Cover:  Cibolo Creek downstream from Boerne, Tex., September 21, 2007.
Simulation of Streamflow and Estimation 

of Ground-Water Recharge in the Upper 

Cibolo Creek Watershed, South-Central 

Texas, 1992–2004 

By Darwin J. Ockerman

In cooperation with the U.S. Army Corps of Engineers, Fort Worth District; 

San Antonio River Authority; San Antonio Water System; and GuadalupeBlanco River Authority

Scientific Investigations Report 2007–5202

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Ockerman, D.J., 2007, Simulation of streamflow and estimation of ground-water recharge in the upper Cibolo Creek 

watershed, south-central Texas, 1992–2004: U.S. Geological Survey Scientific Investigations Report 2007–5202, 

34 p.
iii

Contents

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

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

Purpose and Scope .............................................................................................................................4

Description of Study Area ..................................................................................................................4

Simulation Approach ...........................................................................................................................4

Simulation of Streamflow and Estimation of Ground-Water Recharge ...............................................5

Data Collection and Compilation .......................................................................................................5

Model Development ............................................................................................................................9

Streamflow Calibration .....................................................................................................................12

Evapotranspiration and Interception Testing ................................................................................14

Simulated Streamflow, 1992–2004 ...................................................................................................14

Estimated Ground-Water Recharge, 1992–2004 ...........................................................................18

Simulated Streamflow and Estimated Ground-Water Recharge With Implementation 

of Flood-Control/Recharge-Enhancement Structures ...................................................18

Model Limitations and Applications ...............................................................................................20

Summary .......................................................................................................................................................20

References ...................................................................................................................................................21

Figures

1–2. Maps showing: 

1. Location of Cibolo Creek watershed and study area, south-central Texas ..............2

2. Location of Trinity aquifer outcrop, Edwards aquifer recharge zone (outcrop), 

and Edwards aquifer upper confining unit, upper Cibolo Creek watershed, 

south-central Texas ............................................................................................................3

3. Diagram showing hydrological Simulation Program—FORTRAN (HSPF) flowchart 

for (a) impervious and (b) pervious land segments ................................................................6

4–6. Maps showing: 

4. Land cover in the upper Cibolo Creek watershed, south-central Texas ...................7

5. Data-collection stations that provided data for Hydrological Simulation 

Program—FORTRAN model, upper Cibolo Creek watershed, south-central 

Texas ...................................................................................................................................10

6. Stream-reach network for the Hydrological Simulation Program—FORTRAN 

model, upper Cibolo Creek watershed, south-central Texas ....................................13

7–9. Graphs showing 

7. Measured and simulated daily streamflow at station 08183850 Cibolo Creek 

at Interstate Highway 10 above Boerne, Texas, 1997–2004 .......................................15

8. Measured and simulated daily streamflow at station 08183900 Cibolo Creek 

near Boerne, Texas, 1992–94 ..........................................................................................16

9. Measured and simulated daily streamflow at station 08185000 Cibolo Creek 

near Selma, Texas, 1997–2004 ........................................................................................17

10. Map showing locations of flood-control/recharge-enhancement structures and 

impoundment areas simulated with the Hydrological Simulation Program—

FORTRAN model, upper Cibolo Creek watershed, south-central Texas ..........................19
iv

Tables

1. Process-related model parameters for the Hydrologic Simulation Program—

FORTRAN model ...........................................................................................................................8

2. Basin-related model parameters for the Hydrologic Simulation Program—

FORTRAN model ...........................................................................................................................9

3. Land-cover categories and areas for the upper Cibolo Creek watershed, southcentral Texas ................................................................................................................................9

4. Data-collection stations that provided data for the Hydrologic Simulation 

Program—FORTRAN model, upper Cibolo Creek watershed, south-central Texas ......11

5. Streamflow calibration and testing results, Hydrological Simulation Program—

FORTRAN model, upper Cibolo Creek watershed, south-central Texas, 1992–2004 ......23

6. Simulated evapotranspiration, upper Cibolo Creek watershed, and measured 

evapotranspiration, Honey Creek watershed, south-central Texas, March–

December 2002 ...........................................................................................................................25

7. Selected annual PERLND and IMPLND process-related parameters for the 

Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas .............................................................................................26

8. Monthly values of lower-zone evapotranspiration (LZETP) parameter for the 

Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas .............................................................................................30

9. Measured and simulated average annual streamflow per unit area (runoff) at 

selected sites on Cibolo Creek, south-central Texas, 1992–2004 ......................................31

10. Estimated annual rainfall and ground-water recharge, upper Cibolo Creek 

watershed, south-central Texas, 1992–2004 .........................................................................31

11. Estimated average annual rainfall, diffuse recharge, stream-channel recharge, 

and total recharge by surficial unit, upper Cibolo Creek watershed, south-central 

Texas ............................................................................................................................................32

12. Specifications of flood-control/recharge-enhancement structures simulated with 

the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas .............................................................................................33

13. Simulation results for various scenarios of flood-control/recharge-enhancement 

structure implementation using the Hydrological Simulation Program—FORTRAN 

model, upper Cibolo Creek watershed, south-central Texas. ............................................34

Datum

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

A watershed model (Hydrological Simulation Program—

FORTRAN) was developed, calibrated, and tested by the U.S. 

Geological Survey, in cooperation with the U.S. Army Corps 

of Engineers, San Antonio River Authority, San Antonio 

Water System, and Guadalupe-Blanco River Authority, to 

simulate streamflow and estimate ground-water recharge in the 

upper Cibolo Creek watershed in south-central Texas. Rainfall, evapotranspiration, and streamflow data were collected 

during 1992–2004 for model calibrations and simulations. 

Estimates of average ground-water recharge during 1992–2004 

from simulation were 79,800 acre-feet (5.47 inches) per year 

or about 15 percent of rainfall. Most of the recharge (about 

74 percent) occurred as infiltration of streamflow in Cibolo 

Creek. The remaining recharge occurred as diffuse infiltration 

of rainfall through the soil and rock layers and karst features. 

Most recharge (about 77 percent) occurred in the Trinity 

aquifer outcrop. The remaining 23 percent occurred in the 

downstream part of the watershed that includes the Edwards 

aquifer recharge zone (outcrop). Streamflow and recharge in 

the study area are greatly influenced by large storms. Storms 

during June 1997, October 1998, and July 2002 accounted for 

about 11 percent of study-area rainfall, 61 percent of streamflow, and 16 percent of the total ground-water recharge during 

1992–2004. Annual streamflow and recharge also were highly 

variable. During 1999, a dry year with about 16 inches of rain 

and no measurable runoff at the watershed outlet, recharge 

in the watershed amounted to only 0.99 inch compared with 

13.43 inches during 1992, a relatively wet year with about 

54 inches of rainfall. Simulation of flood-control/rechargeenhancement structures showed that certain structures might 

reduce flood peaks and increase recharge. Simulation of individual structures on tributaries showed relatively little effect. 

Larger structures on the main stem of Cibolo Creek were more 

effective than structures on tributaries, both in terms of floodpeak reduction and recharge enhancement. One simulated 

scenario that incorporated two main-stem structures resulted 

in a 37-percent reduction of peak flow at the watershed outlet 

and increases in stream-channel recharge of 6.6 percent in the 

Trinity aquifer outcrop and 12.6 percent in the Edwards aquifer (recharge zone) outcrop.

Introduction

The U.S. Army Corps of Engineers (USACE), Fort Worth 

District, began a study in 2002 to address opportunities for 

ecosystem restoration (in part, through aquifer recharge), 

flood-damage reduction, and watershed management through 

Best Management Practices (BMP) in the upper Cibolo Creek 

watershed (study area) in south-central Texas (fig. 1). Phase 

1 of the study (the first of three phases) consists of establishing and documenting the existing hydrologic, engineering, 

economic, and environmental conditions for the study area 

(U.S. Army Corps of Engineers, 2001). As part of phase 1, 

the U.S. Geological Survey (USGS), in cooperation with the 

USACE, San Antonio River Authority (SARA), San Antonio 

Water System (SAWS), and Guadalupe-Blanco River Authority (GBRA), developed, calibrated, and tested a watershed 

model of the study area using the Hydrological Simulation 

Program—FORTRAN (HSPF) to simulate existing hydrologic conditions. Phase 2 of the study involves evaluation of 

possible alternatives to address ecosystem restoration, flooddamage reduction, and watershed management opportunities. 

As part of phase 2, the USGS used the HSPF model developed 

in phase 1 to evaluate the effects of flood-control/rechargeenhancement structures on streamflow and aquifer recharge in 

the watershed. Phase 3 of the study is a detailed engineering 

analysis by the project cooperators of possible alternatives 

evaluated in phase 2.

Part of the study area is in the Edwards aquifer recharge 

zone (outcrop) (fig. 2). The Edwards aquifer is one of the 

most productive carbonate aquifers in the Nation and is the 

major source of public water supply in south-central Texas. 

In addition, the Edwards aquifer supplies large quantities 

Simulation of Streamflow and Estimation 

of Ground-Water Recharge in the 

Upper Cibolo Creek Watershed, 

South-Central Texas, 1992–2004

By Darwin J. Ockerman
Figure 1. Location of Cibolo Creek watershed and study area, south-central Texas. 

BEXAR

COUNTY

WILSON COUNTY

KARNES COUNTY

BANDERA COUNTY

MEDINA COUNT

Y

KERR COUNTY

KENDALL COUNTY

COMAL COUNTY

GUADALUPE COUNTY

Cibolo Creek

Guadalupe River

Medina River

San Antonio River

San Antonio

Boerne

Selma

Kerrville

Bandera

New Braunfels

Seguin

Floresville

Sutherland Springs

Poth

Runge Kenedy

Karnes City

Ingram

Base modified from U.S. Geological Survey digital data 1:24,000 quadranglesUniversal Transverse Mercator projection,Datum NAD 83, Zone 14

Cibolo Creek watershed

T E X A S

EXPLAN

ATION

Upper Cibolo Creek watershed (study area)Boundary of Cibolo Creek watershed

LOCATION MAP

99°30'

99°0'

98°30'

98°0'

29°0'

29°30'

30°0'

0 10 20 MILES 5 15

   Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Figure 2. Location of Trinity aquifer outcrop, Edwards aquifer recharge zone (outcrop), and Edwards aquifer upper confining unit, upper Cibolo Creek watershed, south-central Texas. 

0 2 4 6 8 10 MILES

Trinity aquifer outcropEdwards aquifer recharge zone (outcrop)Edwards aquifer upper confining unitCibolo Creek watershed boundaryUpper Cibolo Creek subwatershed boundaryU.S. Geological Survey continuousstreamflow-gaging station and number Zx

EXPLANATION

08185000

98°50'

98°40'

98°30'

98°20'

29°40'

29°50'

Boerne

Selma

IH–10

IH–35

 COUNTY BEXAR Y NT U CO NA MEDI

KENDALL COUNTY

BANDERA COUNTY

KERR COUNTY

GUADALUPE COUNTY

COMAL COUNTY

BEXAR COUNTY

08183850

08185000

Base modified from U.S. Geological Survey digital data 1:24,000 quadrangles Universal Transverse Mercator projection,Datum NAD 83, Zone 14

GULF COASTAL PLAIN

EDWARDS PLATEAU

Edwards aquifer confined zone

Edwards aquifer recharge zone

Trinity aquifer Balcones escarpment

San

Antonio

San Antonio River

Cibolo

Creek

Medina River

Guadalupe River

Boerne Lake

Zx

Zx

Introduction 
of water for agriculture, industry, military installations, and 

recreational activities. The aquifer also is a source of water 

to major springs in the region. These springs supply water to 

downstream users and provide habitat for several threatened or 

endangered species.

The Trinity aquifer, adjacent to the Edwards aquifer to 

the north (fig. 2), also is an important ground-water resource 

in the study area. The Trinity aquifer outcrop (primarily Glen 

Rose Limestone) encompasses most of the study area, and 

many residents in the study area rely on Trinity aquifer wells 

for water supply. 

Purpose and Scope

The purpose of this report is to describe the development, 

calibration, testing, and use of the HSPF model to simulate 

streamflow and estimate ground-water recharge in the upper 

Cibolo Creek watershed. Calibration and testing of the model 

was based on data collected during 1992–2004. Streamflow 

and ground-water recharge estimates also are provided for 

1992–2004. The calibrated HSPF model also was used to 

simulate streamflow and recharge conditions for scenarios 

that included flood-control/recharge-enhancement structures. 

Results of these simulations are included in the report. This 

report documents the work of the USGS as a part of phases 1 

and 2 of the USACE study.

