U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with Clarke County and Warren County, Virginia

Data Collection and Simulation of Ecological Habitat and 

Recreational Habitat in the Shenandoah River, Virginia

Scientific Investigations Report 2015–5005
Cover: View of the Shenandoah River from Lockes Mill boat landing. Photograph by 

Jennifer Krstolic, U.S. Geological Survey.
Data Collection and Simulation of 

Ecological Habitat and Recreational 

Habitat in the Shenandoah River, Virginia

By Jennifer L. Krstolic

Prepared in cooperation with Clarke County and Warren County, Virginia 

Scientific Investigations Report 2015–5005

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Krstolic, J.L., 2015, Data collection and simulation of ecological habitat and recreational habitat in the 

Shenandoah River, Virginia: U.S. Geological Survey Scientific Investigations Report 2015–5005, 30 p., 

http://dx.doi.org/10.3133/sir20155005.

ISSN 2328-031X (print) 

ISSN 2328-0328 (online)
iii

Contents

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

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

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

Description of the Study Area ............................................................................................................2

Analysis of Historic Streamflow..................................................................................................................4

Water Withdrawals and Projections From the Water Supply Planning Initiative...............................7

Hydraulic Data Collection Update...............................................................................................................9

Establishing New Elevation Control Points ......................................................................................9

Discharge and Water-Surface-Level Data Collection....................................................................9

Water-Surface-Level Adjustments .........................................................................................10

Fish-Community Data and Dominant Substrate......................................................................................10

Using RHABSIM Modeling to Determine Fish Habitat Availability and Recreation

Conditions........................................................................................................................................11

Model Calibration................................................................................................................................11

Water-Surface-Level Calibration ............................................................................................11

Velocity Calibration....................................................................................................................11

Habitat Simulation and Development of Weighted Usable-Habitat Area Curves....................11

Habitat-Discharge Relations for Lockes Mill Study Reach and the Millville 

Streamflow-Gaging Station ........................................................................................12

Habitat Time-Series Scenario Analysis for Low-Flow Periods ............................................................15

Habitat Duration for Summer Months of the Historic Record.....................................................15

Times-Series Scenarios for Historic Droughts and Normal Summers ......................................16

Daily Summaries ........................................................................................................................16

Monthly Summaries ..................................................................................................................20

Increased Water-Use Scenario Results .........................................................................................21

Summary and Conclusions.........................................................................................................................25

Acknowledgments.......................................................................................................................................27

References Cited..........................................................................................................................................27

Appendix. RHABSIM model calibration data ......................................................................................29

Figures

1. Map of the Lockes Mill study reach on the Shenandoah River at USGS 

station number 0163633459, transect and elevation control point locations, 

and water depth............................................................................................................................3

2. Map of study area and surrounding counties, watersheds, and streamflowgaging stations within the Shenandoah Basin........................................................................5

3. Weighted usable-habitat area of ecological and recreational habitat for the 

Lockes Mill study reach on the Shenandoah River, Virginia...............................................14

4. Normal range of weighted usable-habitat area during July, August, and 

September for each fish species or life stage.......................................................................15

5. Habitat time series for the Lockes Mill study reach during 2002........................................17
iv

6. Habitat time series for the Lockes Mill study reach during 1999........................................18 

7. Habitat time series for the Lockes Mill study reach during 2012........................................19

8. Number of days per month when habitat for fish or canoeing was within the 

normal range during 1963, 1999, 2002, and 2012 ....................................................................21

9. Habitat time-series increased water-withdrawal scenarios for the 

Shenandoah River at Millville, West Virginia, during 2002 ..................................................23

10. Habitat time-series increased water-withdrawal scenarios for the 

Shenandoah River at Millville, West Virginia, during 2012 ..................................................24

11. Canoeing recreational habitat time-series increased water-withdrawal scenarios, 

main stem Shenandoah River, based on 2002 flow data, and 2012 flow data ..................25

Tables

1. Selected streamflow-gaging stations in the Shenandaoah River Basin.............................5

2. Streamflow statistics for gages on the North Fork, South Fork, and main stem 

Shenandoah River ........................................................................................................................6

3. Water-withdrawal totals for 2005 and projected estimates for 2040 for the 

Shenandoah River Basin .............................................................................................................8

4. Substrate-suitability indices for the Lockes Mill study reach (0163633459), 

main stem Shenandoah River, Virginia....................................................................................10

5. Weighted usable-habitat area in square feet per 1,000 feet of stream for the 

Lockes Mill study reach, main stem Shenandoah River, Virginia.......................................13

6. Normal range of weighted usable-habitat area in square feet per 1,000 feet 

of stream for July, August, and September for each species and 

canoeing for the Shenandoah River........................................................................................20
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

ADCP acoustic Doppler current profiler

GPS global positioning system

HABSIM Habitat Simulation model 

HSC habitat-suitability criteria

JAS July, August, September low-flow period. Signifies statistics were calculated 

 only on the basis of data for those 3 months for the period of record 

PHABSIM Physical Habitat Simulation model

RHABSIM River Habitat Simulation model 

USGS U.S. Geological Survey

VAF velocity adjustment factor

WSL water-surface level

WUA weighted usable-habitat area, in square feet per 1,000 feet of stream

 Abstract

This report presents updates to methods, describes 

additional data collected, documents modeling results, and 

discusses implications from an updated habitat-flow model 

that can be used to predict ecological habitat for fish and recreational habitat for canoeing on the main stem Shenandoah 

River in Virginia. Given a 76-percent increase in population 

predictions for 2040 over 1995 records, increased waterwithdrawal scenarios were evaluated to determine the effects 

on habitat and recreation in the Shenandoah River. Projected 

water demands for 2040 vary by watershed: the North Fork 

Shenandoah River shows a 55.9-percent increase, the South 

Fork Shenandoah River shows a 46.5-percent increase, 

and the main stem Shenandoah River shows a 52-percent 

increase; most localities are projected to approach the total 

permitted surface-water and groundwater withdrawals values 

by 2040, and a few localities are projected to exceed these 

values. 

The habitat model used for this study evaluates the 

suitability of ecological habitat, represented by fish, and 

recreational habitat, represented by canoeing, based on 

depth, velocity, and substrate conditions, which are weighted 

for the physical habitat types (riffles, runs, or pools) present 

within a stretch of river. Weighted usable-habitat area in the 

Lockes Mill reach was maximized for adult smallmouth bass 

and sub-adult smallmouth bass (Micropterus dolomieu) and 

river chub (Nocomis micropogon) when streamflows were 

equal to median flow (900 cubic feet per second) for summer 

months. Ecological maximum weighted usable-habitat 

areas for smaller fish, such as spotfin or satinfin shiner 

(Cyprinella spp.), margined madtom (Noturus insignis), and 

juvenile redbreast sunfish (Lepomis auritus) occurred with 

10th percentile flows (482 cubic feet per second) and lower. 

Recreational weighted usable-habitat areas for canoeing were 

maximized when streamflows were above the 75th percentile 

(1,410 cubic feet per second). During historic droughts, 

streamflows were less than the 10th percentile, and adult 

smallmouth bass and sub-adult smallmouth bass habitat 

was below normal for the majority of days during at least 

2 months of the summer. When streamflows were less than 

the lowest 7-day average in a 10-year period, or 7Q10 flow 

(357 cubic feet per second), margined madtom, river chub, 

and sub-adult redbreast sunfish habitat areas were below normal as well. Streamflows that limit most fish species habitat 

availability range from 300 to 500 cubic feet per second. For 

the drought years simulated, flows that were equal to or less 

than the 10th percentile for summer months did not provide 

adequate depth for canoe passage through riffle habitats. 

A modeling limitation for higher flows than those studied 

during development of the habitat-suitability criteria is that 

modeled habitat availability will decrease as flows increase.

Time-series analyses were used to investigate changes 

in habitat availability with increased water withdrawals 

of 10, 20, and almost 50 percent (48.6 percent) up to the 

2040 amounts projected by local water supply plans. Adult 

and sub-adult smallmouth bass frequently had habitat 

availability outside the normal range for habitat conditions 

during drought years, yet 10- or 20-percent increases in 

withdrawals did not contribute to a large reduction in 

habitat. When withdrawals were increased by 50 percent, 

there was an additional decrease in habitat. During 2002 

drought scenarios, reduced habitat availability for sub-adult 

redbreast sunfish or river chub was only slightly evident with 

50-percent increased withdrawal scenarios. Recreational 

habitat represented by canoeing decreased lower than 

normal during the 2002 drought. For a recent normal year, 

like 2012, increased water-withdrawal scenarios did not 

affect habitat availability for fish such as adult and sub-adult 

smallmouth bass, sub-adult redbreast sunfish, or river chub. 

Canoeing habitat availability was within the normal range 

most of 2012, and increased water-withdrawal scenarios 

showed almost no affect. For both ecological fish habitat 

and recreational canoeing habitat, the antecedent conditions 

(habitat within normal range of habitat or below normal) 

appear to govern whether additional water withdrawals will 

affect habitat availability. As human populations and water 

demands increase, many of the ecological or recreational 

stresses may be lessened by managing the timing of water 

withdrawals from the system.

Data Collection and Simulation of Ecological Habitat and 

Recreational Habitat in the Shenandoah River, Virginia

By Jennifer L. Krstolic
2 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Introduction

Demands on the water resources of the Shenandoah River 

have been an issue since the mid 1990s. In 1998, the U.S. 

Geological Survey (USGS) demonstrated the utility of developing predictive habitat models to address water-use and instreamflow issues and questions concerning fish and recreational 

habitat for the Shenandoah River (Zappia and Hayes, 1998). This 

previous work presented the framework for a physical habitat 

simulation model to be developed, and for habitat time-series 

analysis and alternative-flow scenario analysis to be conducted. 

Since the publication of habitat modeling results in Zappia 

and Hayes (1998), additional low-flow information and fish 

habitat-suitability criteria have become available. With recent 

population growth and projected increases in population and 

water withdrawals, Clarke and Warren Counties cooperated with 

the USGS to update the original habitat simulation model for 

the Shenandoah River to provide water-resource managers with 

current habitat time-series and alternate flow scenario information for decision-making related to drought management, water 

supply planning, and management of ecological and recreational 

habitat needs. 

The total population of the Shenandoah River 

watershed in Virginia and West Virginia was 371,000 in 2010 

(U.S. Census Bureau, 2011). This total watershed population was 

calculated using block group data within each hydrologic unit 

code (HUC) representing the major drainages in the Shenandoah 

River Basin: the South Fork Shenandoah River (population 

263,000), the North Fork Shenandoah River (population 74,000), 

and the main stem Shenandoah River (population 34,000). In 

addition to people living in the watershed, 104,500 people living 

in Frederick County and the City of Winchester also rely on 

the Shenandoah River for some of their water supply, making a 

total of 475,500 people who use the Shenandoah River in some 

capacity. At the writing of Zappia and Hayes (1998), the 1995 

Census reported only 294,000 people living in the Shenandoah 

River watershed (Solley and others, 1998) with an additional 

74,500 people in Frederick County and the City of Winchester 

for a total of 368,500 people. The majority of people (178,000) 

resided in the South Fork Shenandoah River Basin, the North 

Fork Shenandoah River Basin (92,000), and the main stem 

Shenandoah River (24,000) (Solley and others, 1998). 

