Out-of-bank flooding along Clear Creek caused approximately 3,000 homes to flood within the Friendswood city limits during Hurricane Harvey. During the community engagement meetings prior to the 2018 bond election, City of Friendswood community members requested that the Flood Control District evaluate potential stormwater detention options along Clear Creek near the City of Friendswood.
As a result, the Flood Control District contracted with an engineering firm in 2019 to evaluate potential locations for stormwater detention basins between FM 1959 and FM 528. The study is now complete.
Nine potential regional stormwater detention basin alternatives were evaluated in the area. Due to the characteristics of the watershed, the study found that none of the alternatives, without a broader plan for stormwater management measures beyond just regional detention, were significantly beneficial, cost-effective or sustainable. The alternative with the highest cost-benefit ratio removes just 30 structures and 41 acres from the 1% (100-year) storm event. This would come at a cost of $500,000 per structure and would only provide flood reduction to those structures in the immediate vicinity of the alternative. None of the alternatives remove a significant length of roadway from the floodplain.
The potential stormwater detention basins included in this study were primarily located in low-lying areas adjacent to Clear Creek in areas that experience deep flooding during a 100-year storm event. Results of the analysis indicate that the basins in these areas will fill with stormwater early in a storm event, rendering them inefficient at reducing water surface elevations when peak flows are flowing down the channel. The study found that it could be more beneficial to construct regional stormwater detention basins in the mid to upper reaches of Clear Creek’s large tributaries rather than along the main channel where backwater effects from the channel are more prevalent. Stormwater detention basins in the mid to upper areas may significantly reduce peak flow and peak water surface elevations along the main channel. As part of the Clear Creek Federal Flood Risk Management Project, the Flood Control District is exploring basin options on undeveloped land along the Turkey Creek tributary. Once that evaluation is complete, the study will be updated with the findings.