conveyance Archives - Reduce Flooding

Search For Sediment Solutions Should Lead Straight to Colony Ridge

Harris County Flood Control, SJRA, and the Cities of Humble and Houston using funding provided in part by the Texas Water Development Board are searching for sediment solutions in the Upper San Jacinto River Basin. Their major scientific study includes all or parts of seven counties: Harris, Montgomery, Waller, Grimes, Walker, San Jacinto and Liberty – all land draining into Lake Houston.

*From Technical Memorandum 1 of the Upper San Jacinto River Basin Regional Sedimentation Study.*

The high-level goal: to better manage sediment in the river basin. Sediment reduces both floodway conveyance and the storage capacity of Lake Houston. Both contribute to the frequency and severity of flooding.

Among other things, the study partners hope to prioritize sediment hot spots so they can develop sediment solutions and recommendations.

I hope they look at Colony Ridge. It exemplifies a major hot spot and points the way to an obvious sediment solution – better enforcement of existing regulations.

Scope and Status of Sediment Study

The study is now about half complete. With much of the fieldwork complete, the partners will next focus on modeling, hotspot identification, area prioritization and sediment solutions, according to Matt Barrett, Water Resources and Flood Management Division Manager atSJRA.

To date, the study has examined a variety of factors:

Topographical characteristics (watershed size, length, slope, relief, etc.)
Land Cover (degree of development, forested percentage, agricultural, wetlands)
Soil Types and Erodibility
Meteorological (annual rainfall amounts and intensity).

The Colony Ridge area receives some of the highest rainfall totals and highest intensity rains in the river basin.

*From Technical Memorandum #2 of the USJRB Sedimentation Study, Page 16.* *Colony Ridge location circled in red.*

Colony Ridge also ranks among the most erodible areas in the entire river basin.

*Soil erodibility in the basin. From Technical Memorandum #2, Page 13.* *Colony Ridge circled in blue.*

So, you would hope that a development 50% larger than Manhattan, which is decimating forests and filling in wetlands would receive some scrutiny.

Colony Ridge erosion — *Colony Ridge ditch has widened approximately 80 feet in 6 years due to lack of erosion control measures such as backslope interceptor swales and grass.*

Colony Ridge is now 50 percent bigger than Manhattan — *Rivers of mud in Colony Ridge. Even the erosion is eroding.*

Guess which way to colony ridge — *Sediment coming down the East Fork (right) from Colony Ridge*

East Fork Mouth Bar cost $18 million to dredge. — *San Jacinto East Fork Mouth Bar between Kingwood and Huffman cost $18 million to dredge.*

Sediment Solutions Must Address Development Practices

Erosion occurs naturally. But poor development practices can accelerate the rate of erosion unnaturally.

Regulations in Liberty County call for backslope interceptor swales to prevent sheet flow over the sides of ditches. I have yet to see one such system anywhere in the 30+ square miles of Colony Ridge. What you typically see is this.

*All that sediment washes downstream where it reduces the carrying capacity of rivers and the storage capacity of Lake Houston.*

Liberty County regulations also call for planting grass on the side slopes of ditches and detention basins. The grass reduces erosion, too. But you don’t see much grass on those side slopes either.

Compare the ditch above with the ditch below in Harris County to see how grass and backslope interceptor swales can reduce erosion.

*Small swales behind main slopes capture sheet flow heading toward the ditch. Pipes then take runoff to the bottom of ditch, thus reducing erosion on side slopes.*

Here’s Colony Ridge again.

*Three-mile-long Colony Ridge drainage ditch has no grass or backslope interceptor swales.*

Address the Elephant in the Room Before the Next Disaster

Ironically, both Liberty and Harris County have almost identical regulations for erosion control. Harris County enforces them; Liberty County doesn’t.

Enforcement of development regulations is the elephant in the room.

So, as the SJRA and its partners search for sediment solutions, here’s one simple recommendation. Enforce regulations already on the books.

Colony Ridge and other developments that skirt regulations represent a disaster waiting to happen. Unfortunately, it will probably take a disaster, such as Harvey, to cause leaders to take action. But by then, it will be too late.

Posted by Bob Rehak on 10/20/23

2242 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Willow Creek Widening and Stormwater Detention Basins Improving Tomball Drainage

Harris County Flood Control District (HCFCD) has a large active construction project underway in Tomball. Phase I of the project stretches about two-thirds of a mile from SH249 to FM2920 on a tributary of Willow Creek as it arcs around a major shopping center near downtown Tomball and Lone Star College/Tomball. The project includes channel widening and deepening; dry and wet stormwater detention basins; and opportunities for recreational trails.

*Limits of Phase 1 are within red oval. Additional improvements (M124-00-00-E002) will extend further south to Willow Creek itself* *as additional money becomes available.*

Willow Creek: A Study in Contrasts

The Willow Creek watershed is located in northwest Harris County. It drains about half of the City of Tomball. The tributary highlighted above flows through densely developed shopping and medical center areas on the northern end to agricultural and oil and gas interests on the lower end.