 Over the past 12 years, the number of people living in 

the vicinity of the Shenandoah River watershed has increased 

by 106,500 individuals—a 29-percent increase (Solley and 

others, 1998; U.S. Census Bureau, 2011). Water supply planning initiative reports predict population to increase over the 

next 20 years to approximately 649,000 (Central Shenandoah 

Planning District Commission, 2011; Northern Shenandoah 

Valley Regional Commission, 2011), representing a 76-percent 

increase from 1995 population levels. In an effort to plan for 

future water-use needs and maintain the Shenandoah River as an 

environmental resource, the main stem Shenandoah River habitat 

flow model was updated to incorporate new fish habitat-use 

data, low-flow calibration datasets, and future water-withdrawal 

scenarios. These scenarios may serve as general examples to 

other locals for potential habitat impacts to rivers of similar size 

as the Shenandoah River given predicted population growth and 

withdrawal requirements. 

Purpose and Scope

The purpose of this report is to describe updates to methods, 

document modeling results, and discuss implications from an 

updated habitat-flow model for the main stem Shenandoah River. 

Since the initial investigation (Zappia and Hayes, 1998), new 

fish habitat-suitability criteria (Krstolic and Ramey, 2012) and 

water-withdrawal projections (Central Shenandoah Planning 

District Commission, 2011; Northern Shenandoah Valley 

Regional Commission, 2011) have been developed. Additionally, 

new data have been collected to improve and extend the model 

predictions for low-flow conditions. The objectives of the current 

investigation are to enhance the understanding of summer 

low-flow conditions in the main stem Shenandoah River relative 

to the physical habitat needs of fish and to analyze water use 

and recreation needs of humans, such as adequate conditions 

for canoe passage. Water-withdrawal scenarios similar to those 

developed for the North Fork and South Fork Shenandoah 

Rivers (Krstolic and others, 2006; Krstolic and Ramey, 2012) 

were completed for use by resource managers and planners for 

drought management and water supply planning. 

Description of the Study Area

The Shenandoah River watershed was described in Zappia 

and Hayes (1998) and other related publications (Krstolic and 

others, 2006; Krstolic and Ramey, 2012). Elements of the 

landscape that have changed since 1998 will be described as 

well as pertinent differences about study site information. Land 

use in the Shenandoah River Basin in 2006 was predominantly 

rural, with 56 percent forest and wetlands, 33 percent agricultural 

row crops and pasture, and almost 10 percent developed (Fry 

and others, 2011). A decrease in forest and agricultural land 

and an increase in developed land was evident from the 2006 

National land cover dataset (Fry and others, 2011). In 1992, 

approximately 58 percent of the area was forest and wetlands, 

38 percent agriculture, and less than 3 percent of the area was 

developed (Vogelmann and others, 2001). 

The primary study site (Lockes Mill study reach) used 

in Zappia and Hayes (1998) was used for model development 

again in this investigation. This section of river stretches 

approximately 3.2 miles on the Shenandoah River including the 

Lockes Mill site and a Virginia Department of Game and Inland 

Fish (VDGIF) boat landing, to a historic inactive water intake 

downstream. Of the 20 initial transects surveyed for Zappia and 

Hayes (1998) only 14 were accessible and had adequate data to 

be included in the model update (fig. 1). A re-survey of depths 

using side-scan-sonar technology demonstrated that habitats had 

generally remained in the same locations as they were during the 

initial study.
Introduction 

3

Location of study area in Virginia

#

#

# # # #

# # #

#

#

# #

#

#

#

#

#* #

#

Shenandoah

River EXPLANATION

Depth below surface, in meters

–3.0–2.0–0.01 .

# Elevation benchmark

(Included in current model)Elevation benchmark(Omitted from current model)

0 0.5 1 MILE0 0.5 1 KILOMETER

6

3b#

Universal Transverse Mercator projection, NAD 1983, Zone 17N Central meridian -81’ 00”; Elevation from U.S. Geological Survey USGS Topo Map Server, including elevation, hydography, land cover,transportation, and other themes from the National Map, 1:18,000 Contours from U.S. Geological Survey US Topo, 2013, 18,000; Rivers from U.S. Geological Survey National Hydrography Dataset 1:24,000 accessed 2010

River depth from Humminbird side-scan sonar survey conducted by the

U.S. Geological Survey Virginia Water Science Center, 2012 

Lockes

 Mill

VDGIF Lockes Mill

Boat Landing

Discontinued 

water supply intake

Watermelon  Park

0163633459 39°6'

39°5'

18

17

16

15 14b

10

11 12

13 14

9

1

2

3b

5

5b

6

7 7b 8

Morgan Mill Stream

Chapel Run

Lewis Run

Craig RunDog Run

77°56' 77°57' 77°58'

VA

WV

KY

MD

Study

area

Figure 1. Lockes Mill study reach on the Shenandoah River at USGS station number 0163633459, transect and elevation control point locations, and 

water depth. (Water depths are from side-scan sonar survey)
4 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Analysis of Historic Streamflow

The Lockes Mill study reach (station number 

0163633459) along the main stem Shenandoah River is 

located downstream from the confluence of the North Fork 

and South Fork Shenandoah Rivers and the Strasburg gage 

(01634000) and Front Royal gage (01631000) in Virginia, 

and is located upstream from the Shenandoah River at 

Millville, W. Va., gage (01636500) (fig. 2; table 1). The 

modeling results will be discussed in the context of the 

Millville gage, but the way in which the three gages relate to 

each other will be noted for reference. Published streamflow 

statistics for three streamflow-gaging stations are presented 

in this report for reference purposes. Table 2 presents annual 

flow statistics and seasonal flow statistics for the low-flow 

summer period of July, August, and September (JAS). The 

low-flow period as defined in this study and other USGS 

Shenandoah River Basin reports, represents the time of year 

when water supplies are most limited, air temperatures are 

highest, and the demand for water is greatest. Typically 

the flows in October are lower than in July and August; 

however, the irrigation demand and predation risk to 

young-of-year fish are of greater concern in earlier months. 

These flow statistics (table 2) represent a long-term record 

showing that the flow at Strasburg is approximately 

35 percent of the flow at Front Royal, and the combined 

flow at Strasburg plus Front Royal is approximately 

85 percent of the flow at Millville. 

The Millville gage has a record of streamflow beginning in 1896, but has only been in continuous operation 

since 1930. On the basis of data from 1930 to 2002, the 

interquartile range (25th to 75th percentile) for annual 

flows at the Millville streamflow-gaging station ranged 

from 863 to 2,980 cubic feet per second (ft3/s) or 558 to 

1,926 million gallons per day (Mgal/d; Wiley, 2006). For 

this investigation, flow statistics were re-calculated for the 

date range from 1930 to 2012 and compared with those 

published in Wiley (2006) to confirm no major changes to 

the rating in recent years. Compared to the published values 

in Wiley (2006), each flow statistic was within 2 percent, 

and for flow statistics lower than the 50th percentile, the 

values were within 6 ft3/s of the published statistics, 

so published statistics for Millville (1930–2002) were 

referenced throughout this report. Flows equal to or less 

than the 10th percentile for JAS have been used as a drought 

indicator in previous studies (Krstolic and others, 2006; 

Krstolic and Ramey, 2012) and will be evaluated as such 

for this study. The 10th percentile JAS flow for Millville 

is 482 ft3/s or 312 Mgal/d (table 2) (Wiley, 2006). Of note 

is that the lowest 7-day average flow in a 10-year period 

(7Q10; 357 ft3

/s or 231 Mgal/d) is lower than the 10th and 

5th percentile JAS flows for Millville (table 2) (Wiley, 2006). 

The 7Q10 historically has represented an extreme low-flow 

statistic. 

Wiley (2006) compared the computed average 

low-flow statistics for 1930–2002 with each years’ annual 

minimum-flow statistics to examine trends over time. For 

15 streamflow gages across the State of West Virginia, the 

departure of annual minimum flows from the long-term 

average demonstrated an increase in minimum flows around 

1970 (McCabe and Wolock, 2002; Wiley, 2006). These 

departures are considered negative if they are less than the 

long-term average low-flow statistic and positive if they are 

greater than the average low-flow statistic (Wiley, 2006). 

The primary cause for an increase in flows was attributed to 

climate variability (Wiley, 2006). For the streamflow-gaging 

station at Millville, a positive trend was noted for the entire 

time period when considering annual statistics. Increases 

in computed flow statistics generally were observed for 

statistics representing 1–7 day averages every 3 to 10 years. 

This indicates that the extreme low-flow statistics appear to 

be increasing with time. 

Wiley (2006) compared the computed statistics for 

1930–2002 with statistics for 10- to 20-year time periods 

to demonstrate how low-flow statistics vary through time 

and season. The lowest 7-day average flow in a 10-year 

period (7Q10) during the summer for Millville ranged from 

–28.4 to 12.1 percent of the 1930–2002 computed statistic 

depending on the time period examined. For a known 

drought period, 1963 to 1969, the 7Q10 was –28.4 percent 

lower than the long-term statistic. For 1943–1962 and 

1970–1979, the summer JAS 7Q10 was 12.1 percent higher 

than the long-term statistic. These data demonstrate why it 

is important to monitor and assess long-term data in order 

to account for climactic variability. The lowest 30-day 

average flow in a 5-year period (30Q5) during the summer 

for Millville ranged from –28.3 to 17.1 percent of the 

1930–2002 computed statistic depending on the time period 

examined. The only time the 30Q5 was lower than the longterm statistic was from 1963 to 1969. All other time periods 

examined were at least 3.7 percent higher (Wiley, 2006). 

The analysis of long-term streamflow indicates that minimum flows follow cyclical patterns associated with climate, 

and the minimum flows of a stream have regularly been 

23–28 percent lower than the long-term average low-flow 

statistic since systematic streamgaging began. 
Analysis of Historic Streamflow 5

!

! !

!

!

!

FREDERICK

LOUDOUN

CLARKE

MARYLAND

MD

79° 78°

0 10 20 MILES

0 10 20 KILOMETERS

VIRGINIA

Staunton

Waynesboro

Charlottesville

SHENANDOAH

39°

38°

Craig

Dog

Run

Run

Chap 

Lewi

Base from Virginia Counties, Virginia Department of Conservation and Recreation, 2004;

Universal Transverse Mercator projection, NAD 1983, Zone 17N Central meridian -81’ 00”; 

Rivers from U.S. Geological Survey National Hydrography Dataset 1:24,000 accessed 2010

North 

River

River

South 

Middle 

River

River

Shenandoah

South

Fork 

Shenandoah River

North 

Fork 

Shenandoah 

River

Potomac

River

Shenandoah 

River

Watershed

Subwatershed

Streamflow-gaging station

 and number

EXPLANATION

Winchester

ROCKINGHAM

PAGE

WEST VIRGINIA

Berryville

Millville

Harrisonburg

Luray

Front Royal

Strasburg

AUGUSTA

HIGHLAND

ROCKBRIDGE

NELSON

ALBEMARLE

Location of study area in Clarke County, Virginia

RAPPAHANNOCK

STAFFORD

CAROLINE

GREENE

MADISON

CULPEPPER

Fredericksburg

Manassas

Manassas

Park

SPOTSYLVANIA

ORANGE

LOUISA

FAIRFAX

PRINCE

WILLIAM

FAUQUER

WARREN

01631000

# #

#

01632000

01633000

01634000

01628500

01629500

#

#

#

#

01636500

01629500 #

Figure 2. Map of study area and surrounding counties, watersheds, and streamflow-gaging stations within the 

Shenandoah Basin.

Table 1. Selected streamflow-gaging stations in the Shenandoah River Basin.

[mi2, square mile]

Station number Station name Drainage 

area (mi2

) Operating agency Period of record used in this study

01636500 Shenandoah River at Millville, W. Va. 3,041 U.S. Geological Survey 1930–2012

01631000 South Fork Shenandoah River at Front Royal, Va. 1,634 U.S. Geological Survey 1931–2008

01634000 North Fork Shenandoah River near Strasburg, Va. 770 U.S. Geological Survey 1925–2002
6 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Table 2. Streamflow statistics for gages on the North Fork, South Fork, and main stem Shenandoah River.

