At Mayor Pro Tem Dave Martin’s final town hall meeting last night, he and Chief Recovery Officer Stephen Costello gave an update on the status of new, higher capacity floodgates for the Lake Houston Dam. Their talks also addressed dredging and sand traps.
According to the latest estimate, construction of the gates now looks like it could begin in mid-2026, barring unforeseen setbacks.
The City has scheduled more dredging for the San Jacinto West Fork south of where the mouth bar used to be. Also, Costello says the City has completed opening up ditches and tributaries north of the railroad bridge and is now starting on those south of it.
Finally, Costello revealed that Lake Houston has lost almost 20% of its capacity due to sedimentation. To receive future dredging grants, the City must take steps to reduce the rate of sediment inflow. Costello revealed plans for a pilot sand-trap project in a point bar outside the Hallett mine far upstream. He said that the mine had agreed to remove trapped sediment there for free. Otherwise, he did not explain why a possibly more effective location closer to the problem area was not chosen for the pilot project.
For more details on each, see below.
The purpose of adding more floodgates to the Lake Houston Dam: to lower the lake faster in advance of a flood.
- The City must now start to lower the lake so far in advance of a storm that storms can veer away before they arrive. This wastes water.
- The existing gates have 1/15th of the release capacity of the gates on Lake Conroe. This makes a joint pre-release strategy virtually impossible in extreme storms.
After examining and discarding the notion of adding crest gates to the spillway portion of the dam, the City is now focusing on adding 11 tainter gates to the earthen portion of the dam (east of the existing gates).
With Mayor Sylvester Turner’s help, the City secured enough funding for construction during the regular session of this year’s legislature.
Next steps include:
- 3/24 – New environmental and historic preservation assessments, Army Corps permitting
- 12/24 – Construction plans completed
- 1/25 – Bidding
- 6/25 – Award Contract
- 5/26 – Begin Construction
The success of this plan will require the election of a new Mayor and City Council Representative who are committed to the project. Early voting begins next week.
Dredging Volumes, Costs
Dredging at various locations around Lake Houston will likely be a continuous effort for years to come. Sedimentation has already reduced the capacity of Lake Houston an estimated 18%. The City estimates future yearly losses in the range of 360-460 acre feet per year.
One acre roughly equals the size of a football field. So imagine 400 football fields covered with sludge a foot deep. Each year!
To keep this problem in check, the City is already looking at doing additional dredging on the East and West Forks. It and the Army Corps finished major projects in both areas less than four years ago.
East of Atascocita and south of the convergence of the East and West Forks, the City plans to spend another $34 million to remove almost 900,000 cubic yards of sediment.
To date, Costello estimates that dredging nearly 4 million cubic yards of material has cost $186 million.
The City hopes to recoup some of these costs by reselling sand that it recovers from “hilltops” in the lake. Costello showed the heat map below. Notice the heavy sediment concentrations in the lake’s headwaters. This is because sediment drops out of suspension where rivers slow down as they meet standing bodies of water.
In addition to reducing the volume of Lake Houston, the sediment also poses a flood threat. It reduces conveyance of the rivers and lake forcing water up and out. Sediment blockages, such as the mouth bar, can also form dams that back water up.
Sand Traps to Reduce Inflow
In addition to dredging sediment from the lake, Costello also emphasized the need to reduce sediment coming downstream via sand traps. This last effort may be a condition of future grants for dredging.
Costello described two pilot types of pilot projects that the City is working on with the SJRA and sand-mining industry. The first is “sand traps” dug in point bars outside sand mines. The second: in-channel traps.
The idea behind the traps: dig holes in the river or its sand bars where migrating sand can settle out of the flow before it reaches the lake.
The first project may be near the Hallett Mine on the West Fork. According to Costello, the mine has agreed to remove the sand for free, thus reducing long term maintenance costs.
During Q&A after Costello’s presentation, however, he admitted that the City has no plans to try to get sand mines to reduce illegal emissions. In one notable instance, the TCEQ documented 56 million gallons of sludge discharged into the West Fork by the LMI mine.
Controlling sediment is crucial in reducing flooding. Accumulated sediment reduces storage capacity and conveyance for stormwater. The smaller capacity means lakes and rivers will flood faster and higher.
For high res versions of all the slides shown in the Town Hall, see this PDF.
Posted by Bob Rehak on 10/17/23
2241 Days since Hurricane Harvey