Description of Study Area

The study area (upper Cibolo Creek watershed) is north 

of San Antonio and includes parts of Bandera, Bexar, Comal, 

and Kendall Counties (fig. 1). The town of Boerne, in the 

northwestern part of the study area (fig. 2), is the largest 

population center with about 6,100 residents (City of Boerne, 

2003).

Cibolo Creek begins about 10 miles northwest of Boerne 

in southwestern Kendall County and flows southeastward for 

about 100 miles, forming the Bexar-Comal County and BexarGuadalupe County boundaries and crossing Wilson County, to 

its mouth on the San Antonio River in Karnes County (fig. 1). 

The entire drainage area of Cibolo Creek is 856 square miles. 

This study focuses on upper Cibolo Creek and its 274-squaremile drainage area upstream from USGS streamflow-gaging 

station 08185000 Cibolo Creek at Selma (fig. 2). 

The study area is described as having a subtropical, 

subhumid climate characterized by hot summers and mild, 

dry winters (Larkin and Bomar, 1983). Heaviest rainfall tends 

to occur in spring, early summer, and fall. Average annual 

rainfall (1961–90) in the study area is about 34 inches per year 

(Bomar, 1994). During the study period (1992–2004), average 

annual rainfall in the upper Cibolo Creek watershed was 37.43 

inches. The (San Antonio) average monthly low temperature 

ranges from 37.9 degrees Fahrenheit (°F) in January to 75.0 °F 

in July. Average monthly high temperature ranges from 60.8 

°F in January to 95.3 °F in August (Bomar, 1994). 

The study area includes parts of the southern margin 

of the Edwards Plateau (often referred to as the Texas Hill 

Country), the northern limit of the Gulf Coastal Plain, and the 

Balcones escarpment (a prominent topological feature of variable relief that separates the Edwards Plateau from the Gulf 

Coastal Plain) (fig. 2). Altitude in the study area ranges from 

about 728 to 2,000 feet above sea level. Land slopes generally 

are steeper in the upstream part of the study area than in the 

downstream part.

The study area includes outcrops of the Edwards and 

Trinity aquifers. Both aquifer outcrops are characterized by 

thin, rocky soils, and moderate to steep slopes. Compared 

to rocks of the Edwards Group and Georgetown Formation 

(Edwards aquifer), rocks of the Glen Rose Limestone (Trinity 

aquifer) generally have low porosity and little permeability 

(Clark, 2003). However, stream channels crossing both aquifer 

outcrops lose flow through infiltration into faults, sinkholes, 

and other karst features (Texas Board of Water Engineers, 

1960). Because of high infiltration rates to ground water in the 

stream channels, streamflow is relatively infrequent, especially 

toward the downstream end of the study area. More than 95 

percent of the time, streamflow is zero at the USGS gaging 

station Cibolo Creek at Selma (operated since 1946), flowing only during or after relatively heavy rainfall. Streamflow 

losses on the Edwards aquifer outcrop are believed to contribute directly to Edwards aquifer recharge (Puente, 1978). 

Streamflow losses to the Trinity aquifer outcrop also might 

contribute to Edwards aquifer recharge. It is believed that 

some of the Cibolo Creek streamflow infiltration to the Trinity 

aquifer passes laterally through underground channels into the 

Edwards aquifer (George, 1952).

Land cover in the study area is mostly undeveloped 

rangeland, consisting of open to dense stands of juniper, oak, 

and shrub (University of Texas, Bureau of Economic Geology, 

1995). Cultivated land generally is scarce because of poor or 

thin soils. Development (primarily residential) in the study 

area is increasing at a relatively rapid rate. During 1990–2000, 

the populations of Comal and Kendall Counties increased by 

50.5 and 62.7 percent, respectively, compared with an increase 

of 22.8 percent for the State of Texas during the same period 

(U.S. Census Bureau, 2003).

Boerne Lake, upstream from Boerne (fig. 2) and completed in 1978, supplies drinking water for Boerne and is 

the only reservoir in the study area. The Boerne municipal 

wastewater treatment facility discharges about 600,000 gallons 

per day to Cibolo Creek downstream from Boerne (Michael 

Veazy, Texas Commission on Environmental Quality, written 

commun., 2001). Flow from this continual discharge usually 

does not travel very far downstream, but infiltrates within the 

Cibolo Creek stream channel to the underlying aquifers. 

Simulation Approach

Because of the complex combination of watershed characteristics and hydrologic processes affecting streamflow and 

   Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
recharge in the study area, a comprehensive watershed model 

was needed to account for the dynamic water-balance conditions and to simulate streamflow and ground-water recharge. 

Also, a watershed model was necessary to estimate changes 

in streamflow and recharge that might occur because of future 

changes in watershed characteristics (for example, land-use 

changes and implementation of flood-control projects). The 

HSPF model was selected for modeling the study area because 

it is one of the most comprehensive watershed models available, can simulate a wide variety of stream and watershed 

conditions with reasonable accuracy, and enables flexibility 

in adjusting the model to simulate alternative conditions, or 

scenarios (Donigian and others, 1995). 

HSPF is a watershed model used to simulate hydrologic 

processes in complex agricultural, rural, and urban watersheds. 

HSPF uses information such as the time history of rainfall, 

temperature, evaporation, and parameters related to land 

cover, land-use practices, and soil characteristics to simulate 

hydrologic processes that occur in a watershed. The result of 

an HSPF simulation is a time history of the quantity of water 

transported over the land surface and downward through the 

various soil zones to the aquifers (Donigian and others, 1995).

In HSPF, a watershed is represented by a group of 

hydrologically similar areas that are referred to as hydrologic 

response units (HRUs) that drain to a network of reaches 

(RCHRESs) consisting of stream segments, lakes, or reservoirs. Each RCHRES is contained in and corresponds to a 

subwatershed. HRUs reflect areas of similar land use, surficial geology, and other factors deemed important to produce 

a similar hydrologic response to precipitation and potential 

(pan) evaporation. HRUs are divided into segments of pervious land (PERLND) and impervious land (IMPLND). Pervious land is represented conceptually within HSPF by a series 

of interconnected water-storage zones: an upper zone, a lower 

zone, and a ground-water zone. Impervious land is represented 

by simpler surface storage, evaporation, and runoff processes. 

Hydraulic functioning of stream reaches (open or closed channels, or completely mixed lakes) is simulated using storage 

routing (Donigian and others, 1995). 

The HSPF model simulates water movement through 

and across impervious and pervious land to the atmosphere, 

ground water, or surface runoff (fig. 3). The flow of water 

between the storage zones, stream, and atmosphere is affected 

by the process-related model parameters listed in table 1. 

The process-related model parameters for each land 

segment are adjusted to calibrate the model. The following 

process-related parameters can be automatically adjusted, by 

month, to account for seasonal variations: interception storage capacity (CEPSC), interflow index (INTFW), interflow 

recession coefficient (IRC), lower-zone evapotranspiration 

(LZETP), Manning’s n for assumed overland flow plane 

(NSUR), and upper-zone nominal storage (UZSN). For this 

study, monthly variation was implemented only for parameters 

CEPSC and LZETP. The HSPF user’s manual (Bicknell and 

others, 1997) provides a more complete description of each 

parameter.

The six basin-related model parameters listed in table 2 

define the areal extent of each land segment and characteristics of each stream or reservoir segment, including length and 

tables of surface area, volume, and streamflow (discharge), as 

a function of depth. These parameters represent the physical 

characteristics of each land or stream segment in a watershed 

and generally remain unchanged during calibration of the 

model.

Simulation of Streamflow and 

Estimation of Ground-Water Recharge

The major steps for simulating streamflow and estimating 

ground-water recharge for the study area included (1) data collection and compilation; (2) model development, calibration, 

and testing; and (3) simulation of streamflow and groundwater recharge conditions during 1992–2004 for existing 

(baseline) conditions and for conditions representing implementation of flood-control/recharge-enhancement structures.

Data Collection and Compilation

Input data for the HSPF model include spatial data (land 

use, geology, soils, topography, and drainage characteristics 

such as stream-segment length and cross-section data) and 

meteorologic time-series data (rainfall and pan evaporation). 

Time series of streamflow and evapotranspiration (ET) data 

were used for calibration and testing of the model. 

Satellite imagery data collected during 2001 were used by 

USACE to characterize land cover in the study area. The landcover map was refined by MWH Global, Inc., using groundtruthing data collected by the U.S. Department of Agriculture, 

Natural Resources Conservation Service (NRCS) and from 

aerial photographs. The resulting land-cover map (C. Coldren, 

MWH Global, Inc., written commun., 2003) (fig. 4) provided 

23 land-cover categories (table 3). 

The land-cover map (fig. 4), along with geology, soil, and 

topography information, was used to develop model HRUs. 

Study area geology (aquifer outcrop areas) (fig. 2) was based 

on Maclay (1995), Small and Hanson (1994), and Stein and 

Ozuna (1996). Soil associations were obtained from Bexar, 

Comal, and Kendall County soil surveys (U.S. Department of 

Agriculture, 1966; 1984; 1981). Watershed topography (slope) 

was obtained from USGS 7.5-minute digital elevation models 

(U.S. Geological Survey, 2003). The digital elevation models 

also were used to delineate subwatersheds (RCHRES) as part 

of the model development. 

Channel characteristics for each RCHRES (surface area, 

volume, and discharge as a function of depth) were determined for each of the model segments and entered in HSPF 

FTABLES (tables of stream-channel parameters). For gaged 

stream reaches, FTABLE parameters were based on discharge 

measurements made at USGS streamflow-gaging stations 

Simulation of Streamflow and Estimation of Ground-Water Recharge 
Figure 3. Hydrological Simulation Program—FORTRAN (HSPF) flowchart for (a) impervious and (b) pervious land segments (modified from Wicklein and Schiffer, 2002, fig. 3). 

Rainfall

potential ET

Interception

storage

Surface

detention

storage

Interflo

w

storage

Active ground-water

storage

Ground-water

flo

w

Shallo

w

subsurface

flo

w

Overland

flo

w

To

stream

Upper-zone

storage

Delayed

Directinfiltration

Infiltration

Lowerzone

storage

Actual

evaporation

Actual

ET

ETETETETET

Inactive ground water

To

stream

Potentialrunoff

RETSC*

CEPSC*

LZETP*

LZSN*

INFILT*

INFILD*

INFEXP*

INTFW*

AGWETP*

BASETP*

DEEPFR*

UZSN*

LSUR*

NSUR*

SLSUR*

LSUR*

NSUR*

SLSUR*

IRC*

KVARY*

AGWRC*

Surface detention

storage

Overland

flo

w

Surface retention

Rainf

storage

all

potential ET

(b) Pervious land segments

(a) Impervious land segments

Model inputStorageOutflo

w

Decision pointEvapotranspirationDesignates controllingHSPF parameter—Refer to table 1

EXPLAN

ATION

*

ET

 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Figure 4. Land cover in the upper Cibolo Creek watershed, south-central Texas (C. Coldren, MWH Global, Inc., written commun., 2003). 

EXPLANATION

Juniper woodlandJuniper–live oak woodland, very denseJuniper–live oak woodland, denseJuniper–live oak woodland, moderately denseJuniper–post oak woodlandJuniper–persimmon savannaMixed woodlandWater, water edge, and wetlands

Oak–juniper woodland, moderately denseOak–juniper woodland, slightly denseOak–persimmon woodland, denseOak–persimmon woodland, moderately denseOak savannaMesquite savannaShrublandPasture

Shortgrass prairieGrasslandBluestem prairieUrban lawnCroplandExposed ground and rocky slopesImpervious

0 2 4 6 8 10 MILES

98°50'

98°40'

98°30'

98°20'

29°40'

29°50'

Base modified from U.S. Geological Survey digital data 1:24,000 quadrangles Universal Transverse Mercator projection,Datum NAD 83, Zone 14

Simulation of Streamflow and Estimation of Ground-Water Recharge 
(fig. 5; table 4). FTABLE information for ungaged reaches 

were estimated using surveyed cross-section data collected by 

the USACE as part of a flood-mapping study (C. Lofton, U.S. 

Army Corps of Engineers, written commun., 2002). 

Meteorologic data compiled and used as input to the 

watershed model (National Climatic Data Center, 2006) 

comprised rainfall and pan evaporation (fig. 5; table 4). 