[Annual statistics represent conditions over all months of the year. July–August–September statistics represent the 3-month average flow conditions. 

7Q10 is the lowest 7-day average streamflow in a 10-year period. Monthly statistics are updated daily and are available for each streamflow-gaging station 

at http://va.water.usgs.gov/duration_plots/dp_map_potomac.htm]

Percentile

Strasburg1

01634000

Front Royal2

01631000

Millville3

01636500

Strasburg1

01634000

Front Royal2

01631000

Millville3

01636500

Cubic feet per second Million gallons per day

Annual

95 1,910 4,650 8,040 1,234 3,005 5,196

90 1,240 3,160 5,480 801 2,042 3,542

75 630 1,760 2,980 407 1,138 1,926

50 310 948 1,590 200 613 1,028

25 160 533 863 103 344 558

10 110 386 585 71 249 378

5 90 328 482 58 212 312

7Q104 65 247 357 42 160 231

July–August–September

95 947 2,360 3,730 612 1,525 2,411

90 566 1,490 2,440 366 963 1,577

75 367 831 1,410 237 537 911

50 214 557 900 138 360 582

25 143 420 641 92 271 414

10 99 330 482 64 213 312

5 75 290 416 48 187 269

1

North Fork Shenandoah River near Strasburg, Va., period of record represents data from 1925 to 2002 (Krstolic and others, 2006).

2

South Fork Shenandoah River at Front Royal, Va., period of record represents data from 1931 to 2008 (Krstolic and Ramey, 2012).

3

Shenandoah River at Millville, W. Va., period of record represents data from 1930 to 2002 (Wiley, 2006).

4

7Q10 values for Strasburg and Front Royal are from Austin and others (2011); 7Q10 value for Millville is from Wiley (2006).
Water Withdrawals and Projections From the Water Supply Planning Initiative 7

Water Withdrawals and Projections 

From the Water Supply Planning 

Initiative

The Shenandoah River watershed withdrawals for 

surface water and groundwater in 2005 were summarized 

on the basis of data reported to the Virginia Department 

of Environmental Quality (DEQ) in Krstolic and 

Ramey (2012). The 2005 water-use values are similar 

to the baseline water-use data compiled in the Upper 

Shenandoah River Basin Water Supply Plan (Central 

Shenandoah Planning District Commission, 2011) and 

the Northern Shenandoah Regional Water Supply Plan 

(Northern Shenandoah Valley Regional Commission, 

2011). These plans used 2008 and 2006 data, respectively, 

to indicate current conditions and make predictions for 

daily average and peak water demand to the year 2040. 

The Krstolic and Ramey (2012) withdrawal calculation 

combined the permitted, reported values from DEQ as 

summarized and published in Kenny and others (2009) and 

the USGS-published countywide estimates for livestock 

and aquaculture (Lovelace, 2009a, 2009b) to ensure that 

agricultural withdrawals were represented. Aquaculture 

data are considered non-consumptive use by DEQ so it 

was omitted from the current investigation. Although 

agricultural users of greater than 300,000 gallons per month 

are reported, livestock and row crop spatial estimates are 

not part of the DEQ water-supply model, but represent 

agricultural uses that may go unreported. Therefore, the 

data for 2005 permitted and reported withdrawals (Kenny 

and others, 2009) were kept separate from the Lovelace 

(2009b) estimates for livestock, but were summed before 

calculating the 2040 projected demands (table 3). Summary 

data for 2005 water withdrawals for the North Fork, South 

Fork, and main stem Shenandoah River (table 3) represent 

“current” conditions for water supply for this investigation. 

The withdrawal values represent data from Virginia only, so 

the withdrawals may be underrepresented for the main stem 

Shenandoah River in Jefferson County, West Virginia. The 

withdrawal data and future water-withdrawal demands were 

used within the modeling phase without developing returnflow estimates. It is assumed that the current streamflowgaging station records report daily values that already 

incorporate withdrawals and return flows. The withdrawal 

data are reported, tabulated, and verified through multiple 

sources, but returns would need to be estimated for future 

withdrawal regimes. Only withdrawals were considered 

for the modeling phase of this investigation, recognizing 

that this may represent a “worst case” scenario because 

there likely will be some portion of return flows from any 

consumptive-use withdrawal. 

The water supply plans describe surface water and 

groundwater sources and frequently combine them when 

summarizing future demands. To gain a general understanding of the amount of increased water use for municipalities, 

comparisons were made for status of presently permitted 

withdrawals, current water use, and projected 2040 demand. 

On the basis of the reported withdrawals for 2006, average 

water withdrawals represent 50 percent of permitted withdrawals. Localities in the Shenandoah Valley have the legal 

permits to withdraw roughly twice the amount of water than 

were used in 2006. Six out of 13 localities in the North Fork 

and main stem Shenandoah River watersheds and five out 

of 13 other localities in the South Fork watershed project 

that daily average demands will equal or exceed 80 percent 

of their presently permitted withdrawals by the year 2040 

(Central Shenandoah Planning District Commission, 2011; 

Northern Shenandoah Valley Regional Commission, 2011). 

Augusta County, Frederick County, Rockingham County, 

and the City of Harrisonburg each expect an increased water 

demand within the range of 4.4 to 6.5 Mgal/d by 2040. 

This equates to 74 to 250 percent of existing permitted 

capacity for those localities. Most localities approach their 

total permitted surface-water and groundwater values by 

2040, and a few exceed them (Central Shenandoah Planning 

District Commission, 2011; Northern Shenandoah Valley 

Regional Commission, 2011). 

The 2040 demand projections from the water supply 

plans were incorporated into the DEQ water supply model 

during 2013. The current and future water-use estimates 

in the DEQ model were preliminary as of September 2013 

(Robert Burgholzer, Virginia Department of Environmental 

Quality, oral commun., 2013), but provide ratios of current 

(2006 or 2008) to future (2040) water demand for surface 

water that can be used to adjust the 2005 published water 

withdrawals for use in this investigation. The water supply 

plans (Central Shenandoah Planning District Commission, 

2011; Northern Shenandoah Valley Regional Commission, 

2011), as input to the DEQ water supply model, depict a 

wide range of surface-water withdrawals from the North 

Fork (55.9-percent increase), South Fork (46.5-percent 

increase), and main stem Shenandoah (52-percent increase) 

River watersheds. Cumulatively, the 2040 surface-water 

demand projections represent a 51-percent increase from 

2005 surface-water withdrawals. 
8 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Table 3. Water-withdrawal totals for 2005 and projected estimates for 2040 for the Shenandoah River Basin.

[Mgal/d, million gallons per day]

USGS station number and name of watersheds 

in the Shenandoah River Basin

2040 estimates 2005 

totals

2005 water-withdrawal 

data3

20401

surfacewater 

withdrawals 

(Mgal/d)

Estimated 

percentage 

increase2

(percent)

Permitted 

plus 

spatial 

estimate 

withdrawals

(Mgal/d)

Permitted 

withdrawals 

in the DEQ 

and USGS 

databases

(Mgal/d)

Spatial 

estimates for 

agricultural 

withdrawals 

(livestock 

and crop 

irrigation)

(Mgal/d)

01632000 North Fork Shenandoah River at Cootes Store, Va. 0.75 0.00 0.75

01633000 North Fork Shenandoah River at Mount Jackson, Va. 2.69 1.75 0.94

 – North Fork Shenandoah River at mouth 9.66 8.92 0.73

North Fork Shenandoah River cumulative totals 20.41 55.9 13.09 10.67 2.42

 – South River at mouth 4.04 3.51 0.53

 – Middle River at mouth 0.88 0.05 0.83

 – North River at mouth 9.89 8.44 1.45

01628500 South Fork Shenandoah River near Lynnwood, Va. 0.10 0.00 0.10

01629500 South Fork Shenandoah River near Luray, Va. 1.29 0.38 0.91

 – South Fork Shenandoah River at mouth 2.33 1.93 0.40

South Fork Shenandoah River cumulative totals 27.15 46.5 18.53 14.31 4.22

 – Shenandoah River at West Virginia State line near Berryville, Va. 5.37 52.2 3.53 3.22 0.31

Basin totals 52.93 35.15 28.20 6.95

1

Calculation of 2040 surface-water withdrawals = (2005 totals * Percent) + 2005 totals.

2

Percentage increase from the Virginia Department of Environmental Quality water supply model (September 2013), which reflects the surface-water percentage increase in demand from the Upper and Northern Shenandoah water supply plans (Northern Shenandoah Valley Regional Commission, 2011; Central 

Shenandoah Planning District Commission, 2011).

3

Permitted, location-specific withdrawal datasets, such as public water supply, commercial-industrial, thermoelectric, golf course irrigation, and mining 

(Kenny and others, 2009). Spatial estimates for county-level data include livestock (Lovelace, 2009b).
Hydraulic Data Collection Update 9

Hydraulic Data Collection Update

The majority of the data collected in 1996 and 1997 were 

input to the updated habitat-flow model for the Shenandoah 

River. Previously surveyed transect streambed elevations for 

each variably sized model cell, water-surface levels, velocity, 

discharge, and elevation control points were utilized along with 

new water-surface level and discharge data collected in 2011 and 

2012. Transect elevation control points were verified, and new 

water-surface-level datasets were compared with historic datasets 

to ensure accuracy. The historic data and recently collected data 

were combined to create an updated habitat-flow model with 

an extended representation of low-flow conditions and new fish 

habitat-suitability criteria (Krstolic and Ramey, 2012). 

A few challenges complicated the modeling phase of 

the Zappia and Hayes (1998) investigation. The primary 

complication was a change in the channel topography due to a 

flood in September 1996, which altered the channel geometry 

near transects 5b, 7b, 8, and 13. The flood occurred after the 

two high-flow discharge measurements had been made and 

water-surface-level data had been collected, but the velocity and 

depth (channel elevation) surveys had not been completed. For 

the original model this meant that the depth and velocity profile 

after the storm did not match what the stage-discharge relation 

would have predicted for discharge. The stage-discharge relation 

for measurements prior to the storm was adjusted to fit the new 

channel geometry within the Zappia and Hayes (1998) model, 

so that subsequent measurements would fit within that relation. 

The transect water-surface level (WSL) above and below the 

adjusted transects were taken into account to ensure the slope was 

realistic. Because the model stage-discharge relation was adjusted 

to post-flood conditions, it was assumed that new data collected 

for extending the low-flow portion of the rating could be verified 

against the original relation and utilized for development of a new 

model. 

Establishing New Elevation Control Points

It was necessary to verify existing horizontal and vertical 

control points for the transects along the Lockes Mill study 

reach so that water-surface profiles could be surveyed and used 

for additional calibration datasets for the habitat-flow model. 

Fifteen years had passed since the initial investigation, and only 

8 of the original 26 transect elevation control marks (benchmarks) 

were found to be in usable condition. The benchmarks were lag 

bolts in trees, most of which were in areas of substantial growth, 

but the lag bolts were found to be stable and accessible. New 

transect benchmarks were established at each transect when 

necessary, and the few remaining headpins or tail pins from the 

original study were found to be unusable for establishing new 

control, but they were marked for reference purposes. The original survey control was based off of Global Positioning System 

(GPS) coordinates and elevation for the Lockes Mill tailrace near 

transect 16. This location was re-surveyed with survey-grade 

GPS and post processed through the National Geodetic Survey 

(2012) Online Positioning User Service (OPUS), resulting in an 

elevation within 0.09 feet (ft) of the original survey elevation and 

within 0.07 ft of the tax map survey provided by the landowner. 

