The morning of June 11, 1965, residents of Sanderson, Texas, woke up to a wall of water rolling down the canyon. The town was instantly devastated by a flash flood - 28 people were killed, homes and businesses destroyed, and lives changed forever. For many of the town’s inhabitants, the flood is still fresh in their memories.
The town of Sanderson in Terrell County, Texas, is a community of just over 1,000 people. While the flood was almost 50 years ago, the loss of family or friends gripped nearly everyone. Today, townspeople honor those lost with a plaque in the courthouse that displays their names.
The storms generated in this arid region remain high intensity and short in duration, often resulting in flash flood events - dry creek beds can become raging rivers in a matter of minutes. Fortunately, eleven flood-control dams were constructed by the Natural Resources Conservation Service (NRCS) in the 1970s to protect Sanderson against another catastrophe. While the flood problem has been resolved, there has not been a floodplain analysis since the completion of the dams, and citizens still pay expensive flood insurance. Each household pays approximately $700 annually.
Although the county is larger than the state of Rhode Island, it is desolate, and the community does not possess the capacity or means to remap its flood zones. This prompted former U.S. Congressman Ciro D. Rodriguez (TX-23) to request help from UT Austin with Sanderson’s flood mapping. Ellyn Perrone, Congressional Liaison within the office of UT’s Vice President for Research, identified CAEE Professor David Maidment as the go-to person for flood mapping as he has chaired two committees for the National Academies to review floodplain mapping practices within the Federal Emergency Management Agency (FEMA).
After looking over the initial data, Maidment realized this required a team effort, so he opted to make this a term project for his graduate hydrology class. During spring break in March 2010, Maidment and his four students (Rachel Chisholm, Cody Hudson, Laura Hurd and Marcelo Somos Valenzuela) traveled to Sanderson to view the terrain and dams firsthand and to meet with local officials and citizens, who were pushing for new flood maps. Upon their arrival, students also met with survivors of the storm and were moved by their accounts of that tragic morning and the aftermath.
The team later met with Trent Street, the State Design Engineer from the NRCS Temple District and a collaborating engineer from AECOM, Glenn Wright, to gather more data. They also consulted with Melinda Luna, floodplain mapping coordinator for the Texas Water Development Board, who has been leading the state’s efforts in floodplain mapping through LIDAR terrain data.
The main objective of their study was to determine if the 100-year floodplain was altered by the construction of the flood control dams that were built upstream. Once back on campus, they divided the project into four areas of study: mapping, hydrology, dam hydraulics and river hydraulics.
“It was clear that being part of this project would be both a great way to help others and to learn more about the floodplain delineation process”, said graduate student Cody Hudson. For the study, he worked with hydraulic modeling of the flow through the dams. His modeling also determined how much the dams have reduced flood discharges downstream.
The team concluded that the effect of the dams and the resulting modification of the Sanderson floodplain needs to be reviewed by FEMA so that it can be validated as a reasonable reflection of the current conditions there. In addition, the water surface elevations computed in that study need to be laid out on up-to-date digital terrain data so that the extent of inundation during the 100-year flood can be mapped out properly.
Maidment feels that his work on floodplain mapping reports with the National Academies has impressed upon him that an important determinant of an accurate floodwater elevation is an accurate land surface elevation. That being said, he is of the opinion that the official updating of a digital floodplain map for Sanderson will require registered professional engineering and surveying and mapping services.
While the formal floodplain analysis is now in the hands of others, Maidment’s team and their preliminary work greatly helped the City of Sanderson reduce the cost and time frame of the project. At the same time, the students were able to gain valuable experience by completing hands-on coursework. “I now understand how to conduct a proper flood study using ArcGIS”, said graduate student Laura Hurd. “I am hoping to use this in a future job because I see how flood insurance maps can affect a community and individuals.”
“Based on the values in the FEMA Blue Book, I estimate that the contribution of Dr. Maidment’s group is approximately $35,000,” says Wright.
The team was recently commended by Representative Rodriguez in the Congressional Record for their work. He recognized the students “for their outstanding contributions to my district and their dedication to academic success” and stated that “their academic work will directly benefit the people of Sanderson and Terrell County. The community of Sanderson is very appreciative and I am proud to acknowledge their work.”