Table 4 provides information (station name and number, 

location, type of data, and period of record used) for each 

data-collection station identified in figure 5. Three National 

Weather Service (NWS) stations were the primary source of 

rainfall data. The NWS station at Boerne (site 1, fig. 5) was 

used for the upstream part of the study area (RCHRES 10–88); 

the NWS station at Bulverde (site 2, fig. 5) was used for the 

central part of the study area (RCHRES 90–194); and the 

NWS station at Randolph Field (site 4, fig 5) was used for the 

downstream part of the study area (RCHRES 196–212). Data 

from five additional rain gages (sites 3, 7, 8, 9, and 18; fig. 5 

and table 4) were used to fill in missing record for the three 

primary rainfall time series. Missing data were filled from 

the closest station with available data. The NWS stations at 

Boerne and Bulverde only provide daily data. Because hourly 

data are required for the model simulations, the Boerne and 

Bulverde daily data were disaggregated1 to hourly data by 

using the data from the nearest NWS or USGS stations with 

available hourly data. Pan evaporation data from the NWS 

station at Sea World, San Antonio (site 5; fig. 5 and table 4) 

were used for potential evaporation data input to the model. 

Missing data from the Sea World data set were filled in with 

data from the NWS station at Canyon Dam (site 6; fig. 5 and 

table 4) or Sea World average daily values for the appropriate 

month. Because the NWS data are daily totals, the potential 

evaporation data were disaggregated1 to an average hourly rate 

for each day.

1

The rainfall and potential evaporation disagregation program are part of the 

BASINS watershed modeling software package (U.S. Environmental Protection Agency, 2003). Daily rainfall is disaggregated according to the temporal 

rainfall distribution at one or more nearby hourly stations. Daily potential 

evaporation is distributed on the basis of latitude and time of year.

Table 1. Process-related model parameters for the Hydrologic Simulation Program—FORTRAN model (modified from Wicklein and 

Schiffer, 2002, table 1).

[PERLND, pervious land; IMPLND, impervious land] 

Parameter Description1 Land segment

AGWETP Fraction of available potential evapotranspiration demand that can be met from stored ground water PERLND

AGWRC Ground-water recession parameter; an index of rate at which ground water drains from land PERLND

BASETP Fraction of available potential evapotranspiration demand that can be met from ground-water outflow; 

simulates evapotranspiration from riparian vegetation.

PERLND

CEPSC Interception storage capacity PERLND

DEEPFR Fraction of ground water that does not discharge to surface within boundaries of modeled area PERLND

INFEXP Infiltration equation exponent; controls rate of infiltration decrease as a function of increasing soil moisture PERLND

INFILD Ratio of maximum and mean infiltration capacities PERLND

INFILT Index to infiltration capacity of soil; also affects percolation to ground-water zone PERLND

INTFW Interflow index; controls amount of infiltrated water that flows as shallow subsurface runoff PERLND

IRC Interflow recession coefficient; index for rate of shallow subsurface runoff PERLND

KVARY Ground-water outflow modifier; index of how much effect recent recharge has on ground-water outflow PERLND

LSUR Length of assumed overland flow plane PERLND or 

 IMPLND

LZETP Lower-zone evapotranspiration; index value (ranging from 0 to 0.99) representing density of deep-rooted 

vegetation

PERLND

LZSN Lower-zone nominal storage; index to soil moisture holding capacity of unsaturated zone PERLND

NSUR Manning’s n for assumed overland flow plane PERLND or

 IMPLND

RETSC Impervious retention storage capacity IMPLND

SLSUR Slope of assumed overland flow plane PERLND or

 IMPLND

UZSN Upper-zone nominal storage; index to amount of surface storage in depressions and upper few inches of soil PERLND

1

 The user’s manual for Hydrologic Simulation Program—FORTRAN (Bicknell and others, 1997) provides a more complete description of each parameter.

 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Streamflow data for calibrating HSPF runoff were available from two active USGS stations in the study area (sites 10 

and 18; fig. 5 and table 4). Station 08183850 Cibolo Creek at 

Interstate Highway 10 above Boerne measures streamflow in 

the upper 29 square miles of the study area. Station 08185000 

Cibolo Creek at Selma measures streamflow in the entire 

274 square miles of the study area. Data from USGS station 

08183900 Cibolo Creek near Boerne (site 11; fig. 5 and table 

4), discontinued in 1994, were used to test the model calibration. To help quantify streamflow losses to ground water 

that occur between gaging stations, a series of streamflow 

measurements were made at selected stations (sites 12–17; 

fig. 5 and table 4) and at several flow rates along Cibolo Creek 

during periods of runoff in September 2001 and July 2002 

(Gandara, 2003).

Daily discharge from the Boerne wastewater treatment 

plant was input to the model as equal hourly discharges, disaggregated from daily totals.

Measured ET data from an undeveloped rangeland watershed were obtained from stations in the Honey Creek watershed north of and adjacent to the Cibolo Creek Basin (sites 19 

and 20; fig. 5 and table 4). These data were collected from an 

area in the Trinity aquifer outcrop (Glen Rose Limestone) with 

moderate density of juniper and oak vegetation. Data were 

available for March–December 2002. These data were daily 

totals and were used to test HSPF ET simulations. All USGS 

data used for modeling are in the National Water Information 

System (U.S. Geological Survey, 2006).

Model Development

The HSPF model of upper Cibolo Creek was developed 

by (1) defining subwatersheds for the study area; (2) classifying unique HRUs on the basis of combinations of land 

cover, geology, soil, and slope; and (3) determining initial 

(uncalibrated) values of associated model parameters. Initial 

estimates of parameters were determined or estimated from 

default values, previous studies, available observed data, and 

results of simulations from an ecological model, Ecological 

Dynamics Simulations (EDYS) (Price and others, 2001). The 

EDYS model was developed by MWH Global, Inc., for the 

USACE Cibolo Creek project. 

Table 2. Basin-related model parameters for the Hydrologic 

Simulation Program—FORTRAN model.

[PERLND, pervious segment; IMPLND, impervious segment; FTABLE, table 

of depth, surface area, volume, and discharge for each stream reach] 

Parameter Description Units

AREA Drainage area of each 

PERLND or IMPLND

Acres

LEN Stream reach length Miles

DEPTH FTABLE depth Feet

SAREA FTABLE surface area Acres

VOL FTABLE volume Acre-feet

DISCH FTABLE discharge Cubic feet per second

Table 3. Land-cover categories and areas for the upper Cibolo 

Creek watershed, south-central Texas. 

Land-cover category

(fig. 4)

 Area

(acres)

Percentage 

of total 

watershed 

area

Juniper woodland 5,397 3.1

Juniper-live oak woodland, very dense 6,420 3.7

Juniper-live oak woodland, dense 14,312 8.2

Juniper-live oak woodland, moderately dense 14,115 8.1

Juniper-post oak woodland 1,947 1.1

Oak-juniper woodland, moderately dense 29,649 16.9

Oak-juniper woodland, slightly dense 11,861 6.8

Oak-persimmon woodland, dense 5,217 3.0

Oak-persimmon woodland, moderately dense 9,250 5.3

Mixed woodland 8,138 4.6

Juniper-persimmon savanna 2,587 1.5

Oak savanna 5,197 3.0

Mesquite savanna 3,888 2.2

Shrubland 4,703 2.7

Grassland 4,743 2.7

Bluestem prairie 11,433 6.5

Shortgrass prairie 1,684 1.0

Pasture 4,622 2.6

Cropland 5,835 3.3

Urban lawn 11,066 6.5

Exposed ground and rocky slopes 2,178 1.2

Water, water edge, and wetlands 3,939 2.2

Impervious 6,629 3.8

Total 175,098 100

Simulation of Streamflow and Estimation of Ground-Water Recharge   
Y R COUNT A BEX

Y A COUNT MEDIN

KENDALL COUNTY

BANDERA COUNTY

Y KERR COUNT

GUADALUPE 

COUNTY

COMAL COUNTY

BEXAR COUNTY

1

2

3

4

5

6

7 8

9

10

12 13

14

15

16

17

18

19, 20

11

IH–10

U.S. Hwy 281

IH–35

0 2 4 6 10 MILES 8

Upper Cibolo Creek study areaEdwards aquifer rechargezone (outcrop)Cibolo Creek watershedboundaryUpper Cibolo Creeksubwatershed boundary

EXPLANATION

3

10

5

19

Station type and sitenumber—See table 4RainfallStreamflo

w

Pan evaporationEvapotranspiration

Base modified from U.S. Geological Survey digital data 1:24,000 quadrangles Universal Transverse Mercator projection,Datum NAD 83, Zone 14

98°50'

98°40'

98°30'

98°20'

29°40'

29°50'

10 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed

Figure 5. Data-collection stations that provided data for Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, south-central Texas. 
Table 4. Data-collection stations that provided data for the Hydrologic Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas.

[dd, degrees; mm, minutes; ss, seconds; NWS, National Weather Service; --, not available; USGS, U.S. Geological Survey]

Site

number

(fig. 5)

Station name and number Latitude

(ddmmss)

Longitude

(ddmmss) Type of data Period ofrecord used

1 NWS station 410902 near Boerne, Texas 29°48'--" 98°44'--" Rainfall 1992–2004

2 NWS station 411215 near Bulverde, Texas 29°45'--" 98°27'--" Rainfall 1997–2002

3 NWS station 417945 at San Antonio International Airport, 

San Antonio, Texas

29°32'--" 98°28'--" Rainfall 1992–2004

4 NWS station 417422 at Randolph Field, Texas 29°33'--" 98°18'--" Rainfall 1992–2004

5 NWS station 418169 at Sea World, San Antonio, Texas 29°27'--" 98°42'--" Pan evaporation 1997–2004

6 NWS station 411429 at Canyon Dam, Comal County, Texas 29°52'--" 98°12'--" Pan evaporation 1992–2004

7 USGS partial-record station 08178595 Stone Mountain 

drainage channel at Granite Path, San Antonio, Texas

29°38'54" 98°30'04" Rainfall 1997–2001

8 USGS partial-record station 08178627 Elm Waterhole 

Creek Tributary at San Antonio, Texas

29°38'48" 98°24'23" Rainfall 2001–02

9 USGS station 08180945 Leon Creek at Scenic Loop Road 

near Leon Springs, Texas

29°40'32" 98°40'33" Rainfall 2001–02

10 USGS station 08183850 Cibolo Creek at Interstate Highway 

10 above Boerne, Texas

29°48'52" 98o 45'12" Streamflow 1996–2004

11 USGS station 08183900 Cibolo Creek near Boerne, Texas 29°46'26" 98°41'50" Streamflow 1992–1994

12 USGS partial-record station 08183950 Cibolo Creek at 

Ralph Fair Road below Boerne, Texas 

29°44'37" 98°37'24" Streamflow 2001–02

13 USGS partial-record station 08183970 Cibolo Creek at 

Blanco Road above Bulverde, Texas 

29°44'33" 98°30'51" Streamflow 2001–02

14 USGS partial-record station 08183990 Cibolo Creek at 

Bulverde Road near Bulverde, Texas 

29°43'59" 98°27'08" Streamflow 2001–02

15 USGS partial-record station 08183995 Cibolo Creek at U.S. 

Highway 281 near Bulverde, Texas 

29°43'09" 98°26'36" Streamflow 2001–02

16 USGS partial-record station 08184050 Cibolo Creek at 

Smithson Valley Road near Bulverde, Texas 

29°44'54" 98°24'28" Streamflow 2001–02

17 USGS partial-record station 08184300 Cibolo Creek at 

Farm Road 1863 below Bulverde, Texas 

29°43'58" 98°21'23" Streamflow 2001–02

18 USGS station 08185000 Cibolo Creek at Selma, Texas 29°35'38" 98°18'39" Rainfall and 

streamflow

1992–2004

19 USGS station 295104098285900 Honey Creek reference 

evapotranspiration site near Spring Branch, Texas

29°51'04" 98°28'59" Evapotranspiration 2002

20 USGS station 295102098283200 Honey Creek treatment 

evapotranspiration site near Spring Branch, Texas

29°51'02" 98°28'32" Evapotranspiration 2002

Simulation of Streamflow and Estimation of Ground-Water Recharge 11
The HSPF model was configured by dividing the study 

area into 80 subwatersheds. As noted previously, these subwatersheds correspond to HSPF stream reaches (RCHRESs) 

(fig. 6). Considerations in developing the stream reach configuration include (1) defining reaches with flows such that 

travel times approximate the model simulation time step (1 

hour); (2) defining reaches with homogeneous channel properties, such as slope and conveyance; and (3) locating outlets of 

subwatersheds at important points, such as gaging stations, 

tributary confluence, outcrop boundaries, and inflows from 

sources or outflows to sinks. 

Pervious and impervious HRUs were classified as such 

according to land use, geology, soil, and slope characteristics. 

