Trends in Base Flows and Extreme Flowe 

in the Beaver Kill Basin, Catskill 

Mountains, New York, 1915-94

By Barry P. Baldigo

U.S. GEOLOGICAL SURVEY 

Open-File Report 98-65

Prepared in Cooperation with 

the Town of Rockland

r.^m^^^ "^AH ^m

science for a changing world

Troy, New York 

1999
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does 

not constitute endorsement by the U.S. Geological Survey

For additional information write to:

U.S. Geological Survey 

425 Jordan Road 

Troy, NY 12180-8349 

(518)285-5600

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
CONTENTS

Abstract............................................................................. 1

Introduction.......................................................................... 2

Purpose and Scope..................................................................... 2

Acknowledgments.................................................................... 4

Study Area........................................................................... 4

Methods............................................................................ 5

Trends in Base Flows and Extreme Flows.................................................. 6

Relation of Stream Stage to Discharge................................................ 6

Discharge-Duration Curves ........................................................ 7

Peak and Bankfull Discharges ...................................................... 7

Annual Average Discharge and Base Flow............................................ 11

Monthly Average Discharge and Base Flow. .......................................... 12

Annual 1-day and High Flow ...................................................... 12

Monthly 1-day Low and High Flow ................................................ 13

Limitations of Analyses .......................................................... 14

Suggestions for Additional Study................................................... 15

Conclusions........................................................................ 16

Selected References.................................................................. 16

FIGURES

1. Maps showing: A. locations of active and inactive USGS streamflow gaging stations and 

NY 17 in the Beaver Kill Basin and, B. the basin's location in relation to the Catskill 

Park in southeastern New York State. .............................................. 3

2. Graphs showing discharge as a function of stage before and after 1965 at: A. the Cooks

Falls site and, B. the Little Beaver Kill site. (Locations are shown in figure 1.) .............. 7

3. Discharge-duration curves at the Little Beaver Kill site for the 14 years before 1965 and

the 14 years after. .............................................................. 8

4. Graphs showing recurrence probabilities of instantaneous peak flows at (a) the Cooks Falls

site and (b) the Prattsville site for 30 years before 1965 and the 30 years after. .............. 8

5. Total annual precipitation, average annual discharge and base flow, and the ratio of

annual average base flows to annual average flows (annual B/A flow) at the Cooks Falls site, 

1914-94. ..................................................................... 9

6. Total annual precipitation, average annual discharge and base flow, and the ratio of

annual average base flows to annual average flows (annual B/A flow) at the Little Beaver

Kill site, 1924-80............................................................... 11

7. Total July precipitation, average July discharge and base flow, and the ratio of July average

base flows to July average flows (July B/A flow) at the Cooks Falls site, 1914-94............ 12

8. Annual 1-day high flows at the Little Beaver Kill and Cooks Falls sites, 1925-94. ........... 13

Contents
TABLES

1. Drainage area, annual average daily discharge, and average total annual runoff of streams at 

study sites in the Beaver Kill Basin and at the control site in the Schoharie Creek basin, NY.

2. Estimated peak flows of 2-, 10-, 25-, and 100-year recurrence intervals for Beaver Kill at 

Cooks Falls, N.Y., and for three streams in nearby basins before and after 1965. ..........

CONVERSION FACTORS

Multiply

foot (ft) 

mile (mi)

square mile (mi2)

cubic feet (ft3)

cubic foot per second (ft3/s)

By

Length

0.3048

1.609

Area 

2.590

Volume 

0.02832

Flow 

0.02832

To Obtain

meter 

kilometer

square kilometer

cubic meter

cubic meter per second

10

iv Contents
Trends in Base Flows and Extreme Flowr in 

the Beaver Kill Basin, Catskill Mountain*, 

New York, 1915-94

By Barry P. Baldigo

ABSTRACT

Long-term records from five streamflow-gaging 

stations within and near the 300-square mile Beaver 

Kill Basin were analyzed to determine whether 

construction and presence of New York State Route 17 

(NY 17), which was completed in the late 1960's, 

could have altered hydrologic processes in the basin 

and thereby adversely affected the basin's trout 

populations. The hypothesis investigated is that NY 17 

has altered surface-water and shallow ground-water 

flowpaths where it parallels the stream and has 

increased runoff rates and thereby (1) increased the 

range in stream discharge (prolonged the base flows, 

decreased the low flows, and increased the high flows), 

and (2) altered stream-channel morphology through 

increased volume and velocity of stormflows.

Analyses of base flows, discharge-duration curves, 

stage-to-discharge relations, peak and bankfull 

discharges, and flow extremes at a downstream 

(Beaver Kill at Cooks Falls) and a small tributary 

(Little Beaver Kill at Livingston Manor) site provide 

only limited evidence that NY 17 affected hydrologic 

processes within the basin. These effects are best 

indicated by significant increases in the magnitude and 

(or) the frequency of moderate to large discharges 

(exceedence probabilities) on an instantaneous basis at 

the Beaver Kill at Cooks Falls site after 1965. 

Increases in stormflows can not be attributed solely to 

NY 17, however, because the trend was evident long 

before NY 17 was constructed. Changes in land use in 

parts of the watershed may have contributed to gradual 

and continuous increases in stormflows throughout the 

entire 80 (plus) years of record.

Changes in most base-flow and low-flow statistics 

for the downstream (Beaver Kill at Cooks Falls) site

after 1965 are not statistically significant, but, changes 

in flow-duration curves and annual peak flowr are 

evident. Flow-duration curves at this site indicate that 

there is a 16 percent increase in average daily flows 

after 1965. Annual peak flow data indicate that peak 

flows from storms recurring at 2-year (and longer) 

intervals after 1965 are significantly larger than those 

that recur at the same frequencies before 1965. The 

lack of comparable increases in peak flows from 

several nearby reference sites after 1965 indicate that 

the observed increases in peak flows may be unique to 

the Beaver Kill Basin.

Flow-duration curves and many base-flow and 

high-flow statistics for the small tributary paralleled by 

NY 17 in the in the upper reaches of the basir (Little 

Beaver Kill at Livingston Manor) appear to be 

considerably altered since NY 17 was constructed. 

Flow-duration curves at this site indicate that there is 

about a 54 percent increase in average daily flows after 

1965. Increases in the ratio of average annual base 

flow to average annual flow until 1965 then 

subsequent decreases suggest an extreme affect of NY 

17 on hydrology of the subbasin. The effect of NY 17 

on hydrology of the Little Beaver Kill subbasin cannot 

be defined with certainty, however, because the flow 

record after 1965 is too short; discharge monitoring 

was discontinued in 1981.

The increases in peak stormflows in the lo^er 

Beaver Kill basin through the period of record may 

have increased the rates of bed-sediment erosion 

(degradation) and deposition and accelerated changes 

in stream-channel morphology, however, these 

possible effects were not examined. Suggestions for 

further investigation of the effects of NY 17 and of 

other factors on hydrology, channel morphology, fish

Abstra-*
habitat, and fish populations in the Beaver Kill Basin 

include (1) addition of streamflow gages or a creststage gage network at critical locations, (2) a review of 

engineering records and other aerial photographs for 

indications of changes in channel morphology, (3) 

compilation of temperature data and modeling spatial 

extent and magnitude of stressful summer 

temperatures (to selected trout species), and (4) 

confirming the extent and severity of toxic thermal 

episodes using in-situ fish toxicity tests.

INTRODUCTION

Trout fishing in the Beaver Kill, in the southwestern 

Catskill Mountains of New York (fig. 1), has long been 

a major source of income to the region (Francis, 1983). 

