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Natural Water Loss 

and Recoverable Water 

in Mountain Basins of 

Southern California 

~ GEOLOGICAL SURVEY PROFESSIONAL PAPER 417-E 00. 

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~ Prepared in cooperation with 

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~ California Department of Water Resources 

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Natural Water Loss 

and Recoverable Water 

in Mountain Basins of 

Southern California 

By JOHN R. CRIPPEN 

CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

GEOLOGICAL SURVEY PROFES SlONAL PAPER 417-E 

Prepared in cooperation with . 

California Department of Water Resources 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

The U.S. Geological Survey Library has cataloged this publication as follows: 

Crippen, John Robin, 1920-

N atural water loss and recoverable water in mountain 

basins of southern California. Washington, U.S. Govt. 

Print. Off., 1965. 

iii, 24 p. maps, diagrs., tables. 30 em. (U.S. Geological Survey. 

Professional paper 417-E) 

Contributions to stream-basin hydrology. 

Prepared in cooperation with California Dept. of Water Resources. 

Bibliography : p. 24. 

(Continued on next card) 

Crippen, John Robin, 1920- Natural water loss and 

recoverable water in mountain basins of southern California. 

1965. (Card 2) 

1. Water conservation-California. 2. Water-supply-California. 

I. California. Dept. of Water Resources. II. Title. (Series) 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. · 20402 - Price 25 cents (paper cover) 
CONTENTS 

Abstract------------------------------------------- Introduction ______________________________________ _ 

Purpose and scope of report _____________________ _ Acknowledgments ______________________________ _ 

Geographical factors affecting natural water loss _______ _ 

Physiography ___ ------------------------------- Climate ____ ------ __________________________ --- Geology ______________________________________ _ 

Potential evapotranspiration ____ ---------------------

Evaporation from a free water surface as a measure of potential evapotranspiration ________________ _ 

Areal distribution of potential evapotranspiration 

rates----------------------------------------

Page 

El 

1 

2 

2 

2 

2 

5 

8 

10 

10 

12 

Page 

Natural water loss __ -------------------------------- E13 

Determination by plot studies _________________ -__ 13 

Drainage-basin analysis ________________ ------____ 15 

Determination of natural water loss from hydrologic 

relations __________________ -_---- ____ --------- 16 

The retention factor and its relation to geologic 

formations----------------------------------- 20 

Summary of procedures__________________________ 22 

Application of the derived relations ____ - _______ -_----- 22 

Selected references ___ -------------_--- _____ -_------- 24 

ILLUSTRATIONS 

Page 

FIGURE 1. Physiographic map and section showing climatic distribution in southern California-------------------------- E3 

2. Map showing mountain basins in southern California in which natural water loss and recoverable water can be 

estimated-------------------------------------------------------------------------------------- 4 

3. Diagrams showing typical monthly distributions of temperature and precipitation_------------------------- 5 

4. Graph showing areal distribution of annual precipitation in southern California----------------------------- 6 

5. Isohyetal map of the western part of southern California------------------------------------------------ 7 

6. Diagrams showing disposition of precipitation in a mountain basin---------------------------------------- 9 

7. Map showing selected evaporation stations in southern California ______ -_--------------------------------- 12 

8. Graph showing relations between lake evaporation and elevation in southern California______________________ 14 

9. Base curve showing relation between P/E (the ratio of precipitation to evapotranspiration) and R/E (the ratio of 

recoverable water to potential evapotranspiration)-------------------------------------------------- 18 

10. Graph showing relation between basin-retention factor (K) and geologic index (1)-------------------------- 21 

11. Graph showing relation between precipitation and recoverable water--------------------------.------------ 23 

TABLES 

Page 

TABLE 1. Distribution of land surface slopes in selected basins in the San Gabriel and San Bernardino mountains________ E4 

2. Average annual evaporation at selected sites in southern California---------------------------------------- 11 

3. Disposition of precipitation on chaparral in the San Dimas Experimental Forest_ _____________ -------------- 13 

4. Disposition of precipitation on Ponderosa pine at Bass Lake, California___________________________________ 15 

5. Disposition of precipitation on woodland chaparral in the North Fork area, California _____ ------------------ 15 

6. Disposition of precipitation on an aspen-herbaceous covered plot in northern Utah--------------------------- 15 

7. Precipitation water loss, recoverable water and potential evapotranspiration in selected basins of southern 

California-------------------------------------------------------------------------------------- 16 

8. Computation of retention factor K for San Antonio Creek ba~n------------------------------------------ 19 

9. Computation of retention factor K for Palm Canyon Creek basin----------------------------------------- 19 

10. Values of the retention factor K of selected mountain basins in southern California_________________________ 20 

11. Distribution of surficial rock types in selected basins in southern California, and geologic index_-_-_---------- 20 

m 

CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

. NATURAL WATER LOSS AND RECOVERABLE WATER IN MOUNTAIN BASINS 

OF SOUTHERN CALIFORNIA 

By JoHN R. CRIPPEN 

ABSTRACT 

Most of the local water supply of southern California originates 

as precipitation on mountain basins. Much ·Of this water is 

returned to the atmosphere by evaporation and evapotranspiration (natural water loss) before residual or recoverable 

water can be captured in surface or underground storage for 

use by man. Long-term records of precipitation and runoff 

have been obtained from typical mountain basins in the Transverse and Peninsular Ranges. These records provide data 

whereby estimates can be made of natural water loss and re- . 

coverable water in ungaged regions of similar characteristics. 

Such estimates are needed in planning long-range projects 

which rely in whole or in part on the development of. local wat.er 

supplies. 

This study makes use of the long-term data to relate average 

annual water loss to annual precipitation, to potential ev.a.potranspiration, and to the water-retaining qualities of geologic 

formations underlying the basins. Annual precipitation ca·n be 

determined from isohyetal maps which may be prepared from 

available data. Potential evapotranspiration is shown to be 

related to elevation and to geographical environment (for ex- . 

ample, coastal or desert), and maps and graphs showing the 

nature of the relations are presented. Graphs and a table of 

numerical indexes for surficial rock types are provided by which 

the effect of geologic formations on natural water loss can be 

evaluated. 

Recoverable water is a residual of precipitation and natural 

water loss, and in the environment of southern California the 

residual is relatively small. In the basins studied, recoverable 

water ranged from 1 inch in a basin having an annual precipitation of 14 inches to 19 inches in a basin having an annual 

precipitation of 42 inches. In general, the greater the precipitation, the greater the percentage of recoverable water. 

INTRODUCTION 

Man's utilization of natural resources is everywhere 

dependent upon the availability of water. In humid 

regions, where water seems as free and plentiful as the 

air, this dependency is not always apparent; but when 

a burgeoning economy rises in an arid or semiarid 

climate, as in southern California, it is brought to our 

attention with great force. Every change in the relation between water supply and demand strikes our 

economy a hammer blow, and on occasion our social 

and economic structure is strained to meet nature's 

challenge. 

The people of southern California, under the leadership of resourceful and forward-looking planners, have 

successfully met the recurring problems of water 

shortages in many ways. The Los Angeles and Colorado River aqueducts have brought water over mountains and deserts to supply the domestic, agricultural, 

and industrial demands of more than 9 million persons. 

Construction is under way to bring additional supplies 

from the northern regions of the State. These supplies 

will meet the even greater demands anticipated for the 

future. The conservation of water from rain in nearby 

areas has been so highly developed that only a small 

amount does not find itself led to surface or underground reservoirs from which it can be withdrawn 

ondemand. · · 

These projects make us aware of the great cost of 

obt'a,ining water. ·Much time and money have been 

devoted to the gathering of data on precipitation, 

streamflow, ground-water movement, and evaporation. 

The most economical water supply is that which occurs 

naturally near the place of u&e. 

An excellent summary of southern California's water 

problems is giv-en by H. M. Stafford and H. C. Troxell 

in the "Mahoney report" (U.S. Congress, 1953, p. 21-

50) .. 

.The runoff from the mountain-and-foothill areas, or from 

other parts of the coastal basins, is only a small fraction of the 

precipitation; it is the residual after evaporation and transpiration have taken their toll. This toll, the natural water loss, is 

for the most part not directly measurable, and so must be determined as a difference between precipitation and runoff. It is 

discussed here because the toll is preemptive. 

Most of the precipitation in the mountain-and-foothill areas 

enters the soil mantle; subsequently, much of it is extracted 

from the root zone by vegetation. Most of the mountain area 

is covered with a heavy growth of brush (chaparral), with small 

stands of conifers at higher altitudes and water-loving trees in 

certain low areas along streams, where the ground-water level 

is high. The brush cover also extends over the higher foothill 

and valley areas, but grasses predominate on the lower slopes. 

The habitats of the native vegetal species indicate their varying 

water requirements. Thus, the water-loving plants, sensitive 

to shortages, are restricted to areas of assured and continuing 

water supply; the extremely hardy chaparral, adapted to a 

precarious supply, will consume large quantities of water if 

available but can exist on a mere pittance if necessary. 

El 
E2 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

Thornthwaite (1948) has estimated that the maximum yearly 

water requirement, or ''potential evapotranspiration," of the 

vegetation in the South Coastal Basin would range from 24 to 

36 inches, if at no time were there a deficiency in soil water 

within the root zone. By comparison, the average yearly precipitation in the mountain-and-foothill areas was 28 inches 

during the wet period 1935-44, and only 19 inches during the dry 

period 1945-51. Thus, native vegetation is capable of using 

more water than was precipitated in the dry period, and perhaps 

even during the wet period. The runoff from the mountain 

area, however, is evidence that the vegetation has not done so, 

presumably because precipitation occurs chiefly in the season of 

dormant growt.h, and at times is sufficient to induce penetration 

of water below the root zone. 

In the mountain-and-foothill areas, evapotranspiration has 

been shown to amount to about 20 inches, or 84 percent of the 

precipitation. Reducing this loss by only 1 inch would increase 

recoverable water by about 25 percent-from 500,000 acre-feet 

to about 628,000 acre-feet. However, much of the loss is an 

inescapable cost in water for maintaining the native vegetation · 

which slows erosion of the mountain slopes. 

PURPOSE AND SCOPE OF REPORT 

This report presents a procedure for estimating 

average annual water loss and recoverable water in 

mountain basins of southern California. The procedure is based on the synthesis of data from basins where 

adequate data have been obtained and on extrapolation 

of the data to other basins where hydrologic data are 

not adequate. Much of the local water supply originates in such basins, and relatively few mountain areas 

have been gaged for even short periods. There is 

therefore need for making such estimates which are 

essential in planning domestic, agricultural, and industrial development. The specific relationships developed 

in this report are applicable to much of the region 

encompassed in the Transverse and Peninsular mountain ranges of southern California, and the procedure 

recommended is probably valid in many other regions. 

The estimated values obtained by the procedure are 

long-term averages and therefore are affected by several 

factors, but especially by year-to-year variations in 

precipitation. 

