were 9, 48, 

and 430 p/m respectively in the unlogged, 

clearcut and patchcut with roads (Fredriksen 

1973). Maximum 1-day concentrations showed 

about equal proportions: 220, 1,000, and more 

than 10,000 p/m. Fredriksen concluded that 

practices that reduce soil disturbance by logging 

or slash burning should be encouraged; these 

favor rapid regrowth of vegetation and reduce 

deleterious impacts on water quality in forests 

that receive heavy rainfall. 

Erosion is a lesser problem in the snowpack 

zones in most years because the snowpack 

protects the soil from the impact of rainfall, and 

melting snow seldom generates overland flow. 

After the snowpack disappears, the principal 

sources of sediment are areas bared by logging, 

land slippages associated with logging, road cuts, 

and burned areas. Heavy grazing may cause small 

increases in sediment production. Procedures for 

controlling erosion from logging have already 

been described; emergency contour trenches have 

controlled overland flow and sediment discharge 

from burned watersheds during short, highintensity rains (Copeland and Croft 1962). 

C.H. Gleason, in a personal communication about 

1963, reported that, as in southern California, 

trenches sometimes failed when flows from winter 

rain exceeded their surface storage capacity. 

Periodically rainstorms at high elevations find 

little or no snow, and local erosion can be high in 

such snow zones (Anderson 1963), for soils in 

these high elevation zones are less resistant to 

erosion (Willen 1965). 

Landslides-In the Pacific Northwest, where 

roads, and to a lesser extent logging, are 

responsible for accelerated mass soil movements, 

landslides can be reduced by locating roads so as 

to avoid unstable soils and landforms (Fisher and 

Bradshaw 1957, Wallis 1963, Rothwell 1971, 

Burroughs and others 1973), by using skyline, or 

possibly balloon logging in steep, mountainous 

terrain, and by adjusting streamflow increases so 

as not to exceed channel capacities. Adequate 

road drainage and avoidance of sidecasting on 

steep slopes also reduces the hazard of mass 

movement (Dyrness 1967a). Landslides have also 

resulted from the conversion of brushlands to 

grassland range in California (see the section, 

"Type Conversion"). Landslides occur sporadically even in undisturbed steep forest lands. 

Swanston (1969, 1974) and Rice and Krammes 

(1971) have summarized the nature of mass 

movement problems in forest lands, some 

methods of evaluation, and possible management 

techniques. 

Rocky Mountain Forests 

The Rocky Mountain forest area (fig. 1) extends 

nearly the whole length of the western United 

States from central Arizona and New Mexico in 

the south to beyond the Canadian border to the 

north. A dozen major types of forest contribute to 

streamflow from river systems from the Columbia 

to the Rio Grande and thus are the principal 

source of water for irrigation of semiarid lands 

and power developments for the whole West. 

Something of the vegetation types and general 

forest hydrology have been described recently in a 

series of papers. Hibbert and others (1974) have 

described the south chapparal zone, and Clary 

(1975) has described the pinyon-juniper zone. 

H.E. Brown and others (1974) and Baker (1975) 

have outlined the prospects for water yield from 

the ponderosa pine forests of Arizona in relation 

to other multiple-use objectives. Rich and 

Thompson (1974) have outlined opportunities for 

increasing water yield in the mixed coniferous 

zone of Arizona. Overall prospects for increases in 

water yield in Arizona have been estimated by 

Ffolliott and Thorud (1975). Leaf (1975a) has 

summarized the opportunities for watershed 

management in the principal vegetation types of 

the central and southern Rocky Mountains. More 

detail was given by Martinelli (1975) for the 

Alpine zone; by Hoover (1973) and Leaf (1975b) 

for the subalpine zone; by Gary (1975) for the 

ponderosa pine zone of the Colorado front range; 

by Orr (1975) for the ponderosa pine and white 

spruce forests of the Black Hills; and by Sturges 

(1975) for big sage country. Copeland (1969) 

summarized the possibilities for water manage- 
ment for the coniferous forests of the northern 

Rocky Mountains. 

Water yield-The opportunities for management for water yield in several of the vegetation 

types of the Rocky Mountains are unusual. 