Concern has increased recently over the hydrologic and 

thermal effects that recent development and a four-lane 

State highway (NY 17), may have had on fish habitat 

and trout productivity in the Beaver Kill since its 

construction in the 1960's (J. Conyngham, Trout 

Unlimited, oral commun., 1996). Potential hydrologic 

changes within the basin that could be associated with 

NY 17, such as decreased base flow (dry-weather flow) 

and increased and prolonged extremes in low- and 

high-flow conditions, are suspected to have altered the 

aerial extent (quantity) and stability of physical habitat 

within the Beaver Kill and, thereby, adversely affected 

resident fish populations. "Habitat area" refers to the 

wetted surface area of the streambed or channel that 

resident fish populations inhabit at any given time, and 

"habitat stability" refers to the propensity of habitat 

characteristics such as streambed sediment, water 

depth and velocity, channel width, stream discharge, 

cover for fish, bank-erosion rates, and related factors, 

to change or to fluctuate through time.

NY 17 is a four-lane largely elevated highway that 

was built during the 1960's and traverses about 26 mi 

of the Beaver Kill Basin (J. Conyngham, oral 

commun., 1996), where in it parallels the Little Beaver 

Kill, the lower Willowemoc Creek, and the lower 

reaches of the Beaver Kill (fig. 1). The actual 

construction period spanned much of the 1960's and 

completion dates for various sections range from 

about 1965 to 1969 (J. Conyngham, oral commun., 

1996). Parts of the valley floor along many streams in 

the Beaver Kill Basin are paved or covered by fill 

associated with the highway's construction. Sixteen 

bridges over main channels, numerous channel 

truncations and armoring (rip-rap), and an extensive

drainage-culvert system that directs runoff from NY 

17, were also built during the period (J. Conyngham, 

oral commun., 1996). Features and structures such as 

these have been shown to alter shallow ground-water 

flow paths and flow rates, channel stora£?. and 

recharge, and base flow of nearby streams, and these 

changes, in turn, can alter the elevation and slope of 

the water table and diminish the ground-water 

contribution to streams, thereby decreasing base flows 

and increasing the range of discharge fluctuations 

(reducing flow stability) (Blackport and others, 1995). 

Decreased channel sinuosity and roughness, and 

increased channel gradient (through channel 

truncation and armoring), can increase the velocity, 

power, and magnitude of stormflows and thereby alter 

streambed morphology and decrease the overall area 

and stability of stream-channel habitat available to 

resident fish (Binns, 1979; Fausch and others, 1988). 

If changes in habitat are extensive, rates of fish 

survival and reproduction can decline, and the density 

of their populations may decrease (Simcnson and 

others, 1993).

Purpose and Scope

In 1996, the U.S. Geological Survey (USGS), in 

cooperation with the Town of Rockland in Sullivan 

County, began a study to determine whether 

completion of NY 17 in the 1960's could have affected 

hydrologic processes and, thereby adversely affected 

the trout fishery in the Beaver Kill Basin. The major 

objective of the study was to evaluate the hypothesis 

that changes in surface-water and shallow groundwater flowpaths and increased runoff rates due to the 

presence of NY 17 in the Beaver Kill watershed have 

(1) widened the range in stream discharf t (prolonged 

the base flows, decreased the low flows, and increased 

the high flows), and (2) altered stream-channel 

morphology through increased volume and velocity of 

stormflows. All analyses (except for peak flows) were 

based on historical average-daily discharge records 

from one active and three inactive USGS streamflowgaging stations within the basin.

This report (1) describes the four site? studied in 

the Beaver Kill Basin and one reference (unaffected) 

site in the adjacent Schoharie Creek Basin, (2) presents 

results of selected analyses of historical surface-water 

data and discusses significant findings and trends, (3) 

identifies limitations of the information used in the 

analyses, and (4) suggests additional areas of study

Trends in Base Rows and Extreme Flows in the Beaver Kill Basin. Catskill Mountains, New York 1915-94
41 0 52'301

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IBEAVERKILL 

BASIN

EXPLANATION

A ACTIVE GAGE

0 INACTIVE GAGE

 - BEAVER KILL DRAINAGE BOUNDARY

 NEW YORK ROUTE 17

Base from U.S. Geological Survey 

Digial line graph, 1:100,000

Figure 1. Principal hydrologic features of study area in southeastern New York State.

Introduction
and the surface-water monitoring needs that could help 

establish whether NY 17 has affected fish habitat and 

trout populations of the Beaver Kill Basin.

Acknowledgments

Thanks are extended to Jock Conyngham for his 

technical reviews of this document and the analyses, 

and to The Town of Rockland and Trout Unlimited for 

support of this work.

STUDY AREA

Four sites in the Beaver Kill Basin (Delaware 

River system) and one control site in the nearby 

Schoharie Creek basin (Mohawk River system) were 

selected for study (fig. 1). Annual average daily 

discharge, total annual runoff, drainage area, USGS 

station number, and period of record for each site 

are given in table 1. The Beaver Kill at Cooks Falls 

(Cooks Falls site), the downstream site, is the only 

active stream-flow gaging station in the basin. The 

upstream site, the Little Beaver Kill at Livingston 

Manor (Little Beaver Kill site) was discontinued in 

1981. Water flowpaths and runoff at these two sites

could potentially be affected by NY 17. The two other 

sites in the basin the Beaver Kill at Craigie Clair 

(Beaver Kill site) and the Willowemoc Creek at 

Livingston Manor (Willowemoc site), were operated 

during about 1937-70.

Stream-flow records from 1902-94 are available 

from Schoharie Creek at Prattsville, about 35 mi 

northeast of Roscoe (see fig. 1 inset map); Schoharie 

Creek flows into the Mohawk River, a tributary to the 

Hudson River (U.S. Geological Survey, 1996). 

Although the Schoharie Creek watershed also 

underwent development and road construction 

sometime during the period of study, the hydrologic 

effects were probably similar to those occurring in 

the Beaver Kill, except for the construction of NY 

17. No other site in the Catskill region was so close 

and as similar to the Beaver Kill in drainage area, 

nor did any other sites have the lengthy period of 

flow records needed to separate the effects of annual 

precipitation on flows in the Beaver Kill before 1965 

from those thereafter.

Total annual wet precipitation during 1941-94 at 

rain gages maintained by several cooperators for the 

National Oceanic and Atmospheric Administration 

(NOAA) averaged 43.1 in. at eight sites in the 

northern part of the upper Delaware basin and 46.9

Table 1 . Period of record, drainage area, annual average daily discharge, and average total annual runoff of streams at study 

sites in the Beaver Kill Basin and at the control site in the Schoharie Creek Basin, N.Y. [Locations are shown in fig. 1]

Site name, 

informal name, 

and data source

USGS station Period of 

number record

Drainage Annual average Average

area daily discharge total annual

(square (cubic feet per runoff

miles) second) (inches)

Study sites (Beaver Kill Basin)

Beaver Kill at Cooks Falls 1 

(Cooks Falls site)

Little Beaver Kill at Livingston Manor^ 

(Little Beaver Kill site)

Beaver Kill at Craigie Clair 3 

(Beaver Kill site)

Willowemoc Creek at Livingston Manor3 

(Willowemoc site)

Reference site (Schoharie Creek Basin)

Schoharie Creek at Prattsville1 

(Prattsville site)

01420500

01418500

1915-94

1924-81

1937-70

1937-70

241

20

82

63

0135000 1902-94 237

555

45

191

143

460

31.27

30.79

31.63

30.82

26.36

1 U.S. Geological Survey (1996)

2 U.S. Geological Survey (1982)

3 U.S. Geological Survey (1972)

Trends in Base Flows and Extreme Flows in the Beaver Kill Basin. Catskill Mountains, New York 1915-94
in. at the rain gage in the study area at Roscoe, (fig. 