Geology categories include the Glen Rose Limestone of the 

Trinity aquifer outcrop (relatively low to moderate permeability); the Edwards Group and Georgetown Formation of the 

Edwards aquifer outcrop (relatively high permeability); and 

upper confining unit of the Edwards aquifer (relatively low to 

moderate permeability) (Small and Hanson, 1994). The Glen 

Rose Limestone category was subdivided into two categories 

largely on the basis of soil and runoff characteristics. Glen 

Rose—shallow soil (largely composed of Tarrant-Brackett 

association or similar soils) was assigned to the upstream part 

of the study area and includes PERLNDs in subwatersheds 

(RCHRES) 10–88. Glen Rose—deep soil (Crawford-Bexar 

Association) was assigned to PERLNDs in RCHRES 90–176. 

RCHRES 180–190 transition from Glen Rose Limestone to 

Edwards Group and Georgetown Formation. Soil characteristics of PERLNDs in geologically transitional RCHRES 180–

190 are similar to PERLNDs in RCHRES 90–176. Edwards 

Group and Georgetown Formation characterize RCHRES 

192–196. PERLNDs associated with RCHRES 198 and 206 

contain rocks of the Edwards Group and Georgetown Formation, and the Austin Group, one of several geologic units of 

the upper confining unit of the Edwards aquifer. PERLNDs in 

RCHRES 200–204 and 208–212 contain rocks of the Austin 

Group. Soil in RCHRES 192–212 is characterized as mostly 

Crawford-Bexar Association. 

Based on combinations of land cover, geology, and soil 

type, 275 pervious HRU types are possible. The average landsurface slope in a subwatershed generally was applied to all 

pervious HRUs in that subwatershed. Impervious area was 

included as a single impervious HRU type (except for changes 

in surface slope and retention storage), with similar hydrologic 

properties across the entire watershed. In HSPF terminology, 

HRUs correspond to PERLND and IMPLND segments.

Three rainfall time series were developed, representing 

input to the upper, central, and lower parts of the study area. 

The upstream area includes HRUS associated with RCHRES 

10–88; the central area includes HRUs associated with 

RCHRES 90–194; and the downstream area includes HRUs 

associated with RCHRES 196–212. A single potential evaporation time series was applied to the entire study area.

In the study area, substantial amounts of runoff are lost 

to stream-channel infiltration (ground-water recharge) before 

flow reaches the study area outlet. HSPF does not include process parameters or specific features to account for streamflow 

losses. Instead, these losses were accounted for in the model 

as water withdrawals from the stream reaches. The withdrawals were established in the stream reach (FTABLE) configuration as a function of stream discharge or stream volume. These 

withdrawals were routed to ground-water recharge.

Model development was completed by assigning initial 

values to process-related HSPF parameters. These values 

collectively represented a starting point for calibration of the 

model by iterative parameter adjustment. Initial values of 

parameters related to streamflow and ground-water recharge 

were based on previous HSPF studies in the region (Brown 

and Raines, 2002; Ockerman, 2002). Data from the EDYS 

ecological model (C. Coldren, MWH Global, Inc., written 

commun., 2002) also were used to develop initial values for 

ET- and interception-related process parameters (primarily 

CEPSC, LZETP, LZSN, and UZSN). 

The HSPF software (version 12) limits a single simulation run to no more than 500 model operations. Each separate 

PERLND, IMPLND, and RCHRES model element is considered an operation. Because of concerns about exceeding 

operation limits, the Cibolo Creek HSPF model was run as 

two separate models. The upstream part of the model includes 

RCHRES 10–88 and associated PERLNDs and IMPLNDs. 

The downstream part of the model includes all model elements 

downstream of RCHRES 88. To run a simulation for the entire 

watershed, the separate models were run sequentially, and 

the ouput from the upstream model was used as input to the 

downstream model.

Streamflow Calibration

A primary goal of watershed model calibration was to 

match model-simulated streamflow to measured streamflow. 

Criteria such as error in total streamflow volume for the calibration period, low-flow and high-flow distribution, and error 

in peak flows were used to evaluate how well the simulated 

streamflow represented actual streamflow. 

Streamflow data collected at USGS station 08183850 

Cibolo Creek at Interstate Highway 10 above Boerne were 

used to calibrate model streamflow for the part of the study 

area upstream from the station (RCHRES 10–28). Also, model 

parameters obtained from this calibration were applied to 

HRUs in RCHRES 30–88. Data collected at USGS station 

08185000 Cibolo Creek at Selma were used to calibrate the 

rest of the study-area model because streamflow from the 

entire study area is measured at this site. Data from stations 

08183850 and 08185000 for 1997–2000 were used for 

calibration. Data for 2001–04 were used to test the model 

calibration. Data from discontinued USGS station 08183900 

Cibolo Creek near Boerne also were used to test model calibration for the period 1992–94. Model calibration and testing 

results are shown in table 5 (at end of report). 

Calibration and testing results for total flow volumes, 

total of highest 10 percent of flows, total of lowest 50 percent 

of flows, and average of selected storm peaks are shown in 

12 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
COUNTY BEXAR

A COUNTY MEDIN

KENDALL COUNTY

BANDERA COUNTY

Y KERR COUNT

GUADALUPE 

COUNTY

COMAL COUNTY

BEXAR COUNTY

U.S. Hwy 81 2

IH–35

IH–10

Base modified from U.S. Geological Survey digital data 1:24,000 quadrangles Universal Transverse Mercator projection,Datum NAD 83, Zone 14

98°50'

98°40'

98°30'

98°20'

29°40'

29°50'

0 2 4 6 10 MILES 8

184

186

24

10

20 16

30

14 52 60

22

82

26

28 170 50 106

126 144

174

32 166 142

40 68

34

90 114 44 62 54 86

94

56

168

146 130 116 66 58 70

42

160

182

172

64 118

176

100 78 92 96 136

152

88 120

132

124

80 122

128

98 180

134

154 74 188

190

194 192

196

206

208

198

202

210

112

204

200 212

74

Upper Cibolo Creek study areaEdwards aquifer recharge zone (outcrop)Cibolo Creek watershed boundaryUpper Cibolo Creek subwatershedboundary with stream and reservoir reaches (RCHRES), identified by number

EXPLANATIO

N

Figure 6. Stream-reach network for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, south-central Texas. 

Simulation of Streamflow and Estimation of Ground-Water Recharge 13
table 5. The error in simulated streamflow volume (difference between simulated and gaged streamflow) at the outlet 

of the study-area watershed (USGS streamflow-gaging station 

08185000 Cibolo Creek at Selma) for 1997–2004 was about 2 

percent. Simulation errors generally were within limits (table 

5) recommended by Donigian (2002, p. 14) for most categories at all gaging stations. The exception was lowest 50 percent 

of flows at station 08183850. The simulated lowest 50 percent 

of flows for that station during the 2001–04 testing period 

were 15.1 percent less than the measured. The measured total 

of lowest 50 percent of daily flows at station 08183850 represents only 4 percent of the measured total flow volume during 

the 1997–2004 period. The difference between measured and 

simulated totals of lowest 50 percent of daily flows at this site 

represents less than 1 percent of the total flow volume.

Simulated flows at all three gaging stations were evaluated graphically by comparing measured and simulated daily 

time series, exceedance-probability curves, and scatter plots. 

General agreement between the measured and simulated 

exceedance-probability curves indicates adequate calibration 

over the range of flow conditions (figs. 7–9).

Donigian and others (1984) present general guidelines for 

evaluating HSPF calibrations. For annual streamflow volumes, 

model calibration is considered very good when the error is 

less than 10 percent, good when the error is 10 to 15 percent, 

and fair when the error is 15 to 25 percent. By these guidelines, calibration results for annual flow volumes at all three 

gaging stations are considered very good. 

Evapotranspiration and Interception Testing

Another goal of the watershed model calibration was to 

accurately simulate the overall water budget in the watershed, 

including ground-water recharge and ET. Model simulations 

of ground-water recharge cannot be compared with measured 

values because diffuse recharge (direct infiltration of rainfall through the soil layers to the water table), especially in 

a faulted karst environment such as Cibolo Creek, generally 

cannot be measured directly2. Thus, model simulations, or 

estimates, of ground-water recharge depend on accurate model 

representations of the remaining water-budget components 

not associated with ground-water recharge (streamflow, ET, 

and changes in soil-water storage over the simulation period). 

Annual streamflow in Cibolo Creek (measured at station 

08185000 Cibolo Creek at Selma) usually constitutes less than 

10 percent of annual rainfall, and changes in soil-water storage 

(as a percentage of the water budget) were considered minor, 

especially over relatively long simulation periods. Therefore, 

ET plus ground-water recharge accounts for about 90 percent 

of the rainfall on the watershed. Errors in ET simulations can 

result in substantial errors in diffuse ground-water recharge 

estimates.

2

Recharge in the study area occurs as diffuse recharge and as streamchannel infiltration. Although diffuse recharge could not be measured, streamchannel infiltration losses were measured indirectly during the study.

ET, computed from the Bowen-ratio energy balance 

method (Atmospheric Radiation Measurement Program, 

2003), was available for March–December 2002 from the 

Honey Creek watershed (W.H. Asquith, U.S. Geological 

Survey, written commun., 2002) for comparison with simulated ET for the study area. Simulated ET for the most similar 

geology and land cover (PERLND type Glen Rose Limestone, 

juniper-live oak woodland, moderately dense) was compared 

with the measured ET (table 6, at end of report). Monthly 

simulation error ranged from -32 to 47 percent. ET simulations 

in the study area are relatively sensitive to rainfall. Differences 

in rainfall between the upper Cibolo Creek watershed and 

the Honey Creek watershed might contribute to some of the 

simulation error. Long-term error was less: During the entire 

10-month comparison period, simulated ET was 4 percent 

greater than measured ET. 

Another test of HSPF ET simulations involved analysis 

of the simulated canopy interception of juniper woodland 

land cover. A substantial part of the total ET in juniper communities occurs as direct evaporation of intercepted rainfall. 

The Texas Agricultural Experiment Station (TAES), Uvalde, 

Tex., studied interception water loss at 10 sites in the Edwards 

aquifer recharge area (Owens and others, 2001). Among the 

10 study sites, interception water loss to evaporation accounted 

for 43 percent of rainfall. This interception percentage likely 

was higher than that for the vegetation categories used for 

the Cibolo Creek model because the TAES study results 

apply to individual juniper trees or the equivalent of 100-

percent juniper density. The results of the TAES study were 

useful for comparing with HSPF-simulated ET for juniper 

woodland land cover and for evaluating the HSPF model 

partitioning of simulated ET losses between interception 

losses and soil and lower zone ET. During 1997–2004, 

HSPF-simulated interception ET was 39 percent of rainfall for 

juniper woodland land cover. HSPF partitioning of ET losses 

between canopy interception evaporation and soil and plant 

ET appear reasonable for the juniper woodland land-cover 

categories. 

As a result of calibration and testing, a set of HSPF 

process-related parameters were obtained for the study area 

(tables 7 and 8, at end of report). This parameter set was used 

to simulate streamflow and recharge for the study area for 

1992–2004.

Simulated Streamflow, 1992–2004

The upper Cibolo Creek HSPF model has the capability 

to simulate streamflow at the outlet of each stream and 

reservoir (RCHRES) segment (fig. 6). Streamflows at five 

selected sites in the study watershed were compared to demonstrate the effects of stream-channel infiltration losses. Table 9 

(at end of report) lists average annual streamflow per unit area 

of contributing watershed, expressed in inches per year, for 

1992–2004 at each selected site. The most upstream site 

had the greatest runoff (8.90 inches per year) and the most 

14 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Figure 7. Measured and simulated daily streamflow at station 08183850 Cibolo Creek at Interstate Highway 10 above Boerne, Texas, 

1997–2004. 

MEASURED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

10 100 1,000 10,000 100,000

1

10

100

1,000

10,000

1

 Line of equal value

SIMULATED

MEASURED

0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.5 99.8

100

1

10

10,000

1,000

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

EXCEEDANCE PROBABILITY, IN PERCENT

SIMULATED

MEASURED

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

YEAR

10,000

1,000

100

10

1

1997 1998 1999 2000 2001 2002 2003 2004

Simulation of Streamflow and Estimation of Ground-Water Recharge 15
Figure 8. Measured and simulated daily streamflow at station 08183900 Cibolo Creek near Boerne, Texas, 1992–94. 

