Unprecedented rainfall across the State of Texas in May 2015 produced flooding that claimed at least 24 lives across the state and eleven lives in the town of Wimberley, TX alone. The most devastating single event flood over this period occurred during May 23-24 along the Blanco River watershed, which is located in South-Central Texas. Dr. El Hassan and his colleagues examined the effect of storm location and precipitation amount on stream peak flows using the United States Army Corps of Engineers’ Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model iterations and transposed rainfall fields across different areas of the basin. Accumulations from the storm were characteristics for high magnitude events across the Texas Hill Country. However, the rainfall was able to produce a large and deadly flood. Runoff ratios for the May 2015 event estimated from the model were much larger than other storms examined. The main reason for that is the rainfall from the event began directly over the headwaters of the basin and remained stationary for several hours. When the most intense rain cells began to move off the headwaters, the entire mesoscale convective system moved slowly downstream. Analysis of model iterations of the transposed rainfall fields suggests storm location and motion played a significant role in the peak flows. When the intense headwater cells were started over the middle portion of the basin, peak flows were greatly attenuated while the volume of runoff remained the same. Similar phenomena occurred in Cypress Creek during Hurricane Harvey of which El Hassan is currently investigating using the same model. El Hassan is also using the same hydrological model based on a discussion between CAHS’ Water Team members and the West Gulf River Forecast Center-National Weather Service of the National Oceanic and Atmospheric Administration. The latter is interested in understanding the impact of land use changes and extreme events on flooding in the Texas Hill Country. El Hassan conducted this research during his tenure at the University of Texas at San Antonio. More details about this work can be found in the recently published article “Hydrometeorology of the catastrophic Blanco river flood in South Texas, May 2015” in the Journal of Hydrology: Regional Studies at this link: https://www.sciencedirect.com/science/article/pii/S2214581817302124
Ram Ray, Ph.D.
Research Scientist, Natural Resources and Environmental Systems Research
(936) 261-5094
raray@pvamu.edu
Haimanote Bayabil, Ph.D.
Post-doctoral Researcher, Natural Resources and Environmental Systems Research
(936) 261-5021
hkbayabil@pvamu.edu