ACKNOWLEDGMENTS 

This study was a cooperative effort between the U.S. 

Geological Survey and the California Department of 

Water Resources. The report was prepared by the 

Surface Water Branch of the Geological Survey under 

the supervision of Walter Hofmann, District Engineer. 

Uncompleted studies made by H. 0. Troxell (retired) 

of the Geological Survey aided materially in the preparation of this repo.rt. 

GEOGRAPHICAL FACTORS AFFECTING NATURAL 

WATER LOSS 

As water passes through the hydrologic cycle, its 

use by man usually occurs in the stagus between its 

arrival on the land surface in the form of rain, snow, or 

condensed water vapor and its return to the atmo8phere 

or to the sea. Water may be taken from surface 

sources or from aquifers and ground-water 5torage 

reservoirs. The volume of water available from these 

sources in a given land area is equal to the total precipitation on the area less the so-called natural water 

losses. These losses consist of water directly evapo· 

rated into the atmosphere plus water taken up by plant 

life and subsequently transpired to the atmosphere. 

The combined processes of evaporation and transpiration are usually called evapotranspiration. 

Clearly then, the E~tudy of available water and of 

natural water loss requires knowledge of precipitation 

and of evapoti anspiration. Southern California offe.rs 

an excellent "laboratory" in which to acquire such 

knowledge because of its great range of hydrologic 

characteristics. Moisture zones from humid to arid 

exist within relatively few miles of each other, and 

temperatures ranging from hot to cold occur. If the 

moisture and thermal characteristics of the earth's 

climate are each broken into four classifications (humid, 

subhumid, semiarid, and arid; hot, warm, cool, and 

cold) 16 climates may be defined by the possible combinations. Of these 16 possibilities, 12 occur in southern California (Bailey, 1954). 

The classifications of "humid" and "arid" are based 

on the relative magnitudes of precipitation, or moisture 

availability, and potential evapotranspiration, or the 

water loss that could occur if moisture were present at 

all times. Areas where precipitation exceeds potential 

evapotranspiration have a surplus of moisture and are 

humid or subhumid, whereas areas in which potential 

evapotranspiration generally exceeds precipitation are 

arid or semiarid. 

The hydrology .of an area iEt the resultant of complex 

relationships among physiography, climate, and geology. The study of precipitation and evaporation, 

therefore, must start with an understanding of these 

features. 

PHYSIOGRAPHY 

The basins which have provided data for this study 

are all within the Transverse and Peninsular ranges in 

southern California. Use of the proposed method is 

recommended over much of the region shown schematically on figure 1-an outline map showing the physiographic divisions of southern California. Areas of 

use are more specifically shown on figure 2, on which 

mountain basins are shaded. 

Figure 1 indicates that evaporation from the vast 

ocean area to the west, high mountain barriers a relatively short distance inland, and frequent large-scale 

eastward air movement can combine to produce consistent weather patterns. The section at the bottom 

of figure 1 shows this relationship betw-een Glim.~te and 
MOUNTAIN :QASINS OF SOUTHERN CALIFORNIA E3 

36 .l~2~~-·--------~1~2o~·~ ______ _2 19~·--------~ s~·~------~~~~7~·--------~~~~6~·~--------·15

_~ _____ 36" 

\ /1 - \ /)..' A. t Q. N II / ~~ \ ~ I "-J RANGES / "fP.. It "! § ) aAS\N _./' '-<t.o ' ~ ~ -------/ '~ '\. /... '" <' I ,., ............ ------ "-, 

'\ ~ \ /l...~ [,./' ' '----- '< \ ~- r (-> (~ J ~ I 

~ )- !0 / 

35·~---+------~----~'~-~-=-~~1--~~~~~--~-----------k~~-------t------~~-r--~rN 

1 

119" 118° 

• 

Location of selected Weather Bureau stations 

FIGURE 1.-Physiographic map and section showing climatic distribution in southern California. 

physiography. The most prominent physiographic 

feature, as shown by this section, is the steep and 

rugged Transverse Range system which extends from 

the western tip of Santa Barbara County to the Salton 

Sea area in the Colorado Desert. The extreme steepness of these ranges i$ emphasized by the slopes of six · 

mountain drainage basins in the San Gabriel and San 

Bernardino Mountains. (See table 1.) In these six 

mountain basins, 1 percent of the land surface has a 

·slope of 49°-65° or steeper. This slope is equivalent 

to a vertical rise of 115-214 feet in a horizontal distance 

of J 00 feet. The mean land slope ranges from 20 ° 

to 38°. 

In addition to their steepness, these mountains are 

high, rising to more than 10,000 feet above sea level. 

In the San Bernardino Mountains about 21 percent of 

the area has an altitude of 7,000 feet or more, and 54 

percent has an altitude of 5,000 feet or more. These 

ranges, shown on figure 1, are formidable barriers to 

the ocean breezes, and the uplift of incoming maritime 

airmasses causes considerable precipitation to occur 

on· the windward side. 

South of the Transverse Ranges and almost as steep 

are the . Peninsular Ranges. Although generally of 

lower altit'Ude, these mountains also exert considerable 

influence on the precipitation distribution ~ecause of 
E4 

DESERT 

ORO 

34° 

10 0 10 20 30 40 ILES 

119" 116° 

FIGURE 2.-Mountain basins in southern California in which natural water loss and recoverable water ean be estimated. Shaded areas indicate mountain basins. 

their proximity to the ocean. The population of 

southern California is largely concentrated in the 

coastal plains and valleys adjacent to the Peninsular 

and Transverse Ranges. 

To the leeward, east of these two mountain systems, 

are the Mojave &nd Colorado Deserts, which have an 

o•o • ~·--·····M -··-·· ·- .~.. 0..:.. 

area of about 40,000 square miles__.:_greater th,an that 

of many States. The Mojave Desert. is an interior 

. area: of isolated mountain ranges and broad arid valleys 

dotted hy nutr1erous dry lake8 or playas. The Colorado 

Desert contains the Salton Sea and lower Colorado 

ltiver ate.as. . Except for the westernmost part of the 

TABLE !.-Distribution of land aurjace Blopes in selected basins in t~~ Ban Gabriel and Ban Bernardino Mountains 

[Land slope is given as the ratio of the vertical rise to the horizontal distance expres~d as a percent. A SS.percent land slope lies at an angle of 30° from the horizontal (tangent 

30"=0.58)] 

Basin Land surface slope equaled or exceeded in the percellt of basin area indicated 

Mean land 

1 li 10 20 50 80 90 8li 9D slope 

San Cucamonga Antonio Creek Creek __ ------------ 174 124 106 88 64 43 33 25 us 66.2 _______________ 214 151 128 106 75 50 42 34 22 77.5 

J:ttle Creek ___ ----------------- 170 132 114 94 62 38 21 9. 5 4.1 63.6 

ill Creek ____ ----------------- 152 107 91 75 49 33 24 9 6.5 53.0 East Twin Creek ________________ 115 99 91 81 61 39 30 23 13 59.5 

Santa Ana River---------------- 122 89 74 59 31 11 7.5 4.6 2.4 36. 2 
MOUNTAIN BASiNS OF SOUTHERN CALiFORNIA E5 

COASTAL 

January 

MOUNTAIN DESERT 

.. 

" .Q 

~ 0 

July July 

TEMPERATURE 

.. 

.Q 

Cll ,.~ >~ > .s ~s 'tJ.t:l 

0 

u a:~ 3: ::u 

0 0 

July 

Los Angeles 

July 

Squirrel Inn 

July 

Barstow 

PRECIPITATION 

FIGURE 3.-Typical monthly diStributions of temperature and precipitation. 

Mojave Desert (Antelope Valley) and intensely irrigated regions immediately to the north and the south 

of the Salton Sea, the population in these deserts has 

been sparse; however, the establishment of permanent 

residences and planned communities in some of the 

more accessible desert regions is increasing. 

CLIMATE 

Climate is closely associated with the worldwide 

moisture circulation and is subject to modification from 

place to place by prominent physiographic features 

such as the high ranges which exist in southern California. In establishing climatic zones, climatologists 

have found temperature and precipitation to be the 

primary meteorological factors. Temperature serves 

as an index of energy available for evapotranspiration, 

and precipitation is a measure of the available moisture. 

The monthly temperature and precipitation at three 

typical stations-Los Angeles, Squirrel Inn, and 

!740-~-~2 

Barstow-are shown on figure 3. The temperature 

classifications used (cold, cool, warm, and hot) are 

arbitrarily chosen and have limits of 32°, 50°, and 68° 

F, respectively. The locations of the three stations 

are shown on figure 1. 

The monthly temperature distribution at Los Angeles 

is typical of most coastal and lower inland valley areas 

west of the coastal divide. In these areas the temperatures are uniformly mild and are classified as warm 

except for the 3-month period July through September. 

ThiE, favorable temperature diE,tribution attracts many 

new inhabitants to the area. 

Counterbalancing this favorable temperature distribution at Los Angeles is a low annual precipitation of 

about 15 inchelj, most of which occurs in the winter 

months. The temperature records suggest that the 

greatest need for water occurs during the hot months 

of July through September, yet the average precipitation for this period is less than 0.1 inch per month. 
E6 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

Most precipitation occurs from December through 

March, the period in which the need for water is least. 

Thus the precipitation, representing the moisture 

availability, and the temperature, representing the 

evapotranspiration opportunity, are out of phase by 

about 6 months. This time distribution, together with 

low total precipitation, has led most climatologists to 

classify the Los Angeles area as semiarid (Thornthwaite, 1948). 

The second set of diagrams on figure 3, representing 

the higher mountain area, is based on records obtained 

at Squirrel Inn, which is on the divide of the San 

Bernardino Mountains just north of San Bernardino. 

Because of its 5,750-foot altitude, this station shows 

considerably lower winter temperatures but only 

slightly lower summer temperatures than those recorded at Los Angeles. The 6-month period of N ovember through April is cool, and the remaining months 

are warm. 

45 

40 

35 

en 

LLJ 

::c 

(.) 30 ~ 

z 

z 25 0 

i= 

~ a: 

u 20 LLJ 

a:: 

a_ 

_, 

<( 

:::> 15 z 

z 

<t: 

10 

5 

-------_....,. 

The lifting of the incoming maritime airmass when 

it encounters the mountains results in an annual precipitation of more than 40 inches at the higher altitudes, 

and the monthly distribution is very similar to that 

observed at Los Angeles; that is, most rainfall occurs 

in the winter. Thus in the mountains, as at Los 

Angeles, the temperature and precipitation distribution 

are about 6 months out of phase. There is one fundamental difference, however, between mountain and 

valley-floor climates. In the winter the precipitation 

in the mountains provides a surplus of soil moisture 

which accumulates in the root zone. This accumulation of moisture is greater than that needed to satisfy 

the optimum water requirements of the vegetative 

cover, even in the driest summer months. Because of 

this moisture surplus the climate in these areas is classified as humid (Thornthwaite, 1948). 

