Runoff Characteristics for the Houston, 

Texas, Metropolitan Area

Water-Resources Investigations Report 01–4071

U.S. Department of the Interior

U.S. Geological Survey
Cover:

Severe flooding in Houston, June 2001 (photograph courtesy of the Houston Chronicle).
U.S. Department of the Interior

U.S. Geological Survey

Effects of Urban Development on Stormwater 

Runoff Characteristics for the Houston, 

Texas, Metropolitan Area

By Fred Liscum

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01–4071

In cooperation with the Harris County Flood Control District

and the City of Houston

Austin, Texas

2001
ii

U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, 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

8027 Exchange Dr.

Austin, TX 78754–4733

E-mail: dc_tx@usgs.gov

Copies of this report can be purchased from

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225–0286

E-mail: infoservices@usgs.gov
CONTENTS iii

CONTENTS

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

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

Description of Study Area ........................................................................................................................................ 3

Acknowledgments .................................................................................................................................................... 3

Equations for Estimating Effects of Urban Development on Stormwater Runoff Characteristics ...................................... 3

Stormwater Runoff Characteristics ........................................................................................................................... 3

Basin and Rainfall Characteristics ............................................................................................................................ 7

Regression Analysis .................................................................................................................................................. 8

Regression Equations ................................................................................................................................................ 10

Limitations on Values for Basin and Rainfall Characteristics .................................................................................. 11

Evaluation of Regression Equations ......................................................................................................................... 11

Effects of Urban Development on Stormwater Runoff Characteristics ............................................................................... 19

Characteristics That Define Magnitude of Stormwater Runoff ................................................................................ 19

Characteristics That Describe Shape and Duration of Storm Hydrograph ............................................................... 25

Summary .............................................................................................................................................................................. 25

References Cited .................................................................................................................................................................. 26

FIGURES

1. Map showing location of study area and data-collection sites ............................................................................. 2

2. Storm discharge hydrograph showing stormwater runoff characteristics ............................................................. 4

3. Graphs showing changes in indices of urban development with time for sites reflecting the smallest 

and largest increases in urban development during 1964–89 ............................................................................... 9

4. Graphs showing observed versus predicted: 

a. Peak flow (QPEAK) for all storms, by region ........................................................................................... 12

b. Basin lag (BLAG) for all storms, by region ............................................................................................... 13

5. Graphs showing predicted values versus residuals for: 

a. Peak flow (QPEAK) for all storms, by region ........................................................................................... 14

b. Basin lag (BLAG) for all storms, by region ............................................................................................... 15

6. Stem-and-leaf plots showing distribution of residuals for: 

a. Peak flow (QPEAK) for all storms, by region ........................................................................................... 16

b. Basin lag (BLAG) for all storms, by region ............................................................................................... 17

7. Graphs showing observed versus predicted stormwater runoff characteristics for selected streamflowgaging stations reflecting small and large increases in urban development, by region:

a. Peak flow (QPEAK) .................................................................................................................................. 27

b. Peak yield (YPEAK) .................................................................................................................................. 28

c. Direct runoff (ROVOL) .............................................................................................................................. 29

d. Direct runoff duration (RODUR) ............................................................................................................... 30

e. Time of rise to peak flow (TRISE) ............................................................................................................ 31

f. Duration of flow that equals or exceeds 75 percent of peak flow (Q75DUR) ........................................... 32

g. Duration of flow that equals or exceeds 50 percent of peak flow (Q50DUR) ........................................... 33

h. Time of recession from peak flow to base flow (TRECES) ...................................................................... 34

i. Basin lag (BLAG) ...................................................................................................................................... 35
iv 

8. Hydrographs for:

a. 080757770 Hunting Bayou at I–610 showing effects of no increase in basin development 

factor (BDF) ............................................................................................................................................... 20

b. 08075900 Greens Bayou at U.S. Hwy 75 showing effects of large increase in basin development 

factor (BDF) ............................................................................................................................................... 21

c. 08075550 Berry Bayou at Gilpin St. showing effects of small increase in basin development 

factor (BDF) ............................................................................................................................................... 22

d. 08074800 Keegans Bayou at Roark Rd. showing effects of large increase in basin development 

factor (BDF) ............................................................................................................................................... 23

TABLES

1. Data-collection sites in the study area .................................................................................................................. 5

 2. Stormwater runoff, basin, and rainfall characteristics .......................................................................................... 6

 3. Summary statistics for stormwater runoff, basin, and rainfall characteristics ...................................................... 6

 4. Regression equations for estimating selected stormwater runoff characteristics ................................................. 10

 5. Maximum and minimum values of independent variables used to develop regression equations ....................... 18

 6. Standard error of regression between observed and predicted stormwater runoff characteristics 

for available storms at selected sites representing small and large increases in urban development ................... 18

 7. Percent change in stormwater runoff characteristics for selected increases in basin development

factor ..................................................................................................................................................................... 24

VERTICAL DATUM

Sea Level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general 

adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.
Abstract 1

Effects of Urban Development on Stormwater 

Runoff Characteristics for the Houston, 

Texas, Metropolitan Area

By Fred Liscum 

Abstract 

A study was done to estimate the effects of 

urban development in the Houston, Texas, metropolitan area on nine stormwater runoff characteristics. Three of the nine characteristics define the 

magnitude of stormwater runoff, and the remaining 

six characteristics describe the shape and duration 

of a storm hydrograph. Multiple linear regression 

was used to develop equations to estimate the nine 

stormwater runoff characteristics from basin and 

rainfall characteristics. Five basin characteristics 

and five rainfall characteristics were tested in the 

regressions to determine which basin and rainfall 

characteristics significantly affect stormwater runoff characteristics. Basin development factor was 

found to be significant in equations for eight of the 

nine stormwater runoff characteristics. Two sets of 

equations were developed, one for each of two 

regions based on soil type, from a database containing 1,089 storm discharge hydrographs for 42 sites 

compiled during 1964–89.

The effects of urban development on the 

eight stormwater runoff characteristics were quantified by varying basin development factor in the 

equations and recomputing the stormwater runoff 

characteristics. The largest observed increase in 

basin development factor for region 1 (north of 

Buffalo Bayou) during the study resulted in corresponding increases in the characteristics that define 

magnitude of stormwater runoff ranging from 

about 40 percent (for direct runoff) to 235 percent 

(for peak yield); and corresponding decreases in 

the characteristics that describe hydrograph shape 

and duration ranging from about 22 percent (for 

direct runoff duration) to about 58 percent (for 

basin lag). The largest observed increase in basin 

development factor for region 2 (south of Buffalo 

Bayou) during the study resulted in corresponding 

increases in the characteristics that define magnitude of stormwater runoff ranging from about 33 

percent (for direct runoff) to about 210 percent 

(for both peak flow and peak yield); and corresponding decreases in the characteristics that 

describe hydrograph shape and duration ranging 

from about 38 percent (for direct runoff duration) 

to about 64 percent (for basin lag). 

INTRODUCTION 

The Houston, Texas, metropolitan area (fig. 1) 

has been undergoing extensive urban development since 

the 1950s. The U.S. Geological Survey (USGS), in 

cooperation with the Harris County Flood Control 

District and the City of Houston, began the continuing 

Houston Urban Runoff Program (HURP) in 1964 to 

define the magnitude and frequency of floods; to document variations in streamwater quality for different 

flow conditions, seasons, and types of urban development; and to determine the effects of urban development 

on stormwater runoff characteristics. A previous report 

presented data defining the magnitude of floods and 

the water-quality data available for the Houston area 

(Liscum and others, 1996).

Stormwater runoff can be quantified from a 

storm discharge hydrograph, a continuous graph of 

instantaneous stream discharge versus time for a storm. 