Nowhere would the projected use be greater if the 

demand could be met (Cochran 1974). Demands 

for water are for energy production, coal 

gasification, for retrieval of oil from shale, for 

rehabilitation of mining waste sites, and for 

maintenance of aquatic habitat. Nowhere is there 

more compatibility between water management 

and management of other resources. Since timber 

regrowth is slow, water yield increases with 

timber cutting and lasts 3 to 5 times as long as in 

other areas (Hoover 1973); brushland may be 

converted to more profitable grassland with a 

saving in water (Brown and others 1974); alpine 

snowfields may be manipulated to yield prolonged 

flow in summer (Martinelli 1975); the vast area 

(196 million acres) of big sagebrush could be 

cleared to produce extra water (Sturges 1975), 

and use of water by phreatophytes and riparian 

vegetation along streams could be salvaged 

(Horton and Campbell 1974). Conventional silvicultural practices seem to be compatible with 

water yield objectives; in addition, evaporation 

suppression, melt retardation, creation of artificial glaciers, water harvesting from impervious 

areas, and cloud seeding may be used to increase 

water yield. 

An increased water yield of 3 to 4 inches can be 

obtained from the subalpine coniferous forest by 

removing 30 to 50 percent of the total stand in 

small, well distributed patches. These patches 

should be less than eight tree heights in diameter; 

uncut groups of similar size should be left 

standing for maximum efficiency (Hoover 1973). 

The persistence of increases in water yield 

following cutting of lodgepole pine was indicated 

by measurements of water yield following the 

cutting in Fool Creek Experimental Forest. The 

trend line of expected increase (Leaf 1975b, figure 

11)indicates an initial increase (in 1956) of 4.5 

inches and subsequent decline of increases at the 

rate of 0.1 inch per year for the 17 years of record. 

If this trend persisted for 45 years, there would be 

a possible total increase of 101 inches, or 8.4 

acre-feet of additional water per acre of the 

managed forest. 

Less is known about possibilities for improving 

water yields from aspen forest. Soil-water studies 

to date suggest that replacing aspens with 

shallow-rooted vegetation would increase yield 

where soil depths exceed 4 feet (Brown and 

Thompson 1965). Cutting openings will increase 

snow storage in the opened area by one-third 

(Swanson 1973). 

Although not part of the Rocky Mountains 

proper, the Uinta Mountains of northeastern Utah 

may afford similar opportunties for mangement 

for water yield. The area has about 563,000 acres 

of lodgepole pine forest. Johnston (1975) reported 

that clearcutting of lodgepole pine resulted in 

some 4 inches of water remaining in the soil at the 

end of summer, water "available for streamflow." 

Below the subalpine zone in the Rockies lie the 

ponderosa pine and Douglas-fir forests. Ponderosa pine grows on south and west slopes at 

elevations of 3,000 to 5,500 feet in the northern 

Rockies above the sagebrush type, and at 5,500 to 

8,500 feet in the Southwest above the chaparral 

and pinoyn-juniper types. Douglas-fir predominates on the cool, moist north and east slopes, and 

on south slopes at the upper edge of the 

ponderosa pine zone. Ponderosa pine covers 34 

million acres and Douglas-fir 9 million acres. 

Average annual precipitation ranges between 21 

to 28 inches; the average water yield is 4 inches 

from ponderosa pine forest and 7 inches from 

Douglas-fir. Small increases in water yield (0.5 to 

1.0 inch) are attainable on deeper soils by harvest 

cutting but somewhat more from strip and block 

cutting (Brown 1971, Rich 1972, Rich and 

Thompson 1974, H.E. Brown and others 1974, 

Gary 1975). Irregular patch cutting has been 

recommended for cutting in the ponderosa pine 

forests in the Black Hills (Orr 1975). 

At elevations between 4,500 and 8,000 feet 

scattered over 43 million acres in the 4-corners 

states and Nevada is the pinyon-juniper type. 

Present prospects for treatment of this type to 

increase water yield are limited by adverse 

environmental considerations of the known techniques (Clary 1975). 

At the lower elevations below the pine and 

juniper stands there are about 169 million acres of 

big sagebrush that are susceptible to special 

techniques for improving water yield (Sturges 

1975). Much of this area, particularly in 

Wyoming, is characterized by periods of drifting 

snow, and techniques for saving water from this 

source have been perfected (Tabler 1975). 

Rechard (1973) has estimated that in Wyoming 

alone some 2 1/4 million acre feet of water could 
be saved annually -11/4 million by use of snow 

fencing and another million by spraying sagebrush. 