The Barstow meteorological station is in the Mojave 

Desert, about 50 miles north of Squirrel Inn and at an 

/ 

/ 

/ 

/ 

/ 

I 

v 

/ 

I 

I 

i/ 

I 

/ 

1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 

PERCENT OF AREA WHERE PRECIPITATION IS LESS THAN THAT SHOWN 

FIOURB 4.-Areal distribution of annual precipitation in southern California. 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA E7 

10 0 10 20 30 40 50 MILES ~ 

EXPLANATION 

--40--

Isohyetalline 

Shows average annual precipi.tati&n, in inches; interval variable 

FIGURE 5.-IsobyetaJ map of the western part of southern California. 

altitude of 2,100 feet. The average annual temperature 

at Barstow is about 64°F, almost the same as that at 

Los Angeles. However, summer temperatures at 

Barstow are warmer, and winter temperatures are 

colder than those at the coastal station (at Los Angeles). 

In fact, as shown on figure 3, monthly temperatures fall 

in all three classifications of cool, warm, and hot. The 

precipitation of about 4 inches per year recorded at 

Barstow is sufficient to support only drought-reElistant 

desert plant life. Because of this very low precipitation, the desert is largely uninhabited. The aridity 

is due to the fact that potential evapotranspiration 

greatly exceeds precipitation. 

Records from these and many other meteorological 

stations have been useful in constructing the section 

showing climatic distribution in figure 1. As the figure 

shows, climate changes from humid to arid in rather 

short distances. These data clearly show that southern 

California's climate is predominantly arid. Average 

annual precipitation over the part of the State south of 

the 35th parallel is about 8 inches. Figure 4 relates 

the percentage of land area to annual precipitation and 

shows that more than half of the area receives on the 

average less than 5 inches per year. Figure 5, an isohyetal map, shows the long-term mean annual precipitation in coastal and western desert regions of southern California. Even at the small scale of figure 5, the 

great variation of precipitation in relation to altitude 

and to exposure (type of area) is obvious. Maps of 

larger scale, in which the isohyets are more detailed, 

show variation which seems to be closely linked to even 

small topographic features. For a given exposure, a 

close relationship apparently exists between long-term 

average annual precipitation and altitude. The many 

different conditions of exposure and the lack of longterm records make the determination of such relations 

for other than a few very small areas impractical at 

present. 

Two characteri~tics of the precipitation regime of 

southern California are especially noteworthy. The 

first is the great variability of annual precipitation. 

It is almost axiomatic that the year-to-year scatter in 

magnitude of annual precipitation tends to vary inversely with the magnitude of the annual mean. In 
ES CONTRIB.UTIONS TO STREAM-BASIN HYDROLOGY 

other words, the greater the mean annual precipitation, 

the less it will vary percentagewise from year to year, 

and vice versa. Thus, at Big Bear Lake Dam the 

mean annual precipitation is about 37 inches and the 

coefficient of variation (ratio of standard deviation to 

mean) is 0.44, whereas at Indio the mean annual precipitation is 3.1 inches and the coefficient of variation 

is 0.62. 

The other characteristic-a result of the pronounced 

seasonal distribution of precipitation in coastal and 

mountain regions-is the concentration of precipitation 

during winter months and the dearth during the summer. This results in an extended period of surface 

drying even in the most humid areas. Thus, some 

areas having ample deep water supplies may at the 

same time have shallow-rooted brush that becomes 

almost completely desiccated in late summer and 

autumn. This situation contributes to the threat of 

devastating brush and forest fires that occasionally 

plague southern California. 

GEOLOGY 

Experience has shown that geologic factors are commonly as important as climatic factors in determining 

the magnitude and distribution of natural water loss. 

This water loss, or evapotranspiration, is the result of 

a combination of climatic factors and of moisture 

availabHity. Moisture availability is controlled primarily by precipitation distribution and secondarily 

by geologic factors. The permeability of the soil 

mantle initially determines how much of the precipitation will contribute to surface runoff and how much 

will contribute to soil moisture and ground water. 

In southern California, the major part of precipitation 

usually enters the mantle. Of this water, the greater 

part is retained as soil moisture for subsequent evapotranspiration, and the remainder percolates to the 

underlying ground-water body. Hereafter, the movement of the water is largely controlled by the distribution of permeable rocks. 

Sketches and diagrams in figure 6 show the general 

disposition of precipitation on a section of a typical 

mountain basin. The upper part of the figure shows 

a simplified and an idealized geologic section. On 

either side of this section are mountain blocks of relatively impervious bedrock, whereas the center of the 

basin is filled to considerable depth with alluvial 

deposits, which are generally the result of normal 

weathering of the bedrock and transportation of the 

fragmented material toward the center of the valley. 

The lower part of figure 6 is a series of diagrammatic 

sketches showing the disposition of precipitation under 

three different conditions within the basin. Diagram 

A represents conditions prevalent well up on the slopes. 

In this area, the fractured bedrock is covered by a 

shallow mantle of weathered and shattered material. 

The root zone of the vegetative cover is generally within 

this mantle, which is usually less than 5 feet deep, but 

some roots penetrate deeply into the fractures of the 

bedrock. 

The moisture available to supply the demands of 

this root zone comes from two sources: from precipitation that falls on the area and that is retained as soil 

moisture; and from the surplus ground water originating on contiguous areas of higher elevation. This 

surplus precipitation residual, moving along the contact with the relatively impermeable bedrock, tends to 

continuously recharge the moisture in the root zone. 

It is thus po~sible for evapotranspiration at the site 

shown on diagram A to exceed the precipitation, 

although this condition is rare on the higher slopes. 

Diagram B shows conditions in the upper part of 

the valley floor, where the alluvial deposits are generally 

thicker than at A. Even though the root systems of 

the native chaparral might be as much as 20-30 feet 

deep, few roots penetrate into the ground water or its 

capillary fringe. Under these conditions, the only 

moisture available to meet the demands of the root 

zone is precipitation retained in the soil. The precipitation surplus of contiguous areas of higher elevation passes through this section well below the root 

zone. The maximum possible evapotranspiration at 

this location will thus be equal to or less than the 

precipitation. 

The third site, illustrated on diagram 0, is near the 

center of the mountain valley floor, or canyon bed. 

Here the mantle is thicker, and the precipitation surplus 

from the surrounding contiguous areas maintains the 

ground-water level to within a few feet of the land 

surface. As a result, the root zone of the vegetative 

cover is in contact with the ground-water table and, as 

soil-moisture deficiencies tend to arise, the roots draw 

water from the stored ground water. Under this condition, evapotranspiration may greatly exceed precipitation. 

The middle part of figure 6 shows the distribution of 

precipitation and of evapotranspiration across the 

basin. Precipitation is greater at higher altitudes and 

diminishes towards the valley floor. Evapotranspiration (actual, not potential), although greatest on the 

valley floor, is also high near the tops of the basin 

divides because of the greater precipitation. The 

combination of the two distributions results in regions 

of moisture surplus at high altitudes and in a deficiency 

at low altitudes, as shown on figure 6. The difference 

between precipitation and evapotranspiration at any 

given site represents recoverable water, and the basinwide recoverable water is represented by the sum of all 
740-240-65--3 

MOUNTAIN BASINS OF SOUTHERN CALIFORNIA 

··. Gro.und water ·.··. 

·.0 .·~ :: ·< ... ·:~a ... :: 

•• 0 • [) ·r;: 

0· . 

• 0 • 

o • o· • (). 

: .· o· 

o' ,o ..• 

·. ~ : _cs. · ·.. ~- : : : 

c 

I 

@ 

I .. Evapotransp1rat1on 

Precipitation I 1 

1 l 

( J"', ( 7 I 

I 

® 

E vahotran spi ration 

Precipitation I ! 

j ~ 

A 

FIGURE 6.-Disposition of precipitation in a mountain basin. 

E9 
ElO CONTRIBUTIONS TO STREAM -BASIN HYDROLOGY 

such water existing in the basin, as at the sites shown 

on A, B, and 0. 

POTENTIAL EVAPOTRANSPIRATION 

EVAPORATION FROM A FREE WATER SURFACE AS 

A MEASURE OF POTENTIAL EVAPOTRANSPIRATION 

Evapotranspiration is usually defined as the conversion of water into vapor by transpiration and evaporation from vegetative cover and by evaporation from 

the soil. The term "consumptive use" is also applied 

to this process. 

Thornthwaite (1944) defined the term "potential 

evapotranspiration" as "the water loss which will 

occur, if at no time there is a deficiency of water in the 

soil for the use of vegetation." With moisture continuously available, the climatic factors in the evapotranspiration process are the only regional variables 

that affect potential evapotranspiration. Thornthwaite 

(1948) indicated, in a generalized manner, that potential evapotranspiration ranges from 24 inches to more 

than 60 inches in the area covered by this analysis. 

No other known area of comparable size in the United 

States has such a wide range. 

These generalized potential evapotranspiration values 

have not proven completely satisfactory for use, chiefly 

because they lack the sharp areal differentiation necessary in the small basins of southern California where 

climatic factors change over very short distances. One 

of the prime purposes of this analysis is to develop an 

index of potential evapotranspiration properly reflecting all of the more important climatic factors. These 

climatic factors are (a) temperature, which is an index 

of the energy available from the sun, (b) relative humidity, the measure of moisture deficiency of the air, 

and (c) wind, the agency of transport of both energy 

and water vapor. 

Of the climatological data usually available, evaporation from a free water surface most nearly approaches 

potential evapotranspiration. Evaporation from standard Weather Bureau class A pans has been observed 

for long periods at many stations in the densely populated coastal regions and at a few stations in the 

interior desert regions. Most observations have been 

made at low elevations, but some observations were 

made in the mountains. Pan evaporation is generally 

greater than evaporation from natural water surfaces, 

primarily because of the boundary effect of the pan and 

because the response of the pan water to daily and 

seasonal heat changes is faster owing to its shallow 

depth. A natural body of water tends to maintain an 

even temperature, whereas the water in a pan heats 

more rapidly and is thereby subjected to conditions 

favoring rapid evaporation. Many studies have been 

made of this tendency of pan evaporation, and detailed 

information regarding it may be found in appropriate 

references. The consensus of these studies is that 

evaporation from a natural free water surface annually 

averages 0.70 times that from a standard Weather 

Bureau pan. A recent publication of the Weather 

Bureau presents areal refinements of this annual coefficient (U.S. Weather Bur., 1959). 

Because pan evaporation observations are far from 

complete in their coverage, various methods have been 

proposed for utilizing other data and environmental 

characteristics to estimate the amount of evaporation. 

At present, the most useful of these are the methods 

which depend on the "energy-budget" approach. This 

method is based on the hypothesis that a complete heat 

inventory of a water body over a period of time will 

have as residual a net heat (or energy) loss which is 

used in evaporation. 

