SIMULATION OF STORM PEAKS AND STORM 

VOLUMES FOR SELECTED SUBBASINS IN 

THE WEST FORK TRINITY RIVER BASIN, 

TEXAS, WATER YEARS 1993^-94

By Timothy H. Raines

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 96-4110

Prepared in cooperation with the 

TARRANT COUNTY WATER CONTROL AND 

IMPROVEMENT DISTRICT NO. 1

Austin, Texas 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement 

by the U.S. Government.

For additional information write to:

District Chief 

U.S. Geological Survey 

8011 Cameron Rd. 

Austin, TX 78754-3898

Copies of this report can be purchased from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
CONTENTS

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

Introduction .........................................................................................................................................................................^ 1

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

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

Description of Simulation Model ............................................................................................................................. 2

Regional Basin Characteristics ................................................................................................................................. 5

Gaged Subbasins........................................................................................................................................................ 5

Acknowledgments .................................................................................................................................................... 8

Simulation of Storm Peaks and Storm Volumes .................................................................................................................. 9

Model Calibration and Testing ................................................................................................................................. 11

Error Analysis ........................................................................................................................................................... 14

Sensitivity Analysis .................................................................................................................................................. 16

Model Recalibration and Testing .............................................................................................................................. 17

Transfer of Model Parameters to Ungaged Subbasins .............................................................................................. 21

Summary .............................................................................................................................................................................. 22

References Cited .................................................................................................................................................................. 23

FIGURES

1. Map showing location of West Fork Trinity River Basin ..................................................................................... 3

2. Map showing major subbasins in the West Fork Trinity River Basin .................................................................. 4

3 7. Maps showing data-collection network for the:

3. Beans Creek subbasin ................................................................................................................................ 6

4. Big Creek subbasin .................................................................................................................................... 7

5. Garrett Creek subbasin ............................................................................................................................... 8

6. Salt Creek subbasin .................................................................................................................................... 9

7. Walnut Creek subbasin .............................................................................................................................. 10

8. Measured and simulated hydrographs for Walnut Creek at Reno, Texas, September 13-14, 1993 ..................... 12

9. Measured and simulated hydrographs for Garrett Creek near Paradise, Texas, May 11 13, 1994 ...................... 13

10-13. Graphs showing:

10. Measured times of peak and simulated times of peak using calibrated parameters .................................. 14

11. Measured storm peaks and simulated storm peaks using calibrated parameters ....................................... 15

12. Measured storm volumes and simulated storm volumes using calibrated parameters .............................. 16

13. Rainfall and measured storm volume ........................................................................................................ 17

14. Measured and simulated hydrographs for Beans Creek at Wizard Wells, Texas, February 14^16, 1993 ............ 19

15. Measured and simulated hydrographs for Big Creek near Chico, Texas, October 19-20, 1993 ......................... 20

16-18. Graphs showing:

16. Measured times of peak and simulated times of peak using recalibrated parameters ............................... 21

17. Measured storm peaks and simulated storm peaks using recalibrated parameters .................................... 22

18. Measured storm volumes and simulated storm volumes using recalibrated parameters ........................... 23

TABLES

1. Process-related model parameters for the Hydrologic Simulation Program FORTRAN .................................. 24

2. Basin-related model parameters for the Hydrologic Simulation Program FORTRAN ..................................... 24

3. Gaged subbasins in the West Fork Trinity River Basin upstream from Lake Worth ........................................... 25

4. Basin-related parameters for each gaged subbasin ............................................................................................... 25

5. Calibrated annual parameters ............................................................................................................................... 27

6. Calibrated monthly parameters ............................................................................................................................. 28

7. Initial condition values for model calibration ....................................................................................................... 29

CONTENTS iii
8. Measured and simulated storm peaks and storm volumes using calibrated parameters ...................................... 30

9. Mean absolute errors and biases of storm peaks and storm volumes using calibrated parameters ...................... 33

10. Monthly distribution of errors of storm peaks and storm volumes using calibrated parameters ......................... 33

11. Sensitivity of selected parameters ........................................................................................................................ 34

12. Recalibrated annual parameters ............................................................................................................................ 35

13. Recalibrated monthly parameters ......................................................................................................................... 36

14. Initial condition values for model recalibration ................................................................................................... 37

15. Measured and simulated storm peaks and storm volumes using recalibrated parameters ................................... 38

16. Mean absolute errors and biases of storm peaks and storm volumes using recalibrated parameters ................... 41

17. Monthly distribution of errors of storm peaks and storm volumes using recalibrated parameters ...................... 41
Simulation of Storm Peaks and Storm 

Volumes for Selected Subbasins in 

the West Fork Trinity River Basin, 

Texas, Water Years 1993-94

By Timothy H. Raines

Abstract

A model parameter set for use with the 

Hydrologic Simulation Program FORTRAN 

watershed model was developed to simulate storm 

peaks and storm volumes for the 28 subbasins of 

the West Fork Trinity River Basin upstream from 

Lake Worth, northwest of Fort Worth, Texas, from 

the calibration and testing of 5 gaged subbasins. 

These parameters can be transferred to the 23 

ungaged subbasins. The model simulates storm 

runoff for a channel-routing model that can be used 

to improve reservoir operation during floods in the 

basin.

Rainfall and runoff data were collected from 

October 1, 1992, to September 30, 1994. A total of 

55 storms were recorded at the 5 streamgage stations during the 24 months. Twelve different pervious land segments were defined based on types of 

soil, land cover, and watershed slope. A total of 20 

process-related parameters were defined for each 

land segment, and 6 basin-related parameters were 

defined for each stream reach.

The mean absolute errors for the 5 subbasins 

for simulation of storm peaks range from 48.0 to 

470 percent and for simulation of storm volumes 

range from 34.4 to 416 percent. A sensitivity analysis was done to determine what a change in a 

parameter value has on the largest storm peak and 

on the total storm volume. The model then was 

recalibrated and tested on the basis of the analysis 

of the sensitivity of parameters and on the analysis 

of the errors from the initial model calibration and 

testing. The mean absolute errors for the 5 subbasins using the recalibrated parameters for simulation of storm peaks range from 47.1 to 297 

percent, and for simulation of storm volumes range 

from 27.6 to 193 percent.

The model produced better results for simulation of the larger storm peaks and storm volumes 

than for simulation of the smaller storm peaks and 

storm volumes, especially after an extended period 

of no runoff. The same range in errors can be 

expected when transferring the parameters to the 

23 ungaged subbasins. Additional data collection 

and model refinement could decrease the range of 

expected model errors. More storm data and 

improved discharge rating curves could result in 

model parameters that account for the wide seasonal variations in runoff in the study area.

INTRODUCTION

Recent flooding (1990) in the West Fork Trinity 

River Basin upstream from Lake Worth, northwest of 

Fort Worth, Texas, has caused extensive damage to public and private property and has resulted in a need for 

improved flood forecasting to better manage reservoir 

operation. Although simulation models for flood routing in the main channel of the West Fork Trinity River 

and in reservoirs are available for the basin, rainfallrunoff data for the subbasins are lacking. Accurate estimates of storm runoff for the 28 subbasins that drain 

into the West Fork Trinity River Basin upstream from 

Lake Worth are needed for input into a channel-routing 

model. Previous attempts to use event-based simulation 

models have been unsatisfactory because the models 

were unable to accurately estimate the volume, magnitude, and timing of peak flows. A range in evaporation, 

infiltration, and storage capacities measured throughout 

the year results in a wide variation of storm runoff. 

Therefore, continuous-simulation models could provide

Abstract
a better representation of seasonal variations of rainfall 

and runoff than event-based simulation models.

In 1991, the U.S. Geological Survey, in cooperation with the Tarrant County Water Control and 

Improvement District No. 1, began a study lo develop 

a model parameter set to simulate storm peaks and volumes for selected subbasins in the West Fork Trinity 

River Basin. Specific objectives of the study were to 

(1) develop a set of parameters for a continuoussimulation model from the calibration and testing of 5 

gaged subbasins; (2) transfer the parameter set to the 

remaining 23 ungaged subbasins of the West Fork Trinity River Basin upstream from Lake Worth; and (3) use 

the model to simulate storm runoff in the basin to 

improve reservoir operation during floods.

Purpose and Scope

This report describes the simulation of storm 

peaks and storm volumes for 5 gaged subbasins in 

the West Fork Trinity River Basin upstream from 

Lake Worth. Rainfall and runoff data from 55 storms 

used in this report were collected during water years 

1993-94 (October 1. 1992, to September 30, 1994). 

Each subbasin was characterized by twelve various 

pervious land segments that were defined based on 

types of soil, land cover, and watershed slope and 

was subdivided into two to three reaches for input to 

a continuous-simulation model. A total of 20 processrelated parameters were defined for each land segment, 

and 6 basin-related parameters were defined for each 

stream reach.

Description of Study Area

The study area is in the north-central part of 

Texas (fig. 1). The West Fork Trinity River Basin 

upstream from Lake Worth drains about 2,100 square 

miles (mi ). The basin is divided into 28 major subbasins that range from 15.8 to 227 mi and contains 

three major reservoirs: Lake Bridgeport, Eagle Mountain Lake, and Lake Worth (fig. 2).

The study area is characterized by a moderate 

climate with hot, dry summers; warm, wet autumns; 

cool, dry winters; and warm, wet springs. Mean annual 

temperature for the study area is 64 °F (degrees Fahrenheit) with monthly means ranging from 44 °F in 

January to 85 °F in July. Mean annual precipitation, 

mostly as rainfall, totals about 28 inches (in.) (National 

Oceanic and Atmospheric Administration, 1990). 

Rainfall in the study area is generated from frontal systems and convective heating. The frontal systems in 

spring and fall produce moderate- to high-intensity, 

long-duration storms that generally result in the maximum storm peaks for the year. Convective thunderstorms produce widely scattered, high-intensity, shortduration storms that occur mostly in summer. 

Soils in the basin consist mainly of the 

Windthorst-Duffau and the Truce-Bonti primary series. 

The Windthorst-Duffau series consists of deep, sandyloam soils formed in weakly cemented sandstone that 

has moderately low permeability. A representative soil 

profile consists of 10 in. of sandy loam overlying 30 in. 

of sandy-clay loam. The Truce-Bonti series consists of 

deep, clay-loam soils formed in strongly cemented 

sandstone and clay that has low permeability. A representative soil profile consists of 9 in. of fine sandy loam 

overlying 31 in. of clay (U.S. Department of Agriculture, Soil Conservation Service, 1977, 1978, 1981). 

Land cover is characterized by alternating prairies and 

woodlands consisting of mesquite, juniper, shinnery 

oak, post oak, and live oak trees. The rangeland is used 

for grazing beef and dairy cattle, whereas the cropland 

is used for growing peanuts and grain sorghum. The 

average watershed slope varies from gently sloping to 

sloping, or about 2 to 5 percent.

Description of Simulation Model

The Hydrologic Simulation Program 

FORTRAN (HSPF)(U.S. Environmental Protection 

Agency, 1992) is a continuous-simulation model using 

a conceptual framework to represent infiltration, evaporation, interception storage, surface runoff, interflow, 

and base flow on a pervious land segment (PERLND) 

and retention storage and surface runoff on an impervious land segment (IMPLND). Each user-defined land 

segment represents its own unique hydrologic response 

system based on soil type, land cover, watershed slope, 

or other important basin characteristic. These land segments do not need to be contiguous. The runoff from 

each land segment is moved through a system of 

reaches or reservoirs (RCHRES) using storage routing. 