*Looking SW at southern limit of construction toward agricultural and rural areas beyond.* *FM2920 leads into distance.*

*Looking NE in opposite direction toward area of channel widening and detention basins. SH249 cuts left to right across top of frame. FM2920 cuts through upper right corner.* *Tomball in upper right.*

*HCFCD contractors were hard at work on Christmas Eve afternoon when I took these shots.*

*Closer shot of detention ponds north of shopping center out of frame on the right.*

Willow Creek: Present and Future

Willow Creek flows into Spring Creek just upstream of where Spring Creek crosses under I-45. The Willow Creek watershed covers about 54 square miles. The downstream end of the watershed is within the floodplain of Spring Creek.

*Willow Creek Watershed and current HCFCD projects in various stages of completion. This post is about the one near the top center of the frame ending in E001.*

Willow Creek watershed is mostly undeveloped. Significant development is limited to the City of Tomball and a few residential subdivisions in the lower end. The development rate has not been very rapid. However, officials expect it to increase as the City of Tomball continues to expand and urbanization from Houston stretches northwest.

This project will directly benefit mostly areas on the northwest side of the county. However, it may provide some downstream benefit by holding back water in major floods.

Goal: Contain Runoff from 100-Year Event

Phase 1 of this project began construction activities in January 2021. As funding becomes available, future phases of the M124-00-00 project will continue channel conveyance improvements and construct several more stormwater detention basins from F.M. 2920 to the confluence with Willow Creek. Phase II will also deepen the channel improvements from Phase 1 that you see above.

The overall goal of the M124-00-00 project is to enable the channel to contain the 1-percent (100-year) storm event within the channel banks based on existing watershed conditions.
HCFCD

The total project focuses on conveyance improvements of stormwater in the area, as well as reducing flood risk through construction of stormwater detention basins. Stormwater detention basins reduce flooding risks by taking in and temporarily storing stormwater during heavy rain events and releasing the water back into the waterways when the threat of flooding has passed.

Multiple new detention basins along the M124-00-00 channel will add approximately 390 million gallons of storage capacity (an approximate 2,164 percent increase in current storage capacity) to benefit the Willow Creek watershed. That’s enough to contain a foot of water falling on 1200 acres.

Posted by Bob Rehak on 12/26/2021 based on info from HCFCD.org

1579 Days since Hurricane Harvey

Tunneling: A Potentially Valuable Flood Mitigation Tool

Engineering firm Freese & Nichols claims that “Incorporating tunneling into Houston’s stormwater portfolio could significantly reduce flood damages and improve the reliability of existing conveyance and detention infrastructure.” Tunneling technology, the firm says, has improved dramatically in the last 30 years, making projects possible that were once deemed impossible.

Rapid Growth Limits Mitigation Possibilities

Houston’s exponential population growth (16X during the last 100 years) has made both flooding and flood mitigation more difficult to deal with. However, tunneling, says Freese & Nichols bypasses the urban sprawl issue – especially in dense neighborhoods, such as those inside Beltway 8. Tunneling’s low-impact can move stormwater with very little effect on the surface, benefiting communities and addressing environmental concerns.

Tunnels Expand Both Conveyance and Storage

Tunnels, they point out, expand conveyance capacity within a watershed. They can also store stormwater during floods. A 30-50 foot tunnel can store 50 to 150 acre-feet of storm water per mile. More important, it can convey 10,000 to 15,000 cubic feet of water per second. To put that in perspective, that’s about 40-60% of the flow coming from Cypress Creek during Harvey. Or almost 20% of the flow coming from the Lake Conroe Dam.

San Jacinto River Watershed Flow Rates — During Harvey, an estimated 24,100 cfs came from Cypress Creek.

Thus, tunneling could significantly reduce total flow coming down rivers and streams during floods by providing an alternative means of conveyance.

How Tunnels Are Built

This detailed video shows how a modern tunneling machine works. It can construct up to 350 meters of tunnel in a week. That’s between a fifth and a quarter of a mile per week. The machine continuously cases the hole with precision, pre-caste, concrete segments as it excavates through loose sandy soil. It also dynamically balances pressure in the tunnel along the cutting head face to prevent cave ins. Working a hundred feet or more below the surface, it can even evacuate ground water.

*Machine used to build subways and storm tunnels. See fascinating 14 minute video.*

Editor’s note: This 13-minute industrial video is among the best-produced videos of its kind that I have ever seen. It should satisfy professionals as well as non-technical types. If you have students who lean toward science and engineering, make sure they see this; it shows how human ingenuity can fill the gap between problem and solution.

Gravity-Driven Reliability

Once built, gravity drives the system during floods.

Diagram courtesy of Freese & Nichols. Reproduced with permission. Note that this diagram shows the start point within a detention basin. Starting within a detention basin helps reduce sediment accumulation in tunnels.

Success Stories in Other Parts of Texas

Here in Texas, engineers have used the technology successfully to reduce flooding potential in Dallas, San Antonio and Austin. As urban centers grow, the need to move infrastructure underground grows with them. Disruption to life and the environment on the surface are simply too costly otherwise.