Stormwater runoff characteristics define or describe 

the magnitude, shape, and duration of a storm discharge 

hydrograph. Stormwater runoff characteristics are 

related to drainage basin and storm rainfall characteristics. If the relations between stormwater runoff 

characteristics and associated basin and rainfall characteristics can be established, then the stormwater runoff 

characteristics that are measurably affected by urban 

development, and how they are affected, can be determined. Such information can be used by water-resource 
2 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

TEXAS

Study area

Houston

LOCATION MAP

Galveston Bay State 6

State 288

State 6

US 59

US 90A

WALLER

HOUSTON

Creek

Creek

Spring

Creek Cole

S AN JACINTO

Bayou

RIVER

Greens

Halls

Bayou

White o ak Bayou

Cypress

 LAKE

 HOUSTON

 ADDICKS

 RESERVOIR

 BARKER

RESERVOIR

Keegans

Bayou

Bayou

Bayou

Buffalo Bayou

Brays

Sims

Houston Ship

 Channel

Clear

Creek

08076700

08075760

08075770 08075750

HARRIS

WALLER

MONTGOMERY

LIBERTY

GALVESTON

BRAZORIA

FORT 

 BEND

I–45

FM 1960

US 59

FM 1960

US 290

I–10

US 90A

I–10

I–610

I–610

95o45' 95o

30'

95o

15'

30o

15'

30o

29o45'

29o

30'

0 4 8 12 MILES

Base from U.S. Geological Survey

Digital data: 1:100,000, 1983

Universal Transverse Mercator projection

Zone 15

08068400

08068440

08068450

08068438

08075780

08075900

08076200 08076000

08074145 08076500

08074100

08074200

08074150 08074250

08074750

08074780

08074800

08074760

08073750

08074810

08073800

08073630

08074850

08074400

08074500

08074540

08075000

08074910

08074900

08075300

08075400

08077100

08075600

08075550

08075730

08075700

08075650

08075500

08073750

08073630 Data-collection site 

 and number in region 1

Data-collection site 

 and number in region 2

EXPLANATION

Figure 1. Location of study area and data-collection sites.
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 3

managers to estimate storm runoff characteristics—for 

example, peak discharge for a given level of development in a basin for a given rainfall event. 

Past studies have identified the effects of urban 

development on the computed flood peak for selected 

probabilities of occurrence such as recurrence intervals 

of 2 to 500 years (Johnson and Sayre, 1973; Liscum and 

Massey, 1980). However, as those studies emphasize, 

the analysis of surface-water runoff in an urban coastal 

environment such as Houston is complicated by limitations imposed on the runoff process by the nearly flat 

topography and the interactions of urban development 

with the nearly flat topography. 

A study was conducted by the USGS, in cooperation with the Harris County Flood Control District and 

the City of Houston, to estimate the effects of urban 

development on stormwater runoff characteristics in the 

Houston metropolitan area. Nine stormwater runoff 

characteristics were selected for study. Multiple linear 

regression was used to develop equations to estimate the 

nine stormwater runoff characteristics. Five basin characteristics and five rainfall characteristics were selected 

as independent variables and tested in the regressions to 

determine which basin and rainfall characteristics significantly affect stormwater runoff characteristics. The 

effects of urban development on the stormwater runoff 

characteristics were quantified by varying the significant basin characteristic that accounts for urban development in the regression equations and recomputing the 

stormwater runoff characteristics. Two sets of equations 

were developed, one for each of two regions based on 

soil type. The purpose of this report is to present the 

results of the study. 

Data collected for the HURP during 1964–89 

were used in this study. A total of 1,089 storm-discharge 

hydrographs from 42 sites (fig. 1; table 1) were available for analysis (Liscum and others, 1996). 

Description of Study Area

The Houston metropolitan area is in southeastern 

Texas about 45 miles northwest of the Gulf of Mexico 

on an almost level plain. Land-surface altitudes in the 

study area range from 35 feet above sea level in the 

southeastern part to 135 feet in the northwestern part. 

Soils are predominately clay, clay loams, and fine sandy 

loams of low permeability. The Houston metropolitan 

area developed rapidly during 1964–89. Population 

increased from 1.42 million in 1960 to 3.30 million in 

1990 (A.H. Belo Corp., 1991).

The major stream draining the study area is 

Buffalo Bayou (fig. 1), a tributary of the San Jacinto 

River. Buffalo Bayou has been regulated by Barker and 

Addicks (flood-detention) Reservoirs in the western 

part of the area since the late 1940s. From these reservoirs, Buffalo Bayou meanders eastward, is fed by four 

major tributaries (Whiteoak, Brays, Sims, and Greens 

Bayous), and enters the Houston Ship Channel and then 

Galveston Bay on the Gulf of Mexico. The drainage 

area of Buffalo Bayou, excluding the area upstream of 

the reservoirs, is about 810 square miles. 

The climate of the Houston metropolitan area is 

characterized by short mild winters, long hot summers, 

high relative humidity, and prevailing southeasterly 

winds. The 30-year (1961–90) average annual rainfall 

for Houston is 46.1 inches, which is distributed uniformly throughout the year (Ramos, 1997).

Acknowledgments

The USGS acknowledges the support of agencies 

who participated in this study. Principal among those 

are the Harris County Flood Control District and the 

City of Houston. The U.S. Army Corps of Engineers 

also provided support for parts of the study. 

EQUATIONS FOR ESTIMATING EFFECTS 

OF URBAN DEVELOPMENT ON 

STORMWATER RUNOFF 

CHARACTERISTICS 

The effects of urban development on nine stormwater runoff characteristics (table 2) in the Houston 

metropolitan area were estimated from regression equations. Stormwater runoff characteristics are functions of 

selected basin and rainfall characteristics in the regression equations. Stormwater runoff characteristics define 

or describe the magnitude, shape, and duration of a 

storm discharge hydrograph (fig. 2). Basin characteristics affect the hydrologic responses of a watershed. 

Rainfall characteristics define the magnitude and duration of the rainfall that produces the storm runoff.

Stormwater Runoff Characteristics

The stormwater runoff characteristics used to 

develop the regression equations were computed from 

the available storm discharge hydrographs (table 3). 

Peak flow (QPEAK), peak yield (YPEAK) (ratio of 

QPEAK to drainage area), and direct runoff (ROVOL) 

define the magnitude of stormwater runoff. An analysis 
4 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area Centroid of storm rainfall Q50DUR QPEAK, YPEAK BLAG Q75DUR RODUR Q = 0.50 (QPEAK) Q = 0.75 (QPEAK) Centroid of direct runoff TRISE TRECES ROVOL NOTE: Abbreviations of characte

 defined in table 2.

0

700600500400

300

200100

1.00

0.50

0

RAINFALL, IN INCHES STREAMFLOW, IN CUBIC FEET PER SECOND

2400 1200 2400 1200 2400 1200 2400 1200 2400 1

21 22 23 24 

JANUARY 1997

Figure 2. Storm discharge hydrograph showing stormwater runoff characteristics.
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 5

Table 1. Data-collection sites in the study area

USGS station no. Region Station name Latitude Longitude

08068400 1 Panther Branch near Conroe, Tex. 30°11'28" 95°28'44"

08068438 1 Swale No. 8 at Woodlands, Tex. 30°08'38" 95°28'09"

08068440 1 Lake Harrison at Drop Inlet at Woodlands, Tex. 30°08'24" 95°28'33"

08068450 1 Panther Branch near Spring, Tex. 30°08'02" 95°28'38"

08073630 1 Bettina St. Ditch at Houston, Tex. 29°46'32" 95°32'23"

08073750 2 Stoney Brook St. Ditch at Houston, Tex. 29°44'05" 95°30'22"

08073800 2 Bering Ditch at Woodway Dr., Houston, Tex. 29°45'22" 95°29'44"

08074100 1 Cole Creek at Guhn Rd. at Houston, Tex. 29°51'24" 95°30'55"

08074145 1 Bingle Rd. Storm Sewer at Houston, Tex. 29°51'31" 95°29'09"

08074150 1 Cole Creek at Deihl Rd., Houston, Tex. 29°51'04" 95°29'16"

08074200 1 Brickhouse Gully at Clarblak St., Houston, Tex. 29°49'53" 95°31'42"

08074250 1 Brickhouse Gully at Costa Rica St., Houston, Tex. 29°49'40" 95°28'09"

08074400 1 Lazybrook St. Storm Sewer at Houston, Tex. 29°48'15" 95°26'04"

08074500 1 Whiteoak Bayou at Houston, Tex. 29°46'30" 95°23'49"

08074540 1 Little Whiteoak Bayou at Trimble St., Houston, Tex. 29°47'33" 95°22'06"

08074750 2 Brays Bayou at Addicks-Clodine Rd., Houston, Tex. 29°43'02" 95°39'38"

08074760 2 Brays Bayou at Alief Rd., Alief, Tex. 29°42'39" 95°35'13"

08074780 2 Keegans Bayou at Keegan Rd. near Houston, Tex. 29°39'55" 95°35'42"

08074800 2 Keegans Bayou at Roark Rd. near Houston, Tex. 29°39'23" 95°33'43"

08074810 2 Brays Bayou at Gessner Dr., Houston, Tex. 29°40'21" 95°31'41"

08074850 2 Bintliff Ditch at Bissonnet St., Houston, Tex. 29°41'16" 95°30'20"

08074900 2 Willow Waterhole Bayou at Landsdowne St., Houston, Tex. 29°39'01" 95°29'11"

08074910 2 Hummingbird St. Ditch at Houston, Tex. 29°39'44" 95°29'11"