In addition to runoff, water-quality concentrations for 

several constituents can be simulated for each land 

segment.

The HSPF model uses input from three types of 

data: time series, process-related model parameters, 

and basin-related model parameters. Continuous time 

series of precipitation and potential evaporation are 

needed to execute the model. Point-precipitation data

Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water Years 

199S-94
, .

 . ' >} , '- '-V' / (, ' ''i ' -'[

3 ' X.. "^ "~'~X. " ; "" T ' -

LOCATION MAP

Figure 1. Location of West Fork Trinity River Basin.

INTRODUCTION 3
FT "^C"'

MOMACVoK \97"45' -

\

«:!i"m't'? \

\ i f :,^

ka^Ii 33(

10 15 20 MILES

I ... __...!_ _. ...__. J

EXPLANATION

1 Ungaged subhasin

_J Ciaged subbasin

1 Beans Creek subbasin

2 Big Creek subbasin

3 Garrett Creek subbasin

4 Salt Creek subbasin

5 Walnut Creek subbasin

 Subbasin boundary

Figure 2. Major subbasins in the West Fork Trinity River Basin.

measured by raingages are assumed to be uniform over 

a land segment. Potential evaporation data can be estimated from measured pan evaporation or computed 

using minimum and maximum temperatures. Measured runoff time series are used for model calibration 

and testing.

The 20 process-related model parameters listed 

in table 1 (at end of report) represent the physical processes of soil infiltration, soil moisture, evapotranspiration (ET), interception storage of plants, interflow 

recession, ground-water recession, and surface runoff 

for each land segment. The process-related model

Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water Years 

1993-94
parameters for each land segment are adjusted to 

calibrate the model. The following parameters can 

be varied by month to account for seasonal variations: 

interception storage capacity (CEPSC), interflow 

inflow (INTFW), interflow recession rate (IRC), lower 

zone ET (LZETP), Manning's n for assumed overland 

flow plane (NSUR), and upper zone nominal storage 

(UZSN). The HSPF users manual (U.S. Environmental 

Protection Agency, 1992) provides a more complete 

description of each parameter.

The six basin-related model parameters listed 

in table 2 (at end of report) define the areal extent of 

each land segment, the reach length, and a table of values (FTABLE) of surface area, volume, and discharge 

as a function of depth for each reach of the watershed. 

These parameters represent the physical characteristics 

of each reach of a watershed and generally remain 

unchanged during calibration of the model.

Only one parameter set was developed for the 5 

gaged subbasins to establish a level of confidence in 

transferring the parameter set to the 23 ungaged subbasins. Accuracy might be improved by calibrating 

each basin separately; but calibrating each basin separately would not provide a method for or confidence in 

transferring the parameters to the ungaged subbasins. In 

this study, two gaged subbasins were used for model 

calibration and the remaining three gaged subbasins 

were used for model testing. Error and sensitivity analyses were done. The calibration of HSPF was facilitated 

by the use of an expert system interface developed by 

Lumb and others (1994) that provided graphics, error 

statistics, and advice on which parameters to change.

Regional Basin Characteristics

The HSPF simulation run time increases proportionately to the number of land segments used; therefore, the number of land segments used needs to be such 

that a balance is struck between accuracy and computation time. Geographic information system (GIS) coverages of soil type, land cover, watershed slope, roads, 

and urban areas were analyzed by the cooperator for the 

entire basin to identify basin characteristics that could 

produce unique hydrologic responses (Alice Godbey, 

Tarrant County Water Control and Improvement District No. 1, written commun., 1993). Two groups of soil 

types, three groups of land cover, and two groups of 

watershed slopes were identified to represent 12 unique 

pervious land segments. The two groups of soil types 

were classified as low permeability (less than 2 inches

per hour [in/hr]) and moderately low permeability 

(greater than 2 in/hr). Crop, forest, and pasture characterized the three main land-cover groups. The watershed-slope group was divided into flat (slopes less than 

3 percent) and steep (slopes greater than 3 percent). 

Because less than 2 percent of the entire watershed contains roads and urban areas, no impervious land segments were used.

Gaged Subbasins

Because minimal data existed for the 28 subbasins, a network of raingage and streamgage stations 

was installed to obtain rainfall and runoff data to calibrate and test the continuous-simulation model. Five of 

the 28 subbasins were selected for data collection on the 

basis of their representative soil type, land cover, and 

slope for the entire study area. The drainage areas for 

the 5 gaged subbasins range from 36.0 to 62.6 mi2 (table 

3 at end of report).

Each gaged subbasin was subdivided into two to 

three reaches (figs. 3 7). The basin-related model 

parameters for each gaged subbasin are listed in table 4 

(at end of report). The areas of each pervious land segment were computed for each reach using GIS (Alice 

Godbey, Tarrant County Water Control and Improvement District No. 1, written commun., 1993). Beans 

Creek and Big Creek consist mostly of soil group 1, 

whereas Garrett Creek, Salt Creek, and Walnut Creek 

consist mostly of soil group 2. The three land-cover 

groups are fairly well distributed in each of the five 

subbasins. Most watershed slopes are flat (less than 3 

percent) for the five subbasins. The reach length was 

measured from U.S. Geological Survey (USGS) 7.5 

minute quadrangle topographic maps. A channel cross 

section was measured for each reach to compute the 

FTABLE values (David Marshall, Tarrant County 

Water Control and Improvement District No. 1, written 

commun., 1993). The surface area as a function of 

depth was computed by multiplying the average channel width by the reach length. The volume as a function 

of depth was computed by multiplying the average 

cross-sectional area by the reach length. The discharge 

as a function of depth was either taken from the rating 

table at the streamgage station or was estimated using 

Manning's equation (Chow and others, 1988). The 

basin-related parameters were not adjusted during the 

model calibration process.

Flood-stage data were measured at the five subbasins with float, tape, and stilling-well systems that

INTRODUCTION
97°58'

EXPLANATION

Reach boundary 

L Streamgage station 

£> Raingage station

0

L_

4 MILES

J

Figure 3. Data-collection network for the Beans Creek subbasin.

were installed during February to September 1992. 

Each streamgagc station also included telephone communication equipment for remote data access. The 

streamgages were classified as partial-record gages and 

measured only stage above an index elevation. As a 

result, no base-flow data were recorded. Because the 

objective of this study was to simulate storm peaks and 

storm volumes, the assumption was that the partialrecord streamgages would provide adequate data. Discharge rating tables were developed for each streamgage station using a water-surfacc-profile (WSPRO) 

model (Shearman, 1990). The theoretical rating tables 

were refined when a few direct discharge measurements were available. An effort was made to make 

more direct flood measurements, but because of a 

small number of large floods, the short duration of runoff, and the occurrence of flood peaks in the late 

evening and early morning, few flood measurements

Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water Years 

1993-94
-T-7N

97°56'

33°24'

4 MILES

EXPLANATION

Reach boundary

i. Streamgage station 

> Raingage station

Figure 4. Data-collection network for the Big Creek subbasin.

INTRODUCTION
97°48' 97°46

33°08

97°50"

33°06'

33°02'

0123 4 MILES

I______I______I_____I______I

33°04'.'

EXPLANATION

Reach boundary 

A. Streamgage station 

<$> Raingage station

Figure 5. Data-collection network for the Garrett Creek subbasin.

were made during the study period. No flood measurements were available to refine the rating table for Big 

Creek. Continuous channel modification at Salt Creek 

during the study period required repeated shifting of 

the initial rating table. Rainfall was measured with a 

network of 10 tipping-bucket raingage stations 

(installed and operated by the cooperator) in the 5 

gaged subbasins with 1 raingage for about every 25 

mi\ The raingage network was supplemented by two 

to four daily observer stations in each subbasin. Some 

rainfall data were lost because of instrumentation failure due to lightning strikes during the study period. 

These data were estimated using the rainfall totals

measured at the nearby observer stations. Locations of 

the raingage and streamgage stations for each subbasin 

are shown in figures 3 7. Storm-runoff and rainfall 

data used in this report were collected from October 1, 

1992, to September 30, 1994. Daily pan evaporation 

data measured at Lake Benbrook, about 15 miles (mi) 

south of Lake Worth, were used as representative data 

for the study area.

Acknowledgments

David Marshall, Alice Godbey, Louis Vernault, 

Steve Seija, Boyd Miller, Dale White, and Glenn

Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water Years 

1993-94
97°44'

32°58'

EXPLANATION

Reach boundary 

L Streamgage station 

£> Raingage station

Figure 6. Data-collection network for the Salt Creek subbasin.

Sanderson of the Tarrant County Water Control 

and Improvement District No. 1 assisted with data 

collection, parameter estimation, and model development. Also, several residents in the study area measured 

and recorded daily precipitation. Charles Wood, David 

Tudor, Daryl Pinion, Bradley Mansfield, Jeffrey 

Sandlin, Clyde Schoultz, Ralph Oilman, Vernon 

Hastings, Martin Danz, Glenn Rivers, and Jack Benton 

of the U.S. Geological Survey helped in the installation,

operation, and maintenance of the five streamgage 

stations.

SIMULATION OF STORM PEAKS AND 

STORM VOLUMES

To simulate storm peaks and storm volumes, a set 

of process-related model parameters was determined 

from calibration of data collected from the Beans Creek

SIMULATION OF STORM PEAKS AND STORM VOLUMES
32

EXPLANATION

 Reach boundary

L Streamgage station

^ Raingage station

Figure 7. Data-collection network for the Walnut Creek subbasin.

and Walnut Creek subbasins from October 1, 1992, to 

September 30, 1993 (water year 1993). The parameter 

set was tested temporally on the Beans Creek and 

Walnut Creek subbasins using the data from October 1, 

1993, to September 30, 1994 (water year 1994), and 

spatially on the Big Creek, Garrett Creek, and Salt 

Creek subbasins using data collected during the entire

24-month study period. The temporal and spatial testing provided a level of confidence when transferring 

the parameters to ungaged subbasins. An error analysis 

was done to identify sources of error that are not 

explained by the simulation model. A sensitivity analysis was done to identify which parameters had the 

greatest effect on simulation results. The parameters

10 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
were revised on the basis of the results of the error and 

sensitivity analyses.

Model Calibration and Testing

The HSPF model was calibrated using data for 

the Beans Creek and Walnut Creek subbasins collected 

from October 1, 1992, to September 30, 1993 (water 

year 1993). Initial estimates for the 20 process-related 

parameters were (1) based on the physical properties of 

soil, land cover, and slope in the subbasins (Chow and 

others, 1988); (2) assigned the default values listed in 

table 1; or (3) taken from a previous study (Dinicola, 

1990). For each land segment, the default values were 

used as the estimates for the parameters AGWETP, 

BASETP, DEEPFR, and KVARY because no data were 

available to calibrate the base-flow recession parameters. The estimates for the parameters INFEXP and 

INFILD also remained the default values because there 

was no justification to change the defaults. The 14 calibrated annual parameters are listed in table 5 (at end of 

report), the 3 calibrated monthly parameters are listed in 

table 6 (at end of report), and the 3 initial condition values are listed in table 7 (at end of report). Each parameter varied by soil group, land-cover group, or slope 

group corresponding to the physical process the parameter represents. For example, the parameters LZSN, 

INFILT, INTFW, and UZSN varied by soil group and 

represented the different storage and infiltration capacities of the soil, whereas the parameters CEPSC, LZETP, 

and NSUR varied by land-cover group and represented 

the different surface roughnesses, interception storages, 

and evapotranspiration potentials of the land-cover 

groups. The parameters LSUR and SLSUR varied by 

the watershed-slope group. The parameters AGWRC 

and IRC were assumed to be uniform for all land segments. The parameters INTFW, IRC, and NSUR were 

not varied monthly because iterative model simulations 

determined that the parameter values had little or no 

effect in explaining seasonal variations in runoff for this 

study area. Values of the annual parameters AGWRC, 

INFILT, INTFW, IRC, LSUR, LZSN, NSUR, and 

SLSUR values of the monthly parameters CEPSC, 

LZETP, and UZSN were adjusted during the calibration 

process using the software program HSPEXP (Lumb 

and others, 1994). The values for the initial conditions 

AGWS, LZS, and UZS were initially estimated from 

Dinicola (1990) and were revised during calibration. 

