Posted November 6, 2018
One of the first flood mitigation projects to break ground post-Hurricane Harvey, the Army Corps of Engineers began a nearly $70 million project to dredge a portion of the West Fork of the San Jacinto River in September. However, according to city and county officials, the project only scratches the surface of the additional efforts needed to reduce flooding risks in the
Lake Houston area.
The Corps’ initial dredging project will merely return a 2-mile stretch of the river near West Lake Houston Parkway to pre-Hurricane Harvey conditions. Dredging is the removal of sediment and debris from the bottom of a body of water, according to the National Oceanic and Atmospheric Administration.
The amount of sediment deposited during Harvey was significant, but the accumulation of sand and sediment in the San Jacinto River and Lake Houston has been an ongoing problem, according to a 2011 report from the Texas Water Development Board. This collection of sediment reduces the amount of water the river and lake can hold, which increases the risk of flooding.
Stephen Costello, city of Houston chief resilience officer, said along with the Corps’ dredging project, the city and Harris County are looking into additional dredging and other solutions that will reduce the amount of sediment being deposited in the river.
“It’s not going to be fixed with one dredging opportunity,” Costello said. “We have to figure out where the material is coming from and how we can control it at the source rather than dredging every couple of years.”
During Harvey, record rainfall and water from Lake Conroe, Spring and Cypress creeks and other tributaries of the of the San Jacinto River caused widespread flooding throughout the area.
The Corps’ project is limited to returning the river to pre-Harvey conditions because it is an emergency project the Federal Emergency Management Agency tasked the Corps with completing as a result of the storm.
Corps officials said FEMA authorized the emergency dredging project because the damage caused by Harvey worsened flood conditions along the river.
In an email, Corps officials said the dredging will not eliminate future flood risks, but it will diminish some of the risks caused by sandbars that were created during Harvey.
“As sediment comes in and [creates sandbars]it slows down the water … and as the rain comes in, it causes the water levels to increase,” Corps Hydraulic Engineer Michael Garske said.
The Corps awarded the $69.81 million project to Great Lakes Dredge and Dock in July. The contractor began dredging the river in September and is slated to complete the project by the end of May.
Alton Meyer, an engineer and project administrative contracting officer with the Corps, said the contractor is using two 27-ton machines known as dredges to remove the sediment by breaking it up with a rotating blade and then pulling it up and out of the river through pumps and pipelines.
More dredging, other solutions
The limited scope of the Corps project means other measures are necessary to remove the sediment collected in the river, Costello said. To address this the city is working with the state and federal government to extend the Corps’ project farther upstream and downstream.
To target additional sandbars in the area, Costello said the city wants to extend the project from where it ends near West Lake Houston Parkway to where the river meets Lake Houston as well as from where it begins to Hwy. 59.
While his office looks into additional dredging, Costello said the city and Harris County are looking for ways to reduce the amount of sediment being deposited into the river by streams such as Cypress and Spring creeks.
For example, Harris County Flood Control District has submitted a grant application for a $2.7 million regional study of 13 different channels that flow in the San Jacinto River. According to an outline of the study, part of the project includes identifying sources of sediment in the West Fork of the San Jacinto River and finding ways to control them.
“You have natural challenges on Spring and Cypress creeks where it’s sugar sand up there, so … as you have flooding events you have some sedimentation deposition and transport,” Costello said. “Is it a natural process? Yes. Is it a controllable process? Probably, yes. It’s just a matter of figuring out what the solutions are.”
Along with the creeks naturally depositing sand in the river, Costello said he is aware there are public allegations that sand mining, which is the excavation of sand from large open pits along the river, has contributed to the amount of sediment deposited in the San Jacinto River. However, he declined to say whether or not he believes this process has contributed to the amount of sediment found in the river.
Identifying how sedimentation can be controlled in the San Jacinto River and Lake Houston is important, Costello said, because both bodies of water have experienced a decrease in their capacities to hold water since the Lake Houston dam was built in 1954.
According to the 2011 Texas Water Development Board report, Lake Houston and the nearby stretches of the East and West forks of the San Jacinto River held 158,553 acre-feet of water in 1954—which is 1 acre of surface water to a depth of 1 foot. The report found the lake could hold only 124,661 acre-feet of water in 2011.
Nathan Leber, manager of the TWDB’s Hydrographic Survey program, said this loss in capacity was one of the key points he took away from the report. However, he said all reservoirs in the state lose capacity to sedimentation over time.
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Leber said the Coastal Water Authority—which the city of Houston contracts to manage Lake Houston—contacted the TWDB after Harvey to request the state agency complete a follow-up survey to identify how the storm affected the lake’s capacity to hold water. Leber said the TWDB began the study in March and should have the results early next year.
“All reservoirs are built knowing they have a finite lifespan,” Leber said. “What our program aims to do is help the state understand our surface water holding capacity in reservoirs is being diminished over time. We provide this data to reservoir managers, but what they do is up to them.”
Source: Community Impact Newspaper