The mill tailrace is a cobblestone structure that did not have a 

clear marking for the exact location of the original survey, so 

the accuracy of the GPS survey confirmed that the tail race is a 

good control feature to verify the new elevations surveyed for 

this update. New control points were installed and surveyed with 

GPS along the boat launch and the road near the VDGIF Lockes 

Mill landing. The new control points were in view of the transect 

14b benchmark, which was at the boat launch and was still in 

good condition from the original survey (fig. 1). The transect 14b 

benchmark was used as a verification for each new survey 

conducted. 

Total station surveys of the newly installed and existing 

original benchmarks were conducted in 2011 beginning from the 

two newly installed control points, extending upstream on the left 

bank, extending downstream on the left bank, and across the river 

to the right bank from Watermelon Park near transect 7. The four 

separate surveys used the two new control points along the boat 

launch as starting elevations and included surveys of the benchmark 14b lag bolt and the mill tailrace for elevation verification. 

Elevations for the transect 14b benchmark from the four 

surveys were compared with the original survey elevation from 

1996. For each survey, any of the eight intact original transect 

benchmarks available were also surveyed and the updated 

elevations were compared with the original elevations. To assure 

the continuity between original and updated elevations, all new 

survey benchmark elevations were adjusted to match original 

elevations on the basis of the difference between transect 14b 

original and updated elevations or other original benchmarks. The 

difference between updated and original benchmarks resulted 

in survey adjustment factors ranging from 0.25 to 0.90 ft. These 

updated benchmark elevations were used as control points for 

new WSL measurements, but no new transect elevation surveys 

were conducted. 

Discharge and Water-Surface-Level Data 

Collection

Discharge and WSL data were collected in July 2012 

at a measured discharge of 970 ft3

/s, and in September 2012 

at 620 ft3

/s. Digital auto level equipment (Sokia SDL30) and 

traditional leveling equipment (Zeiss) were used to survey 

water-surface profiles from transect 18 to transect 1. Data were 

recorded digitally in the field with hand-held Trimble data storage 

devices. Discharge measurements were made upstream from 

the VDGIF Lockes Mill boat landing by using a power boat and 

acoustic Doppler current profiler (ADCP) running WinRiver II 

software (Turnipseed and Sauer, 2010). Discharge was measured 

in the morning and the afternoon each day that a WSL survey was 

conducted, unless the WSL survey was completed before midday. 

A survey of WSL at transect 14b accompanied each discharge 

measurement to monitor for changes in stage. 
10 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

As an additional verification for changes in stage during 

each data-collection period, continuous HOBO U2 (2008–10, 

Onset Computer Corporation) water-level and temperature 

loggers were deployed at the upstream and downstream ends of 

the study reach and in the middle at transect 8 on both banks. 

The loggers were placed at least 1 ft below the water surface to 

ensure they would be submerged the entire time. Two HOBO 

monitors were placed above water on land surface at either 

end of the study reach for barometric pressure compensation 

calculations. In July 2012 the total change in stage increased 

slightly overnight and decreased on the second day of data 

collection, with a maximum range of values less than 0.06 ft. 

Discharge ranged from 959 to 1,043 ft3

/s during the July surveys. 

The upstream monitor showed the least amount of variation 

because it was located in a pool near the water intake. The 

left bank monitors at transect 8 and transect 1 had the greatest 

amount of variability because they were located in or near 

riffle habitats. In September 2012 stage dropped during data 

collection, although the stage did not change more than 0.076 ft. 

Discharge measurements ranged from 612 to 618 ft3

/s during the 

September surveys. 

Water-Surface-Level Adjustments

Water-surface levels were surveyed using elevation control 

points that had not yet been adjusted to match the Zappia and 

Hayes (1998) published elevations. The resulting WSLs were 

adjusted using the same factors used to adjust the benchmark 

elevations. The WSLs from transect 18 to transect 1 from the 

historic and the current surveys plot as would be expected 

for the range of discharges surveyed. The WSLs associated 

with the 970 ft3

/s discharge measurement in 2012 served as 

a confirmation of accuracy as they plotted close to WSLs 

associated with the 907 ft3

/s discharge measurement from 1997. 

Fish-Community Data and Dominant 

Substrate

The initial investigation on the Shenandoah River (Zappia 

and Hayes, 1998) included flow requirements for aquatic 

biota drawn from a number of sources that were not known 

to be applicable to the Shenandoah River. The purpose of that 

investigation was to demonstrate the utility of the instream flow 

process in this region, and the reader was originally cautioned to 

regard it as such. For this update, fish habitat-suitability criteria 

are available. Habitat-suitability criteria were developed for the 

fish community of the South Fork Shenandoah River in 2008 and 

2009 (Ramey, 2009; Krstolic and Ramey, 2012, tables 10, 11). 

Fish observations were made using three sampling techniques, 

and the habitats of each species were documented for flows 

representing the 10th percentile to the 75th percentile JAS flow 

range on the South Fork Shenandoah River. Habitat-suitability 

criteria (Ramey, 2009; Krstolic and Ramey, 2012) from the 

South Fork Shenandoah River were used for modeling at Lockes 

Mill because the depths and velocity range was quite similar to 

study sites on the South Fork Shenandoah River. Krstolic and 

Ramey (2012) used dominant substrate as a measure of habitat 

differentiation during the River Habitat Simulation (RHABSIM) 

software model process (Thomas R. Payne and Associates, 

1998). Dominant substrate data were available for the main 

stem Shenandoah River; however, fewer classes of substrate 

were recorded by Zappia and Hayes (1998). Krstolic and Ramey 

(2012) recorded substrate classes for various sizes of gravel 

(fine, small, large), cobble (small and large), and boulder (small 

and large), and Zappia and Hayes (1998) simply recorded clay/

silt, sand, gravel, and bedrock. The South Fork Shenandoah 

fish habitat-suitability criteria had to be generalized to represent 

dominant substrate data available for evaluation on the main 

stem Shenandoah River (table 4).

Table 4. Substrate-suitability indices for the Lockes Mill study reach (0163633459), main stem Shenandoah River, Virginia.

[1 indicates 100% suitable, 0.75 indicates 75% suitable, 0.5 indicates 50% suitable, and 0 indicates not suitable]

Numeric 

code

Main stem substrate category

Substrate-suitability index

Sub-adult 

smallmouth 

bass

Adult smallmouth bass

Juvenile 

redbreast 

sunfish

Sub-adult 

redbreast 

sunfish

Cyprinella

spp.

Margined 

madtom

River 

chub

20 Clay/Silt 0 1 0.5 0.5 0 0.000 0

26 Clay/gravel 0 1 0 0.5 0 0.000 0

29 Clay/bedrock 0 0.5 0.5 0.5 0 0.000 0

30 Sand 0.5 0.5 0 0 0 0.000 0

36 Sand/gravel 0.5 0.5 0 0 0 0.000 0

39 Sand/bedrock 0 0 0 0 0 0.000 0

60 Gravel/cobble 1 1 1 1 0.75 0.75 0.75

63 Gravel/sand 0.5 0 0 0 0 0.00 0

69 Gravel/bedrock 0.5 0 0.5 0 0.5 0.5 0.5

90 Boulder/bedrock 1 0.5 0.5 1 1 1.000 1

93 Bedrock/sand 0 0 0 0 0 0.000 0

96 Bedrock/gravel 0.5 1 0 1 1 1.000 1
Using RHABSIM Modeling to Determine Fish Habitat Availability and Recreation Conditions 11

Using RHABSIM Modeling to Determine 

Fish Habitat Availability and Recreation 

Conditions

The program RHABSIM 3.0 for DOS and Windows 

(Thomas R. Payne and Associates, 1998) was used for calibration and simulation of flow and habitat. The methods used in 

the RHABSIM modeling process were similar to methods used 

in Krstolic and Ramey (2012) and Krstolic and others (2006), 

with calibrations of WSL and velocity used to simulate WSL, 

velocity, and habitat for a wide range of flows. Calibration and 

simulation were completed in one model for the Lockes Mill 

Shenandoah River study reach.

Model Calibration

The RHABSIM model calibration incorporates datasets 

representing topographic information for each transect, WSLs, 

velocities, and discharge data for the study reach. The transect 

data are used to calculate stage-discharge ratings to enable 

simulation of depths and velocities for flows not measured 

during hydraulic data collection. The Physical Habitat Simulation (PHABSIM) model developed in Zappia and Hayes (1998) 

was available and imported to RHABSIM so that the same 

transect topographic information and streambed substrate data 

could be utilized. The high-flow datasets representing 1,900 ft3/s 

and 3,200 ft3/s that had been collected in 1996 prior to the flood 

and the adjusted WSL, as they were corrected by Zappia and 

Hayes (1998), were used in their original format. New low-flow 

discharge and WSLs collected in 2012 representing 620 ft3/s 

and 970 ft3/s were added the model. The previously collected 

907 ft3/s calibration dataset was omitted because it was similar 

to the more recent data collected. Other data elements that 

were updated include the distance and average slope between 

transects. The RHABSIM interface includes tools to examine 

the stage-discharge relation for each transect individually and 

the slope profiles for all transects. The tools were used to verify 

the ratings for each transect; two transects were identified 

that did not fit the WSL slope profiles of the other transects. 

The historic WSL for transects 5 and 3b as represented in the 

original PHABSIM model were more than 2 ft above the recent 

survey elevations and were omitted from the model update. 

The calibration technique for the original model was used to 

examine each transect individually and did not require the WSL 

slope profile to be consistent upstream or downstream from the 

transect in question. It is possible that calibration adjustments 

for transects 5 and 3b altered the streambed elevation, making 

the data incomparable to the recent measurements. The recently 

surveyed WSLs for the 620 ft3

/s and 970 ft3/s discharge datasets 

were consistent throughout the study reach, and the slopes 

paralleled the Zappia and Hayes (1998) data quite well. 

Water-Surface-Level Calibration

The WSL calibration method was the same for each 

transect throughout the reach. Given the large distance 

between transects, each transect was calibrated separately 

using the Log-Log regression approach (Thomas R. Payne 

and Associates, 1998), which creates a stage-discharge rating 

for each transect. The rating is then used to predict WSLs for 

simulated discharges that were not measured during the study. 

The predicted values were compared with the field-measured 

WSLs with relatively good agreement. Differences between 

predicted and observed WSLs ranged from 0.02 to 0.15 ft 

for pools and runs, and from 0.05 to 0.43 ft for riffles. Riffle 

WSLs are much more challenging to sample, which makes it 

difficult to get accurate measurements and predictions, especially over such a large date range. The WSL for the 1,900 ft3

/s 

calibration discharge was frequently predicted higher than 

what was observed. Since the two highest calibration flows 

were measured in 1996 prior to the flood, it is likely that the 

discrepancies are related to the adjustments that were made to 

the stage-discharge relation after the channel was altered. 

Velocity Calibration

Velocity data were not re-surveyed for this model update. 

The historic data that matched the streambed topography 

were used. Velocity calibration procedures were similar to 

those used with the North Fork Shenandoah and South Fork 

Shenandoah models (Krstolic and Ramey, 2012; Krstolic and 

others, 2006). The 1-velocity calibration method (Thomas R. 

Payne and Associates, 1998) was selected for all transects. 

Cell-by-cell roughness values were adjusted to ensure a good 

match between the simulated velocity and discharge, and the 

measured velocity and best-estimate discharge calibration 

datasets. The model-calculated discharge for each transect 

was compared to best-estimate calibration discharge for 

the reach to obtain velocity adjustment factors (VAF) for 

each calibration discharge. After VAF were determined for 

calibration discharges, they were incrementally increased for 

each simulation discharge. Measured velocities in the velocity 

calibration dataset were used as a template and adjusted on the 

basis of the predicted depths from WSL simulations and the 

VAF to simulate velocities. 