Much interest has been shown by researchers in the 

relations between pan evaporation and potential evapotranspiration. Potential evapotranspiration, by definition, might lead one to conclude that pan evaporation is 

closely equivalent because of its freedom from the 

heat-reservoir effect operative in lakes and reservoirs. 

However, evapotranspiration is also affected by the 

heat stored in the soil mantle, the shading and protective effect of vegetation, and other factors of the physical environment. Most investigators now believe that 

lake evaporation is closely equivalent to potential 

evapotranspiration. 

Evaporation records from southern California have 

been assembled and studied, and a group of 62 station 

records has been selected on the basis of loca~ion, 

length of record, and type of equipment used. Table 2 

shows the evaporation data used in this report. Three 

types of pans have been included, the "Colorado," 

"screened," and "class A" pans. Coefficients relating 

annual evaporation from these pans to equivalent lake 

evaporation are fairly well established. There are no 

reliable conversion factors to relate pan data directly 

to lake data on a monthly basis. The previously 

mentioned energy-budget method and a recent modification of the mass-transfer (turbulent transport) 

method are used at present to obtain what is probably 

the most accurate annual and monthly evaporation 

data, but data obtained through these methods are not 

as yet of a long enough period to be considered representative of long-term averages. Thus far, annual 

values appear to check reasonably well with adjusted 

pan data. 

As shown in table 2, evaporation in southern California ranges from 30 to 90 inches; however, at most 

stations it ranges between 40 and 80 inches. This 

variation is in close agreement with recent Weather 

Bureau findings (U.S. Weather Bur., 1959). 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA Ell 

TABLE 2.-Average annual evaporation at selected sites in southern California 

[Type of evaporation pan: (1) Standard U.S. Weather Bur. class A pan, coefficient from U.S. Weather Bur. (1959)j· (2) screened pan, coefficient 1.32 X class A pan coefficient; 

(3) Colorado pan, coefficient 1.20 X class A pan coefficient 

Station 

Period of Latitude Longitude Elevation Type of evap- Equivalent 

record (feet) oration pan lake evapora- No. Name tion (inches) 

1 Acton, near _____ ------------------------------ 1932-59 34°40' 118°16' 3, 075 2 76. 0 

2 Backus Ranch _________________________________ 1936-57 34°57' 118°10' 2,620 1 76.5 

3 Baldwin Park_-------------------------------- 1932-54 34°06' 117°58' 387 1 43.5 

4 Barrett Reservoir ______________________________ 1926-45 32°41' 116°40' 1, 600 3 57.7 

5 Beaumont------------------------------------ 1939-57 33°56' 116°56' 2,589 1 58. 2 

6 Big Dalton Darn------------------------------ 1946-59 34°10' 117°48' 1, 575 2 41. 7 

7 Bonsall Basin ___ ------------------_----------- 1939-43 33°19' 117°10' 215 1 45.2 

8 Bouquet Canyon Reservoir __ ------------------- 1935-54 34°35' 118°22' 3,000 3 71. 8 

9 Cachurna Darn ____________ ---- ________________ 1956-61 34°35' 119°59' 781 1 57.8 

10 Camp Singer (Opid's Camp)-------------------- 1930-58 34°15' 118°06' 4,350 2 40.0 

11 Chatsworth Reservoir __ -------- _______________ - 1947-59 34°14' 118°37' 865 2 55.8 

12 Chula Vista __ --------------------------------- 1919-61 32°36' 117°06' 9 1 47.7 

13 Cogswell Darn _________________________________ 1935-54 34°15' 117°58' 2,335 2 63. 3 

14 Dalton Ranch _____________ ----_--- _______ --- __ 1932-42 34°10' 117°54' 800 2 68. 3 

15 El Capitan Reservoir ___________________________ 1935-45 32°53' 116°48' 613 3 63.0 

16 ElSegundo----------------------------------- 1932-39 33°55' 118°25' 135 2 70. 2 

17 Encino Reservoir ______________________________ 1933-59 34°09' 118°31' 1,020 1 58. 7 

18 Fairmont Reservoir _______ --- __ ----- ___________ 1924-59 34°42' 118°14' 3,050 3 90.0 

19 Fern Canyon_ _________________________________ 1937-43 34°12' 117°42' 5, 100 1 53.0 

20 Fullerton evaporation station ___________________ 1935-45 33°52' 117°59' 92 1 50.0 

21 Gibraltar Reservoir ____________________________ 1931-54 34°31' 119°37' 1,210 1 48. 1 

22 Hayfield evaporation stations 1 and 2------------ 1934-45 33°42' 115°38' 1,460 1 85.7 

23 Henshaw Reservoir ____________________________ 1922-54 33°14' 116°46' 2,700 3 55.0 

24 Huntington Beach _____________________________ 1934-45 33°43' 118°02' 15 1 45. 6 

25 Jameson Lake _________________________________ 1932-45 34°30' 119°30' 2,230 1 41.4 

26 Lake Elsinore--------------------------------- 1938-43 33°40' 117°20' 1,260 1 55.5 

27 Lake Hodges ________ -------------------------- 1934-45 33°02' 117°07' 330 3 67.5 

28 Lake ~athews-------------------------------- 1939-54 33°51' 117°26' 1,400 1 53. 6 

29 Lake Wohlford ________________________________ 1941-45 33°10' 117°00' 1,510 1 43.8 

30 Lower Otay Reservoir __________________________ 1927-45 32°37' 116°56' 490 3 52.4 

31 Lower San Fernando Reservoir __________________ 1931-54 34°17' 118°29' 1, 140 1 65.0 

32 ~ission Basin _________________________________ 1939-44 33°13' 117°21' 35 1 40.2 

33 ~orena Reservoir ____ ------------------------- 1935-45 32°41' 116°31' 3,045 3 54.6 

34 ~orris Reservoir 2----------------------------- 1934-49 34°11' 117°53' 1,210 1 42.6 

35 ~ewhall ______________________________________ 1932-45 34°23' 118°32' 1,243 2 67.1 

36 Pacoima Darn _________________________________ 1931-59 34°20' 118°24' 1,500 2 64.8 

37 Palmdale _____________________________________ 1946-59 34°35' 118°07' 2, 648 2 80.5 

38 Pasadena _____________________________________ 1938-45 34°10' 118°10' 915 1 40.2 

39 Pine Canyon __________________________________ 1932-45 34°40' 118°26' 3,275 2 72.6 

40 PradO---------------------------------------- 1931-54 33°53' 117°38' 480 1 56. 7 

41 Puddingstone Darn ____ ------------------------ 1946-60 34°06' 117°48' 1, 030 2 46. 1 

42 Puente Hill_---- ___ ---- ________ ----- __________ 1931-45 33°57' 117°55' 675 2 44. 7 

43 Riverside Citrus Station __ ---------------------- 1925-54 33°58' 117°20' 1, 040 1 47. 7 

44 San Bernardino ________________________________ 1929-32 34°07' 117°16' 1,050 1 45.6 

45 San Dimas Canyon ____________________________ 1939-43 34°09' 117°46' 1,480 1 39. 7 

46 San Gabriel Divide __ -------------------------- 1939-43 34°13' 117°43' 4,350 1 47. 1 

47 San Gabriel Darn L --------------------------- 1939-45 34°12' 117°51' 1,481 2 66. 8 

48 San Jacinto ___________________________________ 1939-53 33°47' 116°57' 1,550 1 51.5 

49 SanPasqual __________________________________ 1947-54 33°06' 116°59' 350 1 51. 7 

50 Santa Ana ____________________________________ 1929-32 33°45' 117°57' 70 1 51.3 

51 Santa Anita Darn ______________________________ 1931-45 34°11' 118°01' 1,400 2 52.4 

52 Santiago Darn _________________________________ 1946-61 33°47' 117°44' 790 1 56.2 

53 Tanbark Flat--------------------------------- 1935-57 34°12' 117°46' 2,680 1 45. 1 

54 Torrance------------------------------------- 1931-54 33°52' 118°19' 57 2 51. 7 

55 Trona ________________________________________ 1920-23 35°46' 117°22' 1, 623 1 72.9 
E12 CONTRmUTIONS TO STREAM-BASIN HYDROLOGY 

TABLE 2.-Average annual evaporation at selected sites in southern California-Continued 

(Type of evaporation pan: (1) Standard U.S. Weather Bur. class A pan, coefficient from U.S. Weather Bur. (1959) 'i (2) screened pan, coefficient 1.32 X class A pan coefficientj (3) Colorado pan, coefficient 1.20 X class A pan coefiicient 

Station 

Period of Latitude Longitude Elevation Type of evap- Equivalent 

record (feet) oration pan lake evapora- No. Name tion (inches) 

56 Tujunga Spreading Ground--------------------- 1933-44 34°13' 118°25' 815 1 55.3 

57 Vail Lake _____________________________________ 1953-60 33°30' 116°59' 1,480 1 57.8 

58 VanNuys------------------------------------ 1942-45 34°111 118°27' 695 1 31.4 

59 Victorville ____________________________________ 1931-33 34°34' 117°17' 2,700 1 52.0 

60 West Saddle Peak __ --------------------------- 1931-44 34°04' 118°41' 890 2 45.7 

61 Yuma Citrus Station _______________________ ---- 1924-61 32°37' 114°39' 181 1 72.1 

62 Yuma ValleY---------------------------------- 1917-40 32°45' 114°36' 127 1 56.9 

AREAL DISTRIBUTION OF POTENTIAL 

EVAPOTRANSPIRATION RATES 

The combined distribution of precipitation and 

potential evapotranspiration is known to be the key to 

the ecology of an area and therefore to the natural 

water loss. 

Although precipitation is one of the basic factors 

to be considered, its discussion in this text is unnecessary 

because of the many excellent summaries of data available, such as the "Climatic Summaries" of the U.S. 

Weather Bureau. The same is not true of potential 

121° 

36° 

120° 119° 

I 

/ 

us· 

\ 

I 

I 

I 

I 

evapotranspiration data. Many spot studies of pan 

and lake evaporation (considered synonymous with 

potential evapotranspiration) have also been made. 

There are ready sources available for precipitation 

data, but no such sources for evaporation data. For 

this reason, the information from table 2 and other 

sources must be utilized in estimating potential evapotranspiration in the study area. 

Figure 7 shows the areal distribution of evaporation 

stations from which data were obtained. There appears 

to be a sharp difference in station density between the 

117° 116° us· 36 • 

055 

35•-t--~L_-----+----------~----~~/~~~-----------+------------~----------t---~ / 02 

34° ~ 

121" 

N ~ 

4Q 

~c 

20 0 20 

09 

120° 

Oc ~ 

;;p4-<1? 33• 

40 60 MILES 

119° 

/ 

( 

\ 390 00/8 

......... _~8 I 037 

--.... 

