UT's digitized water maps may speed response to future floods

     Work at the Center for Research in Water Resources at The University of Texas at Austin may help speed evacuation efforts and better determine flood risk areas in future flash floods.

     Dr. David Maidment, professor of civil engineering, directs the Center for Research in Water Resources which was hired by the U.S. Army Corps of Engineers to create better estimates of extreme flood discharges for the Missouri and Mississippi Rivers after their tragic flood in 1993. He is creating similar water flow maps for Texas.

     Dr. Maidment's research also provides a way to translate storm rainfall maps into flood flow estimates on rivers, which could be used to improve flood forecasting systems.

     "Currently most flood forecasting systems, such as those operated by the City of Austin. and by the Lower Colorado River Authority, depend on rainfall data measured by simple rain gauges. By contrast, the more highly sophisticated NEXRAD radar stations are used to create the storm rainfall maps seen on television," says Maidment. "We want to use NEXRAD to get accurate rainfall measurements at any location, not just the limited sites monitored by rain gauges."

     The U.S. Army Corps of Engineers has hired Dr Maidment's laboratory to produce a NEXRAD-based flood forecasting model for the Addicks and Barker reservoirs on the West Side of Houston. The same technology could be applied statewide to improve flood warning systems.

     The procedure of translating rainfall maps into water flows is aided by a vast effort being undertaken both by the State of Texas and the City of Austin to produce a digital description of the landscape, says Maidment. Following the passage of Senate Bill 1 in the 1997 Texas Legislature, an investment of about $5 million was made by the state in building a 30-meter terrain map of Texas. This map will record the elevation of the land surface of Texas on a mesh of 30-meter square cells, seamlessly covering the whole state, a total of almost .75 billion data points.

     "Texas will be the first state nationwide to have a seamless digitized terrain map," said Maidment. "The City of Austin and the Capital Area Council (CAPCO) are similarly creating a more refined terrain map of Austin and 10 surrounding counties. By tracing the movement of water cell to cell in this mesh, the effect of storm rainfall anywhere in the landscape can be translated into flood flow estimates in streams."

     The Center for Research in Water Resources has produced a computer program called CRWR-PrePro which prepares the terrain and precipitation data for a new flood forecasting program from the U.S. Army Corps of Engineers Hydrologic Engineering Center, called HEC-HMS. The combination of CRWR-PrePro and HEC-HMS permits the synthesis of digital terrain maps and flood discharge calculations. Dr Francisco Olivera at the Center for Research in Water Resources is the principally responsible for CRWR-PrePro.

     The digital terrain base will also assist in the other common Texas weather concern: drought. The Digital Texas mapping project was actually spawned by concern created after the 1996 drought, when legislators recognized they had to quantify the amount of water permitted to be withdrawn by water rights holders during droughts. Currently about 8,000 locations permit water withdrawal from Texas rivers and reservoirs. Maidment's group is calculating how much area of land drains to each elevation and creating a digital map to illustrate it.

     The State of Texas has also contracted with the Center for Research in Water Resources to use its PrePro system to develop watershed data for its pollution assessment of Texas rivers under the Total Maximum Daily Load program. Similarly, the City of Austin is using the Center for Research in Water Resources research to build a cell-based model of non-point sources of pollution as part of its water quality master planning process.

     "The state is transforming its water planning process from a paper-based effort into a digitally-based effort, in effect creating a 'Digital Texas'. Texas is a leader in digital mapping, and the Center's research is contributing to putting water on the maps," says Maidment.