On May 7th and September 19th, sediment-laden runoff from Perry Homes’ Woodridge Village development in Montgomery County flooded the streets and homes of Elm Grove Village and North Kingwood Forest. On September 26, the City of Houston wrote a cease and desist letter to Perry Homes, its subsidiaries and contractors. The letter alleged that runoff damaged the City’s sewer system and residents’ homes. It demanded that Perry Homes’ proxies stop sending sediment into the City.
Sediment Control Measures Not Followed in Subdivision Rules and Regs
If Perry Homes and its contractors had followed all the construction regulations affecting drainage, the flooding of Elm Grove would not have happened and the letter would not have been necessary. So what went wrong? I previously reviewed the sediment control measures in the Montgomery County Subdivision Rules and Regulations. Perry Homes received seven strikes. Among the worst apparent violations:
- They clearcut 268 acres when the rules say no more than 10.
- They are supposed to plant temporary vegetation but haven’t.
- They were supposed to make provisions for increased runoff during construction, but didn’t.
In fact, they have substantially completed only 23% of the permanent detention ponds for the whole subdivision despite clearcutting all 268 acres.
More Regulations in Drainage Criteria Manual Not Followed
Perry Homes also overlooked many provisions in the Montgomery County Drainage Criteria Manual. Twenty-two of the 175 pages also discuss erosion and sediment control (see Section 6 starting on page 85). Among the more serious omissions:
Channel Slopes Severely Eroding
Section 6.2.1 on Grass Establishment states that: “A good grass cover must be established on all areas within the right-of-way (except the channel bottom) disturbed by channel improvements or by any type of construction. An adequate grass stand on the banks helps stabilize the channel and minimize erosion caused by overbank flow and high velocities in the channel. Establishing a good grass cover requires preparing the seedbed, seeding properly. keeping the seed in place, fertilizing, and watering regularly.
The LJA Engineering report never mentions erosion or sediment control by those words. However, it does mention grass-lined and concrete-lined channels and spillways. Only one problem. The channels are not grass lined and most of the areas designated for concrete lining have yet to be lined.
Channel Turns Not Protected
Section 6.2.3 on Minimum Erosion Protection Requirements for Bends specifies that bends in drainage ditches must be protected from erosion by grass, rip-rap, or concrete. The material depends on the radius of the curve, the type of soil, average water velocity and maximum water velocity.
Despite funneling 188 acres of sheet flow into Taylor Gulley, which narrows down into a 3-foot pipe, Perry Homes has done little to increase the channel capacity or detention for that area. Worse, the channel design which may have been adequate for forested wetlands, can no longer handle high volume overland sheet flow.
The most obvious needs are on the eastern side of the development. There, Taylor Gully makes a 120-degree turn, then two quick 90 degree turns and two 45-degree turns, all within two hundred yards. Getting dizzy? The floodwater turns 390 degrees in this area!
At each turn the banks take a beating. The full force of the floodwater slams against the far bank and erodes it.
Straight Drop Spillway Not Installed
Section 220.127.116.11 states that a straight-drop spillway should be installed in drainage channels to adjust channel gradients which are too steep for design conditions.
LJA specifies one between where detention pond N3 will be and the 120-degree turn shown above. However, neither the detention pond, nor the spillway have yet been installed. So water from the north comes barreling down the ditch on the right unchecked. The high velocity increases erosion. Here’s what it looked like after May 7th.
Yesterday I posted about how Perry Homes was supposed to cut only 30 acres of trees on the northern section but cut 188. Still to come in this “What Went Wrong” Series:
- More Things Perry Homes Didn’t Do in the Montgomery County Drainage Manual
- Contradictions in Perry Homes’ Plans
- The Dirt on Perry Homes’ Soil Test
- The Floodplain that Wasn’t
Posted by Bob Rehak on 11/20/2019 with help from Jeff Miller
813 Days since Hurricane Harvey and 62 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.