1) (B.E. Krejmas, U.S. Geological Survey, 

unpublished data, 1996).

METHODS

The hypothesis that overland-water flow, shallow 

ground-water flow, and stream discharge in the Beaver 

Kill Basin changed after construction of NY 17 was 

evaluated through analyses of temporal trends in (1) 

the relation of stream stage to discharge, (2) dischargeduration curves, (3) peak and estimated bankfull 

discharges, (4) annual and monthly discharges and 

base flows, and (5) annual and monthly flow extremes 

(1-, 3-, and 7-day high and low discharges), primarily 

at the two sites that were most likely to have been 

affected by NY 17 - the downstream (Cooks Falls) 

and the upstream (Little Beaver Kill) sites (fig. 1). 

Though construction of NY 17 extended through the 

1960's, the year 1965 was selected as the focal point 

because it was approximately midway in the 

construction period, any hydrologic changes should 

have begun to occur, and no definite completion date 

could be ascertained.

Values for 13 indices for the Cooks Falls and the 

Little Beaver Kill sites were calculated, and the 

temporal trends of these indices were compared with 

(1) precipitation trends, and (2) corresponding trends 

at three reference sites (the Willowemoc and Beaver 

Kill sites and the Prattsville site), both before and after 

1965, to detect signs of downcutting (incising) and 

filling of stream channels and for signs of change in 

related hydrologic processes after construction of NY 

17. The 13 indices listed and explained below were:

(a) Relation of stream stage to discharge; this 

describes the association between the shape of the 

channel, stream stage, and stream discharge.

(b) Discharge-duration curves; these are 

cumulative frequency curves that show the percentage 

of time that specified daily discharges were equalled 

or exceeded during a given period (Searcy, 1959).

(c) Peak and bankfull discharge; bankfull flows are 

peak instantaneous flows that recur with a interval of 

about 1.5 years (exceedence probability of 1/1.5 or 

0.67) (Powell, 1995). Larger stormflows that recur 

every 2-100 years (exceedence probabilities of 0.5- 

0.01) are estimated with the same peak flow 

information. Discharge values were calculated by 

special USGS data-retrieval applications.

(d) annual average daily discharge; estimates for 

each site and year were obtained from USG!T 

records maintained in Troy, N. Y, and are reported in 

cubic feet per second or inches of runoff 

(normalized to subbasin area).

(e) monthly average daily discharge; estimates for 

each site and each month were obtained from USGS 

records maintained in Troy, N.Y., and are reported in 

cubic feet per second or inches of runoff (normalized 

to subbasin area).

(f) annual average base flow; estimates fcr each 

site and year were calculated from USGS records 

using flow-separation models of Rutledge (1993), and 

are reported in inches of runoff (normalized to 

subbasin area).

(g) monthly average base flow; estimates for each 

site and month were calculated from USGS records 

using flow-separation models of Rutledge (1993), and 

are reported in inches of runoff (normalized to 

subbasin area).

(h) ratio of annual average base flow to annual 

average flow (annual B/A ratio); calculated for each 

site and year from estimates of annual average base 

flow (f) and annual average flow (d).

(i) ratio of monthly average base flow to monthly 

average flow (monthly B/A ratio); calculated for each 

site and month from estimates of monthly average 

base flow (g) and monthly average flow (e).

(j) annual 1-day high flow; highest 1-day average 

discharge for each site each year.

(k) annual 1-day low flow; lowest 1-day average 

discharge for each site each year.

(1) monthly 1-day high flow; highest 1-day average 

discharge at each site each month.

(m) monthly 1-day low flow; lowest 1-day average 

discharge at each site each month.

Other indices (e.g., 3- and 7-day low and high 

flows) were examined, but, are not discussed because 

their temporal trends were similar to, and tHir 

associations were less statistically significant (lower 

p values), than those of the 1-day low and high flows. 

Precipitation was used as an independent variable 

where appropriate. Similar analyses were also done 

for the three reference sites (Prattsville, 

Willowemoc, and Beaver Kill) to help evaluate 

whether hydrologic changes at the sites potentially 

affected by NY 17 (Cooks Falls and the Little Beaver 

Kill sites) might have occurred normally du~. to 

regional and temporal variations in precipitation and 

stream hydrologic conditions.

Methods
Total annual wet precipitation data (reported in 

inches) for each year during the period 1941-94 were 

estimated by summing provisional monthly 

accumulations from 8 NOAA rain gages (see study 

area section) and averaging data from all sites. Annual 

variations and long-term trends in precipitation were 

compared to hydrologic changes and trends at 

potentially affected sites (and at unaffected sites) to 

determine whether temporal variations in precipitation 

might have contributed to variations in hydrologic 

indices and whether any changes after 1965 could be 

attributed solely to NY 17, or to a combination of 

natural and man-made factors.

TRENDS IN BASE FLOWS AND 

EXTREME FLOWS

Changes in monthly and annual discharge, base 

flow, and several other hydrologic indices were 

observed at the three reference sites and the two 

possibly affected sites in the Beaver Kill Basin during 

their respective periods of record. These changes are 

presented in terms of significant trends (increasing or 

decreasing) through time and as changes in the slope 

of these trends after the construction of NY 17. 

Although the temporal trends in these indices reflect 

the streams' response to a multitude of factors, and 

although differences among time periods represented 

account for some of the variability of a given index, 

time (year) is not responsible for these trends; the 

potential causes of observed variability include 

fluctuations in precipitation, shifts in land uses and 

predominant forest cover, and changes in hydrologic 

flowpaths related to increased development within the 

basin. Precipitation generally accounts for much of the 

long-term variability in most of the hydrologic indices 

evaluated. A significant change in the slope of an index 

trend after 1965 does not necessarily mean that NY 17 

was the reason for the shift ~ many other factors (most 

of which were not assessed) could have contributed to 

the response.

Hundreds of relations among the 13 indices were 

evaluated, but only those few found to be significant (p 

< 0.05 unless otherwise noted) are discussed. The 

small amounts of variability in each index accounted 

for by factors other than precipitation does not mean 

that these factors are inconsequential, but that their 

effect on hydrologic processes within the basin was 

largely overshadowed by the effect of precipitation. 

These other factors warrant further study because,

unlike precipitation, many can be altered through 

informed watershed management

Although the slopes of several regression lines 

that describe relations between indices and time before 

1965 differed significantly from the slopes after 1965, 

the wide range of values for most indices produce 

large standard errors and confidence lirrrts for the 

best-fit lines.

Relation of Stream Stage to Discharge

Relations between stream stage and discharge at all 

four Beaver Kill Basin sites after 1965 d ;ffered from 

those before 1965 as illustrated in examples for the 

Cooks Falls and Little Beaver Kill sites in figures 2, in 

which low-flow discharges (base flows) at both sites 

were associated with slightly lower stages after 1965 

than before. Although the slopes of the regression lines 

for both sites (simple best-fit regression lines for the 

Little Beaver Kill site are not a true representation of 

the relation and are not shown) are significantly 

different after 1965, the standard errors for each line 

(not shown) overlap considerably; thus, predictions of 

stream discharge from stage using both l ;nes would 

not differ significantly. The small but significant 

decrease in the slope for the Cooks Falls site (fig. 2a) 

indicates that the control was lowered slightly (by 0.05 

to 0.1 ft.), probably through dislodgmen* of the 

sediments that typically form a small part of the 

mostly bedrock control. This lowering would imply 

increased transport of sediment and(or) increased 

water velocities after 1965 at this site. A small increase 

in discharge for a given stage at the Little Beaver Kill 

site after 1965 (fig. 2B) (regression line not shown) 

could be attributed to increased approacl velocities at 

the control structure as a result of gradual filling of the 

control pool by sediment; the control structure itself 

could not have been altered because a concrete weir 

was installed in 1933 (U.S. Geological Survey, 1982).