118° 

059 

' 

05 " 

I 048 \ 

026 I 

[o" 07 1 

032 ~29 023 

49 

\ 

\ 

\ 

\ 

\ 

\ 

22 

0 

FIGURE 7.-Selected evaporation stations in southern California. Numbers correspond to those oftable2. 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA El3 

desert regions and the mountain and coastal regions 

The concentration of stations in the more heavily 

populated regions is very apparent. There is now more 

interest in obtaining evaporation data for desert areas 

than previously because of increasing population, but 

data at present are still sketchy. 

In addition to the data of table 2, several studies have 

been made on meteorological phenomena related to 

evaporation in southern California. Information from 

airborne instruments has been analyzed to determine 

the characteristics of temperature, wind, and vaporpressure deficiency at high altitude. Blaney (1960) 

and H. C. Troxell (written commun.), as well as others, 

have defined the probable evaporation at high altitudes 

and have provided reliable estimates of evaporation at 

uninstrumented sites. Various theoretical methods of 

estimating potential evapotranspiration or evaporation 

have been developed (Thornthwaite, 1948; Penman, 

1948), but in general they are most suitable for application to areas having humid or subhumid climates, and 

their application to much of southern California, which 

has a generally arid climate, appears questionable. 

The relations shown in figure 8 (equivalent lake 

evaporation, altitude, and coastal or desert exposure) 

for areas below 4,000 feet in altitude have principally 

been determined on the basis of the data in table 2 and 

generalized Weather Bureau maps of evaporation, 

whereas the curves for areas above 4,000 feet in altitude 

are based on the previously cited work of Blaney and 

Troxell. The difference in lake evaporation between 

desert and coastal and mountain areas is recognized, 

as is the temperature inversion that has often been 

observed in this region. As altitude increases above 

3,000 feet (the altitude of the highest desert flatlands), 

the two curves tend to merge, and above 6,000 feet 

there is only one curve. 

NATURAL WATER LOSS 

DETERMINATION BY PLOT STUDIES 

Natural water loss from an area, as previously 

mentioned, varies not only with potential evapotranspiration, but also with the availability of water. Measurement of natural water loss is not a simple process. 

Often a test area or block of undisturbed soil and 

vegetation is isolated in some manner, and precise 

measurements are made of the precipitation and the 

ground-water level. Other experimenters have made 

use of the lysimeter, a device so placed in the soil as to 

intercept and measure downward percolating water. 

The difference between incoming water (precipitation, 

if a plot is insulated against seepage from adjoining 

regions) and outgoing water (estimated from lysimeter 

measurements) is considered natural water loss. Other 

estimates have been based on the water budget of entire 

basins, where unmeasured seepage or surface runoff in 

or out of the basin can be considered negligible. 

The relationship involved in such studies can be 

expressed thus: 

Natural water loss - (precipitation + subsurface 

inflow + net change in soil moisture + net change 

in ground-water storage) - (surface outflow + 

subsurface outflow). 

If the algebraic sum of surface and subsurface flow and 

change in ground-water storage is defined as "recover 

able water," the relationship can be simplified to: 

Nat ural water loss - precipitation - recoverable 

water - change in soil moisture, 

The last factor (change in soil moisture) is generally 

negligible if the time period chosen for computing the 

hydrologic balance is the water year. 

For many years investigators have been attempting 

to measure these water losses, mostly through use of 

the lysimeter or plot tests of various sizes and types 

Generally, precipitation, surface runoff, and changes in 

soil moisture were observed, and the remaining data 

were obtained by indirect means. 

One of the first of these tests was begun in 1928 by 

C. A. Taylor, who found that the water loss from basins 

in native chaparral cover in the foothills near San 

Bernardino, Calif., was about 19 inches of water a 

year. These results were confirmed by subsequent 

tests made by other individuals. 

In more recent years, a series of observations was 

made to determine natural water loss in the San Dimas 

Experimental Forest of southern California, 25 miles 

east of Los Angeles. These observations were made 

at an altitude of about 2, 700 feet on test plots of about 

0.01 acre on the steep slopes of San Dimas canyon. 

The soil mantle was about 4-5 feet deep and was a 

residual, it being weathered from a badly fractured 

dioritic rock. Table 3 gives the disposition of the 

precipitation falling on a plot of mixed chaparral as 

reported by Rowe and Colman (1951). 

TABLE 3.-Disposition of precipitation, in inches, on chaparral 

in the San Dimas Experimental Forest 

1940-41 1941-42 1942-43 Mean 

-------------11--------

Precipitation _____ -------------------------------- 47. 8 

Natural water loss-------------------------------- 22.9 Change in soil moisture in root zone______________ 1.1 

Recoverable water-------------------------------- 23.8 

16.8 45.1 

17.6 20.4 

-.8 .7 

0 24.0 

36.6 

20.3 

.4 

15.9 

The annual natural water loss ranged from 17.6 to 

22.9 inches, and averaged 20.3 inches for the 3-year 

period. In 1941-42 the natural water loss exceeded 
E14 

12 

f- \ 

1\ 

f- \ I-- \ 

11 

10 

9 

f-

~ f- \ 

8 

1-

LJ..I 

LJ..I 

u.. 

u.. 7 0 

en 

0 

4 f-

<( 

en 

:::> 

0 6 

I 

1-

z fz 

0 5 i= 

<( 

> LJ..I f- .....1 

LJ..I 

4 

1-

3 

f2 

1-

1 

X 

f0 

30 

CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

~ 

' ~ X 

\ ~ 

1\ 

X ~ ~ 

ar~ '~ r::: areas Coastal 

1\x ~ 

~ \ X 

!\ X 

X 

X X X 

) X X X xx X X 17 X 

Xv X v 

~ X v ~XX X X 

) X 

X X X 

"' lv w"/ )()( • ~ . 

40 50 60 70 

EQUIVALENT LAKE EVAPORATION, IN INCHES 

(POTENTIAL EVAPOTRANSPIRATION) 

......... 

• 

/ 

-

-

-

-

-

-

-

-

-

• • 

\~ -

' 

• -

J -

v 

80 90 

fJGURE 8.-Relations between l!lke evaporatlon and altitude in southern California. Points indicate desert stations; X indicate ~o~tal stations, 

· :P!ltum js m.ean sea level. 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA E15 

the precipitation; this situation was possible because 

of depletion of the soil moisture in the root zone. 

Table 3 also shows the recoverable water, or the precipitation residual after satisfying the natural water 

loss. This recoverable water is made up of surface 

runoff and recharge to ground-water storage. During 

this 3-year period, the annual recoverable water ranged 

from 0 to 24.0 inches and averaged 15.9 inches. The 

data are not entirely complete, as no allowance was 

made at the observation plot for ground-water recharge 

from water which originated at higher altitudes and 

which moved along the contact between the soil mantle 

and the bedrock. A situation of this type is illustrated 

in diagram 0 of figure 6. 

These data are supplemented by additional o bservations made by Rowe and Colman (1951) of a plot at 

Bass Lake having a native Ponderosa pine cover. 

This plot was at an altitude of about 3,500 feet in the 

Sierra Nevada near Yosemite National Park. The 

soil mantle was about 6 feet deep, overlying shattered 

bedrock, and the mantle had a field capacity of 23.4 

inches. The observations made at this site are summarized in table 4. 

TABLE 4.-Disposition of precipitation, in inches, on Ponderosa 

pine at Bass Lake, Calif. 

194!H1 1941-42 1942-43 

---- Precipitation ____________________ 58.6 50.6 50.9 Natural water loss ______________ 22.0 21.2 23.4 

Change in soil moisture in the root zone ______________________ .7 -.3 1.4 Recoverable water ______________ 35.9 29.7 26.1 

1943-44 1944-45 

----

38.5 49.6 

24.4 22.8 

-.3 -1.5 

14.4 28.3 

Mean 

49. 

22. 

-

26: 

6 

8 

1 

9 

During the observation period the annual precipitation averaged 49.6 inches, exceeding that at San Dimas 

by 13 inches. Despite this greater precipitation, the 

natural water loss was only about 2.5 inches more than 

that at San Dimas. Most of the additional precipitation appeared as some form of recoverable water. 

TABLE 5.-Disposition of precipitation, in inches, on woodland 

chaparral in the North Fork area, California 

1936--37 1937-38 1938-39 1939-40 Mean 

Precipitation __ -----________ ----____ --- __ 40.7 60.1 24.6 40.8 41.6 Natural water loss _______________________ 13.9 17.5 16.2 17.8 16.4 

Change in soil moisture in the root zone __ 0 .1 .1 -.2 0 Rer.overable water _______________________ 26.8 42.5 8.3 23.2 25.2 

Table 5 shows the results of Rowe and Colman's 

observations on a plot of native woodland chaparral 

in the North Fork area of the Sierra Nevada about 10 

miles south of Bass Lake. This plot had a land slope 

of about 32 percent and was at an altitude of about 

3,000 feet. The shallower soil mantle had a field 

capacity of only 8.9 inches. Natural water loss for 

this plot, given in table 5, was less than that for the 

other three observation plots. This situation was 

probab]y in a large measure due to the limited field 

capacity of the shallow soil mantle. The recoverable 

water was 25.2 inches, only about 1.6 inches less than 

that observed at Bass Lake, where the precipitation is 

much greater. 

In an environment somewhat different from that 

found in southern California, Croft and Monninger 

(1953) measured the natural water loss of a plot having 

an aspen-herbaceous cover (table 6). This plot in the 

Wasatch Mountains of northern Utah is in a region 

where the major part of the annual precipitation occurs 

as snow, and the surface runoff results largely from 

snowmelt and summer rainfall. 

TABLE 6.-Disposition of precipitation, in inches, on an aspen- herbaceous covered plot in northern Utah 

1947 1948 1949 Mean 

Precipitation------------------------------------- 52.60 M. 75 50.96 52.77 

Natural water loss-------------------------------- 23.09 24. 33 19.64 22.36 

Recoverable water-------------------------------- 39. 51 30. 42 31.32 30. 41 

In these four experimental plots, the mean annual 

precipitation ranged from 36.6 inches on the chaparral 

plot of San Dimas to 52.77 inches on the aspen-herbaceous plot of northern Utah. Despite this wide range 

in precipitation, the mean annual natural water loss 

ranged only 6.4 inches, from 16.4 inches on the woodland 

chaparral in the North Fork area to 22.8 inches at 

Bass Lake. The variation in natural water loss from 

year to year, as well as from place to place, is also 

slight. 

DRAINAGE-BASIN ANALYSIS 

Table 7 shows the average annual natural water loss 

for a group of southern California mountain basins. 

