walnut creek Archives - Reduce Flooding

The San Jacinto River Authority (SJRA), which is managing a feasibility study on two Spring Creek dams, has run into some unexpected hurdles. They involve the benefit-cost ratio and competing uses for the land. Matt Barrett, PE, the SJRA’s Water Resources and Flood Management Division Manager, updated ReduceFlooding on the status of the project.

Project Location Near Montgomery

Harris County Flood Control District, five municipal utility districts, the City of Humble, and the Texas Water Development board are also involved in this project. The dams could reportedly reduce flood levels up to half a foot for 40 miles downstream.

*The proposed Spring Creek Flood Control Dams would lie in far northeastern Waller County, a few miles west of Magnolia in Montgomery County.*

Second Time Around for Spring Creek Dams

The SJRA first recognized the flood mitigation benefits of dams in the Spring Creek watershed back in 1985. But ironically, while the land could have been bought for a song back then, the projects failed to achieve favorable benefit-cost ratios because so few people lived in the then-rural area.

Fast forward 32 years to Hurricane Harvey when more than 10,000 structures downstream flooded. Experts identified more upstream stormwater-detention as one of the top three priorities for flood mitigation.

When I asked Matt Barrett, PE, the SJRA’s Water Resources and Flood Management Division Manager about the status of the dams, he had this to say. “We’re still working on the feasibility study. We ran into a couple hurdles when we started digging further into the proposed reservoirs.”

Benefit-Cost Ratio

What kind of hurdles? “First, after modeling was updated as part of the study, the benefit/cost ratios came out lower than was previously estimated as part of the San Jacinto Regional Watershed Master Drainage Plan,” said Barrett.

“I think we have a solution for this issue,” he said. “Once we optimized dam sizes and incorporated ‘social benefits’ (which the Federal Government now will consider) into the calculations, the BCRs came out at 1.88 and 2.03 for the two reservoirs.” That means the benefits exceed the costs, a crucial hurdle.

“Because of their costs, the reservoirs would almost certainly rely on some level of Federal participation for construction.”
Matt Barrett, PE

Competing Uses for Land

“The other issue,” Barrett continued, “is that each planned reservoir site is also the site of another planned development, which was not identified until we got into the feasibility study.”

A residential/commercial development is planned for the Birch Creek reservoir site, and a large solar farm for the Walnut Creek site.

Barrett said, “No ground has been broken on the former, and I would like to work with the developers to see if we can come up with a scenario where both projects could exist. Construction HAS begun at the solar farm site, and we are coordinating to determine what options there might be for future coexistence at the site.”

Funding Partners Will Determine Path Forward, Timetable

“We are currently scheduling meetings with elected officials to present the project and its challenges,” said Barrett. “We want to get their input. Our goal is to get back together with our funding partners likely early next month to determine our path forward.

“The draft report should be completed by April next year, but that is subject to change. We are behind schedule due to the challenges experienced.”

Project Will Ultimately Depend on Several Factors

Barrett concluded, “Whether the reservoirs ultimately get built will be based on the results of the study and whether there is an entity willing to champion the project through design and construction and ultimately own and take responsibility for operations and maintenance of one or both reservoirs.”

Alternative Possibilities

The SJRA is not actively looking at alternative reservoir sites. However, SJRA and its partners have discussed it. “If we determine the hurdles at the two proposed sites make those sites infeasible, we could consider other sites,” said Barrett. “That said, we selected those two sites because they seemed the most promising. Other sites may not pan out for other reasons. One potential alternative is to look at several smaller detention sites.”

For More Information

See these previous posts on the projects:

Posted by Bob Rehak on 9/15/2023

2208 Days since Hurricane Harvey

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

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Spring Creek Dams Facing Hurdles