These values were varied by soil group.

A total of 55 storms were recorded in the 5 gaged 

subbasins from October 1, 1992, to September 30, 

1994; the minimum was 6 storms for the Big Creek subbasin, and the maximum was 16 storms for the Walnut 

Creek subbasin. The calibrated parameter set (tables 5 

6) was developed from 10 storms that occurred during 

water year 1993 in the Beans Creek and Walnut Creek 

subbasins. The remaining 45 storms were used to test 

the parameters temporally and spatially to assess 

the transferability of the parameter set to ungaged 

subbasins.

The measured and simulated times of peak, storm 

peaks, storm volumes, and errors for the calibration and 

testing simulations are listed in table 8 (at end of report). 

The simulated times of peak are within 3 hours of the 

measured times of peak for the 3 storms for the Beans 

Creek subbasin and the 7 storms for the Walnut Creek 

subbasin during water year 1993. The errors for storm 

peaks range from -60.8 to 214 percent, and the errors for 

storm volumes range from -66.7 to 111 percent for the 

10 storms that were used for calibration (table 8). The 

maximum simulated storm peak and storm volume during water year 1993 for the Beans Creek subbasin are 

greater than the maximum measured values, whereas 

the maximum simulated storm peak and storm volume 

for the Walnut Creek subbasin are less than the maximum measured values. Five of the 10 storm peaks and 

6 of the 10 storm volumes have an absolute error of less 

than 50 percent. The best agreement between the 10 

measured and simulated hydrographs used for the 

model calibration is shown in figure 8 for Walnut Creek 

at Reno during September 13-14, 1993.

Five storms for the Beans Creek subbasin and 9 

storms for the Walnut Creek subbasin during water year 

1994 were used to test the parameters temporally. The 

simulated times of peak are within 3 hours of the measured times of peak for 13 of the 14 storms (table 8). The 

errors for storm peaks range from -98.6 to 416 percent, 

and the errors for storm volumes range from -87.8 to 

258 percent.

Six storms for the Big Creek, 12 storms for the 

Garrett Creek, and 13 storms for the Salt Creek subbasins during both water years were used to test the 

parameters spatially (table 8). The simulated times of 

peak are within 3 hours of the measured time for 19 

of the 31 storms. The errors for storm peaks range from 

-99.6 to 1,000 percent, and the errors for storm volumes 

range from -98.7 to 786 percent. For the testing period, 

6 of the 8 maximum storm peaks of the water year for 

each subbasin and 4 of the 8 maximum storm volumes

SIMULATION OF STORM PEAKS AND STORM VOLUMES 11
rCO 

ite

1.5

0.75

0 L 

4,000 r

3,600 -

Q 3,200

z 

O

LU 2,800

DC 

LU

£ 2,400

LU

U!

O 2,000

CD

D 

O

z 1,600

LU 

CD

< 1,200

X 

O 

C/3

Q 800

400

Measured 

Simulated

2400 0600 1200 1800 

SEPTEMBER 13, 1993

2400

TIME, IN HOURS

0600 1200 1800 

SEPTEMBER 14, 1993

2400

Figure 8. Measured and simulated hydrographs for Walnut Creek at Reno, Texas, September 13-14,1993.

of the water year for each subbasin have a simulated 

value higher than the measured value. Only 10 of the 

45 storms used for testing have an absolute error of less 

than 50 percent for both storm peaks and storm volumes. One of the best agreements between measured 

and simulated hydrographs used for testing is for 

Garrett Creek near Paradise during May 11 13, 1994 

(fig. 9).

The measured times of peak and the simulated 

times of peak for the 55 storms are shown in figure 10. 

The difference between the simulated and measured

time of peak is within 3 hours for most storms; there 

was a tendency for the simulated peak to occur before 

the measured peak.

The measured storm peaks and the simulated 

storm peaks for the 55 storms are shown in figure 11. 

There is a fairly symmetric spread of simulated peaks 

greater than about 70 cubic feet per second (ft3/s) about 

the match line; and there is a cluster of simulated storm 

peaks less than about 70 ft3/s that underestimates measured storm peaks in the 100- to 2,000-ft3/s range.

12 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
2400 1200 

MAY 11, 1994

2400 1200 

MAY 12, 1994

2400 1200 

MAY 13, 1994

2400

TIME, IN HOURS

Figure 9. Measured and simulated hydrographs for Garrett Creek near Paradise, Texas, May 11-13,1994.

The measured storm volumes and the simulated 

storm volumes for the 55 storms are shown in figure 12. 

Overall, there is a fairly symmetric spread of simulated 

volumes greater than about 0.02 in. about the match 

line; and there is a cluster of simulated storm volumes 

less than 0.02 in. that underestimates measured storm 

volumes in a range from about 0.04 to 0.30 in.

The mean absolute error and bias for the measured and simulated storm peaks and storm volumes for 

each water year for the five gaged subbasins are listed 

in table 9 (at end of report). Mean absolute error is the 

average of the absolute values of all storm errors; bias

is the average of all storm errors. A small bias occurs 

when positive errors and negative errors are almost 

equal. For the calibration data from water year 1993, the 

mean absolute error and bias for the three storm peaks 

for the Beans Creek subbasin are 48.0 and 6.7 percent 

and for the seven storm peaks for the Walnut Creek 

subbasin are 63.2 and 6.9 percent. The mean absolute 

error and bias for storm volumes are 46.6 and -9.9 

percent for the three storm peaks for the Beans Creek 

subbasin and are 34.4 and -2.2 percent for the seven 

storm volumes for the Walnut Creek subbasin. For the 

temporal-testing data from water year 1994, the mean

SIMULATION OF STORM PEAKS AND STORM VOLUMES 13
2400

0100

0100 0600 1200 1800 

MEASURED TIME OF PEAK, IN HOURS

2400

Figure 10. Measured times of peak and simulated times of peak using calibrated parameters.

absolute error and bias are 153 and 85.2 percent for the 

Beans Creek subbasin and are 81.0 and -21.9 percent 

for the Walnut Creek subbasin. The results are similar 

for storm volumes; the mean absolute error and bias are 

132 and 68.6 percent for the Beans Creek subbasin and 

are 63.7 and -8.0 percent for the Walnut Creek subbasin. For the spatial-testing data from the other three 

subbasins tested, the mean absolute errors for storm 

peaks range from 68.3 to 470 percent, and the biases 

range from -47.2 to 40! percent. The mean absolute 

errors for storm volumes range from 58.7 to 416 percent, and biases range from -52.4 to 416 percent.

The mean absolute errors in storm volumes 

are less than the errors in storm peaks for every subbasin except Big Creek (table 9). The errors for testing 

simulations generally are larger than the errors for calibration simulations. The mean absolute errors also 

generally increase from water year 1993 to water year 

1994 for the five subbasins.

The monthly distribution of errors for storm 

peaks and storm volumes for the 24-month study 

period is listed in table 10 (at end of report). Forty of 

the 55 storms occurred in 4 months February, May, 

September, and October. The remaining 15 storms are 

distributed through March, April, June, August, 

November, and December. No storms occurred in January and July. The distribution of errors was relatively 

even for simulating storm peaks, but there seemed to be 

a bias for undersimulating storm volumes.

Error Analysis

The types of error from the model calibration 

and testing can be classified as measurement errors 

or systematic errors. Measurement errors are introduced as a result of missing data and inaccurate rating 

tables of stage and discharge. Rainfall data are missing 

for several raingagc stations during January through

14 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
100,000 r

10,000 r

1,000 r

100 r

10 100 1.000 10,000 

MEASURED STORM PEAK, IN CUBIC FEET PER SECOND

100,000

Figure 11. Measured storm peaks and simulated storm peaks using calibrated parameters.

March 1993 and had to be estimated from daily 

observer data. The two streamgage stations with the 

highest simulation errors, Big Creek and Salt Creek 

(table 9), also had the least accurate rating tables which 

result in inaccurate discharge records. The spatial variability of rainfall might not be represented adequately 

with the existing raingage network of two to three 

points in each subbasin.

Systematic errors are associated with the inability 

of the simulation model to represent the physical processes of runoff. These errors are represented in the 

model parameters and model equations. The wide variation in measured rainfall compared to measured storm 

volume indicates the seasonal differences in runoff 

(fig. 13). A total of 4.20 in. of rainfall produced 1.56 in. 

of runoff in May on Walnut Creek, whereas 4.84 in. of 

rainfall produced only 0.36 in. of runoff in September. 

The model parameters and model equations need to 

account for these variations. On average, 11 storms

were measured among 5 gaged subbasins during the 24- 

month study period, ranging from 6 at Big Creek to 16 

at Walnut Creek. Eleven is a very small number of 

storms when calibrating the model to account for a full 

range of storm volumes, seasons, and antecedent soilmoisture conditions. Another limitation of this study 

involved using flood-hydrograph streamgage stations 

with a continuous-simulation model, which provided no 

data to calibrate the parameters related to base flow. The 

pervious land segments used in this model might not 

represent adequately all the different hydrologic 

response units of the study area. Also, some uncertainty 

exists in the values of FTABLES for the reach volume 

and the corresponding discharge, which seems to be 

true for the Big Creek and Salt Creek subbasins.

The measurement and systematic errors account 

for some of the error and bias of the simulated storm 

peaks and storm volumes. However, from the results 

listed in tables 8 9 and shown in figures 10-12, the

SIMULATION OF STORM PEAKS AND STORM VOLUMES 15
0.001

0.01 h

0.001 0.01 0.1 1 

MEASURED STORM VOLUME, IN INCHES

10

Figure 12. Measured storm volumes and simulated storm volumes using calibrated parameters.

calibrated parameter set does not adequately simulate 

the storm peaks and storm volumes. There could be a 

seasonal bias for simulating storm volumes based on 

the monthly distribution of simulation errors presented 

in table 10. Also, the errors seem to increase from water 

year 1993 to water year 1994 (table 9). Additional 

information on the sensitivity of each parameter might 

provide some insight into which parameters might be 

adjusted to provide better calibration and testing 

results.

Sensitivity Analysis

A sensitivity analysis was done on selected 

parameters on the Walnut Creek subbasin to determine 

what effect a change in a parameter value has on the 

largest storm peak and the total storm volume for the 24 

months. The simulation was done using data from 10 of 

the 16 storms for Walnut Creek. A maximum of 10

storms can be used for calibration by the expert system 

of HSPEXP (Lumb and others, 1994). The largest simulated peak discharge is 15,400 ft3/s, and the total simulated storm volume is 4.57 in., using the calibrated 

model parameters for the entire 24 months. The change 

in simulated peak discharge from 17,800 ft3/s listed in 

table 8, using the calibrated model parameters for water 

year 1993, to 15,400 ft3/s, using the calibrated model 

parameters for the 24 months, represents the sensitivity 

of storm peaks to the change in the initial conditions 

(AGWS, LZS, and UZS values) assumed for calibration (table 7) to the simulated values at the end of water 

year 1993.