This presentation gives an overview of the technologies involved several case studies in Texas and the U.S. Here’s a shorter two-page summary. And a link to the Freese & Nichols blog that provides a more detailed discussion of the possibilities.

Weighing Expense Against Flood Cost

Because of the expense, tunneling isn’t the first technology you would consider for flood mitigation. But it can be a valuable addition to the tool chest…especially when weighed against the $125 billion that Harvey cost Houston residents.

Numerous discussions have been held at the county, state and federal levels re: the potential applications of this technology.

Community Impact reported last week that Brian Gettinger—tunneling services leader with Freese & Nichols —said he thinks the concept could work on Cypress Creek.

The newspaper said that Gettinger pitched the tunnel system to the Cypress Creek Flood Control Coalition in March. He said if the tunnel becomes a reality, it could cost $2 billion-$3 billion, would take years to build, and would require federal support because of the high price tag.

Feasibility and Alignment Studies

Harris County Flood Control should soon begin Phase 1 of a $400,000 study. Once started, it could take four months to confirm whether tunneling is feasible in this area. Future phases of the study will dig deeper into specific alignments (Buffalo, Brays, Cypress, etc.), evaluating inflow and outflow points, and specific routes.

Posted by Bob Rehak on 4/22/2019 (Earth Day)

601 Days since Hurricane Harvey

Harris County Flood Control to Begin Restoring Conveyance of Bens Branch In April

Jason Krahn of the Harris County Flood Control District (HCFCD) revealed plans tonight to begin restoring the conveyance of Bens Branch, one of the largest drainage channels in Kingwood. Bens Branch runs diagonally through the center of Kingwood from the new St. Martha Catholic Church to east of Kings Harbor where it joins the San Jacinto West Fork.

Harris County Flood Control will soon begin removing more than
8000 truckloads of sediment clogging Ben’s Branch.

Welcome Relief

News of the project will bring welcome relief to those who live near the creek and who flooded during Hurricane Harvey. Among them are residents of North Woodland Hills, Kings Forest, Bear Branch, Town Center, the Enclave, Kingwood Village Estates, and Kings Harbor.

Restoring Conveyance to 1990 Level

The objective of the project: to restore the conveyance that existed in 1990 when the creek was last widened and improved. Large portions of the creek have severe silting.

Krahn says Flood Control plans to excavate 1.3 miles of the ditch from near Kingwood Drive to past the YMCA – a total of 6,851 linear feet. The project will stop approximately 1,800 feet from Lake Houston. From that area, they plan to excavate 77,365 cubic yards of sediment that have built up since 1990. That equals about 8,600 dump-truck loads.

Flood Control also plans to bring in rock to shore up areas that have severely eroded.

Project Phasing and Timeline

The design phase of the project has completed and bidding will begin within two weeks, says Krahn, the project manager.

To access the areas to be excavated, Flood Control will use a combination of roads and adjacent property owners. They include Kingwood County Club, Harris County Precinct 4 Library, the YMCA, and the Kings Crossing Trail Association.

Expect the following phases:

Establishing access
Erection of construction fencing
Mobilization of equipment such as amphibious trackhoes and shallow-draft barges
Excavating material and storing it along the edges of the creek
Waiting two weeks for it to drain and dry
Hauling it away

Krahn expects to haul off 40 truck loads per day. He says the project should take a total of 250 calendar days. Thus, they should complete the project by next January.

Some trees may have to go, but Krahn vows to make every effort to keep as many trees as he can. He says he understands how much Kingwood values trees. He also points out that any trees on the banks did not exist when the ditch was last excavated; they have grown up since.

Procurement, bidding, and planning will run from April through June. Expect to see boots on the ground no later than July 1.

$2.1 Million Cost Expected

Total cost of the project is projected at about $2.1 million out of a $17 million total maintenance budget for all of Harris County. This money does not come out of the flood bond. It comes from the normal HCFCD maintenance and operations budget.

Soil Already Tested; Non-Hazardous

The county has already sampled and tested the soil that it will remove. It received a Class 2 Non-Hazardous Rating. That means it is not contaminated and can be stored anywhere. Krahn says that the winning contractor will propose disposal sites. Sometimes the fill will be used in road beds, to elevate property, or returned to old sand pits.

Warn Kids to Stay Away

Many people fish and play in the creek and job on its banks. Krahn requested residents to keep their children away from the construction zone once heavy equipment starts moving in. Operators will have their eyes on the job and not people jogging or fishing.

Thanks to Barbara Hilburn

A shout-out to Barbara Hilburn of Kingwood Lakes who has doggedly led the charge on internal drainage improvements since Harvey. Hilburn emphasized the need for a Kingwood-wide study of internal drainage to restore the entire system to its original capacity. She hopes that will work hand-in-hand with other improvements being made to the San Jacinto and the Lake Houston dam to reduce flood risk.

Posted by Bob Rehak on 3/20/2019

568 Days since Hurricane Harvey

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