HB1824 Archives - Reduce Flooding

Details of SJRA Application to TWDB for Grant to Develop Sand Traps

In March, the San Jacinto River Authority (SJRA) awarded engineering firm Freese & Nichols a $250,000 work order for “Conceptual Design” of sand traps. Then in June, SJRA applied for a $200,000 grant from the Texas Water Development Board (TWDB) for “Preliminary Design” of sand traps on the West Fork. What’s this all about? How do the projects relate? Are they worthwhile?

West Fork 90% Blocked After Harvey

After Harvey, the Army Corps documented that the West Fork had become 90% blocked by sediment in places. That contributed to the flooding of thousands of homes and businesses. It also triggered a massive dredging program that is still ongoing. Finally, it launched a search for solutions that stretched all the way to Austin (plus, interestingly, Kerrville and San Antonio). See more below.

SB1824 Opens Door for Sand Traps

House Bill 1824 was introduced by State Rep. Murr from Kerrville and sponsored by Senator Flores from San Antonio. Approved last year, it allows SJRA and Harris County Flood Control District (HCFCD) to remove material from the San Jacinto River and its tributaries to restore, maintain, or expand storm flow capacity without the need for “state permitting” or royalty payments to the state.

SJRA and HCFCD hope to mitigate flooding by constructing one or more “sand traps.” Their plan calls for partnering with Aggregate Production Operations (APOs) in the vicinity of the sand trap(s) to clean them out periodically. It’s not yet clear whether APO’s would do this for a fee, or do it for the sand. One thing is clear, at this point, however. APO’s don’t want to go far. All the locations under consideration are next to sand mines.

Freese & Nichols Already Underway with Phase 1

The first phase of the project, Frees e & Nichols’ conceptual design, is currently underway. It includes:

Evaluating potential sand trap locations and trapping effectiveness
Developing conceptual sand trap designs
Determining downstream benefits of potential sand trap solutions
Recommending which site(s) to carry forward into preliminary engineering.

Phase 2 of Pilot Goes Further

The goal: to move forward with preliminary engineering on two sites, with the likely construction of at least one. This small scale effort, involving only one or two sand traps, is intended to act as a “pilot” before a more costly, full-scale program.

Preliminary results in the first phase indicate that the sand traps will likely be located along the West Fork.

However, to move beyond conceptual design, even on the pilot, SJRA needs more money to supplement local match resources.

If successful, the TWDB grant application for preliminary design will cover:

Environmental permitting investigation
Preliminary land acquisition efforts
Survey
Geotechnical investigation
30% design efforts.

Need for Sediment Control of Some Sort

To date, more than 2.3 million cubic yards of material have been removed from the West Fork, at a cost of more than $90 million. An additional $30 million has been dedicated to continue these efforts. SJRA hopes sand traps will help protect that investment.

It seems, though, that reducing sediment coming out of sand mines might be a simpler, less-risky, more cost-effective solution.

Benefits

Long-term benefits beyond the initial sand trap development “pilot” project are anticipated to potentially extend beyond the immediate benefit area.

Benefits include potential reduction of sediment load entering Lake Houston.

*Primary benefit area is in purple along West Fork. Secondary benefit area is in green (Lake Houston).*

SJRA can not yet quantify the level of flood mitigation provided by the sand trap(s). However, restoring or expanding storm flow capacity could potentially remove structures from the floodplain, they say. The conceptual design phase currently underway will attempt to evaluate downstream hydraulic benefits.

Timing

If this abridged application succeeds, SJRA will need to submit a more detailed application. TWDB won’t report results on that until late this year.

Freese & Nichols should report the results of their conceptual study this September.

SJRA anticipates it can complete the preliminary engineering study in 18 months. However, construction will take longer – up to 36 months.

Next Steps

If results of this pilot project indicate that sand traps are a feasible and effective solution, a larger program in various locations throughout the basin could be implemented.

Preliminary cost estimates will be developed as part of the conceptual design phase currently underway. So SJRA has not yet determined a benefit/cost ratio.

However, the cost of dredging has proved substantial. And the cost of flooding during Harvey proved astronomical. Reducing those costs just 1% could easily justify the cost of this project.

We have too many unknowns at this point to pass judgment.

How much will the project cost?
Will sand traps be effective?
Who will maintain a trap when a sand mine goes out of business?
What will the environmental impact be?
Will the traps accelerate erosion and jeopardize infrastructure such as pipelines and bridges?
Is this the opening volley in an effort to begin large-scale river mining?

Scientific literature and news reports on sand traps generally indicate mixed results.

I will withhold judgement until I learn more.

To review the abridged application, click here.

Posted by Bob Rehak on 7/9/2020

1045 Days after Hurricane Harvey

HCFCD Partners with SJRA on Sediment Trap Project

The SJRA announced earlier this week that the Harris County Flood Control District will partner with the River Authority on a “sediment trap” pilot study for the East and West Forks of the San Jacinto. The two have hired engineering firm Freese & Nichols to conceptually design the traps and identify the optimal locations for them.

