Quantifying Hurricane Harvey Sediment Transport in The Houston-Galveston Region

Date

2021-05

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Abstract

Hurricane Harvey made landfall as a Category 4 hurricane in Port Aransas, Texas on August 26, 2017 and produced the largest precipitation event in recorded US history over Houston and southeastern Texas. Harvey stalled southwest of the Houston area from August 28-30 after weakening to a tropical storm, resulting in over 20,347 km2 of Texas receiving more than 0.75 m (30 in) of precipitation. The ensuing runoff caused mobilization of large sediment volumes within fluvial-estuarine systems in the Houston-Galveston region. I carried out an integrated quantitative analysis to determine the total net sediment transported in the Houston-Galveston area during Hurricane Harvey using pre- and post-Harvey digital elevation models (DEMs), satellite and ground-based images, and sediment dredging reports along major waterways. The 6.21 km3 of precipitation in 12 fluvial-estuarine and 2 controlled reservoir drainages in the Houston-Galveston area mobilized a minimum of 27,227,448 m3 of sediment, equivalent to 6-51 and 30-118 years of annual discharge to Galveston Bay, compared to the modern and the Holocene, respectively. Harvey transported the equivalent 15.5 Astrodomes, 1/3 of the annual sediment load delivered to the Gulf of Mexico by the Mississippi River sediment, and 16% of the size of Galveston island above sea level. Nearly 26% of the transported sediment was deposited in the flood-controlled Addicks and Barker reservoirs located 50 km west of downtown Houston, decreasing their overall holding capacity by 1.2% and 1.6%, respectively. Out of 154,170 homes flooded in Harris County, 10,000 were within the two reservoirs. These homes face increasing flood risk from decreasing reservoir capacities due to sediment infilling and increasing impervious areas. In the stream drainages, sediment was transported from higher elevations west-northwest of Houston to lower elevations towards Galveston Bay. Sediment deposited downstream within stream banks decreases bankfull volume capacities and increases future susceptibility to flooding. In addition, the magnitude of net sediment transport decreases as the degree of channel modification increases. Natural channels tend to disrupt the surrounding urban area by retaining sediment in its floodplains through overbank deposition while artificially straightened channels bypass sediment into downstream navigable channels.

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Keywords

Sediment, volume, channel, fluvial-estuarine, transport, flood

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