The best prospects for substantially increasing 

water yield in dryer areas are by confining or 

extending clearcutting to streamside areas of 

supposedly high water use. Relatively large 

increases can be obtained from the riparian zone, 

provided evapotranspiration is much higher there 

than on the rest of the watershed; e.g., where 

trees and shrubs line water-courses and are 

exposed to bountiful energy adverted from 

surrounding open or brush-covered terrain. This 

condition is exemplified by the phreatophyte 

areas of the arid and semiarid West. After 

describing the many types of riparian conditions, 

Horton and Campbell (1974) have concluded that 

despite this wide diversity, "Only rarely in the 

Southwest are there phreatophyte areas that 

would be best managed by complete preservation." Vegetation zones in arid land often are 

susceptible to adverse effects of treatments on 

sedimentation; special precautions may be 

needed in managing these zones. 

Peak flows-Spring floods that originate from 

melting snow in the forested snow zone are 

normally a minor problem in the Rocky Mountains. Occasionally major upslope or convective 

storms dump large quantities of rain during May 

and June in the foothills below the snow zone. The 

normal high runoff from spring snowmelt can 

aggravate the flooding from such storms. Good 

cutting practices and the exploitation of topographic influences for protection can reduce peaks 

by prevention of overland flow and desynchronizing snowmelt (Goodell 1959). 

An example of delayed melt was studied in 

northern New Mexico. Surveys of snowpack 

conditions there have suggested that at elevations 

near 9,900 feet, management to delay melting 

should favor Douglas-fir over aspen. At elevations 

near 11,150 feet, management to delay melting 

should favor spruce-fir cover and limit cutting in 

old growth stands, particularly on south-facing 

slopes (Gary and Coltharp 1967). 

At lower elevations, especially along foothills 

below 8,000 feet, cloudburst floods are common in 

the summer months. The greatest floods occur 

when high-intensity storms strike watersheds 

after ponderosa pine forests or shrub cover has 

been burned or severely overgrazed; therefore, 

protection from fire and overgrazing is important 

in forest mangement there. 

Sedimentation-The mean annual sedimentation rate for the Rocky Mountain area is 7,000 

p/m, or 1,100 tons per square mile at 2.25 inches 

streamflow. Most of the forest region, however, 

has a maximum rate of 280 p/m, the same as the 

preponderance of forest areas in other regions. 

The snowpack forest produces little sediment in 

the central Rockies. Snowmelt seeps directly into 

the soil without eroding it; therefore, streams 

usually are clear at high elevations. In the 

northern Rockies periodic rain or rain on snow can 

produce high volumes of sediment. To keep 

erosion from logging to the minimum requires 

preplanning the road system, patch or contour 

strip cutting on steep slopes, supervision of 

logging, revegetation of road cuts and fills, 

careful location of landings, and postlogging care 

(Noble 1961, Megahan and Kidd 1972, Megahan 

1975). 

Erosion can be severe at lower elevations 

wherever soil is exposed by logging or fire. Nearly 

all the soils in this region are highly erodible. 

High-intensity rainfalls have produced major 

debris flows. Much of the sediment is torn from 

gullies and channel banks. Contour trenching 

has been used successfully along Utah's Wasatch 

Plateau to contain overland flows that formerly 

generated mud-rock flows. Seeding perennial 

grasses on a burned-over ponderosa pine area in 

Arizona immediately after fire stabilized the area 

(Rich 1962). Prevention of fire and avoidance of 

severe logging disturbance are, of course, more 

effective in controlling erosion than corrective 

measures applied later. In the Front Range, 

improved logging practices and methods of gully 

control are needed (Heede 1975, Gary 1975); in 

the northern Rocky Mountains, controlling erosion from roads is the current major problem 

(Megahan 1974), and control of water quality and 

esthetics associated with mining are growing 

concerns (Johnston and others 1975, Jensen 

1975). 

Southwestern Brushlands 

There are 22 million acres of chaparral and 

woodland in the Southwest, 15 million acres of 

pinyon-juniper, and 15 million acres of riparian 

vegetation or phreatophytes that have little 

commercial value but considerable significance 

for recreation and watershed use. Mean annual 

precipitation ranges between 8 inches at lower 

elevations and 16 inches at higher ones. 