Each parameter was modified to represent a 

reasonable change. The changes in model results relative to a change in the parameter value are listed in 

table 11 (at end of report). The parameters INFILT, 

LZSN, and UZSN have the most effect on both storm

16 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
3.00

2.50

CO 

LU

O 2.00

1.50

1.00

0.50 -

.10 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 

RAINFALL, IN INCHES

4.50 5.00 5.50 6.00 6.50

Figure 13. Rainfall and measured storm volume.

peaks and storm volumes combined; the parameters 

DISCH, LSUR, NSUR, SLSUR, and VOL primarily 

affect the timing and magnitude of the storm peaks with 

relatively less effect on the storm volumes. None of 

these parameters affected the timing of the largest peak, 

but a few of the smaller storm peaks were affected. 

Also, the parameters AGWS, LZS, and UZS represent 

the initial conditions at the start of the simulation and 

did not have an effect on storm peaks that occurred 

more than 6 months into a simulation, but did have an 

effect on the storm peaks and storm volumes that 

occurred early in a simulation. Changing the 11 parameters noted above produced the largest change in model 

results.

Model Recalibration and Testing

A new process-related parameter set was developed from the recalibration of the Beans Creek and

Walnut Creek subbasins from October I, 1992, to 

September 30, 1994, using information derived from 

the error analysis and the sensitivity analysis, and was 

tested on the data from Big Creek, Garrett Creek, and 

Salt Creek. The model was run for the entire period of 

record to provide additional storms for calibration. 

Some values of parameters INFILT, INTFW, LZETP, 

and LZSN were increased and some values of UZSN 

were decreased to decrease the magnitude of the storm 

peaks and storm volumes. Some values of parameters 

LSUR and NSUR were increased, whereas some 

values of SLSUR were decreased. The values of the 

parameter CEPSC were not modified. The values of 

parameters AGWRC and IRC were decreased to 

steepen the ground-water and interflow recession rates. 

The values of parameter BASETP were modified from 

the default value of zero (table 1) to 0.1 to allow available potential evaporation to be satisfied from base flow.

SIMULATION OF STORM PEAKS AND STORM VOLUMES 17
The parameters KVARY, INFEXP, INFILD, DEEPFR, 

and AGWETP retained the default values listed in table 

1. The recalibrated annual parameters are listed in table 

12 (at end of report); the 3 recalibrated monthly parameters are listed in table 13 (at end of report); and the 3 

initial condition values are listed in table 14 (at end of 

report).

The FTABLE volumes from table 4 were 

increased by 25 percent for the Big Creek, Garrett 

Creek, and Salt Creek subbasins to provide more storage in the reaches for each subbasin to decrease the 

magnitude of the storm peaks. The initial values for 

AGWS, LZS, and UZS for water year 1994 (table 14) 

were from the simulation output from the end of water 

year 1993.

Data from the 8 storms for the Beans Creek subbasin and the 16 storms for the Walnut Creek subbasin 

during water years 1993 and 1994 were used to recalibrate HSPF. The remaining 31 storms for the other 3 

subbasins were used to test the recalibrated parameters. 

The measured and simulated times of peak, storm 

peaks, storm volumes, and errors using recalibrated 

parameters for the five subbasins are listed in table 15 

(at end of report).

The difference between the measured and 

simulated times of peak, using the recalibrated parameters, is within 3 hours for 23 of the 24 storms for 

the Beans Creek and Walnut Creek subbasins (table 

15). The errors for the storm peaks range from -99.9 to 

312 percent using the recalibrated parameters (table 

15), compared to -98.6 to 416 percent using the calibrated parameters (table 8). The errors for the storm 

volumes using the recalibrated parameters range from 

-98.8 to 203 percent (table 15), compared to -87.8 to 

258 percent using the calibrated parameters (table 8). 

Although the ranges of errors were decreased using 

the recalibrated parameters, the number of storms 

with absolute errors less than 50 percent did not 

improve. Nine storm peaks and 10 storm volumes of 

the 24 storms using the recalibrated parameters have 

errors less than 50 percent (table 15), compared to 9 

storm peaks and 9 storm volumes of the 24 storms 

using the calibrated parameters (table 8). The improvement in the simulated hydrograph for Beans Creek on 

February 14-16, 1993, using the recalibrated parameters compared to the simulated hydrograph using the 

calibrated parameters, is shown in figure 14. The error 

of the storm peak improved from 82.1 percent (table 8) 

to -18.4 percent (table 15), and the error of the storm

volume improved from 55.0 percent (table 8) to -15.3 

percent (table 15).

The recalibrated parameters were tested for 6 

storms for Big Creek, 12 storms for Garrett Creek, and 

13 storms for Salt Creek during water years 1993 and 

1994. Twenty-two of the 31 simulated times of peak are 

within 3 hours. Most of the nine storms for which the 

simulated time of peak differs by more than 3 hours 

from the measured time of peak correspond to the 

storms for which little or no runoff was simulated. The 

errors for the storm peaks using the recalibrated parameters range from -99.9 to 582 percent (table 15), compared to -99.6 to 1,000 percent using the calibrated 

parameters (table 8). The errors for storm volumes 

using the recalibrated parameters range from -99.6 to 

306 percent (table 15), compared to -98.7 to 786 percent using the calibrated parameters (table 8). Six 

storm peaks and 7 storm volumes for the 31 storms 

using the recalibrated parameters have absolute errors 

less than 50 percent (table 15), compared to 10 storm 

peaks and 11 storm volumes for the 31 storms using the 

calibrated parameters (table 8).

Seven of the 10 maximum simulated storm peaks 

and 5 of the 10 maximum storm volumes for each water 

year for the 5 gaged subbasins exceed the measured 

values (table 15). These results, using the recalibrated 

parameters, are the same as the results using the calibrated parameters (table 8).

The measured and simulated hydrographs for 

Big Creek near Chico during October 19 20, 1993, are 

shown in figure 15. There is relatively good agreement 

between simulated and measured storm peaks using 

the recalibrated parameters, but the storm volume is 

overestimated.

Measured times of peak and simulated times 

of peak using the recalibrated parameters for the 55 

storms are shown in figure 16. The time of peak either 

remained unchanged or was delayed 1 hour from the 

times shown in figure 10 for most of the 55 storms. 

The storms with the largest differences generally were 

the storms for which little or no simulated runoff was 

generated.

Measured storm peaks and simulated storm 

peaks for the 55 storms using the recalibrated parameters are shown in figure 17. The distribution of data 

about the match line is very similar to the distribution 

in figure 11. The same 11 simulated storm peaks of less 

than about 70 ft3/s from figure 11 are less than the corresponding measured storm peaks.

18 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
rCO 

LLJ

0.5

0.25

Q

2

0

O

LU

DC

LU

Q.

1-

LU

U_

0

CD

Z)

O

2

LU

O

DC

I

O

co

Q

1 ,i)UU

1,350

1,200

1,050

900

750

600

450

300

150

0 

24(

I ! I i !

Measured J 

------ Calibrated

------ Recalibrated

A/ \

' \

; \

' \

/ \

/ \

i \

i \

i \

/ \ / . \

i f\ \

i / \ \

i /. . \ \

/ /. . \ \

i / .\ \

i / A \

'/ \\ i / \

/ \ x

/. *\ \

;/ \ \ j '/' \x x

'/' ^^ > ^^

.7 ^^ ~~~ ~-' ~ - - p .......

30 1200 2400 1200 2400 1200 24(

FEB. 14, 1993 FEB. 15, 1993 i FEB. 16, 1993

TIME, IN HOURS

Figure 14. Measured and simulated hydrographs for Beans Creek at Wizard Wells, Texas, February 14-16, 1993.

Measured storm volumes and simulated storm 

volumes for the 55 storms using the recalibrated parameters are shown in figure 18. The distribution of data 

about the match line is very similar to the distribution in 

figure 12. Ten of the 55 simulated storm volumes are 

less than 0.02 in. and are clustered apart from the rest of 

the data, which is similar to the simulated storm peaks 

(fig. 17) where increased infiltration, storage, and evaporation, as represented by the recalibrated parameters, 

generated little or no simulated runoff for some storms.

The mean absolute errors and biases of storm 

peaks and storm volumes for each water year using the

recalibrated parameters for the five gaged subbasins are 

listed in table 16 (at end of report). The mean absolute 

errors for each subbasin for storm peaks range from 

47.1 to 297 percent using the recalibrated parameters 

compared to 48.0 to 470 percent using the calibrated 

parameters (table 9). The mean absolute errors for each 

subbasin for storm volumes range from 27.6 to 193 percent using the recalibrated parameters compared to 34.4 

to 416 percent using the calibrated parameters (table 9). 

The biases for each subbasin for storm peaks range from 

-85.4 to 202 percent using the recalibrated parameters 

compared to -47.2 to 401 percent using the calibrated

SIMULATION OF STORM PEAKS AND STORM VOLUMES 19
<rz

Q

O 

O 

UJ 

CO

<r

UJ 

CL

ILU 

UJ 

LL

O 

CD

13 

O

1.5

0.75

3,600 I 

3,000

O,UUU | ' - - ' '"I 

i *

5,400 |- / \

! / l

4,800 L ' l

! i *

! i

4,200 L 1

i

! ! 1 1 1

 Measured

------ Calibrated

-

- 2,400 ,- I

UJ

O

§

i 1,800

o

CO 

Q

1,200

600

''\

/ \ / \

/ \

/ \

/ \

2400 0600 1200 1800 

OCTOBER 19, 1993

2400 0600 1200 1800 

OCTOBER 20, 1993

2400

TIME, IN HOURS

Figure 15. Measured and simulated hydrographs for Big Creek near Chico, Texas, October 19-20, 1993.

parameters (table 9). The biases for each subbasin for 

storm volumes range from -75.6 to 114 percent using 

the recalibrated parameters compared to -52.4 to 416 

percent using the calibrated parameters (table 9). The 

errors for the five gaged subbasins generally decreased 

using the recalibrated parameters.

The mean absolute errors and biases generally 

are less for the storm volumes than for the storm peaks 

using the recalibrated parameters (table 16), which is 

similar to the results of the initial calibration (table 9). 

In addition, the mean absolute error and bias using the 

recalibrated parameters (table 16) increases from water

year 1993 to water year 1994 for fewer storm peaks and 

storm volumes than using the calibrated parameters 

(table 9).

The monthly distribution of errors for storm 

peaks and storm volumes for the 55 storms using the 

recalibrated parameters are listed in table 17 (at end of 

report). The monthly results are similar to the results 

using the calibrated parameters (table 10); however, the 

annual totals are somewhat reversed: the calibrated 

parameters tend more to undersimulate storm volumes, 

whereas the recalibrated parameters tend more to 

undersimulate the storm peaks. December is the only

20 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
2400

5100 0600 1200 1800 

MEASURED TIME OF PEAK, IN HOURS

2400

Figure 16. Measured times of peak and simulated times of peak using recalibrated parameters.

month that indicates a bias to oversimulating storm 

peaks and storm volumes using the recalibrated parameters. However, more storm data are needed to clearly 

indicate a monthly bias for simulating storm peaks and 

storm volumes for the other 11 months.

