Effect of Urbanization on Runoff in the Whiteoak Bayou Watershed in Houston, Texas

Effect of Urbanization on Runoff in the Whiteoak

Bayou Watershed in Houston, Texas

Effect of Urbanization on Runoff in the Whiteoak

Bayou Watershed in Houston, Texas

Francisco OliveraTexas A&M UniversityDepartment of Civil Engineering

Burren DeFeeUniversity of Arkansas at MonticelloSchool of Forest Resources

AWRA GIS in Water ResourcesHouston, May 8-10, 2006

Whiteoak Bayou WatershedWhiteoak Bayou Watershed

The watershed is located in northwest Houston in Texas.Area = 223 km2.


Precipitation and flow have increased significantly over time.

0

250

500

750

1000

1250

1500

1750

2000

1940 1950 1960 1970 1980 1990 2000 2010

Year

An

nu

al R

un

off

an

d P

reci

pit

atio

n D

epth

(m

m)

Annual Precipitation

Annual Runoff


Cumulative annual runoff.

0

5,000

10,000

15,000

20,000

25,000

1940 1950 1960 1970 1980 1990 2000 2010

Year

Cu

mu

lati

ve A

nn

ual

Ru

no

ff (

mm

)

Year ≤ 1972: 245 mm/yr

Year ≥ 1973: 603 mm/yr

Break point in 1972 - 1973


Peak 12-hour precipitation depths and peak flows have significantly increased over time.

0

200

400

600

800

1940 1950 1960 1970 1980 1990 2000 2010

Year

Pea

k F

low

(m

3/s)

0

50

100

150

200

12-H

ou

r P

reci

pit

atio

n D

epth

(m

m)

Peak Flows

12-Hour Precipitation Depths


Cumulative annual peak flow.

0

2,500

5,000

7,500

10,000

12,500

1940 1950 1960 1970 1980 1990 2000 2010

Year

Cu

mu

lati

ve P

eak

Flo

w (

m3 /s

)

Year = 1967: 113 m3/s

Year = 1968: 293 m3/s

Break point in 1967 - 1968


Parcel data was obtained from the Harris County Appraisal District.

Data included: parcel digital map, parcel area, building square footage, number of floors and year of construction.


Developed parcels and roads.


One point per developed parcel.

19501960

2000

197019801990


Percent developed area and percent impervious cover

0

10

20

30

40

50

60

70

80

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

Year

Per

cen

t

Watershed Impervious Cover Total Developed Area


Developing new parcels can change the spatial configuration of the developed areas.


Edge density and mean shape index.

30

40

50

60

70

80

90

100

110

1940 1950 1960 1970 1980 1990 2000 2010

Ed

ge

de

ns

ity

(m

/Ha

)

1.5

1.6

1.7

1.8

1.9

2.0

Me

an

sh

ap

e in

de

x

Edge density

Mean shape index


Number and mean area of the developed patches.

0

100

200

300

400

500

600

700

800

1940 1950 1960 1970 1980 1990 2000 2010

Nu

mb

er o

f p

atch

es

0

20

40

60

80

100

120

140

160

180

200

Mea

n p

atch

siz

e (H

as)

Number of patches

Mean patch size


Observed and predicted annual runoff values.Break point: 1972 – 1973.

0

200

400

600

800

1000

1200

1940 1950 1960 1970 1980 1990 2000 2010

Year

An

nu

al R

un

off

Dep

th (

mm

)

Observed

Predicted e = 54 mm

S i iR 0.458 P 255

S i i iR 0.593 P 2.05 DA 414


Annual runoff assuming pre-1972 conditions.

0

200

400

600

800

1000

1200

1940 1950 1960 1970 1980 1990 2000 2010

Year

An

nu

al R

un

off

Dep

th (

mm

)

Observed

No adjustment


0

100

200

300

400

500

600

700

800

1940 1950 1960 1970 1980 1990 2000 2010

Year

Pea

k F

low

(m

3/s

)

Observed

Estimated e = 81 m3/s

Observed and predicted annual peak flows.

S i (12)i i iQ 1.57 P 0.149 P 1.27 DA 169


Peak flows assuming impervious remains lower than 10%.

0

100

200

300

400

500

600

700

800

1940 1950 1960 1970 1980 1990 2000 2010

Year

Pea

k F

low

(m

3/s

)

Observed

Estimated IC < 10%


Annual runoff depth for the period 1973 – 2000:

Accounting for increasing urbanization level• Average: 603 mm. Range: 310 mm – 1030 mm

Assuming 1972 urbanization level (i.e., 10% impervious cover)• Average: 340 mm. Range: 50 mm – 600 mm

Annual runoff increment because of urbanization is 77%.Total annual runoff increment is 146%.


Peak flows for the period 1973 – 2000:

Accounting for increasing urbanization level• Average: 299 m3/s. Range: 108 m3/s – 711 m3/s

Assuming 1972 urbanization level (i.e., 10% impervious cover)• Average: 226 m3/s. Range: 57 m3/s – 434 m3/s

Peak flow increment because of urbanization is 32%.Total peak flow increment is 159%


Peak flows tend to increase less than annual runoff depths because a significant part of the additional flow takes place during small events.

It was observed that the 12-hour precipitation increased much more over time than the annual precipitation.

Urbanization below a critical threshold value appears not to affect annual rainfall depth, after which it increases proportional to the developed area. That threshold value took place in 1972-1973 in the Whiteoak Bayou watershed, when the watershed reached a 10% impervious cover.

The variation in the number of developed patches can be interpreted as a measure of the connectivity of the impervious cover and of its capacity to convey flow. The number of patches reached a maximum value in 1972.


Future work:Apply same methodology to other cities in the world:

• Portland, Oregon, an example of a “planned” city as opposed to Houston, Texas.

• Madrid, in collaboration with the Castilla – La Mancha University in Spain.

Consider non-linear regressions.

Effect of Urbanization on Runoff in the Whiteoak Bayou Watershed in Houston, Texas

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