Finding the Right Combination of Factors

Most sediment traps are big holes dug in a river or channel though some are off to the side. As water passes them, velocity decreases. Suspended sediment and sand being pushed along the river bed fall into them.

*Source: EPA*. *The hole reduces water speed which accelerates deposition in a fixed location that’s easy to clean out.*

Sediment traps vary by depth, width, length, shape (wide, long, triangular, etc.), and placement relative to the channel. And as this Army Corps study shows, modifying any one of those factors can greatly affect their efficiency. The challenge: to find the optimal shape, size and location.

The optimal length, for instance, depends on the speed of floodwaters and the settling rate of sediment particles. The trap needs to be long enough to give suspended sand time to fall out of suspension. Otherwise, sand just passes over the trap and continues downriver.

The hope: that the right type of traps placed in the right locations could help reduce flooding by reducing the amount of sediment migrating downriver and then blocking the mouths of each river branch.

Coming Out of HB1824 and River Basin Study

House Bill 1824, passed just last year, helps make sediment traps financially feasible. It allows the partners to remove material from the San Jacinto River and its tributaries to restore, maintain, or expand storm flow capacity without the need for state permitting or a royalty payment to the state.

Also note that the project will use data developed for the San Jacinto River Basin Master Drainage Study. It started in April of 2019 and is now about two-thirds complete.

Scope of Work Outlined

The scope of work outlined for Freese & Nichols includes, but is not limited to:

Reviewing and comparing: current and historical LiDAR surveys and aerial photos to gauge sediment erosion, deposition and location
Evaluating digital elevation maps to identify constrictions
Identifying the ten areas with the largest volumes of sediment deposition, including the two largest at a sand mine.
Reviewing FEMA floodplain, National Wetland Inventory, Texas Historical Commission and Texas Parks and Wildlife information for any problems related to each potential site.
Core sampling of sand bars to determine silt content
Ranking preliminary locations using the following: sediment deposition volume, potential sediment storage volume, proximity to existing roads, proximity to existing APO facilities.
Selecting the four locations with the highest potential based on drainage area, sediment load, geology, road access, etc.
Narrowing that to three locations in conjunction with SJRA and HCFCD
Developing sediment trap conceptual solutions specific to each of the final three selected sites
Estimating rate of sediment accumulation and clean-out intervals
Estimating reduction of sediment accumulation due to trapping
Submitting a final report.

The project does NOT extend into Lake Houston. Freese & Nichols will examine both the East and West Forks plus three miles upstream from the East and West Forks along certain tributaries. Tributaries would include, for instance, Lake Creek and Caney Creek. The idea is to intercept sediment before it can make its way into the lake.

Project Timing

The project timetable indicates completion in early fall of 2020, about the same time as the entire San Jacinto River Basin Study. Thus, any recommendations coming out of this project would not be constructed for this hurricane season. SJRA currently hopes to have the trap(s) installed by the end of 2022.

Pros and Cons of Sediment Traps

Proponents say sediment traps can reduce expensive dredging, restore fish habitat, reduce flood risk and more. However…

The scientific literature on sediment traps reveals mixed reviews. Many efforts fail, primarily because of lack of maintenance budgets and regular clean-outs. The SJRA and HCFCD plan to address that issue upfront by involving the sand mining industry. Notice that of the four location-ranking criteria bolded above, three favor proximity to sand mines:

Sand mines have pits to store sediment.
They have roads that lead to the river that can carry heavy equipment.
Mines have cleaning, sorting and transportation facilities onsite to reduce transportation costs, and thus make material more attractive for resale.

Compensation for Sand Miners

A compensation agreement for sand miners who remove sediment from traps has not yet been worked out. However, Matt Barrett, SJRA’s project engineer, says, “The intended benefit to the APOs of participating in the public-private partnership would be that they could utilize or sell the material they remove from the trap(s). ”

Concerns of Environmental Groups

One of the concerns environmental groups have had about HB1824 (which began life as SB2126) is that it could potentially open the door to river mining and all of its risks.

River mining is outlawed in Europe, many other first-world nations, and even in some third world countries.

It tends to alter the gradient of rivers; cause upstream and downstream erosion; destroy private property along river banks; and undermine infrastructure such as bridges and pipelines.

Thus, the sediment traps raise a question of potential liability. If a pipeline or bridge is undermined or if property is eroded by the traps, who is responsible?

“Stability of the river is key to the long term safety and well-being of our community. We know that our public agencies have an important task. Before spending additional taxpayer dollars, don’t we want to make sure that projects won’t make problems worse AND won’t raise taxpayer costs?” said Jill Boullion, Executive Director of the Bayou Land Conservancy.