Transfer of Model Parameters to Ungaged 

Subbasins

The model produced better results for simulation 

of the larger storm peaks and storm volumes than for 

simulation of the smaller storm peaks and storm volumes, especially after an extended period of no runoff. 

However, only selected data for 55 storms at 5 subbasins during 24 months were used to calibrate and test the 

HSPF model parameters. A continuous-simulation 

model does provide a means to account for some variations in runoff generation compared to event-based 

models. The recalibrated process-related parameter set

can be transferred to the other ungaged subbasins with 

the same range in error expected. The basin-related 

parameters will need to be computed for each ungaged 

subbasin.

On the basis of the results of this study, additional 

collection of storm-runoff data, improvement of discharge rating curves, and identification of additional 

sources of rainfall data could result in model parameters 

that account for the wide variations in runoff and reduce 

the range of expected error in model simulation. A 

longer period of record would provide a better representation of the combinations of storm size, season, and 

antecedent moisture conditions. The smaller storm 

peaks that occur during spring and summer might be the 

result of more widely scattered rainfall with nonuniform 

intensity.

SIMULATION OF STORM PEAKS AND STORM VOLUMES 21
100.000 r

LLI

10,000 r

LL 1,000 r

10 100 1,000 10,000 

MEASURED STORM PEAK. IN CUBIC FEET PER SECOND

100,000

Figure 17. Measured storm peaks and simulated storm peaks using recalibrated parameters.

SUMMARY

The purpose of this study was to simulate storm 

peaks and storm volumes for selected subbasins of the 

West Fork Trinity River Basin upstream from Lake 

Worth northwest of Fort Worth, Texas. The simulated 

flows can be used as input to a channel-routing model 

that can be used to improve reservoir operation in the 

basin during floods.

A model parameter set for use with HSPF was 

developed to simulate storm peaks and storm volumes 

for ungaged subbasins from calibration and testing of 

five gaged subbasins. Rainfall and runoff data were 

collected from October I, 1992, to September 30, 

1994, with a total of 55 storms used in this study. 

Twelve different pervious land segments were defined 

for the study based on 2 groups of soil, 3 groups of land 

cover, and 2 groups of slope. Seventeen parameters 

were defined for each land segment.

The model was calibrated with data from 10 

storms and tested temporally and spatially with data 

from the remaining 45 storms. The mean absolute 

errors for storm peaks for the five subbasins range from 

48.0 to 470 percent and for storm volumes range from 

34.4 to 416 percent using the calibrated parameters. A 

sensitivity analysis was done on selected parameters to 

determine the effect of a change in a parameter value 

on time of peak, storm peak, and storm volume for one 

gaged subbasin.

The results of the parameter sensitivity and error 

analyses from the initial model calibration were used to 

recalibrate the parameters. The mean absolute errors 

for storm peaks for the five subbasins range from 47.1 

to 297 percent and for storm volumes range from 27.6 

to 193 percent using the recalibrated parameters.

The model produced better results for simulation 

of the larger storm peaks and storm volumes than for

22 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 199S-94
0.001

0.01 -

0.001 0.01 0.1 1 

MEASURED STORM VOLUME, IN INCHES

Figure 18. Measured storm volumes and simulated storm volumes using recalibrated parameters.

simulation of the smaller storm peaks and storm volumes, especially after an extended period of no runoff. 

The parameters can be transferred to the 23 ungaged 

subbasins with the same range in error expected. However, additional data collection and model refinement 

could decrease the model errors. In the study area, a 

wide variation in runoff was produced from similar 

magnitudes of measured rainfall. Continuous discharge 

data, improved stage-discharge rating tables, and more 

storm data could improve model calibration.

REFERENCES CITED

Chow, V.T., Maidment, D.R., and Mays, L.W., 1988, Applied 

hydrology: New York, McGraw-Hill, 572 p.

Dinicola R.S., 1990, Characterization and simulation of 

rainfall-runoff relations for headwater basins in western 

King and Shohomish Counties, Washington: U.S. 

Geological Survey Water-Resources Investigations 

Report 89-4052, 52 p.

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

manual for an expert system (HSPEXP) for calibration 

of the Hydrologic Simulation Program FORTRAN: 

U.S. Geological Survey Water-Resources Investigations 

Report 94-4168, 58 p.

National Oceanic and Atmospheric Administration, 1990, 

Climatological data annual summary, Texas: Asheville, 

N.C., v. 95, no. 13, 77 p.

Shearman, J.O., 1990, Users manual for WSPRO a

computer model for water surface profile computations 

(Hydraulic computer program HY 7): U.S. Federal 

Highway Administration, Publication No. FHWA-IP89-027, 177 p.

U.S. Department of Agriculture, Soil Conservation Service, 

1977, Soil survey of Parker County, Texas: 90 p.

____1978, Soil survey of Montague County, Texas: 115 p.

____1981, Soil survey of Tarrant County, Texas: 218 p.

U.S. Environmental Protection Agency, 1992, Hydrologic 

Simulation Program FORTRAN users manual for 

release 10: 660 p.

REFERENCES CITED 23
Table 1 . Process-related model parameters for the Hydrologic Simulation Program FORTRAN 

[ET, evapotranspiration]

Parameter

AGWS

AGWETP

AGWRC

BASETP

CEPSC

DEEPFR

1NFEXP

INFILD

INFILT

INTFW

IRC

KVARY

LSUR

LZETP

LZS

LZSN

NSUR

SLSUR

UZS

UZSN

Description 1

Initial active ground-water storage

Available ET satisfied by active ground water

Active ground-water recession rate

Available ET satisfied by base flow

Interception storage capacity

Fraction of inflow that enters inactive ground water

Infiltration equation exponent

Ratio of maximum and mean infiltration capacities

Index to infiltration capacity of soil

Interflow inflow

Interflow recession rate

Nonexponential ground-water recession rate

Length of assumed overland flow plane

Lower zone ET

Initial lower zone storage

Lower zone nominal storage

Manning's n for assumed overland flow plane

Slope of assumed overland flow plane

Initial upper zone storage

Upper zone nominal storage

Default

None

0

None

0

0

0

2.0

2.0

None

None

None

0

None

0

None

None

.1

None

None

None

Minimum

0

0

.001

0

0

0

0

1.0

.0001

0

0

0

1.0

0

0

.01

.001

.000001

0

.01

Maximum

None

1.0

1.0

1.0

1.0

1.0

10.0

2.0

100.0

None

1.0

None

None

1.0

None

100.0

1.0

10.0

None

10.0

Units

Inches

None

Per day

None

Inches

None

None

None

Inches per hour

None

Per day

Per inch

Feet

None

Inches

Inches

None

Feet per foot

Inches

Inches

1 The users manual for Hydrologic Simulation Program FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of each parameter.

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

[PERLND, pervious land segment; IMPLND, impervious land segment; FTABLE, table of depth, surface area, volume, and 

discharge for each reach]

Parameter Description Units

AREA 

LEN 

DEPTH 

SAREA

VOL 

DISCH

Drainage area of each PERLND or IMPLND 

Reach length 

FTABLE depth 

FTABLE surface area

FTABLE volume 

FTABLE discharge

Acres 

Miles 

Feet 

Acres

Acre-feet

Cubic feet per second

1 The users manual for Hydrologic Simulation Program FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of each parameter.

24 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
Table 3. Gaged subbasins in the West Fork Trinity River Basin upstream from Lake Worth

U.S. Geological Survey 

station number Station name

Drainage area 

(square miles)

08042900

08042950

08044135

08044140

08044800

Beans Creek at Wizard Wells 

Big Creek near Chico 

Garrett Creek near Paradise 

Salt Creek near Paradise 

Walnut Creek at Reno

36.0

50.0

52.7

53.0

62.6

Table 4. Basin-related parameters for each gaged subbasin

[Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: I, low permeability (less 

than 2 inches/hour); 2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or permeability not characterized). The 

second digit designates land cover: C, crop; F, forest; P, pasture; X, all land covers (or land cover not characterized). The third digit 

designates watershed slope: F, flat, less than 3 percent; S, steep, more than 3 percent; X. all slopes (or slope not characterized). For example, 

a land segment characterized by soils of moderately low permeability, a forest cover, and a steep slope has the descriptor 2FS. A land 

segment for which only land cover is characterized (as crop) has the descriptor XCX.

AREA, land-scgmcnl drainage area; LEN. reach length; mi. miles; FTABLE, table of depth (DEPTH), surface area (SAREA). volume 

(VOL), and discharge (DISCH) for a reach; ft, feet; acre-ft, acre-feel; ftVs, cubic feet per second; --, no value]

Parameter 1

LEN (mi)

FTABLE 

DEPTH (ft) 

SAREA (acres) 

VOL (acre-ft) 

DISCH (ft3/s)

AREA (acres) 

ICF 

ICS 

IFF 

1FS

Beans Creek Big Creek Garrett Creek Salt Creek

7.71

0-20.0 

0-23.4 

0-421 

0-2,400

734

76

902

169

9.44

0-20.0 

O-57.2 

0-687 

0-10,600

Reach 2

699

34

,976

195

0-20.0 

0-45.0 

0--567 

0-3,360

52

12

136

13

0-20.0 

0-71.2 

0-1,024 

0-12,100

Walnut Creek

Reach 1

AREA (acres)

ICF

ICS

IFF

IFS

IPF

IPS

2CF

2CS

2FF

2FS

2PF

2PS

1,307

128

2,037

381

4,782

899

127

9

54

6

302

43

844

131

4,622

808

6,736

1,402

130

27

1,048

194

1,158

340

0

0

0

0

0

0

2,701

338

4,409

765

5,220

795

104

80

133

129

253

171

2,856

1,317

4,802

2,476

5,273

2,403

175

141

469

329

586

382

3,106

179

3,513

403

5,610

569

8.55

0-16.0 

0-51.8 

0-498 

0-7,180

148

61

779

416

Table 4 25
Table 4. Basin-related parameters for each gaged subbasin Continued

Parameter 1 Beans Creek Big Creek Garrett Creek Salt Creek Walnut Creek

Reach 2 Continued

1PF

IPS

2CF

2CS

2FF

2FS

2PF

2PS

LEN (mi)

FTABLE

DEPTH (ft)

SAREA (acres)

VOL (acre-ft)

DISCH (ftVs)

AREA (acres)

1CF

ICS

IFF

IFS

1PF

IPS

2CF

2CS

2FF

2FS

2PF

2PS

LEN (mi)

FTABLE

DEPTH (ft)

SAREA (acres)

VOL (acre- ft)

DISC'H(ftVs)

1,900

347

288

39

314

76

647

98

6.74

0-20.0

0-19.2

0-331

0-2,000

568

222

1,439

532

2,192

804

188

9

618

26

729

33

3.88

0-20.0

0-29.9

0-543

0-4,760

3,088

201

250

36

568

144

861

209

6.49

0-20.0

0-39.3

0-472

0-11,600

Reach 3

282

20

1,229

225

2,296

420

319

22

477

89

730

171

4.37

0-20.0

0-68.9

O-847

0-20,000

77

12

2,189

334

4,540

738

6,159

864

13.3

0-20.0

0-43.5

0-548

0-3,360

0

0

0

0

0

0

956

109

1,082

224

1,782

270

2.64

0-20.0

0-18.2

0-236.8

0-4,410

0

0

3,456

489

3,449

898

4,671

948

4.4

0-20.0

0-56.5

0-979

0-9,500

--

~

~

--

--

.-

--

--

--

--

--

690

341

2,309

89

2,514

122

4,043

190

2.70

0-20.0

0-36.0

O426

0-18,100

0

0

0

0

0

0

3,300

93

3,247

205

5,746

306

4.19

0-20.0

0-50.8

0-610

0-22,500

The users manual for Hydrologic Simulation Program FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of each parameter.