Habitat Simulation and Development of 

Weighted Usable-Habitat Area Curves

RHABSIM model cells were centered on the verticals 

where depths and velocities were collected at varying intervals 

along each transect. The length of model cells was varied 

based on the kind of habitat represented along the transect 

and the percentage of the reach upstream or downstream from 

the transect that contained the same habitat type. Transect 

weighting factors (app. 1) were used to determine model cell 

lengths and ultimately areas of available habitat.
12 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

The WSL and velocity simulations and the fish 

habitat-suitability criteria (HSC), developed by Ramey 

(2009) and Krstolic and Ramey (2012), and canoeing HSC 

(Milhouse, 1990; Zappia and Hayes, 1998) were input to 

the Habitat Simulation Model (HABSIM) of RHABSIM 

(Thomas R. Payne and Associates, 1998). HABSIM uses 

the HSC suitable ranges for water depths, water velocities, 

and dominant substrate to assign individual suitability 

ranks (on a scale from 0.0 to 1.0) for depth, velocity, and 

substrate in each model cell. Following Krstolic and others 

(2006) and Krstolic and Ramey (2012), multiplicative 

aggregation (Waddle, 2001) was used to calculate the 

composite habitat-suitability rank for each cell between 

0.0 and 1.0. The area of all suitable habitat cells within a 

reach was summed for a total weighted usable-habitat area 

(WUA). The process was repeated for each species or life 

stage of fish and for canoeing over all simulation flows, 

and a functional relation between habitat and discharge 

was defined and expressed in the form of WUA curves. 

For canoeing, only depth and velocity were of concern. 

The velocity had upper and lower limits defining optimal, 

suitable, and unsuitable velocity. Flows that are faster than 

5 feet per second are considered unsuitable and could be 

unsafe for inexperienced paddlers. For higher flows, fast 

velocities with low HSC ranks combined with depths with 

suitable HSC result in reduced WUA. Adequate water depth 

to avoid scraping bottom is a major consideration when 

paddling; therefore, habitat simulations for canoeing had 

additional restrictions placed on depth to include only cells 

that are 1-ft deep or greater. 

Habitat-Discharge Relations for Lockes Mill 

Study Reach and the Millville StreamflowGaging Station

Habitat was simulated for a range of flows from 60 

to 5,000 ft3/s at Lockes Mill study reach for seven species 

and life stages of fish and for recreation. These flows are 

equivalent to a range of 70 to 5,850 ft3

/s at the Millville 

gage. Because it is advantageous to discuss habitat data 

in the context of long-term historical streamflow data, 

the Millville-equivalent flows were used as input to the 

time-series analysis. The WUA data represent total physical 

habitat available per a simulated 1,000-ft reach of stream 

with habitats present in the study reach for a given streamflow (table 5; fig. 3). 

The WUA curves (fig. 3) help depict the streamflows 

associated with maximum values of WUAs for each 

species and for recreation and how WUA increases or 

decreases as flows change. It should be noted that the WUA 

curves are bell-shaped, having lower WUA at the highest 

flows—a maximum associated with median to low-flow 

conditions—and decreasing WUA as flows decrease. The 

WUA curves have similar patterns for species of similar 

size or life stage as opposed to patterns grouping game 

or grouping non-game species together. For example, the 

maximum WUA for adult smallmouth bass and sub-adult 

smallmouth bass (Micropterus dolomieu) and river chub 

(Nocomis micropogon) all appear to be associated with 

the median flow for JAS (900 ft3

/s). Sub-adult redbreast 

sunfish (Lepomis auritus) maximum WUA is associated 

with the 25th percentile flow (641 ft3/s), which is still within 

the normal range of flows for JAS. Smaller fish, such 

as spotfin or satinfin shiner (Cyprinella spp.), margined 

madtom (Noturus insignis), and juvenile redbreast sunfish 

(Micropterus dolomieu) maximum WUA were associated 

with the 10th percentile flows and lower. The maximum or 

optimum habitat is related to streamflows that consistently 

provide depths with an optimal range for species (table 5). 

Smaller fish or earlier life stage habitat requirements are 

optimized with depths less than 2 ft, and larger adult fish 

habitat requirements are optimized with depths greater than 

2 ft. Canoeing WUA is maximized when streamflows are 

above the 75th percentile, near 2,000 ft3/sec. At discharges 

greater than 2,000 ft3/s, the velocity becomes faster than 

considered suitable for canoeing safely. Although the depth 

is adequate, the velocity could increase to a level that could 

make canoeing dangerous. For all species of fish considered 

during this investigation, except juvenile redbreast sunfish, 

habitat was maximized with streamflows between 482 and 

900 ft3/s at Millville, representing the 10th percentile to the 

50th percentile flows for JAS (fig. 3). 
Using RHABSIM Modeling to Determine Fish Habitat Availability and Recreation Conditions 13

Table 5.

Weighted usable-habitat area in square feet per 1,000 feet of stream for the Lockes Mill study reach, main stem Shenandoah River, Virginia.

[ft3/s, cubic feet per second; Mgal/d, million gallons per day]

Calculated1

Millville 

equivalent 

daily 

discharge 

(ft3/s)

Millville 

equivalent 

daily 

discharge 

(Mgal/d)

Simulated 

discharge 

(ft3/s)

Fish species weighted usable-habitat area

Sub-adult 

smallmouth 

bass

Adult 

smallmouth 

bass

Juvenile 

redbreast 

sunfish

Sub-adult 

redbreast 

sunfish

Cyprinella

spp.

Margined 

madtom River chub Canoeing

70 45 60 7,154 11,866 58,599 26,234 15,511 44,065 40,746 6,222

117 76 100 27,612 17,695 77,500 53,848 35,913 65,396 59,556 26,610

234 151 200 74,235 35,020 107,398 91,504 102,765 87,364 103,516 92,462

351 227 300 107,873 50,988 118,366 100,548 129,657 124,052 147,316 139,005

468 302 400 139,293 60,193 111,628 108,528 141,287 134,599 165,469 181,275

585 378 500 162,788 67,827 102,436 115,064 141,222 136,150 171,726 222,073

725 469 620 168,082 71,669 78,961 116,148 133,606 134,522 174,546 261,763

819 529 700 173,820 74,021 67,328 114,672 122,932 128,202 177,394 283,911

936 605 800 175,798 76,014 63,425 110,794 120,135 120,926 172,184 306,915

1,135 734 970 163,148 71,512 46,061 109,384 106,235 107,486 153,090 333,866

1,170 756 1,000 158,047 70,969 40,713 108,167 99,624 104,887 150,095 337,306

2,223 1,437 1,900 101,625 47,200 13,226 67,558 33,722 57,295 71,516 363,230

2,340 1,512 2,000 91,601 45,153 12,250 60,338 31,617 54,914 67,370 362,219

3,522 2,276 3,010 57,807 30,356 5,010 33,316 9,615 28,304 25,999 324,184

4,680 3,025 4,000 43,748 23,842 2,933 23,381 4,218 11,948 13,582 277,800

5,850 3,781 5,000 28,565 19,130 2,111 15,738 667 8,254 7,802 242,973

1The ratio of measured discharge at Lockes Mill to daily mean discharge for Millville was calculated for all days which had pairs of data. The value of 1.17 was used to calculate the equivalent daily 

discharge at Millville from the measured or simulated flows at Lockes Mill study site. 
14 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

0

50

32

100

65

200

129

300

194

500

323

1,000

646

2,000

1,294

3,000

1,939

5,000

3,232

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

Weighted usable-habitat area, in square feet per 1,000 feet

Discharge, in cubic feet per second (top number in blue) or million gallons per day (bottom number)

7Q10 flow statistic

50 percent of JAS flow

July–August–September (JAS)

 flow percentiles, in percent

EXPLANATION

Ecological (fish) habitat

 Game fish habitat

 Sub-adult smallmouth bass

 Adult smallmouth bass

 Juvenile redbreast sunfish

 Sub-adult redbreast sunfish

 Nongame fish habitat

 Cyprinella spp.

 Margined madtom

 River chub

 Recreational (canoe) habitat

 Canoeing

Greater than 75

25 to 75

10 to less than 25

5 to less than 10

Less than 5

Figure 3. Weighted usable-habitat area of ecological and recreational habitat for the 

Lockes Mill study reach on the Shenandoah River, Virginia. Flow percentiles are based 

on data from the Millville streamflow-gaging station (01636500) from 1930 to 2002 for 

streamflows during the months of July, August, and September. These statistics represent 

the expected range of flows and are based on the historic streamflow record.
Habitat Time-Series Scenario Analysis for Low-Flow Periods 15

Habitat Time-Series Scenario Analysis 

for Low-Flow Periods

For management purposes it is important to understand 

what the normal range of habitat conditions would be for 

each species of interest and which species habitat area may 

become limited during droughts. Time-series analysis allows 

the evaluation of habitat over the historic streamflow record 

to simulate past and future habitat conditions on the basis of 

the current understanding of WUA and streamflow. 

Habitat Duration for Summer Months of the 

Historic Record

Habitat-duration plots were constructed for each 

species or life stage by assigning usable habitat area to each 

discharge value for the period of record for Millville from 

1930 to 2012. Habitat values for JAS were then ordered 

and ranked, and the percentage of time the habitat value 

was equaled or exceeded was calculated. Habitat-duration 

statistics describe the most common and least common 

habitat conditions, and can be used to define a normal 

range of available habitat area for each species or life stage 

of fish (fig. 4). The normal range of habitat for summer 

months (JAS) represented by the 25th to 75th percentiles of 

available habitat is depicted on time-series plots for context. 

Figure 4 illustrates the differing amounts of habitat available 

for each species during summer months in the main stem 

Shenandoah River. Typically the least amount of habitat 

area is available for adult smallmouth bass and sub-adult 

redbreast sunfish, which have narrow ranges of available 

habitat area. River chub and sub-adult smallmouth bass tend 

to have the most available habitat within the study reach in 

the summer, and Cyprinella spp., margined madtom, and 

juvenile redbreast sunfish have wide ranges of available 

habitat. 

20,000

0

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

SA MDO

Weighted usable-habitat area, in square feet per 1,000 feet

Sub-adult smallmouth bass

 (Micropterus dolomieu), (SA MDO)

Adult smallmouth bass

 (Micropterus dolomieu), (A MDO)

Juvenile redbreast sunfish

 (Lepomis auritus), (J LAU)

Sub-adult redbreast sunfish

 (Lepomis auritus), (SA LAU)

Spotfin or satinfin shiner,

 (Cyprinella spp.), (CYP)

Margined madtom

 (Noturus insignis), (NIN)

River chub

 (Nocomis micropogon), (NMI)

Normal range of habitat for July, August,

 and September (JAS)

 75th habitat percentiles

 25th habitat percentiles

SA LAU

A MDO J LAU

CYP

NMI

NIN

EXPLANATION

Figure 4. Normal range of weighted usable-habitat area during July, August, and 

September for each fish species or life stage. (Shaded boxes represent 25th to 75th habitat 

percentiles calculated from a time-series association of the weighted usable-habitat area 

curves to the historic streamflow record at Millville, West Virginia).
16 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Times-Series Scenarios for Historic Droughts 

and Normal Summers

Time-series plots of the habitat availability were 

calculated from the discharge-habitat relations and applied 

to historic daily flows for the streamflow-gaging station at 

Millville following Krstolic and Ramey (2012) to provide 

a picture of habitat availability during a selected set of 

summer flow periods. Drought years were examined as 

examples of times when habitat was potentially limited 

so that species and habitats affected by drought could 

be identified. This assessment sought to describe the 

flow conditions that were potentially stressful for fish 

or recreation habitat availability and to contrast those 

conditions with normal or optimal habitat availability. The 

results and descriptions are interpretations of the WUA 

curves, the time-series plots, and the historic flow record. 

