SJRA Applies for TWDB Grant to Study Feasibility of Flood Control Dams in Spring Creek Watershed

The San Jacinto River Authority (SJRA) has applied for a $500,000 grant from the Texas Water Development Board’s Flood Infrastructure Fund to study the possibility of building two flood control dams in the upper Spring Creek Watershed.

Spring Creek enters the West Fork and Lake Houston at US59. The watershed extends west from there and covers portions of Montgomery, Harris, Grimes, and Waller Counties. Spring Creek itself acts as the county line between Harris and Montgomery Counties.

Feasibility Study Would Build on Basin-Wide Study

The proposed project builds on a Spring Creek Siting Study, currently underway as part of the San Jacinto Regional Watershed Master Drainage Plan project. The latter should be released this fall.

The Siting Study, still in draft form, has identified two potential locations. One is along Walnut Creek and the other on Birch Creek.

Both have potential to mitigate flooding in the watershed. SJRA anticipates the Master Watershed Drainage Plan will recommend them for implementation. See draft spec sheets below.

*Draft Walnut Creek spec sheet supplied as part of grant application*

*Draft Birch Creek spec sheet supplied as part of grant application*

Notice that neither of these projects comes close to competing with the Barker or Addicks Reservoirs in terms of acre-feet of storage. At roughly 20,000 acre feet combined, they are roughly one twentieth the size of Barker and Addicks combined. That said, the proposed reservoirs could each still reduce flooding by up to half a foot for 25-40 miles downstream.

Grant Covers Everything Up Through Costing

The next phase of efforts related to the reservoirs will require, at a minimum:

Environmental due diligence
Site investigations
Literature and mapping review
Permitting requirement investigations
Desktop surveys/assessments
Preliminary coordination with permitting agency
Conceptual design of dams to determine feasibility – geotechnical borings, alternative configurations development, H&H modeling analysis, etc.
Cost estimate development – dam construction costs, as well as costs related to land acquisition, utility conflicts and relocations, environmental mitigation, O&M, etc.
Update benefit/cost ratios (BCR) from SJRWMDP using data developed as part of this effort.

Completion of these tasks will determine feasibility and cost-effectiveness. The grant will also help determine what should proceed to preliminary engineering, final design and construction.

Upstream Benefits of Project

Spring Creek watershed flood mitigation will benefit all areas impacted by Hurricane Harvey, as well as storms in 2016 (Tax Day and Memorial Day), 1994, Tropical Storm Imelda and other recent and historical events.

The most substantial benefits would accrue to structures within the Spring Creek Watershed. SJRA estimates the Birch and Walnut Creek reservoirs could remove 918 and 1,412 structures, from the 100-year floodplain based on Atlas-14 data.

Preliminary benefit/cost ratio (BCR) estimates range from 0.55-0.83 for Birch Creek to 0.78-1.06 for Walnut. However, SJRA feels the combined BCR of the two reservoirs could increase to 2.7 if social benefits typically allowed in FEMA grants are also included.

Downstream Benefits

Project benefits also extend farther downstream. In the event of major storms, the dams could delay water migrating downstream. That would help protect thousands of homes and businesses in the Lake Houston convergence zone. Remember the Plea for DDG (Detention, Dredging and Gates)? Adding to upstream detention was one of the three main strategies advocated by Lake Houston Area leaders after Harvey to reduce flooding.

The proposed dams will likely be earthen embankments with minimal permanent storage (i.e. “dry bottom” reservoirs) with and uncontrolled discharge structures and spillways.

Therefore, they will provide no water supply benefit. However, they could collect and trap sediment, which would otherwise flow into Spring Creek, the West Fork, and ultimately Lake Houston. That would reduce the loss of water storage in Lake Houston.

Timing and Partners

SJRA says it can complete the study within 18 months, but future design and construction will take longer.

SJRA will submit a separate application for an Upper San Jacinto River Basin Regional Sedimentation Study. If funded, it could help determine how much sediment the proposed dams could remove.

SJRA has not yet identified funding for operations and maintenance. This grant will not cover land acquisition, but will ultimately be required to implement construction.

For this specific application, SJRA received input from HCFCD, Harris County Precinct 4, Harris-Montgomery Counties MUD 386, Montgomery County, and Woodlands Water Agency.

To review the complete grant application, click here.

Next Steps

This is an abridged application. TWDB reviews abridged applications to rank the most important projects and ensure they have funding for them. If the abridged app is approved, SJRA must complete a more thorough application. TWDB will pass judgement on those before the end of the year.

Posted by Bob Rehak on 7/10/2020

1046 Days after Hurricane Harvey