08075000 2 Brays Bayou at Houston, Tex. 29°41'49" 95°24'43"

08075300 2 Sims Bayou at Carlsbad St., Houston, Tex. 29°37'33" 95°29'56"

08075400 2 Sims Bayou at Hiram Clarke St., Houston, Tex. 29°37'07" 95°26'45"

08075500 2 Sims Bayou at Houston, Tex. 29°40'27" 95°17'21"

08075550 2 Berry Bayou at Gilpin St. at Houston, Tex. 29°38'32" 95°13'22"

08075600 2 Berry Bayou Tributary at Globe St., Houston, Tex. 29°39'00" 95°14'48"

08075650 2 Berry Bayou at Forest Oaks St., Houston, Tex. 29°40'35" 95°14'37"

08075700 2 Berry Creek at Galveston Rd. at Houston, Tex. 29°40'59" 95°15'11"

08075730 2 Vince Bayou at Pasadena, Tex. 29°41'40" 95°12'58"

08075750 1 Hunting Bayou Tributary at Cavalcade St., Houston, Tex. 29°48'00" 95°20'02"

08075760 1 Hunting Bayou at Falls St. at Houston, Tex. 29°48'22" 95°19'50"

08075770 1 Hunting Bayou at I–610, Houston, Tex. 29°47'35" 95°16'04"

08075780 1 Greens Bayou at Cutten Rd. near Houston, Tex. 29°56'56" 95°31'10"

08075900 1 Greens Bayou at U.S. Hwy 75 near Houston, Tex. 29°57'24" 95°25'04"

08076000 1 Greens Bayou near Houston, Tex. 29°55'05" 95°18'24"

08076200 1 Halls Bayou at Deertrail St. at Houston, Tex. 29°54'07" 95°25'21"

08076500 1 Halls Bayou at Houston, Tex. 29°51'42" 95°20'05"

08076700 1 Greens Bayou at Ley Rd., Houston, Tex. 29°50'13" 95°13'59"

08077100 2 Clear Creek Tributary at Hall Rd., Houston, Tex. 29°36'09" 95°16'41"
6 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Table 2. Stormwater runoff, basin, and rainfall characteristics 

Table 3. Summary statistics for stormwater runoff, basin, and rainfall characteristics 

[Abbreviations of characteristics defined in table 2; statistics based on 1,089 storm discharge hydrographs] 

Stormwater runoff characteristics Abbreviation Units

Peak flow QPEAK cubic feet per second

Peak yield YPEAK cubic feet per second per square mile

Direct runoff ROVOL inches

ROVOL duration RODUR hours

Time of rise to QPEAK TRISE hours

Duration of flow that equals or exceeds 75 percent of QPEAK Q75DUR hours

Duration of flow that equals or exceeds 50 percent of QPEAK Q50DUR hours

Time of recession from QPEAK to base flow TRECES hours

Duration from centroid of storm rainfall to centroid of direct runoff 

(basin lag)

BLAG hours

Basin characteristics Abbreviation Units Rainfall characteristics Abbreviation Units

Drainage area DA square miles Total rainfall RTOT inches

Slope factor SL miles per (feet per mile)0.5 Maximum 60-minute rainfall R60MAX inches

Soil index SI inches per hour Rainfall duration RDUR hours

Basin development factor BDF dimensionless Shortest 85-percent RDUR R85DUR hours

Percent area developed PAD percent Antecedent rainfall index RI inches

Variable

(units)

Mean

Standard

deviation

Minimum

25th

percentile

50th

percentile

(median)

75th percentileMaximum

Stormwater runoff characteristics

QPEAK (cubic feet per second) 1,811 3,439 20.0 229.0 572.0 1,890 32,500

YPEAK (cubic feet per second per square mile) 121.3 144.7 4.48 38.78 75.37 146.0 1,231

ROVOL (inches) 1.61 1.61 .03 .56 .99 2.12 9.02

RODUR (hours) 62.68 37.45 4.80 35.00 58.30 86.80 228.5

TRISE (hours) 10.59 11.99 .30 3.00 7.30 14.00 88.00

Q75DUR (hours) 5.27 4.60 .20 2.00 3.80 7.00 33.00

Q50DUR (hours) 9.30 7.88 .30 3.50 7.30 13.00 62.00

TRECES (hours) 51.16 31.12 3.70 28.80 46.00 74.50 219.5

BLAG (hours) 10.68 7.54 .10 5.10 9.40 14.40 40.80

Basin characteristics

DA (square miles) 20.91 31.87 .13 3.42 10.70 20.20 182.0

SL (miles per [feet per mile]0.5) 2.92 2.72 .13 1.21 2.12 3.65 13.02

SI (inches per hour) 1.15 .87 .20 .20 1.30 2.00 2.00

BDF (dimensionless) 6.36 2.65 0 5.00 6.03 8.00 12

PAD (percent) 62.85 21.05 15.30 48.20 65.66 76.66 100

Rainfall characteristics

RTOT (inches) 3.11 2.11 .25 1.72 2.35 3.87 12.25

R60MAX (inches) 1.65 .75 .18 1.11 1.56 2.00 4.90

RDUR (hours) 17.00 21.85 .30 4.00 9.50 20.80 208.50

R85DUR (hours) 7.27 9.67 .20 1.80 4.30 8.00 72.00

RI (inches) 1.26 .98 .05 .46 1.00 1.85 5.78
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 7

of a series of QPEAKs over time can aid in the design 

of bridges and channels in a watershed as well as in the 

assessment of damage caused by flooding in a watershed. YPEAK can be used to estimate QPEAK at 

ungaged stream sites for selected storms. ROVOL is the 

amount of direct runoff produced by a storm in a basin. 

ROVOL is computed from the storm discharge 

hydrograph by assuming that base flow during the storm 

ranges from the discharge just before the start of the rise 

to the discharge after the hydrograph recession when 

there is little or no change. Knowing ROVOL for storms 

can aid in designing detention structures to reduce flood 

damage. 

The remaining six stormwater runoff characteristics describe the shape and duration of a discharge 

hydrograph. ROVOL duration (RODUR) is the time 

from when direct runoff begins (start of streamflow rise) 

to when discharge returns to base flow. RODUR can be 

considered the width of the direct runoff hydrograph, 

thereby providing an indication of how long a storm 

might affect a basin. Time of rise to QPEAK (TRISE) is 

an indicator of storm rainfall intensity and distribution 

and how efficiently and effectively a basin conveys 

runoff to the receiving stream. Duration of flow that 

equals or exceeds 75 percent of QPEAK (Q75DUR) and 

duration of flow that equals or exceeds 50 percent of 

QPEAK (Q50DUR) are indicators of the shape of the 

storm discharge hydrograph. Time of the recession from 

QPEAK to base flow (TRECES) indicates the efficiency 

of the basin drainage system. Basin lag (BLAG) also 

indicates basin drainage efficiency, as well the temporal 

relation between rainfall and storm runoff. 

In general, increasing urban development could 

cause QPEAK, YPEAK, and ROVOL to increase and 

RODUR, TRISE, Q75DUR, Q50DUR, TRECES, and 

BLAG to decrease (Leopold, 1968; Bedient and Huber, 

1988). 

Basin and Rainfall Characteristics

For the HURP, two types of basin characteristics 

were obtained for each data-collection site (Liscum and 

others, 1996). The first type comprises general descriptors of the basin that do not vary appreciably with time 

(drainage area [DA], slope factor [SL] [ratio of basin 

length to the square root of channel slope], and soil 

index [SI]). The second type comprises two indices of 

urban development in the basin over time (basin development factor [BDF] and percent of urban development 

[PAD] [percent area developed]).

DA is all the contributing area upstream of a 

gaging station and might also include some part of the 

drainage system across a topographic divide (connected 

by a sewer or open ditch). Obvious areas of storage, 

whether natural or constructed, are excluded in the computation of DA. Generally, QPEAKs for a larger DA 

will be greater than QPEAKs for a smaller DA if all 

other factors are identical. SL has two components—

basin length and channel slope. Basin length is the distance along the channel from the streamflow-gaging 

station to the head of the basin, and channel slope is the 

slope between points at 10 percent and 85 percent of the 

basin length. SL has a similar effect on QPEAK as DA 

and also is a measure of basin drainage properties. SI is 

the maximum permeability of the natural soil on the 

basis of soil survey maps of the U.S. Department of 

Agriculture, Natural Resources Conservation Service 

(formerly Soil Conservation Service) (Johnson and 

Sayre, 1973). SI was the basis for defining the two 

regions of the study area. SI for sites north of Buffalo 

Bayou (region 1) ranged from 1.30 to 2.00 inches per 

hour; SI for sites south of Buffalo Bayou (region 2) was 

0.20 inch per hour. 

