Catastrophic Rainfall and Flooding in Texas

Abstract

Heavy rainfall and flooding occurred on the Gulf Coastal Plain physiographic province of southeastern Texas in October 1994 and caused 22 deaths and more than $1 billion in damages. Record flooding occurred in the 1085 km2 Spring Creek catchment, which received peak rainfall accumulations of more than 500 mm during a 12-h period. Rainfall and flooding of greater magnitude occurred 100 km northeast of Spring Creek over Kickapoo Creek. The peak discharge of 2400 m3 s?1 in Kickapoo Creek at a drainage area of 148 km2 places the event just below the Texas and United States envelope curve of peak discharge. Peak rainfall accumulations in Kickapoo Creek at time intervals from 15 min to 24 h approached Texas and United States record values. The storms that resulted in flooding in Spring Creek and Kickapoo Creek were two components of one mesoscale convective system. The Spring Creek and Kickapoo Creek storms exhibited contrasts in storm structure, evolution, and motion that are of fundamental importance for extreme flood response of drainage basins. The Spring Creek storm produced near-record spatial cloud-to-ground lightning frequencies over Spring Creek and large, cold cloud tops. The Kickapoo Creek storm had a relatively low lightning frequency and a low echo centroid structure in radar reflectivity profiles. The envelope curve of flood peaks in Texas is defined by floods from the Edwards Plateau, which is separated from the Coastal Plain by the Balcones Escarpment. On 22 June 1997, flooding in Seco Creek, which is located in the Edwards Plateau 450 km southwest of Kickapoo Creek, resulted in a flood peak with a unit discharge comparable to that of the October 1994 Kickapoo Creek flood. The Seco Creek and Kickapoo Creek storms provide two contrasting examples of how storm structure, evolution, and motion can maximize flood peaks in a drainage basin. The storm properties that maximize flood peaks in Seco Creek and Kickapoo Creek are linked to drainage properties of the Edwards Plateau and Coastal Plain.