SJRA Response to Concerns

The SJRA has consistently denied that it would permit wholesale river mining. Most recently, Matt Barrett, the River Authority’s engineer for the sediment trap project said, “SJRA has no intention of engaging in or facilitating river mining in the San Jacinto River or any of its tributaries. The legislative language in HB1824 allows for the removal of material for the purpose of restoring, maintaining, or expanding the capacity to convey storm flows. Any projects undertaken by SJRA to remove or facilitate the removal of material from the San Jacinto River or its tributaries would be for this purpose.”

“River mining is not part of what we are doing. Only sediment in the trap will be removed,” he said.

Barrett is aware of potential hazards. “SJRA and its consultant are aware of the potential negative impacts that can be caused by trapping and removing sediment from a river or stream – changing the sediment balance – and prior to constructing any sediment trap or implementing removal of any material will perform analysis to ensure that any potential negative effects do not offset the positive.”

He sees the current design project as part of a pilot study that can scale up later. “One of the goals of this relatively small scale project is to serve as a “pilot” that gives us data on the real-world effectiveness of sand traps. If data indicates this is a viable flood risk mitigation solution, then additional funding and partnerships could be sought to expand the concept. We are excited to start this project and seek solutions to reduce flood risk.

For More Information

For more on how on sediment traps work, see this presentation found on the EPA site about a project in Michigan. It’s not directly analogous to south Texas because rainfall rates, soil types and gradients differ. But helps explain the theory of traps.

Click here to see Freese & Nichols’ full scope of work on the sediment trap project on the San Jacinto.

Posted by Bob Rehak on 4/3/2020

948 Days after Hurricane Harvey and 197 since Imelda

Multiple Mouth Bars Forming Around Lake Houston; Check out Walden’s

Yesterday’s second post about the wettest AND driest decade in our lifetimes helped explain something I’ve been puzzling about. Multiple mouth bars are forming around Lake Houston. The loss of tens of thousands of trees during the drought exposed soil. One massive storm after another then washed that soil toward the lake. Voila! Mouth bars.

Diversion Ditch Blockage

We already cleared the massive side bar that blocked the mouth of Kingwood’s diversion ditch.

The ditch (center left) that empties the entire western part of Kingwood at River Grove Park on the west fork of the San Jacinto was virtually closed off by this sandbar that formed during Harvey. An estimated 500+ homes above this point flooded.

West Fork Blockage

The Army Corps removed about a fifth of the West Fork mouth bar.

*Army Corps at work removing a small portion of the West Fork Mouth Bar.* *Photo courtesy of BCAeronautics.*

East Fork Mouth Bar

But an East Fork Mouth Bar grew 4000 feet during Harvey and Imelda. It’s now almost blocking Luce Bayou, just as the Interbasin Transfer Project is nearing completion.

Walden Blockage

And other drainage ditches are now plugging up, too, such as the one at Walden. This is symptomatic of many ditches that empty into Lake Houston.

*Walden drainage ditch now blocked by its own growing mouth bar.*

Here’s what it looks like from a drone from a lower altitude and angle. Video courtesy of Jack and Greg Toole.

Still shot from Jack and Greg Toole’s video. Used with permission.

Cause of Mouth Bars

This is not surprising for a man-made lake that’s 65 years old. Dams have a tendency to hold back sediment. Sediment drops out of suspension where the moving waters in a ditch or stream slow down as they meet the still waters of a lake.

These mouth bars increase flood risk for everyone who lives near them. They form sediment damns that restrict the conveyance of the channels behind them. That forces water up and out of the channel into people’s living rooms.

Clearing the Way for Political Solutions

So how do we get rid of these mouth bars?

State Representative Dan Huberty is organizing another dredging program that should start soon. Primary targets will be the West and perhaps East Fork Mouth mouth bars. These smaller bars represent, believe it or not, a larger problem though. They fall into a jurisdictional quagmire. Does the water body they are on belong to adjacent property owners, the City, the County, or the State?

That will determine where the money for dredging comes from. And more importantly, whether the money that is already available can be used to attack the problem when a dredge is in the lake.

The bar is in an unincorporated section of Harris County. But the City owns the shoreline, and usually the first few hundred feet of channels.

Who will take ownership of problems like Walden’s? These details still need to be worked out.

HB1824 May Help

Ironically, HB1824, which I criticized because I believe it opens the door to river sand mining, may help in cases like Walden’s. The bill allows Harris County Flood Control to take sediment from the San Jacinto and its tributaries without obtaining a permit or paying a fee as long as HCFCD deposits the sediment on private land. (Remember: Lake Houston IS the San Jacinto River.)

I suspect the Walden ditch will become precedent for how such minor tributaries are treated. Walden’s nearness to the West Fork mouth bar would argue for making it part of any dredging program there.

A new year, new challenges!

Posted by Bob Rehak on 1/1/2020 with photo and video from Jack and Greg Toole, and BCAeronautics.

855 Days since Hurricane Harvey and 104 since Imelda

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