MEASURED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND 

SIMULATED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

 Line of equal value 

10 100 1,000 10,000 100,000

1

10

100

1,000

10,000

1

0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.5 99.8

100

1

10

10,000

1,000

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

EXCEEDANCE PROBABILITY, IN PERCENT

MEASURED

SIMULATED

SIMULATED

MEASURED

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

YEAR

10,000

1,000

100

10

1

1992 1993 1994

16  Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Figure 9. Measured and simulated daily streamflow at station 08185000 Cibolo Creek near Selma, Texas, 1997–2004. 

MEASURED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

 Line of equal value

10 100 1,000 10,000 100,000

1

10

100

1,000

10,000

100,000

1

SIMULATED

MEASURED

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

EXCEEDANCE PROBABILITY, IN PERCENT

0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.5 99.8

100

1

10

10,000

1,000

100,000

DAILY STREAMFLOW, IN CUBIC FEET PER SECOND

YEAR

SIMULATED

MEASURED

10,000

100,000

1,000

100

10

1

1997 1998 1999 2000 2001 2002 2003 2004

Simulation of Streamflow and Estimation of Ground-Water Recharge 17
downstream site had the least runoff (3.22 inches per year). 

Runoff consistently decreased downstream primarily 

because of stream-channel infiltration losses along Cibolo 

Creek. 

Simulations indicate that during 1992–2004 about 56 

percent of runoff (water leaving PERLNDs and IMPLNDs 

as surface runoff, interflow, or base flow and reaching the 

channel as streamflow) was lost to channel infiltration: 7.24 

inches per year of runoff (including 0.05 inch per year of 

treated wastewater discharge) reached Cibolo Creek, but only 

3.22 inches per year exited the study area. Average annual 

rainfall on the study area during 1992–2004 was 37.43 inches. 

Therefore, simulated streamflow exiting the study area was 8.6 

percent of the rainfall. 

Streamflow in the watershed is highly variable and dominated by large storms. During the 1992–2004 study period, 61 

percent of the streamflow at station 08185000 Cibolo Creek at 

Selma occurred during three large storms (June 1997, October 

1998, and July 2002). During 2002, 11.10 inches of runoff 

exited the study area, despite the fact that no runoff occurred 

in 8 months during 2002. During calendar years 1996, 1999, 

and 2003, no flow was measured at the Selma station. Runoff 

during 1992–2004 was greater than average and represented 

a greater-than-normal percentage of rainfall. The 1946–2004 

average annual runoff at the Selma station was 1.15 inches, 

which is less than 5 percent of average annual rainfall in the 

upper Cibolo Creek watershed.

Estimated Ground-Water Recharge, 1992–2004

HSPF simulations were used to estimate quantities and 

locations of ground-water recharge during 1992–2004. For 

the entire study watershed, average ground-water recharge 

was 79,800 acre-feet per year, or 5.47 inches per year (about 

15 percent of rainfall) (table 10, at end of report). Annual 

recharge ranged from 14,500 acre-feet (0.99 inch) in 1999 

to 196,000 acre-feet (13.43 inches) in 1992. Overall in the 

study area, most recharge (about 74 percent) occurred as 

stream-channel infiltration (table 11, at end of report). Diffuse recharge accounted for the remaining 26 percent. About 

77 percent (61,500 acre-feet per year) of the ground-water 

recharge occurred in the Trinity aquifer outcrop; about 13 percent (10,200 acre-feet per year) occurred in the area of transition from the Trinity aquifer outcrop to the Edwards aquifer 

outcrop; about 6.4 percent (5,130 acre-feet per year) occurred 

in the Edwards aquifer recharge zone (outcrop); and about 

3.6 percent (2,940 acre-feet per year) occurred in the area of 

transition from the Edwards aquifer recharge zone (outcrop) 

to Edwards aquifer upper confining unit and the area of upper 

confining unit (the two areas combined). 

Ground-water recharge also was greatly influenced 

by large storms. During 1992–2004, 11 percent (53.90 inches) 

of the total 13-year rainfall and 16 percent (178,000 acre-feet) 

of the total 13-year ground-water recharge occurred during 

the three large storms (June 1997, October 1998, and July 

2002). During 1999, a dry year with about 16 inches of 

rainfall and no measured runoff at the watershed outlet, 

recharge in the watershed amounted to only 14,500 acre-feet 

(0.99 inch) compared with 196,000 acre-feet (13.43 inches) 

during 1992, a relatively wet year with about 54 inches of 

rainfall.

Simulated Streamflow and Estimated GroundWater Recharge With Implementation of FloodControl/Recharge-Enhancement Structures

Local water-resource agencies have expressed interest in constructing structures (dams) along Cibolo Creek (as 

well as other streams that cross the Edwards aquifer recharge 

zone) to provide flood control and to potentially increase 

recharge through increased stream-channel infiltration (San 

Antonio River Authority, 1996; San Antonio Water System, 

2006). The structures would potentially increase recharge in 

two ways: (1) Structures constructed on the stream upstream 

from or in the upper reaches of a recharge area (a stream reach 

where streamflow infiltrates to the underlying aquifer) would 

function as detention structures, holding back floodwater for 

a limited period and releasing water at a slower flow rate. 

The slower release would cause slower streamflow recession 

and thus more time for stream-channel infiltration, resulting in increased recharge; and (2) structures constructed on 

the stream in an area of high infiltration, or relatively high 

recharge capacity, would function as retention structures, 

holding back floodwater for an extended period of time, 

allowing for direct infiltration of impounded water to the 

aquifer. Some structures possibly might function in both 

ways.

The calibrated Cibolo Creek HSPF model was used to 

simulate streamflow and recharge for a set of scenarios that 

included various individual structures and combinations of 

structures at several sites in the watershed. The purpose of the 

simulations was to determine whether such structures could 

potentially provide flood control (reduce flood peaks) and 

increase recharge in the upper Cibolo Creek watershed. The 

locations and sizes of the structures were determined by 

considering recommendations from the study cooperators: 

(1) Structures should be located in areas that provide recharge 

primarily to the Edwards aquifer, with recharge to the Trinity 

aquifer as a secondary benefit; (2) structures should be located 

at sites that provide flood-peak reduction in the downstream 

part of the study area (near the Selma station); and (3) structures should be located at sites that meet some minimum 

requirements for a suitable structure location—these requirements include (a) reasonable trade-off between large storage 

volume and small inundation area, and (b) avoiding inundation 

of developed areas. 

Figure 10 shows the locations of structures and impoundment areas simulated. Table 12 (at end of report) shows 

corresponding structure specifications such as dam height, 

spillway height, storage volume, and spillway capacity. Seven 

18  Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Y R COUNT A BEX

Y A COUNT MEDIN

KENDALL COUNTY

BANDERA COUNTY

Y KERR COUNT

GUADALUPE 

COUNTY

COMAL COUNTY 98°50' 98°40'

98°30'

98°20'

29°40'

29°50'

Base modified from U.S. Geological Survey digital data 1:24,000 quadrangles Universal Transverse Mercator projection,Datum NAD 83, Zone 14

0 2 4 6 10 MILES 8

IH–10

U.S. Hwy 281

IH–35

Upper Cibolo Creek study areaEdwards aquifer recharge zone (outcrop)Possible structure and impoundment sitewith identification numberCibolo Creek watershed boundaryUpper Cibolo Creek subwatershed boundary with stream and reservoir reaches (RCHRES),identified by number

EXPLAN

ATION

S–74

192

184

186

24

10

20

16

30

14 52 60

22

82

26

28 170

50

106

126 144 174 32 166 142

40

68 34 90 114 44 62 54 86

94

56

168

146 150

130 116

66

58 69

42 160

182

172

64 118

176

100 78 92 96

148

136

152 88 120

132

124 80 122

128

98 180

134

154

74 156 188

190

194 192

196

206

208

198

200

202

210

212

112

204

S–74

S–86 S–106

S–13

S–12

4

6 S–144

S–160

S–172

S–191

Figure 10. Locations of flood-control/recharge-enhancement structures and impoundment areas simulated with the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, south-central Texas. 

Simulation of Streamflow and Estimation of Ground-Water Recharge 19
of the nine structures were on tributaries of Cibolo Creek. The 

two largest structures (S–160 and S–191) are on the main stem 

of Cibolo Creek. Structure S–160 is on the Trinity aquifer 

outcrop and S–191 is at the transition from the Trinity aquifer 

outcrop to the Edwards aquifer outcrop. 

HSPF simulations were run for each of the scenarios 

listed in table 13 (at end of report). Results of the simulations 

comprise changes in simulated peak discharge (at station 

08185000) during the October 1998 storm (historic peak) and 

changes in simulated channel infiltration (recharge) in the 

Trinity and Edwards aquifer outcrops during 1992–2004.

Simulations of individual tributary structures show 

relatively small effects on flood-peak reduction and groundwater recharge enhancement. All simulated tributary structures 

were on the Trinity aquifer outcrop and increased recharge to 

the Trinity aquifer. Generally, stream-channel infiltration to 

the Edwards aquifer was slightly decreased because increased 

recharge to the Trinity aquifer resulted in less water available to flow downstream across the Edwards aquifer outcrop. 

Simulations with the two large main-stem structures, S–160 

and S–191, showed a greater effect on flood-peak reduction 

and recharge enhancement than the tributary structures. Individually, S–160 and S–191 simulations resulted in decreases 

of the October 1998 peak discharge of about 25 percent and 17 

percent, respectively. The S–160 structure increased recharge 

primarily to the Trinity aquifer, and the S–191 structure 

increased recharge to the Edwards aquifer.

A simulation comprising both main-stem structures, 

S–160 and S–191, resulted in substantial peak-flow reduction 

(37 percent) and an increase in recharge in stream channels. 

With this scenario, stream-channel recharge increased 6.6 

percent in the Trinity aquifer outcrop and 12.6 percent in the 

Edwards aquifer outcrop. Simulation of a combination of three 

tributary structures (S–106, S–126, and S–144) resulted in a 

peak flow decrease of about 11 percent (October 1998 storm 

at station 08185000). A small increase (1.3 percent) in Trinity aquifer recharge was offset by a decrease (2.0 percent) in 

Edwards aquifer recharge. 

Simulations with combinations of tributary structures 

and main-stem structures did not produce results substanially different than with the main-stem structures alone. The 

main-stem structures were more effective than the tributary 

structures for two reasons: First, the main-stem structures have 

larger storage capacity and are more effective at detaining and 

releasing water more slowly along the aquifer outcrop streams, 

potentially increasing recharge. Second, with much larger 

contributing drainage areas, the main-stem structures receive 

larger volumes of inflow and thus affect much greater volumes 

of streamflow than the tributary structures. 

Model Limitations and Applications

Limitations in the available rainfall data are likely the 

most serious source of simulation error and uncertainty for the 

Cibolo Creek study. Streamflow and recharge in the watershed are highly dependent on the occurrence of large storms. 

Data from the available network of rain gages do not always 

adequately represent the spatial and temporal variability of 

rainfall in the watershed. For example, a storm in June 1997 

contributed more than 25 percent of the total streamflow (at 

station 08185000 Cibolo Creek at Selma) during the 1992–

2004 period. Simulated streamflow and peak flows during 

this storm were less than measured flows, likely because of an 

underestimation of rainfall totals in the upstream part of the 

study area. Streamflow also is highly dependent on rainfall 

intensity. Two of three primary rain gages used for the model 

simulations were daily rain gages. The daily totals were disagregated to hourly values on the basis of data from the nearest available gages, which usually were outside the watershed. 

Thus, some uncertainty in rainfall intensity exists for simulations run with this model. 

Simulation errors also are generated because peak discharges reported for the USGS streamflow-gaging stations in 

the study area were not measured directly but were obtained 

by indirect methods (Benson and Dalrymple, 1967). Because 

indirect methods increase uncertainty of gaged streamflow, 

model calibration at higher streamflow is potentially subject 

to greater error. 

Structure designs and sites used for these simulations are 

for simulation purposes only and do not necessarily represent feasible structures or sites. There are several limitations 

related to structure scenarios. First, structures were “designed” 

only to the extent needed to develop hydraulic characteristics 

for the structure in the HSPF model. Mathematical storagedischarge relations were developed for each structure. These 

relations depend largely on dam heights, spillway characteristics (elevation, width, pipe/culvert diameter, and so forth), and 

topographical characteristics at each site. Specifications for 

actual structures in an adjacent watershed, designed for similar 

purposes (San Antonio River Authority, 1996), were used as 

a guide for dam and spillway heights. Actual physical characteristics such as dam type and construction materials were 

not considered in the structure design. Geotechnical analyses 

to determine suitability of any particular site were not done. 

Furthermore, safety factors, such as flood-frequency analyses 

to determine possible extreme flows that the structures could 

be exposed to, were not considered. Finally, cost of land and 

other factors related to possible future acquisition or rights to 

construct structures at specific sites were not considered.