26 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
Table 5. Calibrated annual parameters

[Units listed below parameter name except for parameters with no units; in/hr, inch per hour; ft, feet; in., inches; ft/ft, foot per foot

Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: 1, low permea

2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or permeability not characterized). The second dig

crop; F, forest; P, pasture; X, all land covers (or land cover not characterized). The third digit designates watershed slope: F, flat, les

than 3 percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low pe

steep slope has the descriptor 2FS. A land segment for which only land cover is characterized (as crop) has the descriptor XCX.

Parameter definitions: AGWETP, available evapotranspiration satisfied by active ground water; AGWRC, active ground-water rec

evapotranspiration satisfied by base flow; DEEPFR, fraction of inflow that enters inactive ground water; INFEXP, infiltration equa

maximum and mean infiltration capacities; INFILT, index to infiltration capacity of soil; INTFW, interflow inflow; IRC, interflow 

nonexponential ground-water recession rate; LSUR, length of assumed overland flow plane; LZSN, lower zone nominal storage; N

overland flow plane; SLSUR, slope of assumed overland flow plane. The users manual for Hydrologic Simulation Program FOR

Protection Agency, 1992) provides a more complete description of each parameter.]

Und AGWETP' AGWRC:J 

segment (per day)

1CF

1CS

IFF

1FS

1PF

IPS

2CF

2CS

2FF

2FS

2PF

2PS

H 1 D>

1 2

O1

0

0

0

0

0

0

0

0

0

0

0

0

0.996

.996

.996

.996

.996

.996

.996

.996

.996

.996

.996

.996

BASETP 1

0

0

0

0

0

0

0

0

0

0

0

0

Default value used for this parameter. 

Initial estimates for this parameter taken

DEEPFR 1

0

0

0

0

0

0

0

0

0

0

0

0

INFEXP 1 INFILD 1

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

INFILT23 

(in/hr)

0.015

.015

.015

.015

.015

.015

.045

.045

.045

.045

.045

.045

IRC23 KVARY 1 

INTFW23 (per (per 

day) inch)

0.4 0.01

.4 .01

.4 .01

.4 .01

.4 .01

.4 .01

.8 .01

.8 .01

.8 .01

.8 .01

.8 .01

.8 .01

0

0

0

0

0

0

0

0

0

0

0

0

LSUR23 

(ft) 

3,000 

2,000 

3,000 

2,000 

3,000 

2,000 

3,000 

2,000 

3,000 

2,000 

3.000 

2,000 

from Dinicola( 1990).

Parameter was revised during calibration. 

4 Initial estimates for this parameter taken from Chow and others (1988)
Table 6. Calibrated monthly parameters

[Units listed below parameter name except for parameters with no units; in., inches.

Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: 1, low 

permeability (less than 2 inches/hour); 2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or 

permeability not characterized). The second digit designates land cover: C, crop; F, forest; P, pasture; X, all land covers (or 

land cover not characterized). The third digit designates watershed slope: F, flat, less than 3 percent; S, steep, more than 3 

percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low 

permeability, a forest cover, and a steep slope has the descriptor 2FS. A land segment for which only land cover is 

characterized (as crop) has the descriptor XCX.

Parameter definitions: CEPSC, interception storage capacity; LZETP, lower zone evapotranspiration; UZSN, upper zone 

nominal storage. The users manual for Hydrologic Simulation Program FORTRAN (U.S. Environmental Protection Agency, 

1992) provides a more complete description of each parameter.

Land 

Jan Feb 

segment

XCX 0.05 0.05

XFX .11 .11

XPX .08 .09

XCX .2 .3

XFX .3 .4

XPX .2 .3

1XX .1 .1

2XX .2 .2

Mar

0.05

.16

.10

.5

.6

.5

.2

.4

Apr

0.09

.18

.12

.6

.7

.6

.2

.4

May

0.14

.24

.18

.6

.7

.6

.3

.5

June

CEPSC 1 2

(in.)

0.18

.28

.22

LZETP 1 2

.7

.8

.7

UZSN 1 - 2 

(in.)

.4

.6

July

0.24

.32

.26

.8

.9

.8

.5

.7

Aug

0.28

.32

.26

.9

.9

.9

.6

.8

Sept

0.24

.28

.22

.8

.9

.8

.5

.7

Oct

0.18

.22

.18

.7

.7

.6

.4

.6

Nov

0.12

.18

.12

.5

.6

.5

.3

.5

Dec

0.08

.14

.08

.3

.4

.3

.2

.4

Initial estimates for this parameter taken from Dinicola (1990). 

Parameter was revised during calibration.

28 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
Table 7. Initial condition values for model calibration

[Land segtnents are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: 1, low 

permeability (less than 2 inches/hour); 2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or 

permeability not characterized). The second digit designates land cover: C, crop; F, forest; P, pasture; X, all land covers (or 

land cover not characterized). The third digit designates watershed slope: F, flat, less than 3 percent; S, steep, more than 3 

percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low 

permeability, a forest cover, and a steep slope has the descriptor 2FS. A land segment for which only land cover is 

characterized (as crop) has the descriptor XCX.

AGWS, active ground-water storage; LZS, lower zone storage; UZS, upper zone storage. The users manual for Hydrologic 

Simulation Program-FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of each 

parameter, in., inches]

Station Water year Land segment

Beans Creek 1993 1XX

2XX

1994 1XX

2XX

Big Creek 1993 1XX

2XX

1994 1XX

2XX

Garrett Creek 1993 1XX

2XX

1994 1XX

2XX

Salt Creek 1993 1XX

2XX

1994 1XX

2XX

Walnut Creek 1993 1XX

2XX

1994 1XX

2XX

AGWS 1 2

(in.)

0.01

.01

.2

.2

.01

.01

.2

.2

.6

.6

.6

.6

.6

.6

.2

.2

.6

.6

.2

.2

LZS 12

(in.)

0.5

.5

2.0

2.0

.5

.5

2.0

2.0

3.0

3.0

3.0

3.0

3.0

3.0

2.0

2.0

3.0

3.0

2.0

2.0

UZS 12

(in.)

0.1

.1

.3

.3

.1

.1

.3

.3

.4

.4

.4

.4

.4

.4

.3

.3

.4

.4

.3

.3

1 Initial estimates for this parameter taken from Dinicola (1990). 

Parameter was revised during calibration.

Table 7 29
g Table 8. Measured and simulated storm peaks and storm volumes using calibrated parameters 

[in., inches; frVs, cubic feet per second; Error = 100 * [(S-M)/M]; S, simulated value; M, measured value]

B) __ 

</> S* 

-^ o'

^O 3 

<O

2 % year

i

0)

</>

Q)

i. 1993

w

o 1993

3

< 1993

o

| 1994

</>

o 1994

» 1994

o

| 1994

w ^94

O1 O1

0)w5"

!?. 1993

3

5 1993

(D

1 1993

M

-n 1993

0

3 1994

3

3 1994

33<'

S 1993 w

-3 1993

S 1993

</>

^ 1993

0)

(D

Date of 

storm

Date of 

peak

Rainfall 

(in.) Time of 

peak

Measured

Storm 

peak

(ft3/s)

Storm 

volume 

(in.)

Time of 

peak

Simulated

Storm 

peak

(ft3/s)

S

vo

Beans Creek subbasin

02/14-16/93

02/24-25/93

02/28-03/02/93

10/18-20/93

12/03-04/93

02/21-24/94

05/11 14/94

05/25-26/94

02/15/93

02/25/93

03/01/93

10/19/93

12/03/93

02/22/94

05/13/94

05/25/94

1.86

.96

1.07

4.06

1.86

1.50

5.09

1.89

1300

0800

1400

2100

1500

0600

0400

1200

571

472

378

1,520

364

110

4,230

703

0.262

.183

.200

.929

.179

.150

2.76

.349

1200

0500

1200

1900

1200

0700

0200

0900

1,040

185

374

4,240

1,880

70

2,460

61

0

3

2

Big Creek subbasin

02/14-16/93

02/28-03/02/93

05/08-09/93

06/08-09/93

10/19-20/93

02/2 1-24/94

02/15/93

03/01/93

05/09/93

06/08/93

10/19/93

02/22/94

1.62

1.16

1.50

4.85

3.31

1.63

1500

1400

1600

2400

0500

0600

809

1,850

1,560

9,470

1,620

898

.118

.436

.230

2.32

.193

.142

1 100

1000

1200

2100

0500

0200

1,150

525

6

3,810

5,830

999

Garrett Creek subbasin

12/13-14/92

02-15-16/93

02/24-25/93

02/28-03/02-93

12/14/92

02/15/93

02/25/93

03/01/93

2.77

1.35

1.81

.87

0800

1600

1200

2200

568

660

947

181

.278

.288

.385

.131

0500

1100

0600

1300

2,330

683

1,060

208
Table 8. Measured and simulated storm peaks and storm volumes using calibrated parameters Continued

Water 

year

Date of 

storm

Date of 

peak

Rainfall 

(in.)

Measured

Time of 

peak

Storm 

peak

(ft3/s)

Storm 

volume 

(in.)

Time of 

peak

Simulated

Storm 

peak 

(ft3/s)

Stor

volu

(in

Garrett Creek subbasin Continued

1993

1994

1994

1994

1994

1994

1994

1994

09/13-14/93

10/12-14/93

10/17-21/93

12/03-04/93

02/21-24/94

05/11-13/94

09/08-09/94

09/15-16/94

09/14/93

10/13/93

10/19/93

12/03/93

02/22/94

05/12/94

09/09/94

09/16/94

4.39

1.73

6.13

1.58

1.35

4.09

1.34

1.59

0700

0300

2400

1500

0600

0400

1200

1400

337

284

2,090

437

186

2,230

498

237

0.099

.057

1.600

.112

.051

1.830

.085

.038

0700

1400

2000

1400

1300

0200

1100

1100

597

6

7,030

656

28

2,890

7

11

0.16

.0

1.9

.0

.0

1.0

.0

.0

Salt Creek subbasin

1993

1993

1993

1993

1993

1993

1993

1993

1993

1994

1994

1994

1994

10/15-16/92

11/18-19/92

12/13-15/92

02/03-04/93

02/14-16/93

02/24-25/93

02/28-03/02/93

04/03-05/93

09/13-14/93

10/12-14/93

10/18-19/93

05/11-14/94

09/15-16/94

10/16/92

11/19/92

12/13/92

02/03/93

02/15/93

02/25/93

03/01/93

04/04/93

09/14/93

10/13/93

10/19/93

05/13/94

09/16/94

2.31

1.48

3.50

1.13

1.47

2.98

.90

1.41

4.60

1.97

4.28

5.42

1.99

0200

1100

2000

1800

1200

0400

1200

0500

0500

0100

1800

0700

1300

287

122

544

181

547

1,300

261

261

491

238

965

737

169

.116

.037

.375

.092

.307

.438

.125

.138

.145

.021

.581

.503

.014

0200

1200

2000

1800

1400

0400

1200

1600

0600

0900

1900

0700

1600

234

5

2,060

512

582

7,670

345

32

1,760

124

8,130

8,110

16

.0

.0

.9

.1

.2

1.2

.1

.0

.3

.0

2.3

1.6

.0
Table 8. Measured and simulated storm peaks and storm volumes using calibrated parameters Continued

CO

 < 5'

lulation ofSears 1993-9^

o

i

(D

Q) 

<0

Q)

a

CO 

0

3

0

c

(D

(A

3"

«

(D

O

5? 

a

CO

c

Q)

Ift 5'

(A

5'

5

(D

(D

(0

J

H

5[

30

I

00

Q)

(Ap'

X

Q)

w

Q)

<S

Measured

Water VVCIlCrl

year

Date of

storm

Date of

peak

Rainfall

(in.) Time of 

peak

Storm 

peak

(ft3/s)

Storm 

volume

(in.)