The scenarios presented in this report are for informational 

purposes only, and any selection of flow thresholds and 

desired habitat availability during drought or low-flow 

periods would be at the discretion of resource managers, 

planners, and policy makers in the Shenandoah Valley.

For each species, life stage, or canoeing, daily and 

monthly habitat was examined for drought years (1963, 

1977, 1999, and 2002) and one normal flow year (2012). 

The normal range (25th to 75th percentile range) of flows 

for the streamflow-gaging station at Millville for JAS 

(from 1930 to 2002) is 641 to 1,410 ft3

/s (table 2). During 

the selected drought years examined for this study 

(1963, 1977, 1999, and 2002), the monthly mean flows 

ranged from 392 ft3

/s to 595 ft3/s during June, July, August, 

and September which is below the normal range of flows 

for JAS. During 2012, monthly mean flows ranged from 

776 ft3

/s to 1,199 ft3/s, which is within the normal range 

of flows for JAS (table 2). For management purposes it 

may be useful to evaluate habitat availability on a daily or 

monthly basis so information is presented in both formats. 

Daily Summaries

During historic droughts, daily changes in habitat in 

response to changes in streamflow demonstrated that adult 

smallmouth bass and sub-adult smallmouth bass habitat 

was frequently below normal. When streamflows were 

close to the 10th percentile JAS flow (less than 500 ft3

/s 

or 323 Mgal/d) during 2002 (fig. 5), 1999 (fig. 6), 1977, 

and 1963, adult and sub-adult smallmouth bass available 

habitat was below normal for the majority of days during 

at least 2 months of the summer. Streamflows were less 

than the 7Q10 flow (357 ft3

/s or 231 Mgal/day) for 15 days 

during summer months of 1999. These extreme low-flow 

conditions also resulted in habitat decreases below the 

25th percentile of available habitat for margined madtom, 

river chub, and sub-adult redbreast sunfish. Except for the 

decreases in available habitat described above, available 

fish habitat in the Shenandoah River near Lockes Mill 

during historic droughts was within a normal range for a 

given species or life stage. Flows that limit most species 

habitat ranged from 300 ft3

/s to 500 ft3/s, with particular 

strain to larger game species like adult smallmouth bass. In 

general, if flows were greater than the 10th percentile JAS 

flow, available habitat for all species studied was at least 

suitable. 

As was the case on the South Fork Shenandoah River 

during historic droughts, adequate flows for suitable canoeing rarely occurred on the main stem Shenandoah River. 

On the basis of the habitat modeling results in the Lockes 

Mill section of the Shenandoah River, streamflow must be 

at least 500 ft3

/s to ensure average depths of at least 1 ft 

for paddling. Flows equal to or less than the 10th percentile 

flow for JAS do not provide adequate depth for passage 

through riffle habitats. For the time-series scenarios for 

2002 and 1999, conditions for canoeing were outside the 

normal range (figs. 5B and 6B) for the majority of days 

during JAS. Flows during 2012 were adequate to support 

canoeing at the end of July, most of August, and some of 

September (fig. 7B) because streamflows were greater than 

the 25th percentile JAS flow (641 ft3

/s) during that time. 

Although recreation is certainly a consideration for waterresources management, when flows are only slightly higher 

than the 10th percentile flow for JAS and decreasing as they 

were during the drought years examined, canoe paddling is 

unlikely to be successful.
Habitat Time-Series Scenario Analysis for Low-Flow Periods 17

Discharge, in cubic Weighted usable-habitat area, in square feet per 1,000 feet feet per second

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile50th habitat percentile25th habitat percentile

Sub-adult smallmouth bass

200,000150,000100,000

50,000

Juvenile redbreast sunfish 

A

B

150,000100,000

50,000

Adult smallmouth bass

100,000

80,00060,00040,00020,000

Margined madtom 150,000

100,000

50,000

Sub-adult redbreast sunfish

120,000100,000

80,000

Cyprinella spp. 150,000

100,000

50,000

River chub

200,000150,000100,000

50,000

Canoe

400,000300,000200,000100,000

Discharge for the Millville streamflow-gaging station, 2002 5,000

1,000

100

5,0001,000

100

Discharge for the Millville streamflow-gaging station, 2002

June July August

2002

September June July August

2002

September

Figure 5. Habitat time series for the Lockes Mill study reach (0163633459) during 2002. (

A) adult and sub-adult smallmouth bass, sub-adult redbreast sunfish, and river 

chub weighted usable-habitat area and daily mean discharge for the river at Millville (01636500); (

B) juvenile redbreast sunfish, margined madtom, Cyprinella spp., and 

canoeing weighted usable-habitat area, and daily mean discharge for the river at Millville (01636500).
18 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Discharge, in cubic Weighted usable-habitat area, in square feet per 1,000 feet feet per second

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile50th habitat percentile25th habitat percentile

Sub-adult smallmouth bass

200,000150,000100,000

50,000

Juvenile redbreast sunfish 

A

B

150,000100,000

50,000

Adult smallmouth bass

100,000

80,00060,00040,00020,000

Margined madtom 150,000

100,000

50,000

Sub-adult redbreast sunfish

120,000100,000

80,000

Cyprinella spp. 150,000

100,000

50,000

River Chub

200,000150,000100,000

20,000

Canoe

400,000300,000200,000100,000

Discharge for the Millville streamflow-gaging station, 1999 5,000

1,000

100

5,0001,000

100

Discharge for the Millville streamflow-gaging station, 1999

June July August

1999

June July August

1999

Figure 6. Habitat time series for the Lockes Mill study reach (0163633459) during 1999. (

A) adult and sub-adult smallmouth bass, sub-adult redbreast sunfish, and river 

chub weighted usable-habitat area and daily mean discharge for the river at Millville (01636500); (

B) juvenile redbreast sunfish, margined madtom, Cyprinella spp., and 

canoeing weighted usable-habitat area, and daily mean discharge for the river at Millville (01636500).
Habitat Time-Series Scenario Analysis for Low-Flow Periods 19

Discharge, in cubic Weighted usable-habitat area, in square feet per 1,000 feet feet per second

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile50th habitat percentile25th habitat percentile

Sub-adult smallmouth bass

200,000150,000100,000

50,000

Juvenile redbreast sunfish 

A

B

150,000100,000

50,000

Adult smallmouth bass

100,000

80,00060,00040,00020,000

Margined madtom 150,000

100,000

50,000

Sub-adult redbreast sunfish

120,000100,000

80,000

Cyprinella spp. 150,000

100,000

50,000

River chub

200,000150,000100,000

50,000

Canoe

400,000300,000200,000100,000

Discharge for the Millville streamflow-gaging station, 2012 5,000

1,000

100

5,0001,000

100

Discharge for the Millville streamflow-gaging station, 2012

June July August

2012

September June July August

2012

September

Figure 7. Habitat time series for the Lockes Mill study reach (0163633459) during 2012. (

A) adult and sub-adult smallmouth bass, sub-adult redbreast sunfish, and river 

chub weighted usable-habitat area and daily mean discharge for the river at Millville (01636500); (

B) juvenile redbreast sunfish, margined madtom, Cyprinella spp., and 

canoeing weighted usable-habitat area, and daily mean discharge for the river at Millville (01636500).
20 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Monthly Summaries

Bar charts summarizing the number of days each month 

that habitat was within the normal range for each species 

or life stage and canoeing (table 6) were constructed from 

time-series daily data for JAS 1963, 1999, 2002, and 2012 

(fig. 8). For smaller species, redbreast sunfish, Cyprinella spp., 

margined madtom, and river chub, habitat conditions were 

within a normal range almost all months during the selected 

drought years (fig. 8). Adult and sub-adult smallmouth bass 

and canoeing habitat was lower than the 25th percentile 

of habitat more than half the days of each month during 

1963, 1999, and 2002. The habitat conditions for fish and 

canoeing were possibly as close to ideal as possible in July 

and August 2012 because all species of fish were within the 

normal habitat range for 28–31 days and canoeing was within 

the normal range for 20–31 days.

During wet conditions in September 1999 and 2012, 

available fish habitat did not follow the same patterns as 

might be expected with increases in flow. For example, 

when the maximum flow for September 1999 was 9,650 ft3

/s 

(fig. 8), the number of days that habitat was within the normal 

range was six or less for all fish species. The decreased 

habitat availability with higher streamflows is related to 

storm flow. This demonstrates a modeling limitation for the 

habitat-suitability criteria, because higher flows represent fast 

velocities or depths outside those values studied during the 

development of the fish HSC. For species that prefer shallow 

habitats, high flows can intermittently create instream habitat 

conditions outside the optimal or suitable ranges for depth or 

velocity. Canoe mean monthly suitability responded to flow 

changes as would be expected, increasing with more flow and 

decreasing with less flow. 

These monthly count summary statistics could be 

developed on an on-going basis and integrated with the DEQ 

water supply planning initiative by applying the habitatdischarge relation to daily values of streamflow from USGS 

streamflow-gaging stations throughout the Shenandoah Basin. 

The available daily habitat can be compared with the normal 

habitat range (table 6) determined in this investigation and 

counted if the criteria are met. The monthly count summary 

statistics should also be considered in the context of the 

maximum and mean monthly flow for each month. The reader 

is encouraged to be mindful of the upper limits indicated by 

the HSC so that incorrect assumptions are avoided.

Table 6. Normal range of weighted usable-habitat area in square feet per 1,000 feet of stream for July, August, and September for 

each species and canoeing for the Shenandoah River.

Habitat 

percentile

Fish species weighted usable-habitat area

Sub-adult 

small mouth 

bass

Adult small 

mouth bass

Juvenile 

redbreast 

sunfish

Sub-adult 

readbreast 

sunfish

Cyprinella

spp.

Margined 

madtom River chub Canoeing

75 168,915 72,538 93,909 114,639 135,852 134,562 173,092 338,045

50 157,512 68,347 65,160 109,924 121,187 122,978 164,383 288,040

25 131,256 58,777 34,970 98,770 85,856 94,944 132,931 236,207
Habitat Time-Series Scenario Analysis for Low-Flow Periods 21

1963 1999 2002 2012

July Aug. Sept. July Aug. Sept. July Aug. Sept. July Aug. Sept.

Number of days within

normal habitat range

Maximum discharge,

in cubic feet per second

35

30

25

20

15

10

5

0

10,000

8,000

6,000

4,000

2,000

0

Sub-adult smallmouth bass

Adult smallmouth bass

Juvenile redbreast sunfish

Sub-adult redbreast sunfish

Spotfin or satinfin shiner

Margined madtom

River chub

Recreational habitat

EXPLANATION

Figure 8. Number of days per month when habitat for fish or canoeing was within the normal range 

during 1963, 1999, 2002, and 2012.

Increased Water-Use Scenario Results

Time-series analyses were used to investigate changes 

in habitat availability with increased water use up to the 

2040 amounts projected by local water supply plans (Central 

Shenandoah Planning District Commission, 2011; Northern 

Shenandoah Valley Regional Commission, 2011). On the 

basis of the estimates for water use and population growth, 

cumulative water-withdrawal increases of 10, 20, and almost 

50 percent (48.6 percent) were applied to the Millville 

streamflow record. These percentage increases in water 

withdrawals equate to a maximum reduction in streamflow of 

26.7 ft3

/s or 17.3 Mgal/d more than the present withdrawals 

when the 2040 estimated water-withdrawal totals for the 

basin are considered. As with the time-series analysis, years 

with extreme drought, moderate drought, and normal recent 

conditions were examined to determine potential effects 

on available habitat. Scenarios were run for both game and 

non-game fish ecological habitat and canoeing recreational 

habitat availability with increased water withdrawals. 