BDF is an index of the prevalence of four drainage features—channel improvements, channel linings, 

storm sewers, and curb-and-gutter streets (Sauer and 

others, 1983). BDF can range from 0 to 12 for an entire 

basin. Each of the four drainage features is evaluated 

and assigned a value ranging from 0 (not prevalent) to 

1 (prevalent) for each one-third of a basin. The sum of 

all values represents the BDF for the entire basin. A 

BDF of zero indicates that the four drainage features are 

not prevalent but does not necessarily mean that the 

basin is not partially urbanized. A BDF of 12 indicates 

full development of the drainage features throughout the 

basin. BDF was used on a reverse scale (13 minus BDF) 

in the regression equations because Sauer and others 

(1983) found that doing so improved the linearity of 

regression equations and reduced the standard error of 

regression.

PAD is defined as the percentage of the total 

contributing DA within 200 feet of streets, roads, parking lots, and industrial sites that is drained by open 

ditches or storm sewers. PAD also includes roads in 

rural areas. PAD is highly correlated with the percentage of impervious area (Johnson and Sayre, 1973). 

For this reason, and the fact that PAD is easier than 

impervious area to estimate accurately from aerial 

photographs and other easily obtained maps, Liscum 
8 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

and Massey (1980) used PAD in previous work. Also, 

Southard (1986) confirmed that PAD was highly correlated with percent impervious area. PAD ranged from 

15.30 to 100 percent for the Houston sites (table 3). 

 One measure of urban development in a basin, 

the amount of constructed detention storage (which 

likely lessens the effects of urban development on 

stormwater runoff characteristics), is not represented in 

the database for this study. Constructed detention storage to reduce stormwater runoff was implemented in the 

Houston metropolitan area in the early-to-mid 1980s. 

Constructed detention storage probably did not have an 

appreciable effect on stormwater runoff characteristics 

associated with the storm discharge hydrographs in the 

database of this study. On average, fewer hydrographs 

in the database are from the late 1980s than from the 

earlier (pre-detention-storage) years. Also, a time lag is 

likely between the time when constructed detention 

storage was implemented and when a sufficient amount 

of detention storage was constructed to measurably 

affect stormwater runoff characteristics.

BDF and PAD were computed three times for the 

study—for 1966, 1976, and 1984. These indices were 

computed for each of the 1966–84 storms by assuming 

linear change between 1966, 1976, and 1984. For pre1966 and post-1984 storms, 1966 and 1984 values, 

respectively, were used. Variation in BDF and PAD 

ranged from little to no change in urban basins near 

downtown Houston, such as Hunting Bayou in region 1 

(stations 08075750, 08075760, and 08075770) and 

Berry Bayou in region 2 (stations 08075550, 08075600, 

and 08075650), to large changes in basins that are distant from downtown Houston, such as Greens Bayou in 

region 1 (stations 08075780, 08075900, and 08076000) 

and Keegans Bayou in region 2 (stations 08074780 and 

08074800). Figure 3 shows variation in BDF and PAD 

for four of these stations (08074800, 08075550, 

08075770, and 08075900). 

Three types of rainfall characteristics were determined for each storm at each site: (1) two measures of 

the rainfall amount for the storm—total rainfall (RTOT) 

and maximum 60-minute rainfall (R60MAX) (the 

maximum amount of rainfall in 60 minutes); (2) two 

measures of the duration of storm rainfall—rainfall 

duration (RDUR) and 85-percent duration (R85DUR) 

(the shortest time in which 85 percent of the rainfall 

occurred); and (3) antecedent rainfall index (RI) (a measure of the antecedent soil-moisture conditions). RTOT 

is the total amount of water potentially available for runoff. R60MAX indicates the intensity of rainfall for a 

storm. RDUR is the difference between the time when 

rainfall starts to when rainfall stops. RDUR indicates 

the type of storm—small RDURs are associated with 

thunderstorms and large RDURs with slower moving 

storms. R85DUR is another measure of storm duration 

and intensity. RI is defined by a relation that assumes 

soil moisture decreases logarithmically with time during periods of no rainfall—

RIt = RI0 * kt

, (1)

where 

RI0 is the initial value of the index (in inches), 

RIt is the reduced value of the index t days later (in 

inches), and 

k is a recession factor set to 0.90 for this study 

(Linsley and others, 1982). 

The index for any day is equal to that for the previous 

day multiplied by k. If rainfall occurs on any day, the 

amount is added to the index for that day. 

Regression Analysis

Multiple linear regression was used to develop 

equations that relate stormwater runoff characteristics 

(the dependent variables) to significant basin and rainfall characteristics (the independent variables) for 42 

sites in the two regions of the study area. Logarithmic 

(base 10) transformation of the variables was done to 

enhance the linearity of the equations. A multiple stepwise regression was done for each dependent variable in 

which independent variables were added one at a time 

(forward stepping) to obtain the final equation. The goal 

of the stepwise procedure is to ensure that only statistically significant independent variables are added to an 

equation and to exclude the variables that account for a 

very small part of the variance in the dependent variable 

(P–STAT, Inc., 1989). The intent of the procedure was 

to produce the “best” (as much of the variance in a 

dependent variable as possible explained with a small 

number of independent variables) equations to predict 

the selected stormwater runoff characteristics. Each 

equation was limited to no more than four independent 

variables—the four most significant. Independent variables that were highly correlated (correlation coefficient 

greater than 0.75) with each other were not included in 

an equation. Finally, each equation for a dependent variable was evaluated by considering the coefficient of 
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 9 Figure 3. Changes in indices of urban development with time for sites reflecting the smallest and largest increases in urba

1964–89. 08075770 Hunting Bayou at I–610 08075900 Greens Bayou at U.S. Hwy 75 08075550 Berry Bayou at Gilpin St. 08074800 Keegans Bayou at Roark Rd. Region 1 Region 2 08075770 H

 at I–610 08075900 G

 at U.S. Hwy 

08075550 Be at Gilpin St

08074800 Ke at Roark Rd

Region 1 Region 2

1210

86

42

0

BASIN DEVELOPMENT FACTOR

100

90

80

70

60

50

40

3020

10

0

PERCENT DEVELOPED AREA

0 5,000 10,000

CUMULATIVE JULIAN DAYS SINCE JANUARY 1, 1964

0 5,000 

CUMULATIVE JULIAN DAYS SINCE JANUA
10 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

determination1 (R2), standard error of regression2, and 

residual (observed minus predicted values) plots.

The regression procedure thus comprised the 

following steps: (1) Compute the correlation coefficients between all independent variables. (2) Apply 

multiple stepwise regression to develop an equation 

for each dependent variable. (3) Inspect the resulting 

equations and remove independent variables that were 

highly correlated. Repeat step 2 without the highly correlated variables. (4) Examine R2

 and standard error of 

regression. Select the equation with the largest R2 and 

the smallest standard error of regression. (5) Examine 

residual plots. Accept the equation if two criteria are 

met: First, a plot of residuals versus predicted values 

shows no discernible pattern, indicating constant variance as the predicted value increases; and second, a 

stem-and-leaf plot (Ott, 1993) shows symmetry about 

zero (lack of skewness), indicating that the residuals are 

normally distributed.

Regression Equations

The procedure described above was used to 

develop equations to estimate the nine selected stormwater runoff characteristics (table 4). R2

 ranged from 

1 Coefficient of determination indicates the proportion of the 

total variation of the dependent variable that is explained by the 

independent variables (Sauer and others, 1983).

2 Standard error of regression is one standard deviation on 

each side of the line defined by the regression equation and contains 

about two-thirds of the data (Sauer and others, 1983).