Summary

The U.S. Geological Survey (USGS), in cooperation 

with the U.S. Army Corps of Engineers-Fort Worth District, 

San Antonio River Authority, San Antonio Water System, and 

Guadalupe-Blanco River Authority, developed, calibrated, 

and tested a Hydrological Simulation Program—FORTRAN 

(HSPF) watershed model to simulate streamflow and estimate 

recharge in the 274-square-mile upper Cibolo Creek watershed in Bandera, Bexar, Comal, and Kendall Counties in 

20 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
south-central Texas. Input data for use with the HSPF model 

were developed from available rainfall, evapotranspiration, 

and streamflow data collected during 1992–2004. The error 

in simulated streamflow volume (difference between simulated and gaged streamflow) at the outlet of the study-area 

watershed (USGS streamflow-gaging station 08185000 Cibolo 

Creek at Selma) for 1997–2004 was about 2 percent. 

Simulated streamflows at five selected sites were compared. Streamflow per unit area of contributing watershed, or 

runoff expressed in inches per year, decreased in the downstream direction, primarily because of substantial streamflow 

losses to ground-water recharge in Cibolo Creek. More than 

one-half (56 percent) of streamflow during 1992–2004 infiltrated to ground water in stream channels before it reached the 

USGS gaging station at Selma.

Simulations showed that during 1992–2004 average 

ground-water recharge in the watershed was 79,800 acrefeet per year, or 5.47 inches per year. Most recharge (about 

74 percent) occurred as stream channel-infiltration. Diffuse 

recharge accounted for about 26 percent of total recharge. 

Most recharge (about 77 percent) occurred in the Trinity aquifer outcrop. About 13 percent of recharge occurred in the area 

of transition from the Trinity aquifer outcrop to the Edwards 

aquifer outcrop. About 6.4 percent of recharge occurred in the 

Edwards aquifer recharge zone (outcrop), and a small amount 

(about 3.6 percent) of recharge occurred in the area of transition from the Edwards aquifer recharge zone (outcrop) to the 

Edwards aquifer upper confining unit, and in the upper confining unit. 

Streamflow and recharge in the study area are greatly 

influenced by large storms. During the 1992–2004 period, 

three large storms (June 1997, October 1998, and July 2002) 

accounted for about 11 percent of the study-area rainfall, 61 

percent of streamflow (measured at the Selma station), and 16 

percent of the total ground-water recharge. Annual streamflow 

and recharge are highly variable. During 1999, a dry year 

with about 16 inches of rainfall and no measured runoff at the 

watershed outlet, recharge in the watershed amounted to only 

14,500 acre-feet (0.99 inch) compared with 196,000 acre-feet 

(13.43 inches) during 1992, a relatively wet year with about 54 

inches of rainfall.

The calibrated Cibolo Creek HSPF model was used to 

simulate streamflow and recharge for various scenarios involving flood-control/recharge-enhancement structures located at 

different sites in the watershed. The purpose of the simulations 

was to determine whether such structures could potentially 

provide flood control and increase recharge benefits in the 

upper Cibolo Creek watershed. Simulations showed that larger 

structures on Cibolo Creek, compared with smaller structures 

on tributaries, resulted in larger flood-peak reduction and 

larger increases in recharge. One scenario that included two 

structures on the main stem of Cibolo Creek resulted in a 

37-percent reduction in peak flow at the watershed outlet and 

an increase in recharge in stream channels. With this scenario, 

stream-channel recharge increased 6.6 percent in the Trinity aquifer outcrop and 12.6 percent in the Edwards aquifer 

outcrop. 

References

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balance Bowen ratio: accessed November 8, 2003, at 

http://www.arm.gov/docs/instruments/static/ebbr.html

Benson, M.A., and Dalrymple, Tate, 1967, General field and 

office procedures for indirect discharge measurements: U.S. 

Geological Survey Techniques of Water Resources Investigations, book 3, chap. A1, 30 p.

Bicknell, B.R., Imhoff, J.C., Kittle, J.L. Jr., Donigian, A.S., 

and Johanson, R.C., 1997, Hydrological Simulation Program—FORTRAN, user’s manual for version 11: Research 

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Brown, D.S., and Raines, T.H., 2002, Simulation of flow and 

effects of best-management practices in the upper Seco 

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tx.us/profile.html

Clark, A.K., 2003, Geologic framework and hydrologic 

features of the Glen Rose Limestone, Camp Bullis Training 

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13–16, 2002, Specialty Conference Proceedings: Water 

Environment Federation, 30 p., accessed November 24, 

2006, at http://www.aquaterra.com/TMDL.Nov02.Donigian.

Paper.doc

Donigian, A.S., Jr., Bicknell, B.R., and Imhoff, J.C., 1995, 

Hydrological Simulation Program—FORTRAN (HSPF), in

Singh, V.P., ed., Computer models of watershed hydrology: 

Highlands Ranch, Colo., Water Resources Publications, 

p. 395–442.

Donigian, A.S., Jr., Imhoff, J.C., Bicknell, B.R., and Kittle, 

J.L., Jr., 1984, Application guide for Hydrological Simulation Program—FORTRAN (HSPF): U.S. Environmental 

Protection Agency, Environmental Research Laboratory, 

EPA–600/3–84–065, 177 p.

References 21
Gandara, S.C., 2003, Water resources data, Texas, water year 

2002—Volume 5. Guadalupe River Basin, Nueces River 

Basin, Rio Grande Basin, and intervening coastal basins: 

U.S. Geological Survey Water-Data Report TX–02–5, 

382 p.

George, W.O., 1952, Geology and ground-water resources 

of Comal County, Texas: U.S. Geological Survey WaterSupply Paper 1138, 126 p.

Larkin, T.J., and Bomar, G.W., 1983, Climatic atlas of Texas: 

Texas Department of Water Resources, Limited Printing 

Report LP–192, 151 p.

Lumb, A.M., McCammon, R.B., and Kittle, J.L., Jr., 1994, 

Users manual for an expert system (HSPEXP) for calibration of the Hydrological Simulation Program—FORTRAN: 

U.S. Geological Survey Water-Resources Investigations 

Report 94–4168, 102 p.

Maclay, R.W., 1995, Geology and hydrology of the Edwards 

aquifer in the San Antonio area, Texas: U.S. Geological 

Survey Water-Resources Investigations Report 95–4186, 

64 p.

National Climatic Data Center, 2006, Weather/climate 

events, information & assessments—Weather/climate 

data and products: accessed October 10, 2006, at 

http://www.ncdc.noaa.gov/oa/ncdc.html 

Ockerman, D.J., 2002, Simulation of runoff and recharge 

and estimation of constituent loads in runoff, Edwards 

aquifer recharge zone (outcrop) and catchment area, Bexar 

County, Texas, 1997–2000: U.S. Geological Survey WaterResources Investigations Report 02–4241, 31 p.

Owens, M.K., Lyons, Robert, and Kneuper, Charles, 2001, 

Evaporation and interception water loss from juniper communities on the Edwards aquifer recharge area: Uvalde, 

Tex., Texas Agricultural Experiment Station and Texas 

Agricultural Extension Service, Final Report, accessed July 

23, 2007, at http://uvalde.tamu.edu/intercept/final.pdf

Price, D.L., Passmore, M.F., and McLendon, Terry, 2001, 

EDYS—Ecological dynamics simulation: U.S. Army Corps 

of Engineers, Research and Development Center, Ecosystem Evaluation and Engineering Division, Montgomery 

Watson Harza Ecological Systems Division, fact sheet, 1 p.

Puente, Celso, 1978, Method of estimating natural recharge to 

the Edwards aquifer in the San Antonio area, Texas: U.S. 

Geological Survey Water-Resources Investigations Report 

78–10, 34 p.

San Antonio River Authority, 1996, Salado Creek watershed 

protection and flood prevention project: San Antonio, San 

Antonio River Authority, fact sheet, 2 p.

San Antonio Water System, 2006, Edwards aquifer recharge 

initiative: accessed December 12, 2006, at http://www.saws.

org/our_water/waterresources/projects/edwards_recharge.

shtml

Small, T.A., and Hanson, J.A., 1994, Geologic framework and 

hydrologic characteristics of the Edwards aquifer outcrop, 

Comal County, Texas: U.S. Geological Survey WaterResources Investigations Report 94–4117, 10 p.

Stein, W.G., and Ozuna, G.B., 1996, Geologic framework and 

hydrologic characteristics of the Edwards aquifer recharge 

zone, Bexar County, Texas: U.S. Geological Survey WaterResources Investigations Report 95–4030, 8 p.

Texas Board of Water Engineers, 1960, Channel gain and loss 

investigations, Texas streams, 1918–1958: Texas Board of 

Water Engineers Bulletin 5807D, 270 p.

U.S. Army Corps of Engineers, 2001, Project management 

plan, Guadalupe-San Antonio River Basins, Cibolo Creek 

watershed feasibility study: U.S. Army Corps of Engineers, 

Fort Worth District. 

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accessed May 8, 2007, at http://quickfacts.census.gov/qfd/

states/48000.html

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[Natural Resources Conservation Service], 1966, Soil survey of Bexar County, Texas: Soil Conservation Service, 126 

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[Natural Resources Conservation Service], 1981, Soil survey of Kendall County, Texas: Soil Conservation Service, 

87 p., 22 map sheets.

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[Natural Resources Conservation Service], 1984, Soil 

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(Better Assessment Science Integrating Point and Nonpoint 

sources): accessed April 28, 2007, at http://www.epa.gov/

waterscience /basins/.

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December 5, 2006, at http://rockyweb.cr.usgs.gov/elevation/.

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System (NWISWeb) data available on the World Wide Web, 

accessed October 6, 2006, at http://waterdata.usgs.gov/tx/

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The Guadalupe-Lavaca-San Antonio-Nueces River Basins 

regional study—Biologic assemblages, San Antonio EastLlano East sheets: Austin, pl. 4.

Wicklein, S.M., and Schiffer, D.M., 2002, Simulation of runoff and water quality for 1990 and 2008 land-use conditions 

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Geological Survey Water-Resources Investigations Report 

02–4018, 62 p.

22 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 5. Streamflow calibration and testing results, Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas, 1992–2004.

[acre-ft, acre-feet; ft3/s, cubic feet per second; --, not applicable]

Cibolo Creek at Interstate Highway 10 above Boerne, Texas (08183850) 

Comparison of streamflow volumes and peaks Measured

streamflow

Simulated

streamflow

Error1

(percent)

Criteria2

(percent)

Calibration period 1997–2000

Total flow volume, acre-ft 50,400 49,800 -1.2 10.0

Total of highest 10 percent of daily flows, acre-ft 36,000 34,600 -3.9 15.0

Total of lowest 50 percent of daily flows, acre-ft 1,600 1,750 9.4 10.0

Average of selected storm peaks, ft3/s (three storms) 7,590 8,950 17.9 --

Testing period 2001–04

Total flow volume, acre-ft 91,600 87,500 -4.5 10.0

Total of highest 10 percent of daily flows, acre-ft 59,500 62,800 5.5 15.0

Total of lowest 50 percent of daily flows, acre-ft 6,040 5,130 -15.1 10.0

Average of selected storm peaks, ft3/s (three storms) 5,610 3,260 -41.9 --

Entire (calibration and testing) period 1997–2004

Total flow volume, acre-ft 142,000 137,000 -3.5 10.0

Total of highest 10 percent of daily flows, acre-ft 98,400 97,700 -.7 15.0

Total of lowest 50 percent of daily flows, acre-ft 5,680 4,920 -13.4 10.0

Average of selected storm peaks, ft3/s (six storms) 6,600 6,100 -7.6 --

Model-fit statistics 1997–2004 Annual Monthly Daily Hourly

Number of years, months, days, or hours 8 96 2,922 70,128

Coefficient of determination .94 .98 .95 .87

Coefficient of model-fit efficiency .91 .96 .91 .82

Percent time simulated within 10 percent of measured 37.5 22.9 22.6 22.1

Percent time simulated within 25 percent of measured 41.7 34.4 36.2 36.1

Cibolo Creek near Boerne, Texas (08183900)

Comparison of streamflow volumes and peaks Measured

streamflow

Simulated

streamflow

Error1

(percent)

Criteria2

(percent)

Testing period 1992–94

Total flow volume, acre-ft 96,600 96,600 -4.8 10.0

Total of highest 10 percent of daily flows, acre-ft 58,300 54,900 -5.8 15.0

Total of lowest 50 percent of daily flows, acre-ft 5,510 5,310 -3.6 10.0

Average of selected storm peaks, ft3/s (three storms) 6,980 7,420 6.3 --

Model-fit statistics 1992–94 Annual Monthly Daily Hourly

Number of years, months, days, or hours 3 36 1,096 26,280

Coefficient of determination 1.00 .96 .93 .82

Coefficient of model-fit efficiency .99 .94 .92 .77

Percent time simulated within 10 percent of measured 66.7 25.0 15.0 29.8

Percent time simulated within 25 percent of measured 100 55.6 38.7 39.0

Tables

Tables 23
Table 5. Streamflow calibration and testing results, Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas, 1992–2004—Continued. 

