GIS and Extreme Flood Hydrology

Jim Smith

Civil Engineering and Operations Research

Princeton University

Princeton, NJ 08544

E-mail: jsmith@radap.princeton.edu

Presentation Summary• Case studies of extreme floods in Texas during October 1994 and June 1997 are used to illustrate the capabilities for analysis of flood hydrology using GIS and remote sensing observations of precipitation.

• The October 16-17, 1994 storms in southeastern Texas resulted in record flooding in Spring Creek and Kickapoo Creek. The Spring Creek and Kickapoo Creek storms exhibited striking contrasts in storm structure and motion. The Kickapoo Creek storm produced a flood peak at 148 sq. km. drainage area that was above the envelope curve of flood peaks for the Texas Coastal Plain.

• The June 22, 1997 storm near the Balcones Escparpment produced a flood peak of virtually identical unit discharge in Seco Creek, a 117 sq. km. catchment in the Edwards Plateau physiographic province.

Regional setting for the October 1994 and June 1997 floods

Envelope curve of peak discharge for Texas

Kickapoo Creek peak discharge

Sample flood peak distributions for Kickapoo Creek and Seco Creek

Synoptic scale setting of October 16-17 storm from a composite of GOES water vapor imagery, surface

charts and upper air charts

Upper air sounding from Corpus Christi (10/16/94 12 UTC)

Upper air sounding from Del Rio (10/16/94 12 UTC)

Time series of discharge and basin-averaged rainfall (derived from WSR-88D radar and rain

gage) for the 1085 sq. km. Spring Creek catchment

Rainfall Discharge

WSR-88D reflectivity image of Spring Creek storm at 3:57 UTC on October 17

Red hatched

line on maphas this vertical cross-

section

Lightning strike locations denoted by white “+” signs

Lightning strike locations in the Spring Creek storm

Contour map of storm total cloud-to-ground lightning strikes (strikes/sq.km.) for the Spring

Creek storm

Time series of storm centroid elevation and rain area for the Spring Creek storm (note explosive growth around 4 UTC)

Centroid elevation

(km)

Rainarea

(km2)

Wind shiftboundaryhas high rainfall rates

Time series of wind direction and rainfall rate from the

Texas A&M Central mesonet station in Spring Creek

Winddirection (º)

Rain rate (mm/hr)

Paired time series of rainfall rate estimates from Texas A&M rain gage stations and Houston WSR-

88D radar

RainfallGage 1(mm/hr)

RainfallGage 2(mm/hr)

Contour map of storm total rainfall from Spring Creek storm

Basin-average rainfall and reconstructed hydrograph (using GIUH and radar-derived rainfall fields) for

Kickapoo Creek

Rainfall(mm/hr)

Discharge(m3/s)

WSR-88D reflectivity image of Kickapoo Creek storm (northeast section of image)

Note the “moisture

plume” from the south and the Spring Creek storm to the southwest

Track of the Kickapoo Creek storm (derived from WSR-88D) from 0 - 6 UTC on October 17

Contour map of storm total rainfall for the Kickapoo Creek storm

Time series of discharge and basin-averaged rainfall (from San Antonio WSR-88D and USGS Edwards Plateau raingage network) for Seco

Creek during the June 22, 1997 storm

Rainfall(mm/hr)

Discharge(m3/s)

WSR-88D reflectivity image of the Seco Creek storm

Verticalcross-section

Contour map of storm total rainfall for the Seco Creek storm

North to South motion of Seco Creek storm from A to B is reflected in rainfall time series

B

Rainfall time series (15 minute time step)

A

Time series of fractional basin area with rainfall rates exceeding 50 mm/h for Kickapoo Creek (October 1994) and

Seco Creek (June 1997)

% ofbasinarea

% ofbasinarea

Contour maps of travel times of runoff for Seco Creek and Kickapoo Creek

catchments

Sample distributions of flood volume and volume-to-peak ratio (flood volume divided by peak discharge)

Large floods have lower volume-to-peak ratios, especially for Seco Creek

FloodVolume

Vol/PeakRatio