The values were obtained by use of the basic inflowoutflow equation given earlier (p. E13). These basins 

were selected because the subsurface outflow from the 

basin and the inflow to the basin from adjacent areas 

were probably negligible or could be estimated with 

reasonable accuracy. The effects of ground-water 

storage and of soil moisture storage in the root zone 

have been minimized by beginning and ending the 

period with years of equal wetness. Adjustments have 

been made, where necessary, for any subsurface seepage bypassing the gaging station in the alluvial canyon 

deposits. 

These areas are still largely in their native state, as 

they have only been slightly encroached upon by man's 

activities. The areas range from 3.9 to 319 square 
E16 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

TABLE 7.-Precipitation, water loss, recoverable water, and potential evapotranspiration in selected basins of southern California 

[Data adjusted to the 50-year period 1896-1946. Results are in inches] 

No. I Basin (Sq mi) 

I 

Area I Average 

elevation 

(feet) precipitation recoverable natural evapo- I 

Mean annual I Mean annual I Mean annual I Potential 

water waterloss tra.nspiration 

Mojave River basin 

1 Deep Creek below Green Valley Creek t ____________ 15.8 6,600 2 Crab Creek~------------------------------------ 3. 9 6,400 

3 Deep Creek near Hesperia _____ ------------- ______ 137 5,800 4 VVest Fork ~ojave River~------------------------ 74. 8 4,000 

37. 5 19. 1 

30. 6 12.0 

21. 6 7. 1 

27. 1 8. 1 

18.4 

18.6 

14.5 

19.0 

36. 

36. 

39. 

57. 

3 

7 

6 

5 

Santa Ana River basin 

5 San Antonio Creek _______________________________ 16.9 6,700 41. 9 18.9 23.0 36.7 

6 Cucamonga Creek _______________________________ 10. 1 5,100 38.0 11. 8 26.2 42.2 

7 Day Creek-------------------------------------- 4.6 5, 100 38.0 17.4 20.6 39.2 

8 Lytle Creek _____________________________________ 46.9 5,400 39.3 11.8 27.5 41. 0 

9 Lone Pine Creek _________________________________ 15.0 4, 700 26.2 1.6 24. 6 47.6 

10 Cajon Creek ____________________________________ 40.9 3,900 18.2 3.4 14.8 54.1 

11 VVaterman Canyon Creek _________________________ 4.6 3,600 32.9 8. 8 24. 1 48. 8 

12 East Twin Creek __ ----------------------- _______ 8.6 3,500 32.2 8. 4 23.8 49.4 

13 City Creek ______________________________________ 19.8 3,800 34.8 7. 8 27.0 47.6 

14 Santa Ana River near ~entone ____________________ 202 7,000 29.3 6.5 22.8 36.6 

15 ~ill Creek near Yucaipa _________________________ 42. 9 6,600 39. 1 13.2 25.9 36.8 

Santa Margarita River basin 

161 Temecula Creek at Vail Dam ___________________ --1 319 3, 500 1 20. 1 1 1.71 18.41 51.7 

San Dieguito River basin 

171 Santa Ysabel Creek at Sutherland Dam ____________ , 54. o 1 3,400 1 29.81 4. 71 25. 1 1 50. 5 

Whitewater River basin 

18 Snow Creek------------------------------------- 19 Palm Canyon Creek ____ -------------------------

1 From private records. 

miles, and have altitudes ranging from 3,400 to 7,000 

feet. Owing to differences in both altitude and physiography, the mean annual precipitation ranges from 14 

inches in Palm Canyon Creek basin, in the Colorado 

Desert, to 42 inches in the rugged frontal San Antonio 

Creek basin in the San Gabriel Mountains. Natural 

water loss ranges from 13 inches in the Palm Canyon 

Creek basin to more than 27 inches in the Lytle Creek 

basin of the San Gabriel Mountains. 

The data of table 7 have been obtained thus: Average 

elevation is computed from a hypsometric curve for 

the basin, as in columns 1 and 2 of tables 8 and 9. 

Precipitation is computed on the basis of isohyetal maps 

and the area-altitude distribution, by utilizing the data 

of columns 1, 2, and 3 of tables 8 and 9. Recoverable 

water is measured outflow, adjusted where necessary 

for subsurface seepage--in these basins a very minor 

factor. Natural water loss is the difference between 

precipitation and recoverable water. Potential evapotranspiration is computed by use of the area-altitude 

11.0 6,200 33.2 

94.0 3,900 14. 2 

12.2 21.0 

1. 2 13.0 

40. 

59. 

7 

5 

distribution and the curves of figure 8, as shown in 

tables 8 and 9. 

Recoverable water can be in the form of surface 

water or ground water. It generally ranges from about 

1 inch, as in the Palm Canyon Creek basin, to 19 inches, 

as in the upper Deep Creek basin. This range of values 

is indicative of the water available from the mountain 

areas for man's use. 

DETERMINATION OP NATURAL WATER LOSS PROM: 

HYDROLOGIC RELATIONS 

The relations involving precipitation, natural water 

loss, and recoverable water are many and complex. 

Some fundamental considerations may be used, however, to establish a working hypotheses. 

The first consideration is that natural water loss is a 

combined function of potential evapotranspiration and 

moisture availability. Potential evapotranspiration 

has previously been discussed, and methods have been 

presented for estimating its magnitude in the study 
• MOmfrAIN BASINS GF ·. SOUTlmRN:; CAI/trenN!A .Ei'7 

region. Moisture availability has been shoWn to be 

related to precipitation and to soil and geological 

environment; however, precipitation assumes greater 

importance in mountainous· areas. Because the concepts and methods presented in this ·report can be 

applied only to mountain basins, moisture availability 

will be considered synonymous with precipitation. 

The second consideration is the assumption that there 

is always some recoverable water left from precipitation-recoverable water will be zero only when precipitation is zero. The amount of recoverable water 

may be extremely small for slight amounts of precipitation, but it is finite. This, assumption is borne out 

by the fact that even in desert ·areas, having a mean 

annual precipitation as low as 2 in.ches, flood channels 

of local origin are found. These channels· are evidence 

of the existence of recoverable water, which probably 

occurs only as very infrequent flood runoff. 

Another consideration is that natural water loss· 

cannot be greater than potential evapotranspiration. 

The validity of this assumption is evinced by the 

definitions of natural water loss and potential evapotranspiration. The assumption limits the ratio of natural water loss (L) to potential evapotranspiration (E) 

thus: 

Finally, if soil-moisture changes are considered negligible, the following relation can be deduced from a 

previously stated equation: natural water loss = precipitation - recoverable water, which is symbolically 

expressed as 

L=P-R, or R=P-L. 

If all terms are divided by E, the equation becomes 

dimensionless: 

When there is no natural water loss (a condition 

which, over a period of years, never exists in nature, 

but which imposes a theoretical limit), then 

and when natural water loss is equal to potential evapotranspiration (a condition rarely if ever occurring in a 

mountainous region) 

These four considerations provide a basis for constructing limiting curves wherein must lie all points of 

a relation of P/E to RfE. These limits are shown on 

figure 9, which has as ordinate the ratio P/E and as 

abscissa the ratio RfE. The lower limit, R/E=P/E, 

is a straight line through the origin, and the upper 

limit, R/E= (P/E) -1, is a straight line parallel to 

the lower limit but one unit above. 

The relations and limitations of curves expressing 

the interdependence of PjE, RjE, LjE, described in 

the preceding paragraph, provide a practical tool for 

use in studying natural water loss in the mountain 

areas of · sputhern California. The data of table 7 

provide values- ·of P, L, R, and E for basins having a 

wide range of physical characteristics. Values of E 

were computed from figure 8 and from the area-altitude 

(hypsometric) relations for each basin. The method 

of computing E is explained later.-

The curves of relation must lie within the stated 

limits. Because they describe a relation expressed as 

and because LfE will. never quite reach unity: but will 

tend to approach a const~:rit value at high ratios of PjE, 

R p -=--0 E E ' 

in which 0 approaches a constant positive v~ue, less 

than one, at high values of P/E. The consta:p.t 0, 

equal to L/E, varies from basin to basin, eispecially 

where the n~ture of the geology and soil mantle varies. 

The data of~~ble 7 have been plotted on :figure 9, 

where the points lie- between the limiting curve~. A 

curve of relation between PJE and R/E is also shown 

on ·figure 9. This curve statts at RIE= (PIE) -0. 2 

and approaches the line RfE= (PIE) -0. 6; .in other 

words, the data of the 19 basins indicate- that in this 

region nat"W-al·water loss for the 50-yea:r base period 

generally ranged from 20 to 60 percent of potential 

evapotranspiration. 

The. Clll'V~ ()fi figure 9 shows an- average of the data 

about which the points are scattered. The departure 

of the points from the curve is due to several causes, 

such as the errors in the data of table 7 and the differences in physical characteristics among the basins. 

The error in data is probably small as compared to the 

physical differences; therefore, an adjustment for each 

individual point scattered about the curve has been 

.made by use of a retention factor, K, which will numerically express the effect of physical differences. The 

computation of the K factor for two typical basins is 

shown in tables 8 and 9. 
E18 CONTRIBUTIONS TO •sTREAM-BASIN HYDROLOGY 

RIE 

~ I 

···I 

i 

I 

] 

I 

I 

i 

I 

J 

I 

I 

I 

~ I 

I 

I 

I 

-~ I 

I 

-1 

J 

0.9 

FIGURE 9.-Relation between P/E (the ratio of precipitation to potential evapotranspiration) and R/E (the ratio of recoverable water to potential evapotranspiration). 

Ratios for individual basins from data given in tahle 7. For extreme values of PJE, use the following tabulation: 

PIE 

<0.20 0.2o-. 28 .29- .34 .35- .38 1.46-1.90 

>1.90 

Curve equation: 

R/E 

0 

0.01 

.02 

.03 PIE less o. 59 

PIE less o. 60 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA E19 

TABLE B.-Computation of retention factor K for San Antonio Creek basin 

Percent of Potential 

Altitude basin between Precipitation evapotran- P/E .R/E R R L 

(thousands of feet) given (adjusted) altitudes spiration 

(1) (2) {3) (4) {5) (6) (7) (8) (9) 

1n 1-1n o _________________________________ 0.2 50. 7 27.6 1.84 1. 25 34.4 30.4 20.3 

10. Q-9 ____ -------------------------------- 3.2 49.6 28. 8 1. 72 1. 13 32.5 28. 7 20.9 

9-8------------------------------------ 13. 7 47. 6 31. 0 1. 54 . 95 29.5 26. 0 21. 6 8-7 ____________________________________ 26.4 45.6 33.6 1. 36 . 78 26.2 23. 1 22.4 7-6 ____________________________________ 21. 0 42.4 36.5 1. 16 . 59 21. 5 19.0 23.4 6-5 ____________________________________ 19. 0 38.2 40. 0 . 96 . 41 16.4 14. 5 23. 7 

5-4------------------------------------ 4-3.4 __________________________________ 14. 1 33. 6 43.9 . 76 . 25 11.0 9.7 23.9 

2.4 29. 5 48.4 . 61 .14 6. 8 6. 0 23. 5 

N 18.9 OTE. K=2

1.4=0.883. Col. 6 is obtained by entering data from fig. 9 with PIE from col. 5; col. 7=col. 6Xcol. 4; col. 8=col. 7XK; col. 9=col. 3-col. 8. 