Time of 

peak

Simulated

Storm 

peak

(ft3/s)

Sto

vol

(i

Walnut Creek subbasin

1993

1993

1993

1993

1993

1993

1993

1994

1994

1994

1994

1994

1994

1994

1994

1994

10/15-16/92

12/13-15/92

02/03-04/93

02/14-16/93

02/24-25/93

02/28-03/02/93

09/13-14/93

10/12-14/93

10/18-20/93

02/21-24/94

04/29-30/94

05/11-14/94

05/25-26/94

08/20-21/94

09/08-09/94

09/15-16/94

10/15/92

12/13/92

02/03/93

02/15/93

02/25/93

03/01/93

09/14/93

10/13/93

10/19/93

02/23/94

04/30/94

05/13/94

05/26/94

08/20/94

09/09/94

09/16/94

2.32

3.53

1.53

1.23

2.02

.88

4.84

1.91

4.75

1.46

1.45

4.20

1.68

1.28

2.76

1.87

2400

2100

1800

1200

0600

1300

0500

0700

1800

0400

0300

0700

0800

2400

1000

0900

764

3,180

768

1,080

7,420

901

3,070

211

7,760

480

397

5,980

250

692

2,950

2,240

0.097

.890

.201

.257

.750

.258

.358

.068

1.41

.093

.066

1.56

.048

.082

.304

.254

2400

2100

1500

1200

0500

1200

0500

0700

1800

0600

0500

0700

0700

2400

1100

1300

530

1,880

2,410

429

4,470

388

3,070

440

17,800

28

29

7,670

228

9

540

291

0.0

.

.

.

.

.

.

.

2.

.

.

1.

.

.

.

.
Table 9. Mean absolute errors and biases of storm peaks and storm volumes using calibrated parameters

[Mean absolute error = 100 * [Z(|S-M|)/M]/N; bias = 100 * [Z(S-M)/M]/N; S, simulated value; M, measured value; N, number 

of values]

Station

Beans Creek

Big Creek

Garrett Creek

Salt Creek

Walnut Creek

Water 

year

1993

1994

1993

1994

1993

1994

1993

1994

1993

1994

Storm peaks

Mean absolute error 

(percent)

48.0

153

68.3

136

83.5

99.0

161

470

63.2

81.0

Storm volumes

Bias 

(percent)

6.7

85.2

-47.2

136

83.5

-8.6

116

401

6.9

-21.9

Mean absolute error 

(percent)

46.6

132

85.5

416

62.8

58.7

85.6

168

34.4

63.7

Bias 

(percent)

-9.9

68.6

-31.7

416

23.2

-52.4

9.7

164

-2.2

-8.0

Table 10. Monthly distribution of errors of storm peaks and storm volumes using calibrated parameters 

[Error = 100 * [(S-M)/S]; S, simulated value; M, measured value; , no storms]

Month

January

February

March

April

May

June

July

August

September

October

November

December

Total

Storm-peak errors

Positive Negative

-

8

3

-

3

~

~

-

3

6

~

4

27

~

7

2

2

4

1

-

1

5

4

1

1

28

Storm-volume errors

Positive

-

6

1

~

2

~

-

~

2

7

-

3

21

Negative

~

9

4

2

5

1

~

1

6

3

1

2

34

Table 10 33
Table 11. Sensitivity of selected parameters

[Parameter definitions: AGWETP, available evapotranspiration satisfied by active ground water; AGWRC, active groundwater recession rate; BASETP, available evapotranspiration satisfied by base flow; DEEPFR, fraction of inflow that enters 

inactive ground water; INFEXP, infiltration equation exponent; INFILD, ratio of maximum and mean infiltration capacities; 

INFILT, index to infiltration capacity of soil; INTFW, interflow inflow; IRC, interflow recession rate; KVARY, nonexponential 

ground-water recession rate; LSUR, length of assumed overland flow plane; LZSN, lower zone nominal storage; NSUR, 

Manning's n for assumed overland flow plane; SLSUR, slope of assumed overland flow plane; CEPSC, interception storage 

capacity; LZETP, lower zone evapotranspiration; UZSN, upper zone nominal storage; DISCH, FTABLE discharge; VOL, 

FTABLE volume; AGWS, initial active ground-water storage; LZS, initial lower zone storage; UZS, initial upper zone 

storage; FTABLE, table of depth, surface area, volume, and discharge for each reach. The users manual for Hydrologic 

Simulation Program FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of 

each parameter.

ffVs, cubic feet per second; in., inches; change = 100 * [(A-I)/!]; A = adjusted value; I = initial value; , undefined change]

Parameter 

adjusted

Initial 

value

Adjusted 

value

Change in 

parameter 

(percent)

Time of 

peak

Storm 

peak 

(ft3/s)

Change 

in storm 

peak 

(percent)

Storm 

volume 

(in.)

Change 

in storm 

volume 

(percent)

Annual process-related parameters

AGWETP

AGWRC

BASETP

DEEPFR

INFEXP

INFILD

INFILT

INTFW

IRC

KVARY

LSUR

LZSN

NSUR

SLSUR

0.0

.996

.0

.0

2.0

2.0

.015, .045

.4, .8

.01

.0

2,000, 3,000

1.0,3.0

.20, .35, .25

.01,. 05

0.1

.906

.1

.1

1.5

1.5

.022, .068

.6, 1.2

.1

.2

3,000, 4,000

1.5,4.5

.30, .45, .35

.02, .07

-

-9.0

-

-

-25.0

-25.0

50.0

50.0

900.0

-

50.0, 33.3

50.0

50.0,28.6,40.0

100.0,40.0

1800

1800

1800

1800

1800

1800

1800

1800

1800

1800

1800

1800

1800

1800

15,800

15,500

15,800

1 5,400

15,900

15,200

13,000

14,400

15,200

1 5,400

13,300

13,300

13,000

18,300

2.6

.7

2.6

.0

3.2

-1.3

-15.6

-6.5

-1.3

.0

-13.6

-13.6

-15.6

18.8

4.69

4.73

4.66

4.56

4.80

4.57

3.80

4.85

4.43

4.57

4.35

3.67

4.33

4.80

2.6

3.5

2.0

-.2

5.0

.0

-16.9

6.1

-3.1

.0

-4.8

-19.7

-5.3

5.0

Monthly process-related parameters

CEPSC

LZETP

UZSN

DISCH

VOL

.05 -.32

.2-.9

.1-.8

0-22,500

a -ft 10

.15-.42

.3-1.0

.2-.9

0-11,250

0-1220

200.0-3 1 .2

50.0-11.1

50.0-2.5

Basin-related

-50.0

100.0

1800

1800

1800

parameters

1800

1800

15,100

1 5,000

14,100

13,400

12,100

-1.9

-2.6

-8.4

-13.0

-21.4

4.37

4.68

4.03

4.50

4.42

-4.4

2.4

-11.8

-1.5

-3.3

Initial process-related conditions

AGWS

LZS

UZS

None

.6

3.0

.4

-

.3

2.0

.2

--

-50.0

-33.3

-50.0

.0

1800

1800

1800

1800

1 5,400

1 5,400

1 5,400

15,400

.0

.0

.0

.0

4.57

4.49

4.55

4.57

.0

-1.8

-.4

.0

34 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
Table 12. Recalibrated annual parameters

[Units listed below parameter name except for parameters with no units; in/hr, inch per hour; ft, feet; in., inches; ft/ft, foot per fo

Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: 1, low perme

2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or permeability not characterized). The second d

crop; F, forest; P, pasture; X, all land covers (or land cover not characterized). The third digit designates watershed slope: F, flat, l

than 3 percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low p

steep slope has the descriptor 2FS. A land segment for which only land cover is characterized (as crop) has the descriptor XCX.

Parameter definitions: AGWETP, available evapotranspiration satisfied by active ground water; AGWRC, active ground-water r

evapotranspiration satisfied by base flow; DEEPFR, fraction of inflow that enters inactive ground water; INFEXP, infiltration equ

maximum and mean infiltration capacities; INFILT, index to infiltration capacity of soil; INTFW, interflow inflow; IRC, interflow 

nonexponential ground-water recession rate; LSUR, length of assumed overland flow plane; LZSN, lower zone nominal storage; 

overland flow plane; SLSUR, slope of assumed overland flow plane. The users manual for Hydrologic Simulation Program FO

Protection Agency, 1992) provides a more complete description of each parameter.]

, , INFILT23 IR°23 KVARY> LSUR

INFEXP 1 INFILD 1 INTFW23 (per (per 

(in/hr) Jf ;H (ft) 

day) inch)

AGWETP 1 BASETP 13 DEEPFR 1 

segment (per day)

1CF

1CS

IFF

1FS

1PF

IPS

2CF

2CS

2FF

2FS

2PF

2PS

0

0

0

0

0

0

0

0

0

0

0

0

0.83 0.1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

.83 .1

0

0

0

0

0

0

0

0

0

0

0

0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

0.03

.03

.03

.03

.03

.03

.08

.08

.08

.08

.08

.08

0.5

.5

.5

.5

.5

.5

1.0

1.0

1.0

1.0

1.0

1.0

0.001

.001

.001

.001

.001

.001

.001

.001

.001

.001

.001

.001

0

0

0

0

0

0

0

0

0

0

0

0

3,500

2,500

3,500

2,50

3,50

2,50

3,50

2,50

3,50

2,50

3,50

2,50

1 Default value used for this parameter.

- Initial estimates for this parameter taken from calibration results. 

Parameter was revised during recalibration.
Table 13. Recalibrated monthly parameters

[Units listed below parameter name except for parameters with no units; in., inches.

Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: I, low 

permeability (less than 2 inches/hour); 2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or 

permeability not characterized). The second digit designates land cover: C, crop; F, forest; P, pasture; X, all land covers (or 

land cover not characterized). The third digit designates watershed slope: F, flat, less than 3 percent; S, steep, more than 3 

percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low 

permeability, a forest cover, and a steep slope has the descriptor 2FS. A land segment for which only land cover is 

characterized (as crop) has the descriptor XCX.

Parameter definitions: CEPSC, interception storage capacity; LZETP, lower zone evapotranspiration; UZSN, upper zone 

nominal storage. The users manual for Hydrologic Simulation Program FORTRAN (U.S. Environmental Protection Agency, 

1992) provides a more complete description of each parameter]

Land 

Jan 

segment

XCX 0.05

XFX .II

XPX .08

XCX .2

XFX .3

XPX .2

IXX .1

2XX .2

Feb Mar

0.05 0.05

.11 .16

.09 .10

.3 .4

.4 .5

.3 .4

.1 .2

.2 .3

Apr

0.09

.18

.12

.5

.6

.5

.2

.3

May

0.14

.24

.18

.6

.7

.6

.2

.4

June

CEPSC 1 2 

(in.)

0.18

.28

.22

LZETP 1 2

.7

.8

.7

UZSN 1 '2 

(in.)