The small shifts in stage-to-dischargo relations at 

both sites after 1965 could be loosely interpreted as 

circumstantial evidence of increased stormflows, 

decreased flow stability, increased water velocities, 

increased sediment transport (in the LittH Beaver 

Kill), and of minor changes in stream-channel 

morphology after NY 17 was built. The small 

magnitude of the changes in slopes, however, indicate 

extremely stable channel geometry and control 

structures at both locations, as might be expected at 

bedrock and weir-controlled sites. Comparable

Trends in Base Rows and Extreme Rows in the Beaver Kill Basin. Catskill Mountains, New York 1915-94
changes in stage-to-discharge relations at the three 

sites unaffected by NY 17 (not shown) suggest that 

changes in channel morphology were due to natural or 

human-related processes that occurred throughout the 

Beaver Kill Basin (for example, deforestation, forest 

regeneration, and changes in farming methods or 

intensity). Study of historical changes in streamRegression Line Before 1965

A Before 1965. 

:-- After 1965

i i i i i i i

0.6

LOG1Q STAGE, IN FEET

0.9

channel morphology at other locations would be 

needed (see Suggestions for Additional Study, further 

on) to characterize any changes in stream channels and 

in sediment mobilization in the Beaver Kill Basin.

Figure 2. Discharge as a function of stage before and after 

1965 for the Beaver Kill at Cooks Falls and for the Little 

Beaver Kill at Livinston Manor, N.Y., (Locations are shown in

fig-1.)

Discharge-Duration Curves

Comparison of daily flow-duration frequencies for 

the 14 years before and after 1965 at the Little Beaver 

Kill site (fig. 3) and for the 29 years before 1965 and 

the 29 years thereafter at the Cooks Falls site (not

shown) indicates either that (1) the average daily flows 

underwent a significant (16-54 percent) increase after 

1965, or (2) a large percentage of flows before 1965 

were exceptionally low, and a larger percentage of 

those after 1965 were exceptionally high. Increased 

average daily flows (or increased frequency of large 

flows) in the basin after 1965 would shift the flowduration curve upward and (or) to the right, as 

depicted in figure 3. The recurrence of droughts 

(during the late 1930's, early 1940's, and early 

1960's), and the above-average flows during most of 

the 1970's (Gravlee and others, 1991), suggest that 

temporal fluctuations in regional precipitation could 

be the reason for the shifts indicated in figure. 3. 

Analyses that exclude data from the initial highwayconstruction period (1961-66, which was a trme of 

severe drought) indicate no significant differences 

between average daily flows before 1965 and those 

thereafter. The recurrence of several short drought 

periods in the 1980's and 1990's suggests that the 

number, and (or) the duration, of moderate to high 

flows (expressed as average daily flows) may have 

actually increased at these two sites, but add'tional 

flow records would need to be evaluated to confirm or 

refute this.

If overland and surface-water runoff and streamwater velocities did increase in response to regional 

increases in precipitation and to the presence of NY 17 

and other land-use changes in the basin, the ability of 

the streams to erode and transport bank and channel 

sediments, and thereby alter channel morphcJogy, 

would have also increased after 1965. This possibility 

was evaluated only at the Little Beaver Kill and Cooks 

Falls sites, which had very stable control strictures; 

additional channel-geometry information from other 

sites would be needed to determine the effects of 

increased flows, or of increased frequency of large 

flows, on stream channels and sediment transport and 

deposition throughout the basin.

Peak and Bankfull Discharges

Bankfull discharges at the Cooks Falls and Little 

Beaver Kill sites, and at the Prattsville (reference) site 

were estimated from the largest instantaneou^ flows 

recorded each year during equivalent periods before 

and after 1965. Peak discharges that recur every 1.5 

years on average (0.67 probability of occurrence each 

year) were considered (1) to be the bankfull discharge 

for each site and record period, and (2) to produce

Trends in Base Flow and Extreme Flc-vs
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Before 1965 

After 1965

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PERCENT OF TIME INDICATED DISCHARGE 

VALUE WAS EQUALED OR EXCEEDED

Figure 3. Discharge-duration curves for the Little Beaver Kill 

at Livingston Manor, N.Y., for the 14 years before 1965 and 

the 14 years thereafter. (Location is shown in fig. 1.)

stages which regulate stream-channel morphology 

(Powell, 1995). The relation between peak flows 

(ranked from lowest to highest flows) and exceedence 

probability before and after 1965 at the Cooks Falls 

site is plotted in figure 4A; the discharge that 

corresponds to a probability of 0.67 (on the regression 

line) represents the bankfull discharge that recur

approximately every 1.5 years. Bankfull flows at the 

Cooks Falls gage were from 5 to 15 percent greater 

after 1965 than before bankfull estimates during 

1935-64 range from 10,000 to 10,200 ft3/s, and those 

during 1935-64 range from 10,500 to 11,700 ft3/s (fig. 

4A). Similar or larger increases in bankfull discharge 

at the Little Beaver Kill site (12-32 percent, not 

shown) and at the Prattsville site (10-35 percent) (fig. 

4B) were also noted after about 1965. The similarity of 

increases at the Prattsville site, which was unaffected 

by NY 17, to those at the Cooks Falls and Little 

Beaver Kill sites indicate that the increases either 

resulted from regional increases in precipitation, or 

that other unidentified factors affected brnkfull 

discharges across the region in a similar manner. The 

recurrence of extremely low flows during the 1930's 

and 1940's and early 1960's, and the above-average 

flows during most of the 1970's (Gravlee and others, 

1991), suggest that the increases in peak flows that 

recur every 1.5 years (bankfull discharge0) following 

construction of NY 17 resulted primarily from 

regional increases in precipitation after 1965.

A more obvious change at the Cooks Falls site 

after 1965 was that floodflows that recur at a 2- to 10- 

year (and longer) frequency (excedance probabilities 

of 0.5 and 0.1) at the Cooks Falls site were about 13 

percent larger than those that occurred at those 

frequencies before 1965 (fig. 4A) whereas, the 

floodflows that recur on a 2- to 10-year frequency after

60000

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A. Beaver Kill at Cooks Falls

Regression Line 

>: K/ After 1965

A Before 1965 

c After 1965

B. Schoharie Creek at Prattr/ille

_ Bankful discharge estimates

Regression Line 

Before 1965

60 80 1000 20 40 60 

PROBABILITY OF EXCEEDENCE, IN PERCENT

100

Figure 4. Exceedence probabilities (in percent) for instantaneous peak flows at the Beaver Kill at Cooks Falls and 

the Schoharie Creek at Prattsville (reference site) for 30 years before 1965 and the 30 years thereafter. [Bnkfull 

discharges are estimated as the flows which recur every 1.5 years; equal to flow with an exceedence probability of 

0.67. [Locations are shown in fig. 1.]

8 Trends in Base Rows and Extreme Rows In the Beaver Kill Basin. Catsklll Mountains, New York 1915-94
1965 at the Prattsville site were similar to, or as much 

as 25% smaller than, those before 1965 (fig. 4B). 

