Sediment Movement During Hurricane Harvey Could Negatively Impact Future Flooding
“If Harvey were to happen again today, there would be less room for water in Addicks and Barker reservoirs because of the sediment that got left behind from Harvey,” Wellner said. “That’s the significance – sediment takes up space no longer available for water.”
Stearns uses Lake Houston as an example. A large sand bar recently emerged from the water where the west fork of the San Jacinto River enters the lake near Kingwood. The U.S. Army Corps of Engineers has dredged the top of the bar several times in recent years. “If you have this big mound of sediment blocking water flow to the lake, there’s less area for the water to go,” he said. “During floods, the water goes around that bar of sediment, and into somebody’s house.”
The research team used lidar, or light detection and ranging, a remote sensing technology that measures the elevation of the ground surface, to reach their conclusions, in addition to some ground observations. Lidar allowed them to determine the elevation change from pre-storm to post-storm due to sediment movement.
Causes of Massive Sediment Movement
Stearns said there was so much sediment in the waterways due to compounding factors of the deluge of rain and human modifications to the surrounding environment.
“We found 75% of Houston received over three feet of rain in five days,” he said. “When you get nearly your annual rainfall in such a short amount of time, that’s going to move large amounts of sediment quickly.”
Whether humans created or contributed to more sediment, Stearns and Wellner say it is likely. Because urban sprawl has covered prairie and natural green spaces with impermeable concrete, more water flows into drains and eventually to surrounding bayous. And with more developed land, erosion rates are higher as well, which contributes to the sediment.
“With more rainfall, more run off and more erosion, you are moving more sediment moving through bayous and rivers,” Stearns said.
Information for Policymakers on a Budding Research Topic
The team hopes their study leads researchers and policymakers to collect data on regional sediment movement on a regular basis, not only because of how costly it is to dredge sediment out of waterways, as seen in the ship channel, but also because of the potential impact it can have on flooding in the Houston area. Additionally, they want policymakers to see the impact river straightening can have on sediment movement.
“This study is just the beginning for understanding sediment movement through urban environments,” said Stearns. “With current technology, we were only able to see above-water, but there’s a lot of opportunity to look at underwater sediment movement as well.”
Rebeca Hawley is Senior Media Relations Specialist at the University of Houston. The article was originally posted to the website of the University of Houston.