.3

.5

July

0.24

.32

.26

.8

.9

.8

.4

.6

Aug

0.28

.32

.26

.9

.9

.9

.4

.6

Sept

0.24

.28

.22

.7

.8

.7

.3

.5

Oct

0.18

.22

.18

.6

.7

.7

.3

.4

Nov

0.12

.18

.12

.5

.6

.5

.3

.4

Dec

0.08

.14

.08

.3

.4

.3

.2

.3

Initial estimates for this parameter taken from calibration results. 

~ Parameter was revised during rccalibration.

36 Simulation of Storm Peaks and Storm Volumes for Selected Subbasins in the West Fork Trinity River Basin, Texas, Water 

Years 1993-94
Table 14. Initial condition values for model recalibration

[Land segments are characterized and designated by a 3-digit descriptor. The first digit designates soil permeability: I, low 

permeability (less than 2 inches/hour); 2, moderately low permeability (more than 2 inches/hour; X, all permeabilities (or 

permeability not characterized). The second digit designates land cover: C, crop; F, forest; P, pasture; X, all land covers (or 

land cover not characterized). The third digit designates watershed slope: F, flat, less than 3 percent; S, steep, more than 3 

percent; X, all slopes (or slope not characterized). For example, a land segment characterized by soils of moderately low 

permeability, a forest cover, and a steep slope has the descriptor 2FS. A land segment for which only land cover is 

characterized (as crop) has the descriptor XCX.

AGWS, active ground-water storage; LZS, lower zone storage; UZS, upper zone storage. The users manual for Hydrologic 

Simulation Program-FORTRAN (U.S. Environmental Protection Agency, 1992) provides a more complete description of each 

parameter, in., inches]

Station Water year Land segment

Beans Creek 1993 1XX

2XX

1994 1XX

2XX

Big Creek 1993 1XX

2XX

1994 1XX

2XX

Garrett Creek 1993 1XX

2XX

1994 1XX

2XX

Salt Creek 1993 1XX

2XX

1994 1XX

2XX

Walnut Creek 1993 1XX

2XX

1994 1XX

2XX

AGWS1 2 

(in.)

0.02

.02

.01

.01

.02

.02

.01

.01

.12

.12

.01

.02

.02

.02

.03

.05

.52

.62

.02

.02

LZS 12 

(in.)

0.5

.6

.5

.7

.5

.6

.3

.5

.7

1.1

.4

1.0

.7

1.7

.5

1.3

2.7

3.1

.7

1.1

UZS 12

(in.)

0.11

.12

.01

.02

.11

.12

.01

.01

.11

.12

.01

.03

.05

.08

.03

.05

.21

.32

.01

.02

Initial estimates for this parameter taken from calibration results. 

Parameter was revised during recalibration.

Table 14 37
Table 15. Measured and simulated storm peaks and storm volumes using recalibrated parameters 

[ft3 /s, cubic feet per second; in., inches; Error = 100 * [(S-M)/M]; S, simulated value, M, measured value]

»

o Water 

§ year

3

 o

o>o> 

W

0)

g. 1993

| 1993

< 1993

o

1 1994

0>

u>

3 1994

£ 1994

0>

% 1994

a

w 1994

or

or 

0) 

in

3 1993

| 1993

a>

$ 1993

a>

- 1993

S1

X"

H 1994

!' 1994

5

fD

i 1993

| 1993

g 1993

Q>

-" 1993

Date of 

storm

Date of 

peak

Rainfall 

(in.) Time of 

peak

Measured

Storm 

peak

(ft3/s)

Storm 

volume 

(in.)

Time of 

peak

Simulated

Storm 

peak

(ft3/s)

Storm 

volum

(in.)

Beans Creek subbasin

02/14-16/93

02/24-25/93

02/28-03/02/93

10/18-20/93

12/03-04/93

02/2 1-24/94

05/11-14/94

05/25-26/94

02/15/93

02/25/93

03/01/93

10/19/93

12/03/93

02/22/94

05/13/94

05/25/94

1.86

.96

1.07

4.06

1.86

1.50

5.09

1.89

1300

0800

1400

2100

1500

0600

0400

1200

571

472

378

1,520

364

110

4,230

703

0.262

.183

.200

.929

.179

.150

2.76

.349

1300

0500

1200

1900

1200

0400

0200

0900

466

116

198

3,260

1,500

46

1,990

43

0.222

.044

.15

2.00

.543

.04

1.97

.06

Big Creek subbasin

02/14-16/93

02/28-03/02/93

05/08-09/93

06/08-09/93

10/19-20/93

02/21-24/94

02/15/93

03/01/93

05/09/93

06/08/93

10/19/93

02/22/94

1.62

1.16

1.50

4.85

3.31

1.63

1500

1400

1600

2400

0500

0600

809

1,850

1,560

9,470

1,620

898

.118

.436

.230

2.32

.193

.142

1200

1100

1200

2300

0500

0300

264

171

1

1,560

1,530

31

.07

.07

.00

.39

.78

.03

Garrett Creek subbasin

12/13-14/92

02-15-16/93

02/24-25/93

02/28-03/02-93

12/14/92

02/15/93

02/25/93

03/01/93

2.77

1.35

1.81

.87

0800

1600

1200

2200

568

660

947

181

.278

.288

.385

.131

0600

1300

0700

1400

1,680

716

1,210

273

.68

.32

.41

.26
Table 15. Measured and simulated storm peaks and storm volumes using recalibrated parameters Continued

Water 

year

Date of 

storm

Date of 

peak

Rainfall

(in.) Time of 

peak

Measured

Storm 

peak 

(ft3/s)

Storm 

volume 

(in.)

Time of 

peak

Simulated

Storm 

peak

(ft3/s)

Storm 

volum

(in.)

Garrett Creek subbasin Continued

1993

1994

1994

1994

1994

1994

1994

1994

09/13-14/93

10/12-14/93

10/17-21/93

12/03-04/93

02/21-24/94

05/11-13/94

09/08-09/94

09/15-16/94

09/14/93

10/13/93

10/19/93

12/03/93

02/22/94

05/12/94

09/09/94

09/16/94

4.39

1.73

6.13

1.58

1.35

4.09

1.34

1.59

0700

0300

2400

1500

0600

0400

1200

1400

337

284

2,090

437

186

2,230

498

237

0.099

.057

1.600

.112

.051

1.830

.085

.038

0800

0600

2000

1500

1300

0400

1100

1200

839

1

5,250

643

65

1,710

1

13

0.267

.001

2.32

.284

.067

1.44

.001

.003

Salt Creek subbasin

1993

1993

1993

1993

1993

1993

1993

1993

1993

1994

§1 1994

£ 1994

1994

10/15-16/92

11/18-19/92

12/13-15/92

02/03-04/93

02/14-16/93

02/24-25/93

02/28-03/02/93

04/03-05/93

09/13-14/93

10/12-14/93

10/18-19/93

05/11-14/94

09/15-16/94

10/16/92

11/19/92

12/13/92

02/03/93

02/15/93

02/25/93

03/01/93

04/04/93

09/14/93

10/13/93

10/19/93

05/13/94

09/16/94

2.31

1.48

3.50

1.13

1.47

2.98

.90

1.41

4.60

1.97

4.28

5.42

1.99

0200

1100

2000

1800

1200

0400

1200

0500

0500

0100

1800

0700

1300

287

122

544

181

547

1,300

261

261

491

238

965

737

169

.116

.037

.375

.092

.307

.438

.125

.138

.145

.021

.581

.503

.014

0600

1200

2200

2000

1400

0500

1200

1800

0700

0900

2000

0800

1800

5

1

1,090

386

740

5,300

473

71

1,850

13

4,970

5,030

8

.002

.001

.844

.180

.352

1.31

.369

.055

.456

.010

2.22

1.68

.003
Table 15. Measured and simulated storm peaks and storm volumes using recalibrated parameters Continued

 < g'

2 E

3 S

JSS to 

EW

0

i

CD

0)

(A

0)

a

o

i

0

c

CD

(A

0

CD

CD

O

I

C/)

CO"

0)

5'

(A

5'

CD

1

(A

-n

0

H

33

i

00

u

(A

Water

year

Date of

storm

Date of

peak

Rainfall

(in.) Time of 

peak

Measured

Storm 

peak

(ft3/s)

Storm 

volume

(in.)

Time of 

peak

Simulated

Storm 

peak

(ft3/s)

Storm 

volum

(in.)

Walnut Creek subbasin

1993

1993

1993

1993

1993

1993

1993

1994

1994

1994

1994

1994

1994

1994

1994

1994

10/15-16/92

12/13-15/92

02/03-04/93

02/14-16/93

02/24-25/93

02/28-03/02/93

09/13-14/93

10/12-14/93

10/18-20/93

02/21-24/94

04/29-30/94

05/11-14/94

05/25-26/94

08/20-21/94

09/08-09/94

09/15-16/94

10/15/92

12/13/92

02/03/93

02/15/93

02/25/93

03/01/93

09/14/93

10/13/93

10/19/93

02/23/94

04/30/94

05/13/94

05/26/94

08/20/94

09/09/94

09/16/94

2.32

3.53

1.53

1.23

2.02

.88

4.84

1.91

4.75

1.46

1.45

4.20

1.68

1.28

2.76

1.87

2400

2100

1800

1200

0600

1300

0500

0700

1800

0400

0300

0700

0800

2400

1000

0900

764

3,180

768

1,080

7,420

901

3,070

211

7,760

480

397

5,980

250

692

2,950

2,240

0.097

.890

.201

.257

.750

.258

.358

.068

1.41

.093

.066

1.56

.048

.082

.304

.254

2400

2200

1600

1400

0500

1 100

0500

0700

1800

0600

0500

0700

0700

2400

1100

1300

478

1,680

1,910

572

4,530

633

3,570

8

12,000

26

2

5,900

325

I

539

273

0.09

.90

.44

.23

.65

.29

.46

.00

2.20

.04

.00

1.33

.10

.00

.06

.05
Table 16. Mean absolute errors and biases of storm peaks and storm volumes using recalibrated parameters

[Mean absolute error = 100* [I(|S-M|)/M]/N; bias= 100* [Z(S-M)/M]/N; S, simulated value; M, measured value; N, number 

of values]

Storm peaks

Station

Beans Creek

Big Creek

Garret! Creek

Salt Creek

Walnut Creek

Water year

1 993

1 994

1 993

1 994

1 993

1 994

1 993

1 994

1 993

1 994

Mean absolute error 

(percent)

47. 1

1 26

85.4

51. 1

86.4

82.9

132

297

55.7

71.7

Bias 

(percent)

-47 1

44.2

-85.4

-51.1

86.4

-26.3

71.6

202

-8.6

-52.9

Storm volumes

Mean absolute error 

(percent)

37.4

100

75.6

193

86.9

77.4

122

162

27.6

77.0

Bias 

(percent)

-37.4

27.1

-75.6

114

86.9

-11.7

65.4

96.3

20.9

-36.7

Table 17. Monthly distribution of errors of storm peaks and storm volumes using recalibrated parameters 

[Error = 100 * [(S-M)/S]; S, simulated value; M, measured value; --, no storms]

Month

January

February

March

April

May

June

July

August

September

October

November

December

Total

Storm-peak errors

Positive Negative

-

6

2

-

2

-

-

-

3

4

-

4

21

-

9

3

2

5

1

--

1

5

6

1

1

34

Storm- volume errors

Positive Negative

-

7

3

-

2

-

-

-

3

5

5

25

-

8

2

2

5

1

-

1

5

5

1

-

30

Table 17 41