Peak-flow data from the Prattsville and most nearby 

sites (see below and fig. 5) indicate that smaller 

amounts of precipitation caused storm flow

magnitudes to be similar or smaller in the region 

during the 30 years since NY 17 was constructed than 

during the 30 years before. Storms of the post-1965 

period at the Cooks Falls site would also have been 

smaller than those of the pre-1965 period if

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A. SCHOHARIE CREEK AT PRATTSVILLE, NY - 01350000 

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1960 1980 2000

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1920 1940 1960 1980 2000

WATER YEAR

Figure 5. Annual peak flows and 15-year weighted moving average of the annual peak flows for the period of 

record through 1996, and long-term discharge estimates for 10-, 50, and 100- year floods (recurrence inte*vals) at 

streamflow gaging stations in Schoharie Creek at Prattsville, the Beaver Kill at Cooks Falls, and Schoharh Creek 

at Burtonsville, N.Y. (Locations are shown in fig. 1. Data from U. S. Geological Survey [1996]. Modified from Lumia 

[1998], fig. 11. Water year refers to a period from October 1 of one year to September 30 of the next year.)

Trends in Base Flow and Extreme Flov*
precipitation trends for the two watersheds were 

approximately equal. Though significant differences 

between pre- and post-1965 peak-flow trends 

(regression lines) are evident (fig. 4), and, estimates 

for 2- to 10-year stormflows after 1965 would be of 

slightly greater magnitude, except for the period 1914- 

34 (table 2), they would not be statistically different 

from those before 1965 in the lower Beaver Kill Basin. 

Many factors, including precipitation and NY 17, 

could have increased the magnitude or frequency of 

moderate to large stormflows since 1965.

A report on flood frequencies of New York streams 

(Lumia 1998), indicates either a deceased, or an 

unchanged recurrence interval for annual peak flows 

and for the 15-year weighted moving average of the 

annual peak flows for nearby Catskill sites (Esopus 

Creek at Coldbrook, Catskill Creek at Oak Hill, East 

Branch Delaware River at Margaretville, and East 

Branch Delaware River at Fishs Eddy) after 1965; as 

does the reference site (Schoharie Creek at Prattsville) 

(fig. 5A). Other streams, such as Callicoon Creek at 

Callicoon, (adjacent to the Beaver Kill Basin) and 

Roundout Creek Near Lowes Corners, also show 

decreases in annual peak flows after 1965 (table 2). 

Even though small increases in the magnitude of 

annual peak flows after 1965 at the Cooks Falls site are 

evident (fig. 5B, table 2), the variability in the data is 

large; thus, differences in the magnitude of 2-, 10-, 25- 

, and 100-year stormflows for the 29 years before and 

the 29 years thereafter are generally not statistically

significant (table 2). Though no significant differences 

for any period are evident at adjacent site" (table 2), 

the magnitude of 2-, 10-, 25-year stonnfbws at the 

Cooks Falls site are significantly larger from 1965-94 

than they were from 1914-34. Data from one nearby 

site (Schoharie Creek at Burtonsville) (fig. 5C) show a 

similar increase in peak flows (Lumia 19?8); this 

suggests that the trend is not unique to the. Beaver Kill 

Basin and, therefore, the increases in stormflows can 

not be caused solely by NY 17. The relat:vely steady 

increase in annual peak flows and in the 15-year 

weighted moving average of the annual p^ak flows 

that started long before NY 17 was constricted and 

continued through the period of record at the Cooks 

Falls site, (fig. 5B) further indicate that o*her basinwide factors are the probably cause of increased 

stormflows in the basin. The increasing trend in annual 

peak flows (and in the 15-year weighted moving 

average of the annual peak flows) of the Peaver Kill at 

Cooks Falls and stable or decreasing trends at most 

nearby watersheds since the early 1900's suggest that 

a variety of factors, possibly unique to the Beaver Kill 

watershed, have altered hydrologic processes that 

affect the magnitude of peak flows or stermflows in 

the basin. The recurrence of extended droughts in the 

Catskill region during the 1920's, 1930Y 1940's, and 

1960's (Gravlee and others, 1991) suggests that the 

long-term increasing trend in peak flows may, in part, 

be a result of a increases in precipitation in the Beaver 

Kill basin. The increasing trend in peak f iws of the

Table 2. Estimated peak flows of 2-, 10-, 25-, and 100-year recurrence intervals for Beaver Kill at Cooks Falls, N.Y., and for 

three streams in nearby basins before and after 1965. Significant differences in peak flows between periods are denoted by 

"1". [Discharges are in cubic feet per second. Data from USGS files in Troy, N.Y. Dash indicates no record. Locations are 

shown in fig. 1.]

Estimated peak flows of select recurrence interval

Location

Beaver Kill at 

Cooks Falls

Schoharie Creek 

at Prattsville

Rondout Creek near

1914- 

34

6,646

11,780

.

2 years

1935- 

64

11,850

15,090

2^05

10 years

1965- 

94

113701

15350

2,647

1914- 

34

12,430

20,250

-

1935- 

64

20,970

40,320

6,047

1965- 

94

23,9001

31370

5,123

1914- 

34

16,210

39,540

-

25 years

1935- 

64

26,500

58,690

8471,

1965- 

94

29.2101

40,690

6,614

100 years

1914- 

34

23,100

62,960

-

1935- 1965- 

f4 94

36,000 37,060

94,111 55,940

12,950 9,139

Lowes 

Corners2

Callicoon Creek at 

Callicoon3

4,483 3,9% 8,113 7,019 10,420 8,883 14,530 12,130

2-, 10-, and 25-year peak discharges for 1965-94 are significantly different from those for 1914-34 

Record began in 1940, not 1935

10 Trends in Base Flows and Extreme Rows in the Beaver Kill Basin. Catskill Mountains, New York 1915-94
Beaver Kill gets stronger as more current peak flow 

information (1995-97) are included (fig. 5B). 

Regardless of potential effects from NY 17, the ever 

increasing magnitude and frequency of peak flows and 

the resulting swifter (and more powerful) velocities of 

waters in the Beaver Kill could have (1) increased the 

rate of sediment transport and (2) altered streamchannel morphology through new patterns of 

degradation and deposition in stream channels and on 

the flood plains of the basin.

Annual Average Discharge and Base Flow

Precipitation generally accounted for 75 to 92 

percent of the variability in annual average base flow 

and annual average discharge, and from 16 to 30 

percent of the variability in the annual B/A ratio (ratio 

of annual average base flow to annual average 

discharge) at all five sites. Temporal trends in annual 

average base flow, annual average discharge, and 

annual B/A ratios at the Cooks Falls site (fig. 6A) and 

the basin's reference sites (the Beaver Kill - not shown

and the Willowemoc - not shown) were not significant 

but the trends in annual average base flow (increasing 

from 1924-80) and in annual B/A ratio (increasing 

during 1924-65, then decreasing during 1966-80; see 

fig. 6B) at the Little Beaver Kill site were significant. 

Although precipitation can account for about 30 

percent of the variability in annual B/A ratios for the 

Little Beaver Kill, time (year) and the significant 

change in slope after 1965 (fig. 6B) can account for 14 

to 25 percent of the variability. These trends at the 

Little Beaver Kill site could be interpreted as evidence 

that NY 17 has affected the annual average flows and 

(or) base flows at the Little Beaver Kill site. Trends in 

the annual average base flow and annual average 

discharge for the Cooks Falls site (fig. 6A) parallel 

those at the Little Beaver Kill site (fig. 6B) during the 

overlapping period (1924-80), but the trends a* the 

Cooks Falls site are not significant when data from 

1980-94 (and 1915-23) are included in the anrlysis. 