Table 4. Regression equations for estimating selected stormwater runoff characteristics 

[Abbreviations of characteristics defined in table 2; R2, coefficient of determination]

Region Equation R2

(percent)

Standard error

of regression

No. of

storms

equation

based on (percent) (log 10

units)

Characteristics that define magnitude of stormwater runoff

1 QPEAK = 312 DA0.728 (13 – BDF)–1.04 RTOT0.984 RI0.135 87 55 0.22 408

2 QPEAK = 475 DA0.735 (13 – BDF)–1.07 RTOT0.837 RI0.093 87 57 .23 331

1 YPEAK = 243 SL–0.410 (13 – BDF)–1.10 RTOT0.958 RI0.127 75 54 .22 408

2 YPEAK = 475 DA–0.265 (13 – BDF)–1.07 RTOT0.837 RI0.93 64 57 .23 331

1 ROVOL = 0.403 (13 – BDF)–0.303 RTOT1.30 RDUR0.081 RI0.205 73 56 .23 408

2 ROVOL = 0.613 (13 – BDF)–0.268 RTOT1.22 RI0.213 70 55 .22 331

Characteristics that describe shape and duration of discharge hydrograph

1 RODUR = 13.7 DA0.199 (13 – BDF)0.227 RTOT0.298 R85DUR0.154 67 43 .18 408

2 RODUR = 10.7 SL0.410 (13 – BDF)0.439 RTOT0.274 R85DUR0.117 66 41 .17 331

1 TRISE = 1.93 DA0.199 RTOT0.741 R60MAX–0.519 R85DUR0.255 55 82 .31 408

2 TRISE = 1.63 DA0.278 RTOT0.501 R60MAX–0.357 R85DUR0.266 50 80 .31 331

1 Q75DUR = 0.374 DA0.294 (13 – BDF)0.678 RTOT0.678 R60MAX–0.425 77 52 .21 408

2 Q75DUR = 0.367 DA0.274 (13 – BDF)0.646 RTOT0.682 R60MAX–0.431 55 61 .25 331

1 Q50DUR = 0.665 DA0.287 (13 – BDF)0.723 RTOT0.625 R60MAX–0.454 80 47 .19 408

2 Q50DUR = 0.624 DA0.271 (13 – BDF)0.711 RTOT0.665 R60MAX–0.471 57 58 .23 331

1 TRECES = 9.50 DA0.223 (13 – BDF)0.337 RTOT0.282 R85DUR0.084 62 49 .20 408

2 TRECES = 9.17 SL0.435 (13 – BDF)0.473 RTOT0.314 RI0.091 58 48 .20 331

1 BLAG = 0.720 DA0.333 (13 – BDF)0.781 RTOT0.126 R85DUR0.106 77 52 .21 408

2 BLAG = 0.693 SL0.481 (13 – BDF)0.969 RTOT0.296 RI0.110 62 57 .23 331
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 11

64 to 87 percent, and the standard error of regression 

ranged from 54 to 57 percent, for the characteristics that 

define the magnitude of stormwater runoff. R2

 ranged 

from 50 to 80 percent, and the standard error of regression ranged from 41 to 82 percent, for the characteristics 

that describe the shape and duration of the discharge 

hydrograph. BDF, the index of urban development, was 

significant for all but one of the nine runoff characteristics; the exception was TRISE.

The development of the equations is summarized 

by considering two of the characteristics, QPEAK and 

BLAG. QPEAK is representative of the characteristics 

that define the magnitude of storm runoff, and BLAG is 

representative of the characteristics that describe the 

shape and duration of a discharge hydrograph.

For both regions, QPEAK was found to be a function of DA, BDF, RTOT, and RI. The constants and 

exponents of the variables in the two equations are of 

similar magnitude. As the equations indicate, QPEAK 

increases as DA, RTOT, and RI increase. The equations 

confirm that increases in urban development, represented by increases in BDF, increase QPEAK. Graphs 

of predicted versus observed QPEAK for the two 

regions (fig. 4a) show reasonable agreement, as would 

be expected from the magnitude of R2 (table 4), which 

indicates that the independent variables account for 

about 87 percent of the variance. The standard error of 

regression, in percent, indicates that about two-thirds of 

the observed QPEAKs are within plus or minus 57 percent of the corresponding predicted QPEAKs. Plots of 

QPEAK residuals versus predicted QPEAKs for the two 

regions (fig. 5a) show no discernible pattern; and stemand-leaf plots of the residuals indicate no appreciable 

skewness (fig. 6a).

For region 1, BLAG was found to be a function of 

DA, BDF, RTOT, and R85DUR (table 4). For region 2, 

BLAG was found to be a function of SL, BDF, RTOT, 

and RI. The equations show that as DA, SL, RTOT, 

R85DUR, and RI increase, BLAG increases. This result 

is logical—an increase in any of these characteristics 

would result in more storm runoff and larger peak flows, 

which in turn would increase the time for runoff from 

the farthest reaches of the basin to exit the basin 

(another definition for BLAG). The equations also show 

that as BDF increases, BLAG decreases because a 

developed drainage system allows storm runoff to exit 

the basin more rapidly than an undeveloped drainage 

system. R2 (62 to 77 percent) and standard error of 

regression (52 to 57 percent) indicate acceptable agreement between predicted and observed BLAGs (fig. 4b) 

(table 4). Plots of the residuals versus predicted BLAGs 

indicate no discernible pattern for either region (fig. 5b). 

Stem-and-leaf plots of the residuals indicate slight skew 

toward negative residuals and thus the potential for the 

equations to over-predict BLAG (fig. 6b); however, the 

distribution of the residuals appears to be near normal.

Limitations on Values for Basin and Rainfall 

Characteristics

Of the five basin and five rainfall characteristics 

selected as independent variables, the significant characteristics for the equations for each region are

Region 1: DA, SL, BDF, RTOT, R60MAX, 

RDUR, R85DUR, and RI; 

Region 2: DA, SL, BDF, RTOT, R60MAX, 

R85DUR, and RI. 

The equations can be used to estimate stormwater 

runoff characteristics not only for ungaged sites but also 

for different conditions at gaged sites, such as different 

levels of basin development and different rainfall 

events. However, the values for the independent variables should not exceed the ranges of values that were 

used to develop the equations (table 5). If values outside 

those ranges are used, the standard errors of regression 

likely will increase. 

Evaluation of Regression Equations

The regression equations were evaluated on the 

basis of the standard error of regression between the 

observed and predicted values for the nine stormwater 

runoff characteristics and scatterplots of observed 

versus predicted values for the available storms for 

four sites—two drainage basins representative of those 

with the smallest increases in urban development during 

the study and two representative of those with the largest increases. As shown in figure 3, changes with time 

in BDF and PAD for region 1 streamflow-gaging station 

08075770 (Hunting Bayou) and region 2 station 

08075550 (Berry Bayou) range from none to moderate. 

Considerably larger changes with time in BDF and PAD 

are associated with region 1 station 08075900 (Greens 

Bayou) and region 2 station 08074800 (Keegans 

Bayou). 

For the sites in both regions representing small 

increases in urban development (08075550 and 

08075770), the standard errors of regression for 

QPEAK, YPEAK, and ROVOL (41 to 46 percent) 
12 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area

Figure 4a. Observed versus predicted peak flow (QPEAK) for all storms, by region.

OBSERVED QPEAK, IN CUBIC FEET PER SECOND

PREDICTED QPEAK, IN CUBIC FEET PER SECOND Predicted 

Predicted 

100,000

10,000

1,000

100

10

100,000

10,000

1,000

100

10

10 20 50 100 200 500 1,000 2,000 5,000 10,000 20,000 

Region 1: Sites north of Buffalo Bayou; 408 storms

Region 2: Sites south of Buffalo Bayou; 331 storms
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 13Figure 4b. Observed versus predicted basin lag (BLAG) for all storms, by region.

PREDICTED BLAG, IN HOURS

OBSERVED BLAG, IN HOURS

100

10

1

0.1

0.01

100

10

1

0.1

0.01

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 

Predicted 

Predicted 

Region 1: Sites north of Buffalo Bayou; 408 storms

Region 2: Sites south of Buffalo Bayou; 331 storms
14 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 5a. Predicted values versus residuals for peak flow (QPEAK) for all storms, by region.

RESIDUAL, IN LOG UNITS

Region 1: Sites north of Buffalo Bayou; 408 storms

Region 2: Sites south of Buffalo Bayou; 331 storms

Z

Ze

1.0

0.5

0

-0.5-1.0

1.0

0.5

0

-0.5-1.0

10 20 50 100 200 500 1,000 2,000 5,000 10,000 20,000 

PREDICTED QPEAK, IN CUBIC FEET PER SECOND
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 15Figure 5b. Predicted values versus residuals for basin lag (BLAG) for all storms, by region. Region 1: Sites north of Buffalo Bayou; 408 storms Region 2: Sites south of Buffalo Bayou; 331 storms Zero residual Zero residual 1.0 0.5

0

-0.5

-1.0

PREVALUE

1.0

0.5

0

-0.5

-1.0

-1.5

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 

PREDICTED BLAG, IN HOURS

RESIDUAL, IN LOG UNITS
16 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

(table 6) are less than those based on all sites (54 to 

57 percent) (table 4). For the sites in both regions 

representing large increases in urban development 

(08074800 and 08075900), standard errors for QPEAK 

and YPEAK (64 to 73 percent) are larger than those 

based on all sites; standard error for ROVOL is about 

the same (53 to 54 percent). On the basis of scatterplots 

of observed versus predicted values for the three characteristics (figs.7a–c at end of report), the regression 

equations produced reasonable results. The generally 

DISTRIBUTION OF RESIDUALS FOR QPEAK, IN LOG UNITS

Region 1: Sites north of Buffalo Bayou; 408 storms

Region 2: Sites south of Buffalo Bayou; 331 storms

2.5

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

2.5

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

NUMBER OF OBSERVATIONS

Figure 6a. Stem-and-leaf plots showing distribution of residuals for peak flow (QPEAK) for all storms, by region.
EQUATIONS FOR ESTIMATING EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 17

larger standard errors of regression associated with 

the sites representing higher development rates are 

shown graphically by greater scatter of points about the 

predicted-equals-observed lines for sites 08074800 and 

08075900 than for sites 08075550 and 08075770.

