John DingmanCalifornia Water Symposium 2008

Impacts of Urbanization on Peak Flow Using Remote Sensing

Removal of natural storage, retention, and recycling of precipitation

Runoff Groundwater

recharge Widening of stream

channels Floodwater velocities In the magnitude and

frequency of flooding Channel morphology

changes because of the altered hydrology (Anacostia, 1991).

The influence of impervious materials on urban development leads to:

Center for Watershed Protection

City of San Ramon

The population has increased 11% and the number of housing units increased 13% in 2006 (Demographics Research Unit 2007).

New development in the urban watershed is called Windemere, which began in 2001.

Urban

Urban

Rural

Field MeasurementsConduct a cross-

sectional profile at two catchments

Measure high water marks and calculate peak flow.

MethodsRemote Sensing

To quantify area of developed landMeasure density of development.

Delineated Urban and Rural Watersheds 10 meter resolution

digital elevation model

Watershed Delineation

Urban Rural

Landsat 28 meter 6 band ImageryClassification of Developed and Non-

Developed LandsSpectral signatures:

VegetationBuildings , Roads

Remote Sensing Data

Landsat 28 meter 6 band ImageryClassification of Developed and Non-

Developed landsSpectral signatures:

VegetationBuildings , Roads

Remote Sensing Data – Maximum Likelihood Classification

Results: Maximum Likelihood Classification

Urban Rural

Results: Maximum Likelihood Classification

QT = KAaPb

QT = Peak Discharge (cfs)A = Drainage areaP = Mean annual basin-wide precipitationK,a,b are constants

Rantz Method

RI (years) Urban (cfs) Rural (cfs)

2 373 523

5 1051 1482

10 1619 2280

25 2343 3287

50 3401 4657

V = (1.49 * R0.67 S0.5)/ n

Rural Drainage BasinR = 3.28S = 2/3n = 0.05 - 0.10

Urban Drainage BasinR = 3.55S = 2/3n = 0.10 – 0.15

Mannings Equation – High Water Marks

Rural Drainage Basin

Urban Drainage Basin

Mannings Equation – High Water Marks

n = 0.05 n = 0.1

Velocity 53.9 27.0 ft/s

Q (peak flow) 5216.6 2608.3 cfs

n =0.1 n = 0.15

Velocity 28.4 19.0 ft/s

Q (peak flow) 8418.2 5612.2 cfs

Based on the high water marks in the Urban Drainage Basin the calculated flow suggest greater than a 50 year RI for the largest peak flow (mid-January).

The Rural Drainage Basin was 10-50 years RI.

The development in the Tassajara Valley, with the use of impervious materials, may be increasing the peak flow of the streams.

Conclusion