Therefore the significant decrease in annual B/A ratio 

and in annual average base flow (relative to average 

annual discharge) at the Little Beaver Kill site after

A. Cooks Falls, 1914-1994

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1910

Base Flow«

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\ Annual B/A Ratio

80

B. Little Beaver Kill, 1924-1980

1930 1950 1970 

YEAR

1990 1920 1940 1960 

YEAR

1980

Figure 6. Total annual precipitation, average annual discharge and base flow (reported in inches of runoff), and the ratio of 

annual average base flows to annual average flows (annual B/A ratio) for: A. the Beaver Kill at Cooks Falls, N.Y., 1914-94, 

and B. the Little Beaver Kill at Livingston Manor, N.Y., 1924-80. (Locations are shown in fig. 1.)

Annual Averqge Discharge and Base flcrv 11
1965 either could be real, or could be an artifact of the 

shortened period of record at the site. Additional 

discharge records from the Little Beaver Kill site 

would be needed to confirm a real and sustained effect 

of NY 17 on annual average flows and base flows in 

this subbasin.

Monthly Average Discharge and 

Base Flow

Comparisons of monthly average discharge, base 

flow, and B/A ratios for all four sites with total 

monthly precipitation and to time (year) reveal only a 

few significant associations; these are presented 

below. Monthly average discharges and base flows at 

the Cooks Falls and the Little Beaver Kill sites (and at 

the two reference sites ~ Beaver Kill and Willowemoc 

sites) were, as expected, strongly related to 

precipitation but did not show any significant 

temporal trend, nor did the slope of any relations 

change after 1965.

Cooks Falls Site. Total monthly precipitation at 

Cooks Falls (1941-94) could account for 17 to 76 

percent of the variability in monthly B/A ratio and 

none of the monthly B/A ratios, except for July, 

showed a significant temporal trend during the period, 

nor did the slope of most monthly trends change 

significantly after 1965 (fig. 7). The increasing trend in

20

15

-10

Precipitation

100

80

60

40

20

S

1900 1920 1940 1960 1980 2000 

YEAR

Figure 7. Total precipitation, average discharge and base 

flow (reported in inches of runoff), and ratio of average 

base flows to average flows (July B/A ratio) for July at the 

Beaver Kill at Cooks Falls, N.Y., 1914-94. (Location is 

shown in fig. 1.)

July B/A ratios with time, and a significant change in 

the slope of temporal relations after 196f, could 

account for about 11 percent of the variability in July 

B/A ratios (fig. 7); precipitation could account for 

about 54 percent of the variability. These results 

indicate that the average base flows for July at this site 

increased relative to the average discharges for July 

during 1914-65, then decreased relative to the average 

discharges for July during 1966-94 (fig. 7). Therefore, 

NY 17 would appear to have slightly decreased July 

base flows of the Beaver Kill at the Cooks Falls site. 

The effects of this decrease on fish communities would 

be difficult to interpret, however, because (1) August 

typically has lower average base flows than July; (2) 

August flows, rather than July flows, generally 

constitute the lowest monthly base flows which in 

turn produce the smallest wetted-streamtxQd area (fish 

habitat) and limit the year-round carrying capacity 

(total fish biomass) for a given reach; and (3) base 

flows for August and other months of low flow appear 

to be unaffected by NY 17. The decreased base flows 

during July could, however, result in an increased 

magnitude of peak stormflows (flashiness) during 

summer, and thereby affect flow and hab; tat stability 

throughout parts of the basin.

Little Beaver Kill Site: Total monthly precipitation 

(1941-80) at the Little Beaver Kill site could account 

for 0 to 72 percent of the variability in monthly B/A 

ratios (1924-80), and none of the monthly B/A ratios, 

except for August, showed a significant temporal trend 

during the period, nor did the slope of any trends 

change significantly after 1965. The increasing trend 

in August B/A ratios with time, could account for 12 

percent of the variability in August B/A ratios, and 

precipitation could account for 42 percert of the 

variability. August B/A ratios increased (not 

decreased, as hypothesized), during the period of 

record (1924-80) in response to an insignficant 

decrease in average August discharges with time; thus, 

the increase in August B/A ratios may be an artifact of 

the shortened period of record.

Annual 1-day Low and High Flows

In general, precipitation could account for as much 

as 52 percent of the variability in annual 1-day low 

flows and 1-day high flows at all four sites in the 

Beaver Kill Basin. Only a few temporal trends in flow 

extremes are discernible and none, except for the Little

12 Trends In Base Rows and Extreme Rows In the Beaver Kill Basin. Catskill Mountains, New York 1915-94
Beaver Kill site, showed a significant change in the 

slope of the temporal relations after 1965.

At the Little Beaver Kill site, a significant temporal 

trend and reversal in the slope of the relation in annual 

1-day high flows after 1965 (fig. 8), accounted for 

about 12 percent of the variability in annual 1-day 

high flows. The regression line in figure 8 indicates a 

decreasing trend in 1-day high flows during 1925-65, 

and an increasing trend during 1966-80. This finding 

would seem to indicate that hydrologic changes 

occurred in the Little Beaver Kill subbasin after 1965. 

The discharge values (not the regression line) for the 

Cooks Falls site in figure 8 also show an increasing 

trend in 1-day high flows from 1965-80 that is similar 

to that for the Little Beaver Kill site; but, the trend at 

the Cooks Falls site reverses after 1980 when the flow 

record at the other site is discontinued. The similarity 

in trends at both sites from about 1940-80 and the 

reversal at Cooks Falls after 1980 suggests that the 

trends in 1-day high flows at the Little Beaver Kill site 

after 1965, like the trends in base flow, could be an a 

result of a shortened record. The available hydrologic 

records are insufficient, however, to confirm or refute 

this possibility.

The significant reversal in the temporal trends of 

annual 1-day high flows and of annual average base 

flows at the Little Beaver Kill site after 1965 (figs. 6B, 

8), could possibly reflect genuine hydrologic changes 

caused by NY 17 within the subbasin. NY 17 would 

be expected to have a greater (and possibly different) 

hydrologic affect on the Little Beaver Kill subbasin 

than on the Cooks Falls basin because (1) the Little 

Beaver Kill subbasin is much smaller than the Beaver 

Kill at Cooks Falls and (2) NY 17 passes through 

about one half of the Little Beaver Kill drainage but 

through only about one-third of the Beaver Kill at 

Cooks Falls drainage, therefore, flows might be more 

reactive to perturbations in the Little Beaver Kill 

subbasin than in the Beaver Kill at Cooks Falls basin. 

The other two thirds of the Beaver Kill at Cooks Falls 

watershed contain the Willowemoc and the northern 

branch of the Beaver Kill, which are both not affected 

by NY 17 (fig. 1).

A significant temporal trend (increasing with 

time) is indicated for annual 1-day high flows (r - 

0.08) for the period of record at the Cooks Falls site 

(1915-94), but no significant change in the slope of 

the relation (regression line) is evident after 1965, 

even though trends in 1-day high flows partly

10000

1000

100

A A

A J^Little Beaver Kill Site1920 1940 1960 

YEAR

1980 2000

Figure 8. Annual 1-day high flows for the Little Bearer Kill at 

Livingston Manor, N.Y., and the Beaver Kill at Cook«? Falls, 

N.Y., 1925-94. (Locations are shown in fig. 1.)

resembled those at the Little Beaver Kill durirg 1925- 

80 (fig. 8). The trend provides further evidenc- that 

the long-term increases in the frequency and (or) 

magnitude of peak and stormflows in the lower basin 

is (1) the result of normal variations in precip;tation, 

(2) due to protracted and interminable changer in land 

uses and related development, and (3) not relf ted to 

any single abrupt perturbation of hydrologic 

processes within the basin

Monthly 1 -day Low and High Flows

With three exceptions (described below), monthly 

1-day low and high flows at Cooks Falls and a* the 

Little Beaver Kill sites did not show significant trends 

through time, nor did the slope of the trends cl ange 

significantly after 1965. Monthly low and high flows 

were significantly related to total monthly 

precipitation during more than half of the months

Little Beaver Kill Site. Annual differences in 

April's total precipitation, a significant trend with 

time, and a significant change in the slope of the 

relation after 1965, accounted for 28 percent of the 

variability in monthly 1-day high flows at this site 

for April (not shown); precipitation alone accounted

Monthly 1-day Low and High Flovr<* 13
for 21 percent of the variability. A small increasing 

trend in April's 1-day low flows was also significant 

(r2 = 0.06) at this site during 1924-81 (not shown). 