Cibolo Creek at Selma, Texas (08185000) 

Comparison of streamflow volumes and peaks Measured

streamflow

Simulated

streamflow

Error1

(percent)

Criteria2

(percent)

Calibration period 1997–2000

Total flow volume, acre-ft 230,000 226,000 -1.7 10.0

Total of highest 10 percent of daily flows, acre-ft 230,000 226,000 -1.7 15.0

Total of lowest 50 percent of daily flows, acre-ft 0 0 0 10.0

Average of selected storm peaks, ft3/s (three storms) 56,700 48,300 -14.8 --

Testing period 2001–04

Total flow volume, acre-ft 248,000 262,000 5.6 10.0

Total of highest 10 percent of daily flows, acre-ft 248,000 262,000 5.6 15.0

Total of lowest 50 percent of daily flows, acre-ft 0 0 0 10.0

Average of selected storm peaks, ft3/s (three storms) 26,800 17,800 -33.6 --

Entire (calibration and testing) period 1997–2004

Total flow volume, acre-ft 478,000 488,000 2.1 10.0

Total of highest 10 percent of daily flows, acre-ft 478,000 488,000 2.1 15.0

Total of lowest 50 percent of daily flows, acre-ft 0 0 0 10.0

Average of selected storm peaks, ft3/s (six storms) 41,700 33,000 -20.9 --

Model-fit statistics 1997–2004 Annual Monthly Daily Hourly

Number of years, months, days, or hours 8 96 2,922 70,128

Coefficient of determination 1.00 1.00 .97 .91

Coefficient of model-fit efficiency .99 1.00 .97 .90

Percent time simulated within 10 percent of measured 75.0 79.2 91.7 92.6

Percent time simulated within 25 percent of measured 75.0 80.2 92.5 93.3

1 Error = [(simulated-measured)/measured]x100.

2

 Default error criteria from HSPEXP (Lumb and others, 1994).

24 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 6. Simulated evapotranspiration, upper Cibolo Creek watershed, and measured 

evapotranspiration, Honey Creek watershed, south-central Texas, March–December 2002. 

[ET, evapotranspiration]

Month Simulated ET (inches)

Cibolo Creek1

Measured ET (inches)

Honey Creek

Error2

(percent)

March 1.6 2.2 -27

April 3.2 3.0 7

May 2.0 2.9 -31

June 2.1 3.1 -32

July 4.7 4.1 15

August 3.6 3.7 -3

September 3.7 2.8 32

October 2.7 2.2 23

November 2.8 1.8 47

December 2.2 1.4 38

March–December 28.6 27.5 4

1 Simulated ET for PERLND type Glen Rose Limestone, juniper-live oak woodland, moderately dense.

2 Error = [(simulated-measured)/measured] x 100. 

Tables 25
Table 7. Selected annual PERLND and IMPLND process-related parameters for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, southcentral Texas. 

[Parameter definitions in table 1; PERLND, pervious land segment; IMPLND, impervious land segment; --, not applicable]Glen Rose Limestone—shallow soil, moderate slope 

Land cover AGWETP AGWRC BASETP CEPSC DEEPFR INFILT INTFW IRC KVARY LSUR LZSN NSUR RETSC UZSN

PERLND

Juniper woodland 0.01 0.97 0 0.50 0.15 0.18 0.58 0.54 0 350 2.7 0.31 -- 0.34Juniper-live oak woodland, very dense .01 .97 0 .50 .15 .18 .58 .54 0 350 2.7 .31 -- .34Juniper-live oak woodland, dense .01 .97 0 .45 .15 .18 .58 .54 0 350 2.7 .31 -- .34Juniper-live oak woodland, moderately dense .01 .97 0 .40 .15 .18 .58 .54 0 350 2.7 .31 -- .34Juniper-post oak woodland .01 .97 0 .45 .15 .18 .58 .54 0 350 2.7 .31 -- .34Oak-juniper woodland, moderately dense .01 .97 0 .40 .15 .18 .58 .54 0 350 2.7 .31 -- .34Oak-juniper woodland, slightly dense .01 .97 0 .35 .15 .18 .58 .54 0 350 2.7 .31 -- .34Oak-persimmon woodland, dense .01 .97 0 .30 .15 .18 .58 .54 0 350 2.7 .31 -- .34Oak-persimmon woodland, moderately dense .01 .97 0 .25 .15 .18 .58 .54 0 350 2.7 .31 -- .34Mixed woodland .01 .97 0 .15 .15 .18 .58 .54 0 350 2.7 .31 -- .34Juniper-persimmon savanna .01 .97 0 .40 .15 .18 .58 .54 0 350 2.7 .31 -- .34Oak savanna .01 .97 0 .25 .15 .18 .58 .54 0 350 2.7 .31 -- .34Mesquite savanna .01 .97 0 .12 .15 .18 .58 .54 0 350 2.7 .31 -- .34Shrubland .01 .97 0 .12 .15 .18 .58 .54 0 350 2.7 .31 -- .34Grassland .01 .97 0 .10 .15 .18 .58 .54 0 350 2.7 .31 -- .34Bluestem prairie .01 .97 0 .12 .15 .18 .58 .54 0 350 2.7 .31 -- .34Shortgrass prairie .01 .97 0 .15 .15 .18 .58 .54 0 350 2.7 .31 -- .34Pasture .01 .97 0 .12 .15 .18 .58 .54 0 350 2.7 .31 -- .34Cropland .01 .97 0 .10 .15 .18 .58 .54 0 350 2.7 .31 -- .34Urban lawn .01 .97 0 .12 .15 .18 .58 .54 0 350 2.7 .31 -- .34Exposed ground and rocky slopes .01 .97 0 .05 .15 .15 .58 .54 0 350 2.7 .31 -- .34Water, water edge, and wetlands .01 .97 0 .12 .15 .15 .58 .54 0 350 3.0 .31 -- .34

IMPLND

All impervious -- -- -- -- -- -- -- -- -- 350 -- .10 0.05 --

26  Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 7. Selected annual PERLND and IMPLND process-related parameters for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, southcentral Texas—Continued. 

Glen Rose Limestone—deep soil, moderate slope 

Land cover AGWETP AGWRC BASETP CEPSC DEEPFR INFILT INTFW IRC KVARY LSUR LZSN NSUR RETSC UZSN

PERLND

Juniper woodland 0.01 0.93 0.01 0.50 0.45 0.26 0.90 0.50 0 350 3.9 0.31 -- 0.42Juniper-live oak woodland, very dense .01 .93 .01 .50 .45 .26 .90 .50 0 350 3.9 .31 -- .42Juniper-live oak woodland, dense .01 .93 .01 .45 .45 .26 .90 .50 0 350 3.9 .31 -- .42Juniper-live oak woodland, moderately dense .01 .93 .01 .40 .45 .26 .90 .50 0 350 3.9 .31 -- .42Juniper-post oak woodland .01 .93 .01 .45 .45 .26 .90 .50 0 350 3.9 .31 -- .42Oak-juniper woodland, moderately dense .01 .93 .01 .35 .45 .26 .90 .50 0 350 3.9 .31 -- .42Oak-juniper woodland, slightly dense .01 .93 .01 .30 .45 .26 .90 .50 0 350 3.9 .31 -- .42Oak-persimmon woodland, dense .01 .93 .01 .30 .45 .26 .90 .50 0 350 3.9 .31 -- .42Oak-persimmon woodland, moderately dense .01 .93 .01 .25 .45 .26 .90 .50 0 350 3.9 .31 -- .42Mixed woodland .01 .93 .01 .15 .45 .26 .90 .50 0 350 3.9 .31 -- .42Juniper-persimmon savanna .01 .93 .01 .40 .45 .26 .90 .50 0 350 3.9 .31 -- .42Oak savanna .01 .93 .01 .25 .45 .26 .90 .50 0 350 3.9 .31 -- .42Mesquite savanna .01 .93 .01 .12 .45 .26 .90 .50 0 350 3.9 .31 -- .42Shrubland .01 .93 .01 .12 .45 .26 .90 .50 0 350 3.9 .31 -- .42Grassland .01 .93 .01 .10 .45 .28 .90 .50 0 350 3.9 .31 -- .48Bluestem prairie .01 .93 .01 .12 .45 .28 .90 .50 0 350 3.9 .31 -- .48Shortgrass prairie .01 .93 .01 .15 .45 .28 .90 .50 0 350 3.9 .31 -- .48Pasture .01 .93 .01 .12 .45 .28 .90 .50 0 350 3.9 .31 -- .48Cropland .01 .93 .01 .10 .45 .28 .90 .50 0 350 3.9 .31 -- .48Urban lawn .01 .93 .01 .12 .45 .28 .90 .50 0 350 3.9 .31 -- .48Exposed ground and rocky slopes .01 .93 .01 .05 .45 .20 .90 .50 0 350 3.9 .31 -- .42Water, water edge, and wetlands .01 .93 .01 .10 .45 .20 .90 .50 0 350 3.9 .31 -- .42

IMPLND

All impervious -- -- -- -- -- -- -- -- -- 350 -- .10 0.06 --

Tables 27
Table 7. Selected annual PERLND and IMPLND process-related parameters for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, southcentral Texas—Continued. 

Edwards aquifer outcrop—moderate slope 

Land cover AGWETP AGWRC BASETP CEPSC DEEPFR INFILT INTFW IRC KVARY LSUR LZSN NSUR RETSC UZSN

PERLND

Juniper woodland 0.01 0.90 0.01 0.50 0.85 0.34 0.80 0.45 0 350 3.6 0.31 -- 0.42Juniper-live oak woodland, very dense .01 .90 .01 .50 .85 .34 .80 .45 0 350 3.6 .31 -- .42Juniper-live oak woodland, dense .01 .90 .01 .45 .85 .34 .80 .45 0 350 3.6 .31 -- .42Juniper-live oak woodland moderately dense .01 .90 .01 .40 .85 .34 .80 .45 0 350 3.6 .31 -- .42Juniper-post oak woodland .01 .90 .01 .45 .85 .34 .80 .45 0 350 3.6 .31 -- .42Oak-juniper woodland, moderately dense .01 .90 .01 .40 .85 .34 .80 .45 0 350 3.6 .31 -- .42Oak-juniper woodland, slightly dense .01 .90 .01 .35 .85 .34 .80 .45 0 350 3.6 .31 -- .42Oak-persimmon woodland, dense .01 .90 .01 .30 .85 .34 .80 .45 0 350 3.6 .31 -- .42Oak-persimmon woodland, moderately dense .01 .90 .01 .25 .85 .34 .80 .45 0 350 3.6 .31 -- .42Mixed woodland .01 .90 .01 .15 .85 .34 .80 .45 0 350 3.6 .31 -- .42Juniper-persimmon savanna .01 .90 .01 .40 .85 .34 .80 .45 0 350 3.6 .31 -- .42Oak savanna .01 .90 .01 .25 .85 .34 .80 .45 0 350 3.6 .31 -- .42Mesquite savanna .01 .90 .01 .12 .85 .34 .80 .45 0 350 3.6 .31 -- .42Shrubland .01 .90 .01 .12 .85 .34 .80 .45 0 350 3.6 .31 -- .42Grassland .01 .90 .01 .10 .85 .37 .80 .45 0 350 3.6 .31 -- .48Bluestem prairie .01 .90 .01 .12 .85 .37 .80 .45 0 350 3.6 .31 -- .48Shortgrass prairie .01 .90 .01 .15 .85 .37 .80 .45 0 350 3.6 .31 -- .48Pasture .01 .90 .01 .12 .85 .37 .80 .45 0 350 3.6 .31 -- .48Cropland .01 .90 .01 .10 .85 .37 .80 .45 0 350 3.6 .31 -- .48Urban lawn .01 .90 .01 .12 .85 .37 .80 .45 0 350 3.6 .31 -- .48Exposed ground and rocky slopes .01 .90 .01 .05 .85 .30 .80 .45 0 350 3.6 .31 -- .42Water, water edge, and wetlands .01 .90 .01 .10 .85 .30 .80 .45 0 350 3.6 .31 -- .42

IMPLND

All impervious -- -- -- -- -- -- -- -- -- 350 -- .10 0.12 --

28  Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 7. Selected annual PERLND and IMPLND process-related parameters for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, southcentral Texas—Continued. 

