Drainage ditches in Colony Ridge appear to violate Liberty County drainage standards from both 2004 and 2019.

• Both 2004 and 2019 regulations require developers to plant the slopes of ditches with grass to control erosion.
• In addition, 2019 regulations require backslope interceptor swales, another erosion-control measure. These prevent stormwater from running down the sides of ditches.
• According to residents, the developer has made little effort to do either or to bring older ditches up to current standards.

The violations contribute to sedimentation of the East Fork San Jacinto and its tributaries, and flooding from Lake Houston to Plum Grove.

Soil-Stabilization Violations

2004 Liberty County Road and Drainage Standards for Subdivisions and Development stipulate in Section 3.72 on Page 28 that, “All channels, and adjacent area, which has been disturbed by construction equipment shall be seeded with Bermuda grass or other grass as approved by the Precinct Commissioner or Designated Agent at the rate of eight pounds per acre (8 lb/ac). Seeding shall conform to Item 164 Seeding for Erosion Control of the “TxDOT Standards”.

Liberty County’s Subdivision and Development Regulations, revised January 2019 contain the identical language on slope stabilization. See Section 40.9.11 Channel Excavation (Page 91).

Backslope Interceptor Swale Requirement

2019 regulations also mandate additional erosion-control measures. The section on Erosion Control on page 100 states: “All drainage facilities must be designed and maintained in a manner which minimizes the potential for damage due to erosion. No bare earthen slopes will be allowed. Various slope treatments, including turf establishment, concrete slope paving, and rip-rap, are accepted. Flow velocities should be kept below permissible values for each type of slope treatment. Interceptor structures and backslope swale systems are required to prevent sheet flows from eroding the side slopes of open channels and detention facilities.” [Emphasis added.]

The emphasis on “All” and “maintained” would seem to require developers to bring all ditches up to the 2019 standard, but that clearly has not happened.

What Backslope Swales Look Like

Liberty County regulations don’t provide schematics of backslope interceptor swales, but Harris County Flood Control regulations do. See below. At the top of the ditch embankment, a notch is cut into the horizontal area. This notch collects rain and channels it to a series of corrugated metal or HDPE drains that empty into the bottom of the channel. This prevents water from pouring over the banks of the channel and eroding them.

Stark Contrast Between Regulations and Reality

As you look at the pictures below, see if you can spot the:

• Backslope swales (notches)?
• Drain pipes?
• Grass-lined banks?

You can’t. They aren’t there.

Properly constructed backslope interceptor swales constitute a best management practice (BMP). They can prevent the type of erosion you see above. This educational PowerPoint explains how these structures work as well as the dangers of not building them correctly.

But construction technique does not seem to be the problem in Colony Ridge. They simply have not been built. That’s why erosion on the sides of the channels is so rampant.

Consequences of Erosion

All this eroded sediment has to go somewhere. And it did.

Colony Ridge isn’t 100% responsible for ALL this sedimentation. Natural erosion and sand mines also contributed. But substandard drainage practices in a 12-13,000 acre development had to play a large role.

The City of Houston is still dredging the West Fork Mouth Bar, more than three years after Harvey. Cost to taxpayers to date: more than $100 million. No one yet knows how much it will cost to remove the East Fork Mouth Bar.

Plum Grove residents have also documented clogged streams and bayous that they say have contributed to local flooding. Plum Grove is suing the developer. The TCEQ found construction practices bad enough to affect human health.

It seems like prevention would be more effective than correction.

The Right Way

Ironically, Harris County has regulations similar to Liberty County’s that govern construction of drainage ditches. But the results are much different when and where people actually follow the regulations. See below.

Posted by Bob Rehak on 12/5/2020

1194 Days since Hurricane Harvey and 453 since Imelda

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.