Maximum rainfall intensities are high, but their 
frequency is low; 24-hour rainfall at a 10-year 

frequency ranges from 1.5 to 4.0 inches for most 

of the region and up to 12 inches in southern 

California. The mean annual streamflow for large 

watersheds is only 0.5 to 2.5 inches, the lowest of 

the six regions. The potential for management of 

the seven major vegetation zones in Arizona has 

been reviewed and summarized by Ffolliott and 

Thorud (1975). 

Water yield-Water yield from chaparral may 

be increased by clearcutting, burning or treating 

with herbicide, then replacing the chaparral with 

grass. The lack of protection by natural ground 

cover requires the substitution of vegetation to 

prevent excess erosion. Though regional potential 

increases are estimated to be only 1 inch or less 

(table 14), recent studies suggest possibility of 

much greater returns on some areas: for example, 

3 to 14 inches in Arizona, depending on annual 

rainfall (Rich and Thompson 1974); 3 inches for 

grass-covered areas in southern California (Bentley 1967). 

High values for water make high conversion 

costs justifiable. If annual water yield is increased 

by 3 inches, with water valued at $50 per acre-foot 

and with low annual operating costs, an initial 

cost of more than $100 per acre for converting 

California chaparral to grass would be justified. 

Typical costs per acre for converting chaparral to 

grass range roughly between a minimum of $25 

per acre and a maximum of $80 (Bentley 1967). 

Costs have been somewhat lower in Arizona. 

Prescribed burning of 3,000 acres of chaparral on 

the Tonto National Forest in Arizona cost $10 per 

acre with subsequent herbicide spraying at $20 

per acre. The increase in water yield (1.6 inches), 

increased forage growth, and reduced fire hazard 

had an estimated total value over a 10-year period 

of $97 per acre, or a benefit-cost ratio of about 3 to 

1. The estimated value of forage, $60 per acre, 

was about twice the total cost, $30 per acre (Suhr 

1967). A 1974 analysis of the economics of 

conversion of 104,000 acres in the Salt-Verde 

Basin in Arizona (T.C. Brown and others 1974) 

indicated an expected increase in basin runoff of 

2.5 percent, in cattle carrying capacity by 3.6 

percent, and a decrease in fire-fighting costs by 3 

percent, for a net annual return of $2.51 per 

converted acre. 

Both in southern California and in Arizona the 

area covered by chaparral that is suitable for 

conversion to grass is limited by shallow soils and 

steep sloping land. Bentley (1961) estimated 9 

percent for the San Gabriel Mountain chaparral; 

T.C. Brown (1974) estimated 21 percent of 

Arizona chaparral was suitable. 

Peak flows-Floods are a major problem in the 

chaparral of southern California, where fires 

have often triggered disastrous, debris-laden 

discharges. The flood threat persists until cover is 

reestablished, and peak flows remain greater for 

10 years or more after a fire. Complete recovery of 

plant cover may take 40 years. 

Flood control is tied closely to fire control, 

which should include, where possible, the 

conversion of highly inflammable chaparral to a 

grass cover or to a less flammable condition by 

reducing its age and favoring more fire-resistant 

species. Typically, these measures are effective 

where the flood potential is low; elsewhere, 

mechanical control by debris dams and channelizing is needed for control of flood waters and the 

entrained sediments. 

Sedimentation-The mean annual sedimentation rate is 6,400 p/m or 2,300 tons per square 

mile with a runoff of 5 inches. 

Burning brushlands in southern California 

increases sedimentation enormously, but fire 

control alone will not prevent it. For instance, 

Anderson (1949b) estimated that average annual 

sedimentation was 600 to 9,970 cubic yards per 

square mile with a then-current annual burn of 0.6 

to 3.2 percent; after a proposed fire control 

program reduced annual burns to 0.2 percent, he 

estimated the sediment yield would range from 

516 to 8,280 cubic yards per square mile. 

There seems to be no successful method for 

stopping erosion after wildfire in southern 

California. The several methods that have been 

tried (see "Southern California and Arizona 

Chaparral") are either limited in effectiveness or 

are quite expensive. 

