GIS and Extreme Flood Hydrology

1. GIS and Extreme Flood Hydrology Jim Smith Civil Engineering and Operations Research Princeton University Princeton, NJ 08544 E-mail: jsmith@radap.princeton.edu

2. 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 Plateauphysiographic province.

3. Regional setting for the October 1994 and June 1997 floods

4. Envelope curve of peak discharge for Texas Kickapoo Creek peak discharge

5. Sample flood peak distributions for Kickapoo Creek and Seco Creek

6. Synoptic scale setting of October 16-17 storm from a composite of GOES water vapor imagery, surface charts and upper air charts

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

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

9. Time series of discharge and basin-averaged rainfall (derived from WSR-88D radar and rain gage) for the 1085 sq. km. Spring Creek catchment Discharge Rainfall

10. WSR-88D reflectivity image of Spring Creek storm at 3:57 UTC on October 17 Lightning strike locations denoted by white “+” signs Red hatched line on map has this vertical cross-section

11. Lightning strike locations in the Spring Creek storm

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

13. Time series of stormcentroid elevation and rain area for the Spring Creek storm (note explosive growth around 4 UTC) Centroid elevation (km) Rain area (km2)

14. Time series of wind direction and rainfall rate from the Texas A&M Central mesonet station in Spring Creek Wind direction (º) Wind shift boundary has high rainfall rates Rain rate (mm/hr)

15. Paired time series of rainfall rate estimates from Texas A&M rain gage stations and Houston WSR-88D radar Rainfall Gage 1 (mm/hr) Rainfall Gage 2 (mm/hr)

16. Contour map of storm total rainfall from Spring Creek storm

17. Basin-average rainfall and reconstructed hydrograph (using GIUH and radar-derived rainfall fields) for Kickapoo Creek Rainfall (mm/hr) Discharge (m3/s)

18. 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

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

20. Contour map of storm total rainfall for the Kickapoo Creek storm

21. 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)

22. WSR-88D reflectivity image of the Seco Creek storm Vertical cross-section

23. Contour map of storm total rainfall for the Seco Creek storm

24. North to South motion of Seco Creek storm from A to B is reflected in rainfall time series A B Rainfall time series (15 minute time step)

25. Time series of fractional basin area with rainfall rates exceeding 50 mm/h for Kickapoo Creek (October 1994) and Seco Creek (June 1997) % of basin area % of basin area

26. Contour maps of travel times of runoff for Seco Creek and Kickapoo Creek catchments

27. Sample distributions of flood volume and volume-to-peak ratio (flood volume divided by peak discharge) Flood Volume Large floods have lower volume-to-peak ratios, especially for Seco Creek Vol/Peak Ratio