The decrease in slope of the 1-day high flows for 

April after 1965 and, the increase in 1-day low flows 

through the period of record, is inconsistent with the 

trends that were hypothesized.

Cooks Falls Site: Only the 1-day low flows for 

August (r2 = 0.07), and the 1-day high flows for 

December (r2 = 0.07), showed a significant temporal 

trend at this site. The increase in slope for the 1-day 

low flows for August after 1965 was significant, but 

again is inconsistent with the decrease that was 

hypothesized.

These results indicate that either (1) the observed 

trends were caused by factors other than NY 17, (2) 

the hypothesized trends were incorrect, or (3) NY 17 

has little or no effect on the monthly 1-day high and 1- 

day low (average) flows within the Beaver Kill Basin.

Limitations of Analyses

The methods used in this study could have failed to 

detect certain hydrologic changes associated with NY 

17 in the Beaver Kill Basin if those changes were 

different from those hypothesized, or were masked by 

the effects of other factors, such as the following:

(1) Inconsistent temporal components to changes 

in the basin may have produced nonstandard 

hydrologic affect signals (e.g., binary vs. continuous) 

after NY 17 was constructed, and some of these 

signals were not recognized by our linear trend 

analyses. For example, increased sedimentation 

(directly associated with construction of NY 17) could 

have caused short-term (1-, 2-, 5-, 10-year) increases 

in channel deposition followed by channel degradation 

as the sediment was transported out of the system. 

Potential short-term changes in stage-to-discharge 

relations and stream channel morphology might have 

been masked by analyses of data for 14- or 29-year 

periods before and after 1965.

(2) Construction of secondary roads and railroads 

and associated hydraulic structures (ditches, culverts, 

and embankments), within the Beaver Kill basin 

before NY 17 was built, and before streamflow 

records were maintained, could have overshadowed 

lesser hydrologic changes that NY 17 would have 

produced alone.

(3) Large seasonal and yearly fluctuations in total 

precipitation (which account for most of the variability

in most hydrologic factors, as noted earlier), could 

have masked lesser but significant hydro1 ogic changes 

in the basin which might be strongly associated with 

NY 17. For example, small changes in annual average 

and base flows (and their temporal trends) due to NY 

17 might be impossible to differentiate because of very 

high precipitation during the 1970's.

(4) Gradual alteration of surface-water and shallow 

soil-water flowpaths through natural and 

anthropogenic processes such as forest regeneration 

(after deforestation that occurred in the first half of the 

20th century), reduced farming, and increased housing 

development could have resulted in hydrologic 

changes that could either counteract possible effects 

related to NY 17 or conceal these hydrologic changes 

within preexisting trends. For example, long-term 

increases in peak flows at the Cooks Falls site (fig. 5B) 

are obviously related to some factor(s) o*her than NY 

17 until about 1965, thereafter, any real effect of NY 

17 on peak flows could not be separated from the longterm trend.

In addition, the Schoharie Creek site nay have been 

an inadequate reference site. It was used as the primary 

reference site, however, because it was tin only nearby 

subbasin of a size similar to that of the Ccoks Falls site, 

it was in the same physiogeographic region, and it had 

a record covering the same period as that of the Cooks 

Falls site. Hydrologic processes within the Schoharie 

Creek at Prattsville watershed may affect streamflow 

somewhat different from those in the Bearer Kill Basin 

and its subbasins, as reflected in the lowe*- average 

flows and annual runoff (table 1) and higHr peak flows 

(fig. 4) at the Prattsville site than at the Cc oks Falls site. 

The differences between the basins are generally not 

relevant to our analyses, as data from the reference site 

are assessed primarily to distinguish regional from 

basin-specific origins for changes in hydrologic trends 

within the Beaver Kill.

Certain hydrologic changes also may have been 

undetected because the historical data (mostly daily 

discharges) that were available represented incomplete 

periods of coverage (years of record for erch site), were 

of insufficient resolution (daily), and may also reflect 

an inadequate number and placement of jraged sites 

within the basin, to indicate major changes in stream 

hydrology after construction of NY 17. For example:

(a) The locations of active and discortinued 

streamflow gages (fig. 1) were not ideal for an 

evaluation of subbasins that are entirely traversed, 

and not traversed* by NY 17. Two locations that

14 Trends in Base Flows and Extreme Flows In the Beaver Kill Basin. Catskill Mountains, New York 1915-94
would have been ideal for this purpose would have 

been on the Beaver Kill and the Willowemoc Creek 

near their confluence at Roscoe (fig. 1). Data from a 

new Beaver Kill (unaffected) site would provide a 

better reference for comparison with data from the 

Willowemoc (affected) site.

(b) The periods of record for the two discontinued 

stream gages were generally too short to characterize 

changes in hydrologic trends after NY 17 was 

constructed. A longer period of record for the Little 

Beaver Kill (1924-81) and the Beaver Kill (1937-70) 

sites would have unproved detection of changes in 

trends that may have occurred after NY 17 was built

(c) The available discharge data (mostly daily, 

except for peak flows) may have insufficient resolution 

to indicate hydrologic trends; hourly or 15-minute 

discharge data might identify any such trends more 

precisely, but these data are either unavailable or 

available only in undigitized (graphic or punch tape) 

formats. Regeneration of early unit values was beyond 

the scope of this study.

SUGGESTIONS FOR ADDITIONAL STUDY

In addition to analysis of hourly or 15-minute 

discharge data, renewed discharge monitoring at the 

three discontinued gages, and (or) adding streamflowgaging stations on the Beaver Kill and Willowemoc 

Creek near their confluence at Roscoe, would improve 

the ability to define discharge regimes and detect longterm changes in hydrologic characteristics throughout 

the Beaver Kill Basin. Discharge data from these sites 

could be used to verify changes and long-term trends 

in hydrologic characteristics and identify changes in 

the quantity and stability of fish habitat throughout the 

Beaver Kill Basin since NY 17 was completed.

Immediate needs for quantifying changes and 

trends in high flows (flood stages) at several sites 

throughout the basin could be met through use of lowcost crest-stage gages maintained by local observers. 

These simple devices register peak stages, which can 

be recorded after large flows and related to annual 

measures of stream cross sections (channel 

morphology) to provide estimates of annual peak and 

bankfull discharges, flood-recurrence intervals, and 

several-stream classification characteristics.

Another potential method of identifying changes in 

stream-channel morphology and fish habitat in the 

Beaver Kill would be a review of New York State 

Department of Transportation records and aerial

photographs that may document conditions on the 

flood plain, along the riverbank, and in the streambed 

before and after construction of NY 17. A complete 

analysis of these data could help characterize (1) the 

percentage of river reaches that were truncated and 

straightened during construction of NY 17, raT-oad 

beds, and other roadways; (2) the amount of floodplain area that was lost through basin development and 

construction of elevated land structures; (3) the 

percentage of stream banks that were hardened or 

armored in recent decades to reduce erosion; and 

(4) the periods during which sediment may har'e been 

deposited or eroded, and channels incised or built up, 

after major construction activities within parts of the 

Beaver Kill Basin. Results of these analyses could be 

of value because a large amount of channel 

straightening seems to have occurred in the Little 

Beaver Kill subbasin upstream from the gaging station 

during the NY 17 construction period (J. Conyngham, 

oral commun., 1998).