Success has been reported in Arizona, where 

mechanical erosion control was combined with 

seeding of lovegrasses on four small watersheds 

from which chaparral had been grubbed and used 

as a mulch; this process reduced sediment rates 

from untreated chaparral of about 2,000 to 5,000 

tons per square mile per year to 16 to 31 tons 

(Rich 1961). Conversion of chaparral to grass on 

slopes steeper than 60 percent or on especially 

unstable soils is not recommended (Hibbert and 

others 1974). 

Erosion control has been more successful in 

northern and central California than in southern 

California. Seeding grasses on three burned-over 
chaparral watersheds reduced erosion rates per 

acre from 2.2 to 1.1 ton, from 1.7 to 0.5 ton, and 

from 1.5 to 0.4 t0n-k~~ than the erosion from 

the original chaparral cover (Burgy 1958). As in 

the southern California conversion, some of these 

areas subsequently have been subject to severe 

slope instability, indicated by massive land slides." 

Steep forest and brushlands that have been converted 

to grass were found to be a principal source of increased sedmimentation (Wallis and Anderson 1965). 

V - TOMORROW'S FORESTRY AND WATER 


The study of forestry and its effects on water 

yield, floods, and water quality has led to three 

convictions: 

(1) Substantial increases in water yield are 

attainable by creating openings in forests 

(2) The undisturbed forest provides the maximum storage for flood-producing precipitation and the maximum soil stability 

(3) With care in logging, timber can be 

harvested from many forests without unduly increasing sediment in streams, water 

temperature, and water chemical content. 

Tomorrow presumably will see these general 

convictions translated, as necesary, into forest 

operations as one means of meeting society's 

demands for water, sufficient in amount and of 

required quality, with minimum damage in 

delivery. However, implementing of these ideas 

will not exhaust the potential of forestry to control 

water: current research points toward other 

interesting possibilities. 

Water Yield 

Now that increased water yield resulting from 

forest cutting has been achieved and demonstrated at many places, refinements of research 

are in order to answer such questions as: Where 

and by what techniques will cutting produce the 

greatest or most economical yield of water? Can 

antitranspirants be used to provide seasonal 

increases without cutting? How does water yield 

interact with management for recreation? What is 

the most effective role of the forest in providing 

needed increases in water yield? This last 

question also involves comparative costs and 

benefits. 

Selection of Areas for Cutting 

Maximum increase in water yield will result 

from cutting trees or removing brush that 

transpires at or near maximum rates and 

durations. Therefore, favorable locations are 

areas that have deep soil, riparian zones where 

vegetation has access to groundwater, areas that 

have direct drainage to channels (treat slopes 

adjacent to channels, or cut strips perpendicular 

to contours), and areas where streamflow per unit 

of precipitation is least (dense forest, sites that 

receive the most heat energy, and sites subject to 

frequent drying). A caution: losses from direct 

evaporation are likely to be high on exposed 

south-facing slopes and may partially offset 

reductions in transpiration when openings in the 

forest are created there. 

Hewlett (1961) demonstrated that the base flow 

of Coweeta's mountain watersheds derives from 

soil-water drainage; this suggests that cutting 

trees at the base of slopes produces more 

water than removing trees higher on slopes 

(Lynch and others 1974). 

Maximum delay in yield will result from 

accumulating snow in shaded places and at higher 

elevations, perhaps by using snow fences 

(Martinelli 1973) and by lengthening water-flow 

paths as much as possible. 

Antitranspirants and Antievaporants 

The possibilities of spraying chemicals on the 

forest canopy to reduce transpiration (and thereby 

increase streamflow) by forming a film over the 

leaves, by increasing their reflectivity, or by 

closing stomata have recently been studied. No 

great success has been reported. A first estimate 

was that evaporation from a closed canopy could 

be reduced by about one-sixth by cutting the 

width of stomata in half (Waggoner and Zelitch 

1965). Later, reductions up to 15 percent in annual 

' R. H. Burgy and 2. G. Parazifirou. 1971. Effect of vegetation management on slope stability. (Unpublished report on 

file, Dep. Water Sci., Univ. Calif., Davis.) 
evapotranspiration were found with jack pine 

grown in lysimeters and sprayed with phenylmercuric acetate (Waggoner 1967). However, 

since mercury compounds, such as the one 

applied by Waggoner, pose a serious environmental problem, they cannot be used over large areas. 