For the site in region 1 representing small 

increases in urban development (08075770), the 

standard errors of regression for the characteristics that 

define the shape and duration of a storm discharge 

hydrograph (RODUR, TRISE, Q75DUR, Q50DUR, 

DISTRIBUTION OF RESIDUALS FOR BLAG, IN LOG UNITS

Region 1: Sites north of Buffalo Bayou; 408 storms

Region 2: Sites south of Buffalo Bayou; 331 storms

2.5

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

2.5

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

NUMBER OF OBSERVATIONS

Figure 6b. Stem-and-leaf plots showing distribution of residuals for basin lag (BLAG) for all storms, by region.
18 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Table 5. Maximum and minimum values of independent variables used to develop regression equations

[Abbreviations of characteristics defined in table 2] 

Table 6. Standard error of regression between observed and predicted stormwater runoff characteristics for 

available storms at selected sites representing small and large increases in urban development 

[Abbreviations of characteristics defined in table 2; in percent] 

Independent variable (units) Minimum Maximum

Region 1: Sites north of Buffalo Bayou

DA (square miles) 0.13 182

SL (miles per [feet per mile]0.5) .13 13.0

BDF (dimensionless) 0 12

RTOT (inches) .42 10.9

R60MAX (inches) .18 4.90

RDUR (hours) .50 208.5

R85DUR (hours) .20 72.0

RI (inches) .05 5.76

Region 2: Sites south of Buffalo Bayou

DA (square miles) .32 94.9

SL (miles per [feet per mile]0.5) .25 8.74

BDF (dimensionless) 0 12

RTOT (inches) .25 12.25

R60MAX (inches) .25 3.91

R85DUR (hours) .30 42.8

RI (inches) .05 5.78

Characteristic

Small increases in BDF Large increases in BDF

Station no.: 08075770 08075550 08075900 08074800

Region: 1 2 1 2

QPEAK 44 44 64 73

YPEAK 46 44 67 73

ROVOL 41 43 54 53

RODUR 29 28 36 35

TRISE 70 76 62 103

Q75DUR 37 64 40 80

Q50DUR 39 58 38 88

TRECES 34 40 44 37

BLAG 42 74 32 49
EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 19

TRECES, and BLAG) averaged 42 percent, less than 

the average standard error for region 1 for all sites 

(54 percent). For the site in region 2 representing small 

increases in urban development (08075550), the standard errors of regression for those six characteristics 

averaged 57 percent, about the same as the average 

standard error for region 2 for all sites (58 percent). 

For the sites in regions 1 and 2 representing large 

increases in urban development, the standard errors of 

regression for the six characteristics averaged 42 and 

65 percent, respectively. As with the characteristics 

that define the magnitude of stormwater runoff, the 

generally greater standard errors of regression for the 

equations that describe shape and duration associated 

with the sites representing larger development rates are 

shown graphically by greater scatter of points about 

the predicted-equals-observed lines for sites 08074800 

and 08075900 than for sites 08075550 and 08075770 

(figs. 7d–7i at end of report).

In general, the equations for stormwater runoff 

characteristics for the two sites representing small 

increases in urban development yielded smaller standard errors of regression than those for stormwater runoff characteristics for the two sites representing large 

increases in urban development. In general, standard 

errors of regression are smaller for the two region 1 sites 

than for the two region 2 sites (table 6).

Overall, the equations were judged acceptable. 

However, two potential sources of error are noted. First, 

the equations for QPEAK and YPEAK could yield inaccurate predicted values if the DAs used to develop the 

equations are too large; that is, if the entire drainage 

basin does not contribute to flow at the streamflowgaging station. If the entire basin does not contribute 

to flow, SL could be inaccurate also. In this situation, 

the regression coefficients for DA, and possibly SL, 

would be inaccurate, and thus predicted QPEAKs and 

YPEAKs also would be inaccurate. Second, TRISE, 

Q75DUR, Q50DUR, and BLAG could be predicted 

inaccurately if the entire drainage basin does not contribute to flow at the streamflow-gaging station. The 

likelihood of an entire basin not contributing to flow is 

a function of storage in the basin. Natural storage is 

assumed to be accounted for in the database; however, 

constructed storage (detention ponds) for new development that was implemented in the Houston metropolitan 

area in the early-to-mid 1980s is not accounted for in the 

database. Constructed storage in a basin would decrease 

DA and could affect SL. A determination of the fraction 

of a basin that actually contributes to storm runoff or the 

amount of detention storage in the basin during a storm 

would increase the accuracy of all equations involving 

DA or SL.

EFFECTS OF URBAN DEVELOPMENT 

ON STORMWATER RUNOFF 

CHARACTERISTICS 

The effects of urban development on stormwater 

runoff characteristics can be seen by comparing storm 

hydrographs from early in the program with those from 

the same sites later in the program. Little change in 

storm discharge hydrographs occurred during the program period for stations gaging stormwater runoff from 

basins where negligible to moderate urban development 

occurred, such as stations 08075770 and 08075550 

(figs. 8a, c). However, the effect of urban development 

on stormwater runoff characteristics is apparent in 

hydrographs for stations gaging stormwater runoff from 

basins where substantial urban development occurred, 

such as stations 08075900 and 08074800 (figs. 8b, d).

All the equations for predicting stormwater 

runoff characteristics except the equation for TRISE 

include BDF as a significant variable. The other index 

to urban development, PAD, was not significant for any 

stormwater runoff characteristic (and also was correlated with BDF). Thus the effect of urban development 

in the equations is accounted for only by BDF.

Characteristics That Define Magnitude of 

Stormwater Runoff

QPEAK, YPEAK, and ROVOL define the 

magnitude of stormwater runoff. Increasing urban 

development increases the magnitude of each of these 

stormwater runoff characteristics, all other factors being 

equal. Storm hydrographs show that the magnitude of 

stormwater runoff changes only slightly for basins that 

have undergone only small increases in development 

(figs. 8a, c); however, storm hydrographs show much 

larger changes in the magnitude of stormwater runoff 

for basins that have undergone large increases in development (figs. 8b, d). 

The effects of increases in urban development 

on QPEAK, YPEAK, and ROVOL were estimated 

from the equations by varying BDF in computations of 

the characteristics. The percent changes in QPEAK, 

YPEAK, and ROVOL depend not only on the range 

of change in development but also on the amount of 

beginning and ending development—that is, the beginning and ending values of BDF. The most extreme 
20 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area

Figure 8a. Hydrograph for 080757770 Hunting Bayou at I–610 showing effects of no increase in basin development factor 

DISCHARGE, IN CUBIC FEET PER SECOND

Rainfall Mar. 17–19, 1988 

Discharge Jan. 19–21, 1968;  BDF = 6

Discharge Mar. 17–19, 1988;  BDF = 6

Rainfall Jan. 19–21, 1968

1,000

900

700600

800500400300200100

0

0 6 12 18 24 30 36 42 48 54 60 66 

TIME FROM ONSET OF RAINFALL FOR STORM, IN HOURS
EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 21Figure 8b. Hydrograph for 08075900 Greens Bayou at U.S. Hwy 75 showing effects of large increase in basin developme

DISCHARGE, IN CUBIC FEET PER SECOND

Rainfall June 26–28, 1989 

Discharge Sept. 21–24, 1967;  BDF = 1.4

Discharge June 26–28, 1989;  BDF = 9

Rainfall Sept. 21–24, 1967

20,00019,00018,000

17,000

16,00015,00014,000

13,000

12,00011,000

10,000

9,000

8,0007,0006,000

5,0004,000

3,000

2,0001,000

0 

0 6 12 18 24 30 36 42 48 54 60 66 72 

TIME FROM ONSET OF RAINFALL FOR STORM, IN HOURS
22 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 8c. Hydrograph for 08075550 Berry Bayou at Gilpin St. showing effects of small increase in basin development fac