This study ignored a major environmental factor ~ 

stream-water temperature ~ which might be altered 

through increased water temperatures and rates and 

volumes of summer-storm runoff from the NY 17 road 

surface. Little is known about the capacity for NY 17 

to alter runoff regimes or to affect stream temperatures 

in parts of the Beaver Kill Basin; increased wa*er 

temperatures during summer storms could increase 

thermal stresses on resident fish and decrease the 

dissolved oxygen concentrations and thereby 

adversely affect the survival of certain fish species and 

the health and distribution of their populations A 

study of summer thermal conditions (1) at 

representative stream reaches throughout the br^in, (2) 

in surface runoff from NY 17 and from undisturbed 

subbasins, and (3) at stream reaches upstream and 

downstream from runoff sources associated with NY 

17, could document the temporal and spatial ertent of 

elevated temperatures that might adversely affect 

survival and populations of trout and other resident 

fish species.

An effort to characterize trout survival at selected 

locations through on site bioassays and(or) population 

assessments could document (1) the effects of 

highway-heated storm runoff on trout survival, (2) the 

thermal limits (temperature thresholds) for trout 

survival, and (3) the potential effects of thermal 

episodes on trout populations within this system. 

These data, and information on the spatial extent of 

elevated water temperatures, would in turn help

Suggestions for Additional Stud < 15
delineate the temporal and spatial distribution of 

adverse thermal conditions resulting from summerstorm runoff from NY 17 hi the Beaver Kill Basin.

CONCLUSIONS

Analyses of base flows, discharge-duration 

curves, stage-to-discharge relations, peak and 

bankfull discharges, and flow extremes (1-day low 

and high flows) provide only inconclusive evidence 

that NY 17 has altered discharge patterns within the 

Beaver Kill Basin.

Increases in high-flow indices during the period of 

record at the Cooks Falls site are primarily related to 

the trends in precipitation and to periodic droughts, but 

the lack of comparable changes at nearby streamflowgaging stations, and the absence of a sharp change in 

the trends after 1965, indicate that these increases 

were primarily due to continual, gradual shifts of 

hydrologic processes throughout the basin, rather than 

to NY 17. These changes probably occurred partly hi 

response to gradual changes hi land uses within the 

Beaver Kill watershed. The increases hi high-flow 

indicators before the construction of NY 17 occurred 

at about the same rate as they did thereafter, thus, the 

effect of NY 17 on streamflow of the Beaver Kill, if 

any, appears to be minimal and could have only 

augmented existing trends hi the basin. The increases 

in peak flows in the lower Beaver Kill basin during the 

past 80 years, though only weakly related to NY 17, 

have probably increased the Beaver Kill's ability to 

alter channel morphology and sediment transport.

Increases in daily discharge duration and in 1- 

day high flows, and decreases in annual average base 

flows and in the ratios of annual average base flows 

to annual average flows after 1965 at the Little 

Beaver Kill site, would seem to indicate that 

hydrologic processes within the subbasin have been 

altered by NY 17, but this can not be substantiated 

from the short period of discharge record since the 

completion of NY 17.

Hydrologic trends at the Cooks Falls and Little 

Beaver Kill sites in the Beaver Kill Basin since the 

mid-1960's appear to reflect (1) long-term trends 

and large annual variations hi regional precipitation,

(2) gradual changes in anthropogenic pressures and 

natural processes occurring throughout the basin, and

(3) changes in high-flow indices that may or may not 

be related to NY 17. Hydrologic changes in the basin 

are most clearly indicated by differences in the

duration and (or) the frequency of moderate to large 

discharges that are expressed on a daily (average) or 

peak (instantaneous) basis.

Though concern over potential changes hi trout 

habitat was the impetus for this investigation, the 

hydrologic information used by this study could not 

directly address effects that the above mentioned 

hydrologic changes may have had on the quantity and 

stability of habitat and resident trout populations 

within the Beaver Kill Basin. Future evaluations of the 

potential effects of NY 17 on stream-chennel 

morphology, trout habitat, and resident f ^h 

populations of the Beaver Kill might include 

documentation of (1) stream discharge and peak flows 

at additional sites, (2) historical changes hi channel 

morphology and in sediment transport at nongaged 

sites, (3) the ability of NY 17 to affect summer stream 

temperatures and the spatial extent of ad T°.rse thermal 

conditions across the basin, and (4) the effects of 

increased summer stream temperatures en trout 

survival and on resident trout populations across the 

Beaver Kill Basin.

SELECTED REFERENCES

Binns, N. A., 1979, A habitat quality index for Wyoming 

trout streams: Wyoming Game and Fisl Department, 

Fish Resources Report 2, 75 p.

Blackport, R., MacGregor, R., and Imhof, J., 1995, An 

approach to the management of groundwater resources 

to protect and enhance fish habitat: Canada Journal of 

Fisheries and Aquatic Sciences Manuscript Report 

2284, 70 p.

Fausch, K. D., Hawkes, C. L., and Parsons, M. G., 1988, 

Models that predict standing crop of stream fish from 

habitat variables --1950-1985: U.S. Forest Service 

General Technical Report PNW-GTR-213, 52 p.

Francis, A. M., 1983, Catskill rivers ~ birthplace of American fly fishing: Pisscataway, N.J., Winchester Press, 

258 p.

Gravlee, G. C. Jr., Lumia, R., Wolcott, S. V'., and others, 

1991, New York Floods and Droughts, in Paulson, 

R. W, Chase, E. B., Roberts, R. S., aiH Moody, D. 

W (compilers), National Water Summary 1988-89: 

U. S. Geological Survey Water Supply Paper 2375, p. 

415-424.

Lumia, R., 1998, Flood of January 19-20,19^6 in New York 

State, U. S. Geological Survey Water-Resources Investigations Report 97-4242, 61 p.

Powell, R.O., 1995, Stream channel stability: New York 

City Department of Environmental Projection, 106 p.

16 Trends in Base Rows and Extreme Rows in the Beaver Kill Basin. Catskill Mountains, New York 1915-94
Rutledge, A.T., 1993, Computer programs for describing the 

recession of ground-water discharge and for estimating 

average ground-water recharge and discharge from 

streamflow records: U.S. Geological Survey Water 

Resources Investigations Report 93-4121, 45 p.

Searcy, J.K., 1959, Flow-duration curves: U.S. Geological 

Survey Water Supply Paper 1542-A, 33 p.

Simonson, T. D., Lyons, J., and Kanehl, P.D., 1993, 

Guidelines for evaluating fish habitat in Wisconsin 

streams: U.S. Forest Service General Technical 

Report NC-164, 36 p.

U.S. Geological Survey, 1972, Water Resources Data for 

New York, Part 1: U.S. Geological Survey Surface 

Water Records, 302 p.

______, 1982, Water Resources Data -New York, 

Water Year 1981, Volume 1. Eastern New Yotf- excluding Long Island: U.S. Geological Survey Report 

USGS-WRD-NY-81-1,330 p.

______, 1996, Water Resources Data ~ New York,

Water Year 1994, Volume 1. Eastern New Yor^ excluding Long Island: U.S. Geological Survey Wat?r-Data 

Report NY-94-1,448 p.

Selected References 17