Austin Group (Edwards aquifer confining unit)—moderate slope 

Land cover AGWETP AGWRC BASETP CEPSC DEEPFR INFILT INTFW IRC KVARY LSUR LZSN NSUR RETSC UZSN

PERLND

Juniper woodland 0.01 0.95 0.01 0.50 0.50 0.37 1.15 0.54 0 350 4.0 0.31 -- 0.62Juniper-live oak woodland, very dense .01 .95 .01 .50 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Juniper-live oak woodland, dense .01 .95 .01 .45 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Juniper-live oak woodland, moderately dense .01 .95 .01 .40 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Juniper-post oak woodland .01 .95 .01 .45 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Oak-juniper woodland, moderately dense .01 .95 .01 .40 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Oak-juniper woodland, slightly dense .01 .95 .01 .35 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Oak-persimmon woodland, dense .01 .95 .01 .30 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Oak-persimmon woodland, moderately dense .01 .95 .01 .25 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Mixed woodland .01 .95 .01 .15 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Juniper-persimmon savanna .01 .95 .01 .40 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Oak savanna .01 .95 .01 .25 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Mesquite savanna .01 .95 .01 .12 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Shrubland .01 .95 .01 .12 .50 .37 1.15 .54 0 350 4.0 .31 -- .62Grassland .01 .95 .01 .10 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Bluestem prairie .01 .95 .01 .12 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Shortgrass prairie .01 .95 .01 .15 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Pasture .01 .95 .01 .12 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Cropland .01 .95 .01 .10 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Urban lawn .01 .95 .01 .12 .50 .40 1.15 .54 0 350 4.0 .31 -- .62Exposed ground and rocky slopes .01 .95 .01 .05 .50 .30 1.15 .54 0 350 4.0 .31 -- .62Water, water edge, and wetlands .01 .95 .01 .10 .50 .30 1.15 .54 0 350 4.0 .31 -- .62

IMPLND

All impervious -- -- -- -- -- -- -- -- -- 350 -- .10 0.15 --

Tables 29
Table 8. Monthly values of lower-zone evapotranspiration (LZETP) parameter for the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek watershed, southcentral Texas.

[PERLND, pervious land segment]All geology-soil combinations 

Land cover Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

PERLND

Juniper woodland 0.4 0.4 0.5 0.6 0.7 0.7 0.7 0.8 0.8 0.6 0.5 0.4Juniper-live oak woodland, very dense .4 .4 .5 .6 .7 .7 .7 .8 .8 .7 .5 .4Juniper-live oak woodland, dense .3 .3 .4 .6 .7 .7 .7 .7 .7 .7 .5 .4Juniper-live oak woodland, moderately dense .3 .3 .4 .6 .7 .7 .7 .7 .7 .6 .5 .4Juniper-post oak woodland .3 .3 .4 .6 .7 .7 .7 .7 .7 .6 .5 .4Oak-juniper woodland, moderately dense .3 .3 .4 .6 .7 .7 .7 .7 .7 .6 .5 .4Oak-juniper woodland, slightly dense .3 .3 .4 .6 .7 .7 .7 .7 .7 .6 .5 .3Oak-persimmon woodland, dense .3 .3 .3 .5 .6 .7 .7 .7 .7 .6 .4 .2Oak-persimmon woodland, moderately dense .2 .2 .3 .5 .6 .7 .7 .7 .7 .6 .4 .2Mixed woodland .1 .2 .3 .5 .6 .7 .7 .7 .7 .6 .5 .2Juniper-persimmon savanna .2 .3 .3 .5 .6 .7 .7 .7 .7 .6 .5 .2Oak savanna .1 .1 .3 .7 .8 .8 .8 .8 .8 .5 .3 .2Mesquite savanna .1 .2 .3 .6 .6 .7 .7 .7 .6 .5 .2 .1Shrubland .1 .1 .3 .7 .8 .8 .8 .8 .8 .4 .3 .1Grassland .1 .1 .3 .7 .8 .8 .8 .8 .8 .4 .3 .1Bluestem prairie .1 .1 .3 .7 .8 .8 .8 .8 .8 .4 .3 .1Shortgrass prairie .1 .1 .3 .7 .8 .8 .8 .8 .8 .4 .3 .1Pasture .1 .1 .3 .7 .8 .7 .7 .7 .7 .6 .5 .2Cropland .1 .2 .3 .5 .6 .7 .7 .7 .7 .6 .5 .2Urban lawn .1 .1 .3 .7 .8 .8 .8 .8 .8 .4 .2 .1Exposed ground and rocky slopes .1 .1 .3 .4 .4 .4 .4 .4 .4 .3 .2 .1Water, water edge, and wetlands .1 .1 .3 .7 .8 .8 .8 .8 .7 .4 .3 .1

30 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 9. Measured and simulated average annual streamflow per unit area (runoff) at selected sites on Cibolo Creek, south-central 

Texas, 1992–2004. 

[Sites listed in downstream order; USGS, U.S. Geological Survey; RCHRES, stream or reservoir reach; --, not available] 

Site

number

(fig. 5)

Location

Drainage

area

(square 

miles)

Measured 

runoff

(inches per year)

Simulated

runoff

(inches per year)

10 USGS station 08183850 Cibolo Creek at Interstate Highway 

10 above Boerne, Texas (downstream from confluence of 

RCHRES 26 and RCHRES 28)

29 -- 8.90

12 USGS partial-record station 08183950 Cibolo Creek at Ralph 

Fair Road below Boerne, Texas (outlet of RCHRES 88)

112 -- 7.65

15 USGS partial-record station 08183995 Cibolo Creek at U.S. 

Highway 281 near Bulverde, Texas (outlet of RCHRES 154)

179 -- 4.58

17 USGS partial-record station 08184300 Cibolo Creek at Farm 

Road 1863 below Bulverde, Texas (outlet of RCHRES 180)

240 -- 3.76

18 USGS station 08185000 Cibolo Creek at Selma, Texas (outlet of 

RCHRES 212)

274 3.16 3.22

Table 10. Estimated annual rainfall and ground-water recharge, 

upper Cibolo Creek watershed, south-central Texas, 1992–2004. 

Year Rainfall

(inches)

Recharge

(acre-feet)

Recharge

(inches)

1992 54.24 196,000 13.43

1993 28.02 45,600 3.13

1994 36.01 49,500 3.39

1995 28.68 33,200 2.28

1996 24.19 15,600 1.07

1997 48.70 94,000 6.44

1998 48.88 119,000 8.16

1999 15.83 14,500 .99

2000 34.38 66,900 4.58

2001 44.49 125,000 8.57

2002 49.45 124,500 8.53

2003 26.92 48,000 3.29

2004 46.69 105,000 7.20

Average 37.43 79,800 5.47

Tables  31
Table 11. Estimated average annual rainfall, diffuse recharge, stream-channel recharge, and total recharge by surficial unit, upper Cibolo Creek watershed, south-central 

Texas. [Rainfall and recharge estimates are average annual values] 

Surficial unit

Stream segments

(RCHRES)

(fig. 6)

Area

(acres)

Rainfall

(inches)

Diffuse

recharge1

(acre-feet)

Streamchannel

recharge2

(acre-feet)

Total

recharge3

(acre-feet)

Trinity aquifer outcrop (largely upper Glen Rose Limestone) 10–88 71,860 39.10 4,050 11,200 15,200Trinity aquifer outcrop (largely lower Glen Rose Limestone) 90–176 74,123 36.87 12,000 34,300 46,300Transition from Trinity aquifer outcrop to Edwards aquifer outcrop 180–190 13,689 36.87 2,710 7,490 10,200Edwards aquifer outcrop 192–196 6,801 35.03 2,200 2,930 5,130Transition from Edwards aquifer outcrop to Edwards aquifer upper confining unit 198, 206 3,693 31.15 95 350 445Edwards aquifer upper confining unit 200–204, 208–212 4,930 31.15 60 2,430 2,490

Entire watershed 175,096 37.43 21,100 58,700 79,800

1 Direct infiltration of rainfall through soil and rock layers and karst features to ground water.2 Infiltration of streamflow, primarily through karst features in the channel, to ground water.3 Sum of diffuse and channel recharge. 

32 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Table 12. Specifications of flood-control/recharge-enhancement structures simulated with the Hydrological Simulation Program—FORTRAN model, upper Cibolo Creek 

watershed, south-central Texas. [Structures S–74, S–86, S–106, S–126, S–134, S–144, and S–172 on tributaries; structures S–160 and S–191 on main-stem Cibolo Creek] 

Structure

identification

number

(fig. 10)

Contributing

drainage

area

(acres)

Dam 

height

(feet)

Dam width

(feet)

Emergency

spillway

height

(feet)

Inundation

surface area

at emergency

spillway 

(acres)

Inundation

surface area

at top of dam

(acres)

Storage volume

at emergency 

spillway 

(acre-feet)

Storage volume

at top of dam

(acre-feet)

Maximum

spillwaycapacity 

(cubic feet

per second)

S–74 2,410 75 1,800 60 145 211 2,640 5,330 75,800S–86 4,150 58 3,500 43 276 513 4,030 9,970 54,700S–106 5,280 60 2,800 45 333 504 5,100 11,380 76,000S–126 3,811 50 2,700 39 211 335 2,950 5,960 37,700S–134 2,237 65 2,350 52 235 344 4,580 8,310 50,900S–144 4,615 50 2,750 44 177 299 2,790 5,420 37,400S–160 126,340 50 2,650 40 580 858 6,840 13,800 75,500S–172 8,203 37 1,900 26 251 376 2,880 6,350 35,200S–191 159,610 80 800 60 620 1,025 11,280 27,600 100,000

Tables  33
Table 13. Simulation results for various scenarios of flood-control/recharge-enhancement structure implementation using the Hydrological Simulation Program—FORTRAN 

model, upper Cibolo Creek watershed, south-central Texas. [Structures S–74, S–86, S–106, S–126, S–134, S–144, and S–172 on tributaries; structures S–160 and S–191 on main-stem Cibolo Creek; --, not applicable] 

Scenario

(see fig. 10 for

structure

location)

Simulated peak

discharge at

USGS station

08185000 during

October 1998 flood1

(cubic feet per second)

Change in

simulated peak

discharge from

baseline scenario

(percent)

Channel infiltration

recharge—Trinity

aquifer outcrop, 

1992–2004

annual average

(acre-feet)

Channel infiltration

recharge—transition

from Trinity aquifer

outcrop to Edwards

aquifer recharge zone

(outcrop), 1992–2004

annual average

(acre-feet)

Channel infiltration

recharge—Edwards

aquifer recharge

zone (outcrop), 

1992–2004

annual average

(acre-feet)

Channel infiltration

recharge—transition

from Edwards aquifer

recharge zone (outcrop)

to Edwards aquifer

upper confining unit, 

1992–2004 annual average

(acre-feet)

Baseline (no structures) 77,600 -- 45,500 7,490 2,930 2,780Scenarios with individual structures

S–74 77,600 0 45,600 7,480 2,920 2,770S–86 77,600 0 45,600 7,480 2,920 2,770S–106 76,400 -1.50 45,700 7,510 2,940 2,780S–126 74,800 -3.60 45,800 7,450 2,900 2,760S–134 76,000 -2.10 45,800 7,480 2,920 2,770S–144 73,400 -5.40 46,700 7,420 2,890 2,750S–160 58,000 -25.3 48,500 7,410 3,070 2,930S–172 71,400 -8.00 46,600 6,990 2,840 2,730S–191 64,500 -16.9 45,500 7,490 4,310 3,250

Scenarios with multiple structures

S–160, S–191 48,900 -37.0 48,500 8,320 3,300 3,220S–106, S–126, S–144 69,000 -11.1 46,100 7,390 2,870 2,730S–126, S–144, S–160 56,800 -26.8 48,700 7,380 3,050 2,930S–126, S–144, S–191 56,900 -26.7 45,800 7,370 4,210 3,200

1 Simulated peaks are hourly average discharges. Actual instantaneous peak discharge at 08185000 on October 17, 1998, was 98,100 cubic feet per second. This reported discharge was estimated using indirect measurement techniques (Gandara, 2003)

34 Simulation of Streamflow and Estimation of Ground-Water Recharge in the Upper Cibolo Creek Watershed
Prepared by the USGS Lafayette Publishing center.

Information regarding water resources in Texas is available at 

http: //tx.usgs.gov/