DISCHARGE, IN CUBIC FEET PER SECOND

Rainfall June 5, 1981

Discharge Apr. 14–15, 1966;  BDF = 5

Discharge June 5, 1981;  BDF = 7

Rainfall Apr. 14–15, 1966

1,000

900

800700

600

500

400300

200

100

0 

0 6 12 18 24 30 36 42 4

TIME FROM ONSET OF RAINFALL FOR STORM, IN HOURS
EFFECTS OF URBAN DEVELOPMENT ON STORMWATER RUNOFF CHARACTERISTICS 23Figure 8d. Hydrograph for 08074800 Keegans Bayou at Roark Rd. showing effects of large increase in basin developmen

DISCHARGE, IN CUBIC FEET PER SECOND

TIME FROM ONSET OF RAINFALL FOR STORM, IN HOURS

1,000

900800700600500400300200100

0

0 6 12 18 24 30 36 42 48 54 60 66 72 78 

Rainfall Feb. 9–11, 1983

Discharge Aug. 30–Sept. 2, 196 BDF = 0

Discharge Feb. 9–11, 1983;  BDF = 8

Rainfall Aug. 30–Sept. 2, 1966
24 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

case, a change from a completely undeveloped basin 

(BDF = 0) to a completely developed basin (BDF = 12) 

showed extreme changes for QPEAK, YPEAK, and 

ROVOL. The equations predict potential changes in 

QPEAK and YPEAK in regions 1 and 2 of about 1,300 

to about 1,600 percent and in ROVOL of about 100 to 

about 120 percent (table 7). However, changes of this 

magnitude are unlikely. No basin in the study area 

showed such a large change in BDF during the study. 

Five other cases using more representative changes in 

BDF were used to estimate the effects of increasing 

urban development in regions 1 and 2. The cases (three 

hypothetical and two observed) are 

1. BDF increases from a low-development value of 

3 to a moderate-development value of 6: The 

case-1 changes in development caused computed QPEAK and YPEAK for both regions to 

increase about 45 percent and computed 

ROVOL to increase about 10 percent (table 7). 

2. BDF increases from 5 (the 25th percentile [table 

2]) to 8 (the 75th percentile): These mid-range 

increases in development caused computed 

QPEAK and YPEAK for both regions to 

increase about 65 percent and computed 

ROVOL to increase about 15 percent. 

3. BDF increases from a moderate-development 

value of 7 to a completely developed value of 

12: In this case, the development increase 

caused computed QPEAK and YPEAK for 

region 1 to increase about 545 and 620 percent, 

respectively; and for region 2 both characteristics increased about 580 percent. Computed 

ROVOL for regions 1 and 2 increased about 72 

and 62 percent, respectively. 

From the results of these three hypothetical cases, the 

characteristics that define the magnitude of stormwater 

runoff increase at a greater rate as basin development 

increases. 

4. BDF increases from 1 to 9, the largest observed 

change in region 1 (for station 08075900 

[fig. 3]). 

5. BDF increases from 0 to 8.5, the largest observed 

change in region 2 (for station 08074800 

[fig. 3]). 

The observed increases in development in regions 1 

(case 4) and 2 (case 5) during the study increased computed QPEAK about 212 percent, computed YPEAK 

about 210 to 235 percent, and computed ROVOL about 

33 to 40 percent. 

Table 7. Percent change in stormwater runoff characteristics for selected increases in basin development factor 

[TRISE not included because BDF not significant in equation for TRISE; abbreviations of characteristics defined in table 2] 

Case BDF increase in equation Region

Percent change in stormwater runoff characteristic

QPEAK YPEAK ROVOL RODUR Q75DUR Q50DUR TRECES BLAG

-- 0 to 12 1 1,340 1,580 118 -44.1 -82.4 -84.3 -57.9 -86.5

2 1,456 1,456 98.9 -67.6 -80.9 -83.9 -70.3 -91.7

1 3 to 6 1 44.9 48.0 11.4 -7.78 -21.5 -22.7 -11.3 -24.3

2 46.5 46.5 10.0 -14.5 -20.6 -22.4 -15.5 -29.2

2 5 to 8 1 63.0 67.7 15.3 -10.1 -27.3 -28.8 -14.6 -30.7

2 65.4 65.4 13.4 -18.6 -26.2 -28.4 -19.9 -36.6

3 7 to 12 1 545 618 72.1 -33.4 -70.3 -72.6 -45.3 -75.3

2 580 580 61.6 -54.5 -68.6 -72.0 -57.2 -82.4

4 1 to 9 (largest observed 

change)

1 213 235 39.5 -22.1 -52.5 -54.8 -30.9 -57.6

5 0 to 8.5 (largest observed 

change)

2 211 211 32.9 -37.2 -49.6 -53.0 -39.5 -64.2
SUMMARY 25

Characteristics That Describe Shape and 

Duration of Storm Hydrograph 

RODUR, Q75DUR, Q50DUR, TRECES, and 

BLAG define storm hydrograph shape and duration. 

BDF is a significant variable in the equation for estimating each of these characteristics. Increasing urban 

development causes each of these characteristics to 

decrease, all other factors being equal. This follows 

from the fact that the drainage efficiency for the basin 

increases as the basin is developed. 

As with the characteristics that define the magnitude of stormwater runoff, the effects of increases in 

urban development on RODUR, Q75DUR, Q50DUR, 

TRECES, and BLAG were estimated from the equations by varying BDF in computations of the characteristics. As with the characteristics that define the 

magnitude of stormwater runoff, the percent changes in 

the five shape and duration characteristics depend on the 

beginning and ending values of BDF as well as on the 

range of change in BDF. The development scenarios 

were the same as those for QPEAK, YPEAK, and 

ROVOL. Not surprisingly, the most extreme case, a 

change from a completely undeveloped basin (BDF = 0) 

to a completely developed basin (BDF = 12) resulted in 

the greatest decreases in the five characteristics (table 

7). For this case, decreases in the characteristics ranged 

from about 44 percent for computed RODUR in region 

1 to about 92 percent for computed BLAG in region 2. 

For the three hypothetical, more representative cases of 

increased development, the decreases ranged from 

about 8 percent for computed RODUR in region 1 to 

about 82 percent for computed BLAG in region 2. As 

with the characteristics that define the magnitude of 

stormwater runoff, the rates of change in the shape 

and duration characteristics increase as basin development increases—but in the opposite direction from the 

magnitude-defining characteristics. For the largest 

increases in BDF in regions 1 and 2 observed during the 

study, decreases in shape and duration characteristics 

ranged from about 22 percent for computed RODUR in 

region 1 to about 64 percent for computed BLAG in 

region 2. 

SUMMARY

A study was done by the U.S. Geological Survey, 

in cooperation with the Harris County Flood Control 

District and the City of Houston, to estimate the effects 

of urban development in the Houston, Texas, metropolitan area on nine stormwater runoff characteristics. 

Three of the nine characteristics define the magnitude of 

stormwater runoff (peak flow, peak yield, and direct 

runoff), and the remaining six characteristics describe 

the shape and duration of a storm hydrograph (direct 

runoff duration, time of rise to peak flow, duration of 

flow that equals or exceeds 75 percent of peak flow, 

duration of flow that equals or exceeds 50 percent of 

peak flow, time of recession from peak flow to base 

flow, and basin lag). Multiple linear regression was 

used to develop equations to estimate the nine stormwater runoff characteristics from basin and rainfall characteristics. Five basin characteristics (drainage area, slope 

factor, soil index, basin development factor, and percent 

of urban development) and five rainfall characteristics 

(total rainfall, maximum 60-minute rainfall, rainfall 

duration, 85-percent duration [the shortest time in 

which 85 percent of the rainfall occurred], and antecedent rainfall index) were tested in the regressions to 

determine which basin and rainfall characteristics significantly affect stormwater runoff characteristics. 

Basin development factor was found to be significant in 

equations for eight of the nine stormwater runoff characteristics (all except time of rise to peak flow). Basin 

development factor is an index of the prevalence of four 

drainage features—channel improvements, channel linings, storm sewers, and curb-and-gutter streets—and 

can range from 0 (drainage features not prevalent in a 

basin) to 12 (drainage features prevalent throughout a 

basin). Two sets of equations were developed, one for 

each of two regions based on soil type, from a database 

containing 1,089 storm discharge hydrographs for 42 

sites compiled during 1964–89. Region 1 is an area 

north of Buffalo Bayou that contains 22 sites, and region 

2 is an area south of Buffalo Bayou that contains 20 

sites. Soils are more permeable in region 1 than in 

region 2. 

The effects of urban development on the eight 

stormwater runoff characteristics were quantified by 

varying basin development factor in the equations 

and recomputing the stormwater runoff characteristics. 