TABLE 9.-Computation of retention factor K for Palm Canyon Creek basin 

Percent of Potential 

Altitude basin between Precipitation evapotran- PIE R/E R R L 

(thousands of feet) given (adjusted) altitudes spiration 

(1) (2) {3) (4) (5) (6) (7) (8) {9) 

8-7 _______________________________________ 1. 0 27.4 33.5 0. 82 0. 29 9. 7 11. 1 16. 3 

7-6--------------------------------------- 5. 8 22. 9 36.6 • 63 • 15 5. 5 6.3 16. 6 

6-5--------------------------------------- 12. 9 19. 2 41. 1 • 47 • 06 2. 5 2. 9 16. 3 

5-4--------------------------------------- 31. 1 15. 8 51. 1 . 31 . 02 1.0 1. 1 14. 7 4-3 _______________________________________ 23. 9 12. 6 66.7 . 19 0 0 0 12. 6 3-2 _______________________________________ 13. 8 9. 7 77. 8 • 125 0 0 -------- 9. 7 

2-1--------------------------------------- 10. 8 7. 4 80. 0 . 092 0 0 -------- 7. 4 

1~0.5------------------------------------- • 7 6. 2 79. 1 • 078 0 0 -------- 6. 2 

Total ____ -------____________________ 100. 0 _____________________ ------ __ ---- ______ ----- __ -- ___________ _ 

Weighted basin mean _______________________ .;..___ 14. 2 59. 5 -------- -------- 1. 05 1. 2 13. 0 

1.2 1 NOTE. K=l.os= 1.143. Col. 6 is obtained by entering data from fig. 9 with P/E from col. 5; col. 7=col. 6Xcol. 4; col. 8=col. 7XK; col. 9=col. 3-co . 8. 

The computations for tables 8 and 9 were performed 

by using zones of altitude, because of the profound 

effect of altitude on the climate of a mountain basin. 

The values of precipitation, potential evapotranspiration, and recoverable water in each basin are therefore 

weighted according to percentages of the basin lying 

between selected altitudes. 

Tables 8 and 9 are intended as aids in computing 

recoverable water (R, col. 7) within the selected altitude 

zones by means of the relations so far developed. We 

can thereby find the retention factor K, which is used 

to adjust the weighted basin mean of R (bottom value 

of col. 7) to a value representative of a specific basin, 

as shown in table 7. The adjusted values appear in 

column 8 of tables 8 and 9, and the weighted basin 

mean given at the bottom of column 8 is equal to the 

value of R for the basin, as shown in table 7. Later in 

the report, after the development of a method for 

esthnating the retention factor K for an ungaged basin 

is treated, the same procedure will be utilized in computing a value for the weighted basin mean of R to 

which K may be applied. The result will be an adjusted value of the weighted basin mean of R, or an 

estin1ate of recoverable water leaving the ungaged 

study basin. 

In tables 8 and 9, the computations for columns 1-4 

ha ve previously been described in the discussion of 

table 7, and the computations required for columns 5 

through 9 are obvious. 

By applying the retention factors to the base curve 

of figure 9, a family of curves can be constructed which 

fit the data of the individual streams. K values, 
E20 CONTRIIIUTIONS TO STREAM-BASIN HYDROLOGY 

ranging from 0.28 to 1.34, have been computed for the Inspection of figure 9 indicates that, for given values 

19 basins listed in-table.7 and ar~ shown in -table 10. - ofP.andE, an-increase inK is associated with a greater 

.. .· . . amount of recoverable water, and a decrease in K is 

TABLE 10.-Valu~s otthe. retenhon facto: K ?!.selected mounta~n associ' t. ed WI'th a greater natural water loss Stream- ba~ns ~n southern Califorma a . . · flow is the most easily observed index of recoverable 

• 0 0 _ Drainage .. __ .

1 

.w.ater .. in..mountain.-basins; this .fact indicates .that there 

No. Basin area K 

(sq mi) may be an association between the value of K and basin 

--r·---------...--------=----r---- characteristics conducive to sustained flow, such as 1 D~pCreekbelowGreenV~lleyCreek •• '------------·----- 15.8. 1.10 d d, h f 'l 1 d d 't f 2 crab Creek near Green Valley Lake _________________ .,._____ 3. 9 1 .. 07 type an ept o SOl mant e, type an ensi y o 

3 Deep Creek near Hes~ria __ ~. ___________ ~------------------ 137 1.10 l d b · sl 

4 west Fork MoJave R1ver near Hesperia.·------------------ 74.8 1.16 vegeta cover, an average asin ope. 5 San Antonioccreek neaructarel mont ______ ,__________________ 1

1o

6.· 91 •• 8875 The geology of most mountai'n reo-lons of southern 

6 Cucamonga reek near p and ••• ------------------------- ~ 

7 Day Creek near Etiwanda •• ~------------------------.;._____ 4. 6 1.12 Calif · h b d · d f 

8 Lytle creek near Fontana •. -------------------------~----- 46.9 .69 orma as een mappe to Varying egrees o 

9 Lone Pine Creek near Keenbrook.-----------------•----•-- 15.0 • 28 fi h B thi · f 

10 Cajon Creek near Keenbrook------------------------~----- 40.9 1.34 re nement over t e past years. ecause s In orma11 Water.man Canyon Creek near Arrowhead Springs________ 4. 6 0 94 I 12 East Twin Creek near Arrowhead Springs ______ '-----~--~-- 8. 6 • 92 tion is widely available and because geo ogy and soil 

13 City Creek near Highland •. ------------------------------- 19.8 . 68 ·14 Santa Ana Rivernear Mentone~~~.:; ___ -: ____________ ~------- · 202 . 56 · tYPe are strong determinants of the hydrologic regime, 15 Mill Creek near Yucaipa •• -------------------------------- 42.9 • 71 

~~ J:~!c¥~~~e~~e~~ ~~~~~iaiid.-naill::::::::::::::::::: ~. 0 :~g the possibility of establishing a correlation between 

18 Snow Creek near White Water____________________________ 94u .. oo 1 •. 9014 geology and K factors was explored. By outlining 19 Palm Canyon Creek near Palm Springs __________________ _ 

the study basins on geologic maps, listing the main 

THE RETENTION FACTOR AND ITS RELATION TO 

GEOLOGIC FORMATIONS 

The considerations used in this report to determine 

natural water loss are: (1) the average relation between 

P/E and R/E, (2)" the area-altitude relation, (3) the 

areai dist:Iibution of precipftation and potential evapo--

transpiration in the basin, and (4) the retention factor 

K. The average relation between P/E and R/E is 

shown in :figure 9, the are~-altitude relation can be 

determined -fi'om topographic maps, the areal distribution of preCipitation· can be taken from isohyetal maps, 

and ·the areal distribution of potential evapotranspiration can be detennined from figure 8. • A method of 

formations in each basin, and grading first the runoff, 

and then K values, against formation type, a relation 

was soon apparent, which was further refined by 

trial-and-error assignment of values to the various 

formations. In the final relation, 'the following reten-

-tiVity. values "were ___ assigned- to the surficiaT 0 roc~ 

determining K remains to be developed. . 

types: . _ 

A. _Quaternary; ex-cept {)ld alluvium __ _; ·10 

B. Old all~rVitini~---.,.~.---~~:_~----:---- IQQ · 

C. Tertiary, eroept Potato Sandstone""' 0 

D. Potato Sandstone of F. E .. Vaughan_ 100 

E.· M·esozoic _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

F. Paleozoic _________________ ·______ 20 

G. Precambrian__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 40 

TABLE H.-Distribution, in percent of area, of surficial rock types in selected basins in Southern California and geologic index 

[Rock types are described in text] 

Distribution (percent of area) of surficial rocks by type and for 

value indicated 

No. Basin Index 

A :n c D E F G (I) . 

(10) (100) . (0) (100) (10) (20) (40) 

1 Deep Creek below Green Valley Creek ______________________ 0 0 0 0 100 0 0 1, 00 

2 Crab Creek near Green Valley Lake _________________________ 0 0 0 0 100 0 0 1,00 

3 Deep Creek near Hesperia_-------------------------------- 1 0 2 0 89 8 0 1,06 

4 West Fork Mojave River near Hesperia _____________________ 16 1 17 0 66 0 0 92 

5 San Antonio Creek near Claremont------•------------------ 19 2 0 0 75 0 4 1, 30 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

6 Cucamonga Creek near Upland----------------------------- 3 6 0 0 91 0 0 1,54 

7 Day Creek near Etiwanda_-------------------------------- 0 0 0 0 100 0 0 1, 00 

8 Lytle Creek near Fontana _____ ----------------------------- 16 2 0 0 38 0 44 2,50 

9 Lone Pine Creek near Keenbrook--------------------------- 27 1 5 0 11 0 56 2, 72 

10 Cajon Creek near Keenbrook·----------·------------------- 25 10 46 0 19 0 0 1, 44 

11 Waterman Canyon Creek near Arrowhead Springs ____________ 0 6 0 0 94 0 0 1, 54 

12 East Twin Creek near AITOwhead Springs ____________________ 0 5 0 0 95 0 0 1,45 

13 City Creek near Highland ___ ---------------·-------------- 0 8 2 0 90 0 0 1,70 

14 Santa Ana River near Mentone _____________________________ 3 21 4 0 55 17 0 3,02 

15 Mill Creek near Yucaipa ____ ·-----·---·-------------------· 8 0 0 7 85 0 0 1, 63 

16 Temecula Creek at Vail Dam------------------------------ 11 8 0 0 70 11 0 1,83 

17 Santa Ysabel Creek at Sutherland Dam.-------------------- 2 0 0 0 98 0 0 1, 00 

18 Snow Creek near White Water __ -----------------·--------- 0 0 0 0 0 100 0 2,00 

19 Palm Canyon Creek near Palm Springs ______________________ 0 7 0 0 54 39 0 2,02 
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA E21 

A geologic index has been computed for each basin 

by multiplying these assigned values by the percentage 

of basin predominantly underlain by each category of 

mantle. Such data are shown in table 11, from which 

the Mill Creek basin provides the following example: 

8 percent category A, 8X 10= 80 

7 percent category D, 7X100= 700 

85 percent category E, 85 X 10 = 850 

SUin==index_________________ 1,630 

The geologic index (I) values thus determined provided a measure of the retentivity that was plotted 

against K. There appears to be a loose but useable 

relation, which is expressed by the curve of figure 10. 