Spraying 70 acres of hardwoods at the Coweeta 

Hydrologic Laboratory proved dissappointing: 

streamflow did not increase, apparently because 

the spray did not reach the stomata-bearing 

undersides of the leaves. Spraying aspen in Utah 

produced a better coverage of spray so that the 

width of the stomata and velocity of sap were 

reduced by about half; however, this spraying 

saved only about 1/2 inch of soil water (Hart and 

others 1969). Spraying red pine plantations in 

Connecticut saved more than 1 inch of soil 

moisture (Turner 1968). Anderson and Krieth 

(1975) report a 50 percent reduction of transpiration by using film-forming commercial antitranspirants; plants showed no apparent injury. 

Davenport and others (1969), in reviewing the 

potential of antitranspirants, noted that they 

would be most effective when resistance to the 

passage of water from roots to leaf surface is 

minimal, when stomata-bearing surfaces are well 

covered, when new foliar growth following 

treatment is minimal, and when optimum rates of 

concentration and application are used. If and 

when successful antitranspirants are developed 

and these conditions met, this treatment, combined with cloud seeding, could increase runoff by 

more than the sum of the increases from the 

separate treatments (Satterlund 1969). 

Antievaporants have been applied to the soil 

under forest vegetation to reduce summer losses 

of soil-water. The results of different trials have 

differed widely. In contrast, the application of 

antievaporants to snow surfaces has been 

consistently effective. In the first tests of the use 

of hexadecanol on brushfields and red fir forests 

in California, the only significant reductions in the 

next summer's evapotranspiration were in the 

bulldozed brushfields and in areas where there 

had been heavy applications under snow (680 

pounds per acre). However, evaporation from 

snow was reduced by the application of hexadecan01 (12 pounds per acre) to the snow surface 

(Anderson and others 1963). One application may 

be enough to last throughout the spring melt 

season (Smith and Halverson 1971). This treatment indicated possible saving of nearly 2 inches 

of water from open areas in the forest. 

Recreation Use and Environmental Quality 

Recreational use and environmental quality of 

forests are receiving progressively increased 

attention. Recognition of their importance will 

dictate modifications in forest management for 

water yield as well as for other purposes. The 

effects of management practices on water quality, 

visual appeal, fish and wildlife, and habitat, and 

other values must be considered and evaluated. 

Allee and Smith (1974) have graphically reported 

devastating results to stream environment in the 

Olympic Peninsula when forest management operations failed to consider these associated values 

adequately. 

Cutting practices will increasingly be modified 

to leave forests that are pleasing to the eye as well 

as effective in producing timber and water (Litton 

1968, Baker 1975). Setting aside special areas for 

wilderness, scenic river, wild areas, parks, and 

historic sites (as well as providing more areas for 

normal camping, picnicking, and hiking) will 

make special demands on water supply and pose 

new problems in water quality. Special treatments 

of forests may be required to satisfy the objectives 

of forest recreation. 

Comparison with Alternatives 

There is no question that water yield can be 

increased substantially by clearcutting selected 

forest areas or that the cost of this added water is 

less than that of other methods now deemed 

practical. Producing water by managing vegetation costs less than distilling sea water, transmitting water, or harvesting water. And the energy 

required to convert salt water and to pump water 

in transmission projects may reduce the feasibility 

of these alternatives as concern over limited 

energy supplies increases. 

Cloud seeding may prove to be the cheapest 

source of additional water wherever it is 

successful. Kriege (1969) reported a 13-percent 

increase in annual rainfall over 12 years in the 

Santa Clara Valley of California, at a cost of less 

than 40 cents per acre-foot ($4 per acre-foot if one 

estimates that only 10 percent of the increase is 

salvageable). Hurley (1968) estimated that a $25 

million cloud-seeding research program would 

make it possible to increase winter precipitation 

over the Upper Colorado Basin by 15 percent by 

the mid-1970's at a cost of water increases of 

$1.OO to $1 SO per acre-foot. 
Cloud seeding over forested watersheds that 

have been cut to increase water yield may produce 

more water than the sum of the increases 

obtained by the two methods used independently 

(Satterlund 1969, Leaf 1975b). Cloud seeding and 

forestry are also related in another way: Cooper 

and Jolly (1970) have reviewed the possible 

ecological effects on forests of weather modification, and Ives and others (1970) have discussed 

programs to evaluate the environmental impacts 

of cloud seeding in the Upper Colorado Basin 

forests. 