While scenarios were run for each species that was 

modeled, only the species with somewhat obvious declines 

in habitat availability with increased withdrawals are 

discussed in this section. Adult and sub-adult smallmouth 

bass frequently had habitat availability outside the normal 

range for habitat conditions during drought years such as 

2002, yet 10- or 20-percent increases in withdrawals did not 

contribute to a large reduction in usable habitat (fig. 9A, B). 

When withdrawals were increased by 50 percent and habitat 

conditions were outside the normal range, there was an 

additional decrease in usable habitat (fig. 9A). During 2002 

drought scenarios, reduced habitat availability for sub-adult 

redbreast sunfish or river chub was only slightly evident with 

50-percent increased withdrawal scenarios (fig. 9C, D). This 

result is not surprising because the habitat availability primarily is based on suitability criteria that assess changes in depth 

or velocity as primary habitat indicators. For a river as large as 

the Shenandoah River, a reduction of 17.3 Mgal/d equates to a 

decrease in depth of less than 0.02 ft. For a recent normal year 

like 2012, increased water-use scenarios did not affect habitat 

availability for fish such as adult and sub-adult smallmouth 

bass, sub-adult redbreast sunfish, or river chub (fig. 10). 

For recreational habitat represented by canoeing, 

drought conditions that were already much lower than the 

normal range for canoeing were decreased with increases in 

withdrawals. For the 2002 drought, the increased withdrawals 

contributed to a constant decrease as habitat continued to drop 

lower than normal (fig. 11A). In contrast, canoeing habitat 
22 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

availability was within the normal range for most of 2012, 

and any increased water-withdrawal scenario applied to that 

time series of habitat showed almost no affect (fig. 11B).

The increased water-withdrawal scenarios confirm 

that habitat availability will be reduced with increased 

water withdrawals. Although short-term investigations in 

the Shenandoah River Basin have not confirmed whether 

habitat and flow alteration could affect fish species diversity 

or abundance, investigations in other basins have shown 

reductions in abundance, demographic parameters, and 

species diversity with respect to decreases in flow magnitude 

of base flow, mean discharge, or total discharge (Poff and 

Zimmerman, 2010). Most of the studies summarized in Poff 

and Zimmerman (2010) represented large alterations and 

lacked data for moderate ranges of flow alteration, so more 

work is needed to ascertain whether there is a threshold 

response with lower levels of alteration. One study quantified 

the response of fluvial fish to environmental or anthropogenic variables (Armstrong and others, 2011) and found that 

a one-unit (1 percent) alteration in the August median flow 

resulted in a 0.9-percent decrease in relative abundance of 

fish (in counts per hour). The 50-percent water-withdrawal 

increase scenario could result in as much as a 3-percent 

reduction in the median JAS flow statistic if water returns 

were minimal. If Armstrong and others (2011) calculations 

were applicable to the Shenandoah River, the relative 

abundance of fish could be reduced by 2.7 percent. 

These scenarios illustrate the importance of the timing 

of water withdrawals for maintaining habitat and sustaining 

flows during low-flow conditions. For both ecological fish 

habitat and recreational canoeing habitat, the antecedent 

conditions (habitat within normal range of habitat or 

below normal) appear to govern whether additional water 

withdrawals will affect habitat availability. The increased 

water-withdrawal scenarios contributed to greater reductions 

in habitat if streamflow was already below normal. Potential 

management strategies toward maintaining flows and habitat 

in the normal range could include withdrawing water to 

off-stream storage prior to low-flow months or preferentially 

withdrawing during storms in the summer. Implementing 

water-conservation practices during drought and repairing 

water delivery system leaks to improve efficiency, thus 

reducing water withdrawals, are both strategies that would 

proactively work toward maintaining the flow regime and 

available habitat. As the population and water demands 

increase, many of the ecological or recreational stresses may 

be lessened by managing the timing of water withdrawals 

and working to keep the projected withdrawals as low as 

possible. 
Habitat Time-Series Scenario Analysis for Low-Flow Periods 23

Weighted usable-habitat area, in square feet per 1,000 feet

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile

50th habitat percentile

25th habitat percentile

Habitat, no increases

10 percent increased withdrawals

20 percent increased withdrawals

50 percent increased withdrawals

A. Adult smallmouth bass

5,000

8,000

7,000

6,000

4,000

B. Sub-adult smallmouth bass

150,000

200,000

100,000

50,000

C. Sub-adult redbreast sunfish

120,000

110,000

100,000

90,000

D. River chub

100,000

200,000

150,000

June July August

2002

September

Figure 9. Habitat time-series increased water-withdrawal scenarios for the Shenandoah River at Millville, 

West Virginia, during 2002. (A) adult smallmouth bass, (B) sub-adult smallmouth bass, (C) sub-adult redbreast 

sunfish, and (D) river chub weighted usable-habitat area with 10-, 20-, and 50-percent increase in water use.
24 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia Weighted usable-habitat area, in square feet per 1,000 feet

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile

50th habitat percentile

25th habitat percentile

Habitat, no increases

10 percent increased withdrawals

20 percent increased withdrawals

50 percent increased withdrawals

5,000

8,000

7,000

6,000

4,000

150,000

200,000

100,000

50,000

120,000

110,000

100,000

90,000

100,000

200,000

150,000

June July August

2012

September

A. Adult smallmouth bass

B. Sub-adult smallmouth bass

C. Sub-adult redbreast sunfish

D. River chub

Figure 10. Habitat time-series increased water-withdrawal scenarios for the Shenandoah River at 

Millville, West Virginia, during 2012. (A) adult smallmouth bass, (B) sub-adult smallmouth bass, (C) sub-adult 

redbreast sunfish, and (D) river chub weighted usable-habitat area with 10-, 20-, and 50-percent increase in 

water use.
Summary and Conclusions 25

A. Canoeing habitat scenarios for 2002

350,000

300,000

250,000

200,000

150,000

100,000

350,000

300,000

250,000

200,000

150,000

100,000

Weighted usable-habitat area, in square feet per 1,000 feet

EXPLANATION

Normal range of habitat for

July, August, and September

75th habitat percentile

50th habitat percentile

25th habitat percentile

Habitat, no increases

10 percent increased withdrawals

20 percent increased withdrawals

50 percent increased withdrawals

B. Canoeing habitat scenarios for 2012

June July August September

Figure 11. Canoeing recreational habitat time-series increased water-withdrawal scenarios, main stem 

Shenandoah River, based on (A) 2002 flow data, and (B) 2012 flow data.

Summary and Conclusions

This report describes updates to methods, documents 

modeling results, and discusses implications from an updated 

habitat-flow model for the main stem Shenandoah River in 

Virginia. The 2010 population within the Shenandoah River 

watershed and adjacent areas that used water from the river 

represented a 29-percent increase from 1995 records, and the 

2040 predicted population represents a 76-percent increase from 

1995 records. Given that water withdrawals are also predicted 

to increase with population, there has been interest in assessing 

how increases in withdrawals may affect habitat and recreation 

in the Shenandoah River. Water withdrawals for 2005 were 

compared with projected water demands for 2040 from the 

recently completed water supply planning initiative documents 

written by the two planning district commissions within the 

Shenandoah River Basin. Most localities projected demands 

that approach their total presently permitted surface-water and 

groundwater withdrawal values by 2040, and a few are projected to exceed them. The projected surface-water withdrawals 

vary by watershed, the North Fork Shenandoah River shows 

a 55.9-percent increase, the South Fork Shenandoah River 

shows a 46.5-percent increase, and the main stem Shenandoah 

River shows a 52-percent increase. Cumulatively, the 2040 

surface-water withdrawal values represent a 51-percent increase 

from 2005 surface-water withdrawals. This equates to adjusted 

daily mean flows for the Shenandoah River at Millville, West 

Virginia, that are 17.3 Mgal/d (26.7 ft3

/s) less than they were in 

2005. 

 Seasonal flow statistics for the Shenandoah River at 

Millville for the low-flow summer period of July, August, and 

September (JAS) were of interest for understanding effects on 

habitat with increases in water withdrawals during low-flow 

periods. Long-term record flow statistics for streamflow-gaging 

stations in the Shenandoah River Basin show the flow at 

Strasburg is approximately 35 percent of the flow at Front 

Royal, and the combined flow of Strasburg plus Front Royal 

is approximately 85 percent of the flow at Millville. Flows 

equal to or less than the 10th percentile for JAS (482 ft3

/s or 

312 Mgal/d) were evaluated as drought indicators for this study. 

New water-withdrawal projections were complemented 

by additional low-flow water-surface level (WSL) profiles and 

discharge data to enhance the habitat simulation model. It was 

necessary to verify and install new elevation control points 

along the Lockes Mill study reach, with updated elevations 

adjusted to the previous study values. New discharge and WSL 

profile data were collected and combined with the two highflow datasets previously published in an early model from 1998. 

After the data were combined, the model was re-calibrated, and 

a new habitat-discharge relation was developed for ecological 

habitat for fish and recreational habitat for canoeing. 
26 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

The habitat-discharge relation weighted usable-habitat 

area (WUA) curves have similar patterns for species of 

similar size or life stage as opposed to patterns grouping game 

or grouping non-game species together. For example, the 

maximum WUA for adult smallmouth bass, sub-adult smallmouth bass, and river chub all appear to be associated with the 

median flow for JAS (900 ft3

/s). Smaller fish, such as Cyprinella spp., margined madtom, and juvenile redbreast sunfish 

maximum WUA were associated with the 10th percentile flows 

and lower. Canoeing WUA is maximized when streamflows 

are above the 75th percentile, near 2,000 ft3

/s. 

To place the habitat-discharge relation in context, time 

series of habitat were used to calculate habitat-duration 

statistics to define normal habitat availability for the summer 

months. Habitat-duration statistics describe the availability of 

usable habitat for a given species for a range of streamflow, 

given the known physical conditions of the reach. The range 

of available habitat for adult smallmouth bass and sub-adult 

redbreast sunfish at the Lockes Mill study reach is narrow 

compared to other fish species, predominantly because these 

fish favor deeper pool habitats that are not as common as run 

habitats within the study reach. 

Time-series plots of the habitat availability and daily 

streamflow during drought years illustrate how ecological or 

recreational habitat conditions may be affected by drought. 

For each fish species, life stage, and for canoeing, daily habitat 

availability was examined for drought years (1963, 1977, 

1999, and 2002) and one normal flow year (2012). During historic droughts, streamflows were less than the 10th percentile 

flow (500 ft3

/s or 323 Mgal/d), and adult smallmouth bass and 

sub-adult smallmouth bass habitats were below normal for 

the majority of days during at least 2 months of the summer. 

When streamflows were less than the 7Q10 flow (357 ft3

/s 

or 231 Mgal/d), margined madtom, river chub, and sub-adult 

redbreast sunfish habitats were below normal as well. Streamflows that limit most fish species habitat availability range 

from 300 to 500 ft3

/s. Although recreation is a consideration 

for water-resources management, when flows are only slightly 

higher than the 10th percentile flow for JAS, canoe paddling 

is unlikely to be successful because flows equal to or less 

than the 10th percentile do not provide adequate depth for 

passage through riffles. Flows during 2012 were adequate to 

support canoeing because streamflows were greater than the 

25th percentile JAS flow (641 ft3

/s) during that time.