From figure 8, the I value of 1,630 for Mill Creek yields 

K=0.70. This value is reasonably close to the K 

value of 0.71, computed on the basis of hydrologic data 

from the basin (table 7). The relation between I and 

K is fairly well defined for basins on the coastal side of 

the mountain crests. The three basins (Cajon, Palm 

Canyon, and Snow Creeks) on the desert slopes of the 

mountains all appear to indicate a higher K value for 

a given I value. These curves are shown on figure 10. 

Available hydrologic data for this study, as for many 

others, do not justify a refined statistical analysis because of 

1.80 

1.60 

1.40 

1.20 

............................................ ,,, 

~0 

........ , 

a lack of refinement. This does not mean, however, that the 

data caiUlot be used to provide a practical basis for choosing 

the best of several choices involved in a given problem. 

In this study, for example, the K values determined by 

the geologic index I are generally very close to those 

determined from hydrologic data. Of course, no standard of absolute accuracy is available for comparison. 

Data corresponding to table 7, collected for another 

50-year period, would probably differ somewhat from 

those used in this study. 

It is noteworthy that the magnitude of error in computation of recoverable water affects the magnitude of 

error in natural water loss in a nonlinear manner. In 

regions of high precipitation natural water loss is 

generally not much more than 50 percent of precipitation, and error in computed recoverable water is about 

equal, percentagewise, to the error in natural water loss. 

In more arid regions, recoverable water is a much smaller 

part of total precipitation, and an error in computed 

recoverable water produces a smaller relative error in 

natural water loss. For example, if the K value of 0.45, 

from figure 10, were used to compute natural water loss 

in the Lone Pine basin (No.9), the error in R would be 

about 62 percent, but the resulting error in L would be 

only 4 percent. 

~ 

........ ', 

'.......... ~19 

0:: 

~ u 

<( 

u. 

1.00 

' ........ .............. 

11 ------L.?esen 

)(12 )( 18 --

~ --------....---. __ . __ ----- 0.80 

0.60 

0.40 

0.20 6 8 

17 )( 

10 12 14 16 18 20 22 24 26 28 

GEOLOGIC INDEX, {I), IN HUNDREDS 

Fiouu 16.-Relatlon between basin-retention factor (K) and geologic index (1). Data from tables 10 and 11. 

740-240-64--4 

x14 

30 34 
E22 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY 

SUMMARY OF PROCEDURES 

Use of the method of estimating natural water loss 

and recoverable water presented herein requires knowledge of long-term precipitation averages which may 

be obtained from U.S. Weather Bureau re~orts and can 

often be supplemented by data from other sources. 

Precipitation data are most easily used from isohyetal 

maps, which may be already available or which can be 

prepared from available data. A refinement of the 

results by use of the geologic index requires use of 

geologic maps so that a breakdown of rock types into 

categories corresponding to or similar to those of table 

11 can be made. The use of the precipitation and 

geologic data in conjunction with the concepts and relations presented in this report probably provides the 

most reliable estimates available. 

The procedure is outlined as follows: 

1. From topographic maps of the basin or region studied 

derive the relation between selected altitudes and 

percentage of area above those altitudes (the 

hyposmetric curve). 

2. Based on the chara.cteristics of the hypsometric 

curve, establish from 8 to 12 zones of altitude as 

shown in columns 1 and 2 of table 8. Deter~ine the long-term mean annual precipitation P for 

each altitude zone and compute the basin ~ean annual precipitation, as has been done in column 

3 of table 8. 

3. Complete column 4, altitude zone and basin mean 

values of potential evapotranspiration, E, by use 

of figure 8. Compute the ratio PjE for each zone 

·of altitude as shown in column 5, table 8. 

4. From figure 9, determine the RjE ratio and compute 

R (cols. 6 and 7, table 8). 

5. Compute the value for geologic, index I. A table 

similar to table 11 may be helpful, and the criteria 

for the retentivity of formations should correspond 

to t~ose tabulated on p. E20. The geologic index 

apphed to figure 10, showing the relation between 

K and I, will provide the K factor applicable to 

the basin. 

6. Multiply each value of R, in column 7, by K to 

obtain the adjusted R, column 8. Compute the 

basin mean adjusted R. 

7. For each zone of altitude, subtract adjusted R from 

P to obtain L, and compute basin mean L. 

8. Within the limits of computational error, basin 

mean L should be equal to basin mean P less 

basin mean adjusted R. This equality is a check 

on the arithmetic only, not on the accuracy of 

the data. 

The method may also be used, with some loss of 

accuracy, for regions in which geologic information is 

not available. For such regions, follow steps 1-4. 

The K factor must be determined by a method other 

than that described in step 5. Perhaps general knowledge of the basin and comparison with a basin for 

which K is defined can provide a basis for an estimated 

value of K for the basin in question. If no such basis 

is apparent, inspection of figure 10 indicates that for 

desert basins a value of K of 1.10 would be a reasonable 

estimate, and for other regions a K value of 0.8 might 

be appropriate. After a K value is decided upon, 

steps 6-8 as previously described should be followed. 

APPLICATION OF THE DERIVED RELATIONS 

The data and procedures outlined in this report 

provide a means of making consistent estimates of 

natural water loss and recoverable water within the 

mountain regions of southern California. The method 

is based on long-term records of past history, and 

therefore the predictions should be considered applicable to long-term periods, perhaps 25 years or more. 

The study of climatic variations, such as trends in 

annual precipitation and the random or nonrandom 

grouping of wet and dry years, is beyond the scope of 

the report. However, because these factors seem applicable in some measure to short periods, they cannot 

be ignored and must be recognized as introducing a 

considerable degree of uncertainty into short-term 

predictions. For example, we can be reasonably certain that there was more recoverable water in southern 

California during the wet period 1904-13 than during 

the comparable period 1945-54. Precipitation brought 

about 70 percent as much water into the area during 

the latter period as was made available during the 10 

wet years, and recoverable water probably differed by 

an even larger percentage. 

There are two limiting conditions to the use of the 

suggested methods: time and area of use. The lin1itations imposed by time have already been discussed. 

The data and the estimates must be based on a length 

of time that is relatively long, as compared to the time 

span of most hydrologic records. This limitation is 

forced upon us because in short-term periods precipitation may differ greatly from that in long-term periods 

and because the change in volume of ground-water 

storage may be relatively large in the short term. 

Limitations on the area of use are not as clearly defined as those of time. The most reliable estimates are 

those for moderate-sized basins lying entirely within 

the Transverse and Peninsular Mountain Ranges of 

southern California, as shown on figure 2. To some 

degree, the methods can be used in more level regions 

but complications may be introduced by the inflow of 

ground water from areas contiguous to the region 

being studied, a condition which might produce "re-
MOUNTAIN BASINS OF SOUTHERN CALIFORNIA E23 

coverable" water bearing little relationship to characteristics of the region itself. The underground outflow 

of relatively large volumes of water will not affect the 

total volume which is theoretically recoverable, but 

for practical considerations such water might be very 

difficult to utilize fully. The general concepts of the 

approach of this report are applicable in hydrologic 

basins everywhere, but the relations presented are defined only for the area loosely described as the Southwest. It is to be expected that the relations of potential evapotranspiration to altitude, and of PfE to R/E 

will vary with changes in general climatic conditions, 

topography, and latitude, and therefore the relations 

should be those found to hold in the region under study. 

50 

40 

en 

w 

I 

() 

z 

z 

a:: 

w 

1- 30 

<( 

3: 

w 

....I 

co 

<( 

a:: 

w 

> 0 

() 

w 

a:: 

20 

This report demonstrates a method of making 

quantitative estimates of average annual water loss 

and recoverable water in mountain basins of southern 

California. Recoverable water, as shown, is only a 

relatively small part of the total introduced by precipitation. It can be expected to range from 1 inch to 20 

inches, for the long run, and it varies from basin to 

basin because of climatic and physiographic differences 

among basins. In general, the greater the precipitation, the greater is the percentage of recoverable water. 

Figure 11 graphically shows the relationship between 

mean annual precipitation and mean annual recoverable 

water. In regions of less than 20 inches of precipitation, recoverable watf}r may range from 1 inch or less 

/ 

/ 

/ v 

6o/ 

v 

/ I 40 

....I 

/ I 

<( 

::::> 

z 

z 

<( 

z / o1 05 v 07 / 03 

<( 

w 

~ 

10 / 150 

o2 018 / 60> 

/ o4 oll v 12o 13, 

/ 

14o / 

/o10 17( v .... ~ o16 v 

0 

10 20 30 40 50 60 

MEAN ANNUAL PRECIPITATION, IN INCHES 

FIGURE 11.-Relation between precipitation and recoverable water. Sma1ler circles indicate data from basins used in formulating relations. Larger circles indicate basin 

data from tables 3 to 6. 
E24 C()NTRIDUTIONS TO STREAK-BASIN HYDROLOGY 

to 6 inches; at 30 inches of precipitation, rec.overable 

water may be from 3 to 15 inches; and at 40 inches of 

precipitation (which occurs only at high altitudes), 

recoverable water may range from 12 inches to 24 

·inches. The shape of the envelope of figure 11 is due 

to the fact that precipitation increases with altitude 

while potential evapotranspiration decreases. 

In the future there will be longer records of data 

from more widely scattered sites. This data, together 

with increased knowledge of the relations among contributing factors, may make possible a more definitive 

analysis of hydrologic phenomena. .Also, the science 

of meteorology may progress to the point where shortterm estimates will be justified. The data and methods 

presented in this report are onTy as reliable as our 

present-day knowledge. 

SELECTED REFERENCES 

Bailey, H. P., 1954, Climate, vegetation, and land use in southern 

California, in Geology of southern California: California 

Dept. Nat. Resources, Div. Mines, Bull. 170, chap. 1, 

p. 31-35. 

Blaney, H. F., 1960, Evaporation from water surfaces in 

mountain areas of western United States: Internat. Assoc. 

of Sci. Hydrology Bull., no. 17, March, 1960, p. 27-37. 

Croft, A. R., and Monninger, L. V., 1953, Evaporation and other 

water losses on some aspen forest types in relation to water 

available for stream flow: Am. Geophys. Union Trans., 

v. 34, p. 563-574. 

Dawdy, D. R., and Langbein, W. B., 1960, Mapping mean areal 

precipitation: Internat. Assoc. of Sci. Hydrology Bull., 

no. 19, p. 16-23. 

Linsley, R. K., Jr., Kohler, M.A., and Paulhus, J. L. H., 1958, 

Hydrology for Engineers: New York, McGraw-Hill Book 

Co., chap. 5, p. 90-120. 

Peck, E. L., 1962, An approach to the development of isohyetal 

maps for mountainous areas: Am. Geophys. Union Trans., 

v. 67, no. 2, p. 681-694. 

Penman, H. L., 1948, Natural evaporation from open water, 

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--- 1948, An approach toward a rational ·classi:fie-ation of 

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--- and others, 1954, Hydrology of the San Bernardino and 

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0 

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