Potential Role of the Forest 

The Water Resources Council (1968) has 

predicted that by the year 2020 consumptive use 

of water in the East will have increased by about 

30 million acre-feet annually, and in the West by 

40 million. Potential increases of water yield from 

forest land could satisfy perhaps one-half or more 

of these increased needs. 

Planning reservoir design and operation together with treatment of forest land to increase 

water yield can make both more effective 

(Hawkins 1969); the amount can be increased and 

the quality of water improved. 

Timber harvest designed to increase water yield 

seems to offer a comparatively economical means 

for producing at least part of the volume of water 

needed to satisfy increasing demands. 

Drought periods provide special opportunities 

for forest management for water yield. Where 

water in the soil may be saved by removing 

vegetation, the planned conversion of brushfields 

to forest might well be timed to coincide with 

critical drought periods; in this way, the saving in 

water incidental to brush removal might help to 

offset costs of reforestation. The temporal and 

spatial sequence of conversion might thus achieve 

maximum returns for the present and create 

future forests to meet both timber and water-yield 

objectives (Anderson 1966). The extension of 

forests into some areas now occupied by alpine 

flora may be feasible by techniques that were 

developed for the Alps (Aulitzky 1967). The use of 

trees to shade artificial glaciers or deliberately 

avalanched snow accumulations may make these 

techniques more effective in prolonging low 

season streamflow (National Academy of Sciences 

1971). Martinelli (1973 and 1975) has discussed 

use of snow fences and other techniques to 

prolong water yield in alpine areas. 

Flood Prevention 

Tomorrow's forestry may contribute to flood 

prevention in three ways: 1) by acknowledging the 

flood-preventing role of the forest, 2) by 

enhancing that role by protection and reforestation, and 3) by pursuing imaginative research to 

strengthen this role. 

Forest Role 

Foresters should accept the forest as the best 

natural cover for preventing floods when it is 

protected from overgrazing, severe fire, or by 

denudation by insects or disease. Present-day fire 

control and restriction of grazing pretty well 

assure that most forest areas meet flood prevention 

criteria fairly well except the chaparral of the 

Southwest, with its peculiar climate and unusually 

high fire hazard. Certainly the recent extremely 

large fires in the Pacific Northwest are cause for 

concern also. 

The forest can prevent excessive acceleration of 

floods under sustained-yield timber management. 

Flood-producing rainstorms, overland flow, and 

streamflow are controlled about equally well by 

sapling, pole, and sawtimber stands. One important key to flood prevention is continued maintenance of an undisturbed forest floor over most 

of the area. Where disturbance is necessary to 

enable forest harvesting, it should be held to a 

minimum; and overland flow should be controlled 

by proper location, construction, and maintenance 

of roads, trails, and landings, and by special 

techniques designed to offset adverse effects. 

Where snowmelt contributes to floods, special 

techniques can hold flood-water discharges from 

watersheds to a minimum. 

Protection and Reforestation 

The forester's flood-prevention function is twofold: protection and reforestation. Protection 

from fire, overgrazing, and destructive logging is 

closely associated with timber production and recreational use as well as with water production. 

No further justification of protection is required. 

We reiteratethat the occasional, superficial ground 

fire has little effect on forest soil and water; only 

repeated fires or high-intensity fires that completely 

consume the forest floor will damage it seriously. 

Grazing is another matter; relying on the forest 

alone as a source of forage can destroy both feed 
and feeder. Further care in logging, especially 

in the location and design of logging roads, will be 

required in future forest protection. 

Perhaps the most productive action in forest 

flood prevention and control is the afforestation 

of idle, abandoned lands that are sources of overland flow and sediment. Of the 35 million acres of 

unused plantable land, top priority in forestation 

should be given to those unforested areas that are 

truly sources of present or future flood and sediment 

damages. The nature and expected extent of such 

damages need to be better assessed. 

Research 

Research to devise practices that will improve 

flood prevention should be centered on the three 

major components of forest floods: local surface 

flow, subsurface flow, and snowmelt. The first 

involves control of runoff from such impervious 

surfaces as roads, landings, and skid trails. The 

second involves determining the possibility of 

slowing down subsurface flow by temporary storage, utilizing incompletely filled soil-detention 

storage, or by developing access to underground 

storage beneath subsurface flow planes. Capitalizing on this available storage capacity may involve 

combining surface forest with subsoiling, using 

explosives underground, or digging wells. No 

systematic research on soil engineering for modifying soil-water storage has been reported, but such 

research was recommended in a National Academy 

of Sciences (1971) report. Discovery and use of 

those strategic areas that can hold the key to flood 

prevention through desynchronization of flow is 

also involved. 