For smaller species, redbreast sunfish, Cyprinella spp., 

margined madtom, and river chub, habitat conditions were 

within a normal range almost all days of each summer month 

during selected drought years 1963, 1999, and 2002. Whereas, 

adult and sub-adult smallmouth bass and canoeing habitat 

was lower than the normal range of habitat the majority of 

days during summer months of 1963, 1999, and 2002. Ideal 

habitat conditions for fish and canoeing were represented by 

model simulations for July and August 2012. However, in 

September 1999 when the maximum flow for the month was 

9,650 ft3

/s, habitat was only within the normal range six days 

or less for all fish. Storm flows occurred with faster velocities 

or deeper depths than those studied during the development of 

the fish habitat-suitability criteria, thus demonstrating a modeling limitation represented by flows outside the study range. 

Time-series analyses were used to investigate changes 

in habitat availability with increased water use of 10, 20, 

and almost 50 percent (48.6 percent) up to the 2040 amounts 

projected by local water supply plans of the two planning 

district commissions within the Shenandoah River Basin. 

These percentage increases in water withdrawals equate to 

17.3 Mgal/d more than the present withdrawals when the 2040 

estimated water-withdrawal totals for the basin are considered. 

Increased water-withdrawal scenarios were run for both 

game and non-game fish ecological-habitat availability and 

canoeing recreational-habitat availability. Adult and sub-adult 

smallmouth bass habitat availability frequently was outside 

the normal range for habitat conditions during drought years, 

yet only when withdrawals were increased by 50 percent 

during drought years, were large reductions in habitat evident. 

For small species such as sub-adult redbreast sunfish or river 

chub that were usually within the normal range for habitat 

conditions, 2002 drought scenarios plus 50-percent increased 

withdrawal scenarios resulted in only slightly reduced habitat 

availability. For a recent normal year, like 2012, the increased 

water-use scenarios did not affect habitat availability for fish.

Recreational habitat represented by canoeing decreased 

with increases in withdrawals. For the 2002 drought, the 

increased withdrawals contributed to a constant decrease 

as habitat continued to drop lower than normal. In contrast, 

canoeing habitat availability was within the normal range for 

most of 2012, and any increased water-withdrawal scenario 

applied to that time series of habitat showed almost no affect.

The increased water-withdrawal scenarios confirm that 

habitat availability will be reduced during drought years with 

increased water withdrawals. While short-term investigations 

in the Shenandoah River Basin have not confirmed whether 

habitat and flow alteration could affect fish species diversity 

or abundance, investigations in other basins increasingly 

support this assertion. A study of fluvial fish assemblages in 

Massachusetts demonstrated decreases in relative abundance 

of fish in response to anthropogenic alteration to August 

median flows. In applying similar methods to those used in 

Massachusetts to the Shenandoah River, a 50-percent waterwithdrawal increase could result in a 2.7 percent reduction in 

relative abundance of fish.

These increased water-withdrawal scenarios in this 

investigation illustrate the importance of the timing of water 

withdrawals for maintaining habitat and sustaining flows 

during low-flow conditions. For all simulations of habitat, the 

antecedent conditions (habitat within normal range of habitat 

or below normal) appear to govern whether additional water 

withdrawals will affect habitat availability. Withdrawing water 

to off-stream storage prior to low-flow months, preferentially 

withdrawing water during storms in the summer, and 

implementing water-conservation practices during droughts 

are management strategies which may help to maintain flows 

and habitat in the normal range. As the population and water 
References Cited 27

demand increase, many of the ecological or recreational 

stresses may be lessened by managing the timing of water 

withdrawals and implementing proactive conservation strategies to keep the projected withdrawals as low as possible.

Acknowledgments

The author thanks the cooperators, Clarke and Warren 

Counties, for support of this scientific work. We also thank 

the Northern Shenandoah Valley Regional Commission and 

Central Shenandoah Planning District for their continued 

support and interest in this work. The continued interest 

and feedback received from policy makers, planners, utility 

managers, State agency staff, and private citizens enhanced the 

study process.

Appreciation is extended to local landowners for allowing access to the river from their properties. Watermelon 

Park allowed access to the river along the campground that 

facilitated re-visiting historic monitoring locations. 

Vital field assistance was provided by the lead technician 

for the project, Roger Moberg (USGS, Richmond, Va.) and 

other experienced technicians and hydrologists: Brent Banks, 

Carlos Rodriguez, James Duda, Karl Dydak, Geoff Austin, 

Russ Lotspeich, Don Hayes, and Gary Speiran (USGS, 

Richmond, Va.). Additional field assistance was provided by 

Jon Campbell (USGS, Reston, Va.). The author also thanks 

the peer reviewers who increased the effectiveness of this 

document.

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Survey Scientific Investigations Report 2011–5143, 

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http://pubs.usgs.gov/sir/2011/5143/.)

Central Shenandoah Planning District Commission, 2011, 

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Shenandoah Planning District Commission, accessed 

January 14, 2014, at http://www.cspdc.org/programs/

environment/programs_environment.htm.

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water in the United States in 2005: U.S. Geological Survey 

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ecological and recreational characteristics during 

low-flow periods: U.S. Geological Survey Scientific 

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Ramey, R.C., 2009, Habitat suitability criteria for fishes of 

the South Fork of the Shenandoah River and an investigation into observer effects associated with two techniques 

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Appendix 29

Appendix. RHABSIM model calibration data from the hydraulic data collected at the Lockes Mill study reach (0163633459), main stem 

Shenandoah River, Virginia.

[Calculated discharge is an RHABSIM calculated value. SZF, stage zero flow; WSL, water-surface level; slope, average water-surface slope for all discharges 

measured; verticals, number of measurement points along the transect; ND, no data collected]

Transect Observed 

WSL1

 (ft)

Simulated 

WSL (ft)

Reach 

calibration 

discharge1

(ft3/s)

Modelcalculated 

discharge 

(ft3/s)

Verticals

Transect 

weighting 

factor

Slope1

(ratio)

SZF1

(ft)

Average 

Depth

Wetted 

Width

Velocity 

mean

1 372.2 372.09 3,010 ND 74 0.31 0.000 368.8 2.21 526.51 ND2

371.48 371.63 1,900 ND 1.67 477.55 ND2

371.01 371.07 970 1,106.7 1.37 427.77 1.57

370.85 370.75 620 ND 1.29 402.22 ND2

2 373.12 373.06 3,010 ND 67 0.06 0.000 369.4 2.92 490.88 ND2

372.54 372.61 1,900 ND 2.37 485.66 ND2

371.95 372.04 970 945.9 1.81 480.35 1.06

371.82 371.72 620 ND 1.68 479.15 ND2

5b 373.85 373.86 3,010 ND 43 0.4 0.001 371 1.89 440.46 ND2

nd nd ND nd nd ND2

373.47 373.44 970 1,334.5 1.55 430.39 1.66

373.28 373.3 620 ND 1.37 425.35 ND2

6 375.03 374.9 3,010 ND 45 0.01 0.001 371.3 2.79 384.07 ND2

374.2 374.44 1,900 2,018.4 2.07 366.98 2.35

373.89 373.86 970 ND 1.8 359.04 ND2

373.61 373.54 620 ND 1.54 356.17 ND2

7 375.86 375.81 3,010 ND 41 0.25 0.001 371.3 3.71 312.91 ND2

375.2 375.24 1,900 2,037.4 3.08 309.46 1.89

374.44 374.53 970 ND 2.38 303.6 ND2

374.2 374.13 620 ND 2.15 301.22 ND2

8 377.12 377.04 3,010 ND 78 0.01 0.000 372 3.41 503.65 ND2

376.43 376.52 1,900 ND 2.8 490.11 ND2

375.8 375.87 970 1,005.8 2.24 477.13 1.19

375.56 375.48 620 ND 2.03 471.28 ND2

10 378.38 378.32 3,010 ND 53 0.33 0.001 374.8 2.8 525.68 ND2

377.88 377.89 2,330 2,305.2 2.31 522.94 1.7

377.77 377.84 1,900 ND 2.21 521.78 ND2

377.15 377.25 970 ND 1.61 515.25 ND2

377.02 376.92 620 ND 1.49 513.9 ND2

12 380.02 379.95 3,010 ND 62 1 0.000 377.1 3.27 519.31 ND2

379.65 379.6 2,150 2,148.4 2.92 515.76 1.33

379.48 379.56 1,900 ND 2.77 512.18 ND2

379.03 379.09 970 ND 2.38 501.61 ND2

378.9 378.83 620 ND 2.26 498.55 ND2

13 380.6 380.42 3,010 ND 75 0.06 0.000 376 3.79 525.07 ND2

379.88 379.86 2,390 2,406.2 3.15 512.88 1.41

379.45 379.79 1,900 ND 2.75 507.61 ND2

378.95 379.03 970 ND 2.35 489.17 ND2

378.83 378.61 620 ND 2.24 486.9 ND2
30 Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia

Appendix. RHABSIM model calibration data from the hydraulic data collected at the Lockes Mill study reach (0163633459), main stem 

Shenandoah River, Virginia.—Continued

[Calculated discharge is an RHABSIM calculated value. SZF, stage zero flow; WSL, water-surface level; slope, average water-surface slope for all discharges 

measured; verticals, number of measurement points along the transect; ND, no data collected]

Transect Observed 

WSL1

 (ft)

Simulated 

WSL (ft)

Reach 

calibration 

discharge1

(ft3/s)

Modelcalculated 

discharge 

(ft3/s)

Verticals

Transect 

weighting 

factor

Slope1

(ratio)

SZF1

(ft)

Average 

Depth

Wetted 

Width

Velocity 

mean

14 380.72 380.52 3,010 ND 47 1 0.001 375.6 4.29 569.01 ND2

379.76 379.95 2,240 2,260.9 3.38 562.46 1.2

379.45 379.88 1,900 ND 3.09 558.24 ND2

379.06 379.09 970 ND 2.73 552.72 ND2

378.89 378.65 620 ND 2.57 549.43 ND2

14b3 380.25 380.15 3,010 ND 26 0 0.000 375.6 2.3 597.06 ND2

379.6 379.75 1,900 ND 1.78 559.48 ND2

379.21 379.25 970 ND 1.49 524.6 ND2

379.04 378.95 620 ND 1.37 509.95 ND2

15 380.42 380.33 3,010 ND 40 0.1 0.000 376.5 5.26 491.5 ND2

380.18 379.92 2,200 2,187.1 5.03 490.92 0.87

379.75 379.87 1,900 ND 4.62 489.3 ND2

379.24 379.3 970 ND 4.12 487.37 ND2

379.07 378.98 620 ND 3.95 486.7 ND2

16 380.7 380.61 3,010 3,007.9 50 0.1 0.000 376.5 5.76 401 1.16

380.03 380.16 1,900 ND 5.12 399.01 ND2

379.56 379.6 970 ND 4.67 397.61 ND2

379.36 379.28 620 ND 4.48 396.39 ND2

18 380.71 380.6 3,010 ND 52 1 0.000 376.5 4.92 403.1 ND2

379.96 380.11 1,900 1,860.6 4.2 400.84 0.95

379.45 379.5 970 ND 3.71 398.74 ND2

379.25 379.16 620 ND 3.52 397.93 ND2

1

Value calculated from field measurements.

2

No velocity dataset collected for this water-surface level.

3

No velocity datasets were collected for any discharges that were simulated, so the model could not calculate discharge. The transect was weighted 0, so it 

does not factor into the habitat calculations but remains as part of the study for reference, water-surface calibration, and because it is central to the elevation 

control network.
Approved for publication January 8, 2015

For further information about this publication contact:

Director

U.S. Geological Survey

Virginia Water Science Center

1730 East Parham Road

Richmond, VA 23228

http://va.water.usgs.gov/

Prepared by the Raleigh Publishing Service Center
Krstolic—Data Collection and Simulation of Ecological Habitat and Recreational Habitat in the Shenandoah River, Virginia—Scientific Investigations Report 2015–5005

ISSN 2328-031X (print) 

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155005