Increasing urban development, as represented by 

increasing basin development factor in the equations, 

increases the three stormwater runoff characteristics 

that define the magnitude of stormwater runoff and 

decreases the five characteristics that describe the shape 

and duration of a storm hydrograph. Storm hydrographs 

show that the magnitude of stormwater runoff and the 

hydrograph shape and duration change only slightly 

for basins that have undergone small increases in 
26 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

development; however, storm hydrographs show much 

larger changes in the magnitude of stormwater runoff 

and the hydrograph shape and duration for basins that 

have undergone large increases in development. 

The largest observed increase in basin development factor for region 1 during the study was from 1 to 

9. Corresponding increases in the characteristics that 

define magnitude of stormwater runoff ranged from 

about 40 percent (for direct runoff) to 235 percent (for 

peak yield). Corresponding decreases in the characteristics that describe hydrograph shape and duration ranged 

from about 22 percent (for direct runoff duration) to 

about 58 percent (for basin lag). The largest observed 

increase in basin development factor for region 2 during 

the study was from 0 to 8.5. Corresponding increases in 

the characteristics that define magnitude of stormwater 

runoff ranged from about 33 percent (for direct runoff) 

to about 210 percent (for both peak flow and peak 

yield). Corresponding decreases in the characteristics 

that describe hydrograph shape and duration ranged 

from about 38 percent (for direct runoff duration) to 

about 64 percent (for basin lag). 

REFERENCES CITED 

A.H. Belo, Corp., 1991, 1992–93 Texas almanac and State 

industrial guide: Dallas, Tex., The Dallas Morning 

News, Inc., 656 p.

Bedient, P.B., and Huber, W.C., 1988, Urban hydrology, in

Hydrology and floodplain analysis: Reading, Mass., 

Addison-Wesley, p. 335–419.

Johnson, S.L., and Sayre, D.M., 1973, Effects of urbanization 

on floods in the Houston, Texas, metropolitan area: 

U.S. Geological Survey Water-Resources Investigations 

Report 3–73, 50 p. 

Leopold, L.B., 1968, Hydrology for urban land planning—A 

guidebook on the hydrologic effects of urban land use: 

U.S. Geological Survey Circular 554, 18 p.

Linsley, R.K., Kohler, M.A., and Paulhus, J.L.H., 1982, 

Hydrology for engineers: New York, McGraw-Hill, 

508 p.

Liscum, Fred, Brown, D.W., and Kasmarek, M.C., 1996, 

Summary of surface-water hydrologic data for the 

Houston metropolitan area, Texas, water years 1964–89: 

U.S. Geological Survey Open-File Report 96–250, 44 p.

Liscum, Fred, and Massey, B.C., 1980, Technique for estimating the magnitude and frequency of floods in the 

Houston, Texas, metropolitan area: U.S. Geological 

Survey Water-Resources Investigations Report 80–17, 

29 p.

Ott, R.L., 1993, An introduction to statistical methods and 

data analysis: Belmont, Calif., Wadsworth Publishing 

Co., 1,031 p.

P–STAT, Inc., 1989, Regression—Linear relationships, in

User’s manual: Princeton, N.J., ISBN 0–933754–08–06, 

v. II, p. 42.1–42.27.

Ramos, M.G., ed., 1997, 1998–1999 Texas almanac: Dallas, 

Tex., The Dallas Morning News, Inc., 672 p.

Sauer, V.B., Thomas, W.O., Jr., Stricker, V.A., and Wilson, 

K.V., 1983, Flood characteristics of urban watersheds in 

the United States: U.S. Geological Survey Water-Supply 

Paper 2207, 63 p.

Southard, R.E., 1986, An alternative basin characteristic for 

use in estimating impervious area for urban Missouri 

basins: U.S. Geological Survey Water-Resources 

Investigations Report 86–4362, 21 p. 
F

igure727

Figure 7

Figure 7a. Observed versus predicted peak flow (QPEAK) for selected streamflow-gaging stations reflecting small and lardevelopment, by region.

PREDICTED QPEAK, IN CUBIC FEET PER SECOND

10,000

1,000

100

10

10,000

1,000

100

10

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equ

08075770, sma urban devel

08075900, larg urban develo

Predicted equ

08075550, sm urban devel

08074800, larg urban devel

100,000

100,000

10 20 50 100 200 500 1,000 2,000 5,000 10,000 20,000 

OBSERVED QPEAK, IN CUBIC FEET PER SECOND
28 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 7b. Observed versus predicted peak yield (YPEAK) for selected streamflow-gaging stations reflecting small and lar

development, by region.

PREDICTED YPEAK, IN CUBIC FEET PER SECOND PER SQUARE MILE

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equa

08075770, small  urban develop

08075900, large  urban develop

Predicted equa

08075550, smal urban develo

08074800, large  urban develop

10,000

1,000

100

10

1

10,000

1,000

100

10

1

1 2 5 10 20 50 100 200 500 1,000 2,000 

OBSERVED YPEAK, IN CUBIC FEET PER SECOND PER SQUARE MILE
Figure 7 29 Figure 7c. Observed versus predicted direct runoff (ROVOL) for selected streamflow-gaging stations reflecting small and l

development, by region.

PREDICTED ROVOL, IN INCHES

OBSERVED ROVOL, IN INCHES

100

10

1

0.1

0.01

100

10

1

0.1

0.01

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equa

08075770, small  urban develop

08075900, large  urban develop

Predicted equa

08075550, smal urban develo

08074800, large  urban develop
30 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 7d. Observed versus predicted direct runoff duration (RODUR) for selected streamflow-gaging stations reflecting smin urban development, by region.

OBSERVED RODUR, IN HOURS

PREDICTED RODUR, IN HOURS

1,000

100

10

1

1,000

100

10

1

1 2 5 10 20 50 100 200 

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equa

08075770, smal urban develo

08075900, large  urban develo

Predicted equ

08075550, sma urban develo

08074800, larg urban develo
Figure 7 31 Figure 7e. Observed versus predicted time of rise to peak flow (TRISE) for selected streamflow-gaging stations reflecting 

increases in urban development, by region.

PREDICTED TRISE, IN HOURS

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equ

08075770, sm urban devel

08075900, larg urban devel

Predicted eq

08075550, sm urban deve

08074800, lar urban deve

100

10

1

0.1

100

10

1

0.1

0.1 0.2 0.5 1 2 5 10 20 

OBSERVED TRISE, IN HOURS
32 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 7f. Observed versus predicted duration of flow that equals or exceeds 75 percent of peak flow (Q75DUR) for selecstations reflecting small and large increases in urban development, by region.

PREDICTED Q75DUR, IN HOURS

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equ

08075770, sm urban devel

08075900, larg urban devel

Predicted eq

08075550, sm urban deve

08074800, lar urban deve

100

10

1

0.1

100

10

1

0.1

0.1 0.2 0.5 1 2 5 10 20 

OBSERVED Q75DUR, IN HOURS
Figure 7 33 Figure 7g. Observed versus predicted duration of flow that equals or exceeds 50 percent of peak flow (Q50DUR) for selec

stations reflecting small and large increases in urban development, by region.

PREDICTED Q50DUR, IN HOURS

OBSERVED Q50DUR, IN HOURS

100

10

1

0.1

100

10

1

0.1

0.1 0.2 0.5 1 2 5 10 20 

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equ

08075770, sm urban devel

08075900, larg urban devel

Predicted eq

08075550, sm urban devel

08074800, lar urban devel
34 Effects of Urban Development on Stormwater Runoff Characteristics for the Houston, Texas, Metropolitan Area 

Figure 7h. Observed versus predicted time of recession from peak flow to base flow (TRECES) for selected streamflow-ga

small and large increases in urban development, by region.

PREDICTED TRECES, IN HOURS

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equa

08075770, smal urban develo

08075900, large  urban develo

Predicted equ

08075550, sma urban develo

08074800, larg urban develo

1,000

100

10

1

1,000

100

10

1

1 2 5 10 20 50 100 200 

OBSERVED TRECES, IN HOURS
Figure 7 35 Figure 7i. Observed versus predicted basin lag (BLAG) for selected streamflow-gaging stations reflecting small and large 

development, by region.

PREDICTED BLAG, IN HOURS

Region 1: Sites north of Buffalo Bayou

Region 2: Sites south of Buffalo Bayou

Predicted equ

08075770, sma urban develo

08075900, larg urban develo

Predicted equ

08075550, sm urban devel

08074800, larg urban devel

100

10

1

0.1

100

10

1

0.1

0.1 0.2 0.5 1 2 5 10 20 

OBSERVED BLAG, IN HOURS
Liscum— Effects of Urban Development on Stormwater Runoff Characteristics for the 

Houston, Texas, Metropolitan Area

District Chief U.S. Geological Survey 8027 Exchange Dr.Austin, TX 78754–4733