To manage the snowpack to prevent floods 

produced by rain on snow and spring snowmelt, 

we need to develop procedures that permit accurate 

prediction of snowpack contributions to floods 

based on the size of the pack, the meteorological 

factors, and the interactions between them and 

aspect, slope, elevation, and vegetation patterns. 

Second, means of hastening or slowing snowmelt 

should be studied further. These would involve 

reforestation, various kinds of cutting on strategic 

areas, and sowing from the air of chemical substances that alter snowmelt. 

Erosion-Sedimentation 

-Water Quality 

Tomorrow's control techniques will probably 

include greater attention to erosion control and 

greater use of the forest to improve water quality. 

Use of the dilution potential obtained by increased 

water yield, possibly with the aid of detention 

structures or controlled snowmelt, should be 

studied further. The effect of forest cover and its 

management on the biology and chemistry of 

water bodies must be better understood. 

Erosion control is easier when surface disturbance 

has been held to the minimum by use of overhead 

logging systems-whether balloon, helicopter, or 

skyline systems. Faster logging by more use of 

improved equipment can also reduce the exposure 

time for disturbed areas and permit earlier installation of control measures. 

The future use of forestry to increase water 

yield and control floods and erosion will depend 

on the imaginative wedding of insights offered 

by research to the ever-growing battery of techniques and equipment for inventory and computations. These may be illustrated by some speculations 

bearing on management of snow basins (Anderson 

1966): 

Inventory techniques around the corner 

include machine interpretation of aerial photos, 

including such simple inventory characteristics 

as forest species, densities, and tree heights, 

but also including special characteristics such 

as radiation, extent of snow cover, and snow 

volumes (as in cornices). Instruments for 

aerial appraisal of the depth and densities of 

the soil and fractured rock mantle in mountain watersheds hold promise of becoming 

available . . . 

Snow physics research will give a basis for 

prediction of snow and snow water behavior. 

The alternative is "cut and try tests" on the 

some 6,000 different "forest sites" of the 

West. Further understanding of heat and water 

budgets, together with knowledge of surface 

winds and turbulence, may serve to explain 

the extreme variation in snow accumulation, 

snowmelt, and evapotranspiration loss. Such 

explanations will inevitably lead to better designed management techniques and reduction 

in the number of experimental tests that need 

to be made of alternative techniques. 

Some testing of management techniques by 

controlled experiments may quite possibly be 

accomplished largely by finding and evaluating analogous situations in nature. Interactions of forests and terrain seem to be 

suited to such testing by selection. Other 
experimental testing obviously involves laboratory and field tests. Methods of control of 

the melting of snow, such as by albedo 

control, need further development. Control 

of evaporation and condensation of snow by 

chemicals, such as the long-chain alcohols, 

should be pursued. Further tests of control of 

snow drifting, of piling snow by avalanche 

initiation, and of creation of artificial glaciers 

might be considered. The soil-water "reservoir" 

is practically uninvestigated from the viewpoint of management of its characteristics, 

except by simple resorting to vegetation removal and type conversion. Sterilization of 

the deeper soil layer to prevent root penetration and transpiration losses seems possible. 

The prospects for management of forests for 

water are bright. Goodell (1965) has set for the 

proper goal: 

The culture of the forest so that there is 

no water wasted by plant material that is 

neither economically important, necessary to 

the protection of the soil or of water quality, 

nor necessary to the production of wood of 

desired specifications. 
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The Forest Service of the U.S. Department of Agriculture 

. . . Conducts forest and range research at more than 75 locations from Puerto Rico to 

Alaska and Hawaii. 

. . . Participates with all State forestry agencies in cooperative programs to protect and improve the Nation's 395 million acres of State, local, and private forest lands. 

. . . Manages and protects the 187-million-acre National Forest System for sustained yield 

of its many products and services. 

The Pacific Southwest Forest and Range Experiment Station 

represents the research branch of the Forest Service in California and Hawaii. 

GPO 789-512