Hurrican Harvey: Analyzing and Preventing Floods Inside a Levee

Abstract Only - Hurricane Harvey produced a modern flood record on the Brazos River in Sugar Land, Texas, and more than $5 billion in property was protected from this riverine flood by FBC LID 2. Hurricane Harvey also produced more than 31 inches of rain inside FBCLID 2 levees, flooding 200+ homes and coming within inches of hundreds more. Was structural flooding caused by a record riverine flood, record rainfall, old drainage infrastructure, or human error? Immediately flowing Harvey, FBC LID 2 was determined to answer these questions for residents and identify projects that could prevent future flooding.
FBC LID 2 partnered with the City of Sugar Land and Freese & Nichols (FNI) to perform an H&H analysis in all neighborhoods with flooded homes. In under 2 months FNI completed their study of both City streets and storm sewers and FBC LID 2 drainage ditches and pump stations. During the first three days of Hurricane Harvey 22 inches of rainfall flowed out of the levee under gravity, but over the final two days 9 more inches of rain had to be pumped out as the Brazos River reached flood stage. The following are key findings from the FNI H&H analysis:
The pump station did not meet current, local drainage criteria, which could have prevented all structural flooding during Harvey.
Surveys revealed more than half the flooded home foundations were below regulatory flood elevations through a combination of poorly inspected development and/or ground subsidence.
The pump station could have turned on several hours earlier to remove additional water from behind the levee. However, at that time, runoff was still pouring out of flood gates under gravity flow, and FBC LID 2 does not operate pumps until the levee gates are closed. FNI confirmed this standard pumping procedure did not increase internal flood elevations.
Additional pump capacity was identified as the most effective way to lower internal flood elevations and keep water out of homes during future storms.
Less than 6 months after Harvey, FBC LID 2 has already engaged an engineering firm to design a new pump station. Another firm was also selected to evaluate other drainage improvements, besides increasing pump capacity, that increase storage and flood protection inside the levee. The FBC LID 2 prompt and analytical response to Harvey included many public forums to keep residents informed of what happened during Harvey and, more importantly, what will keep it from happening again.