More on What Went Wrong Near Elm Grove and How to Help Protect Residents from Future Flooding
According to residents in Elm Grove and North Kingwood Forest, their homes never flooded before May 7th, 2019, including during Hurricane Harvey. Then bulldozers cleared the 262 acres north and west of them to create a new subdivision called Woodridge Village.
Reconstruction of Events
After talking with dozens of residents, mapping flood damage, reviewing flood videos, and photographing the aftermath, I think the following happened on May 7, 2019.
Before May 7th, contractors had finished clearing most of Woodridge Village’s 268 acres, most of which was hard clay. This accelerated runoff. They had also begun grading the land, filling in historical drainage channels and wetlands. But they had not yet totally completed any of the replacement drainage, even though one pond was substantially completed.
A large, long, linear ditch ran along the county line. Approximately half of this ditch (labeled S1 by the developer) bordered Sherwood Trails. Contractors had fully excavated the ditch but not fully finished it. The other half of the ditch that bordered Elm Grove did not yet have:
- A large diamond-shaped detention pond designed to hold 49 acre-feet of stormwater
- Any connectivity between that ditch and another ditch to the east, which LJA Engineers clearly intended as part of their plan. See below.
Here’s an enlargement of the crucial S2 detention area that shows the flow. All water from the northern section of Woodridge, drains to the part of Taylor Gully running from the triangular detention area N2 on the left toward the upper right.
Several things happen when the water reaches the upper right.
- Most of the runoff is forced to make a 120 degree right turn.
- It’s joined by more water flowing south along the eastern edge of the property to the north, and the gas pipeline easement north of North Kingwood Forest.
- All of that flows into a much smaller ditch…
- …that narrows down into a 3′ pipe…
- At that point, it is supposed to make another 90-degree turn into…
- …a grassy-lined channel that conveys the water into S2
- …where it mixes with stormwater from S1…
- …and flows through a box culvert…
- …into Taylor Gully where it’s joined by water shooting out of the 3′ pipe.
Here’s an even closer view of how all that works.
The Big Lebowski Connection
In the movie The Big Lebowski, Walter says to The Dude, “That’s right, Dude, the beauty of this is its simplicity. Once the plan gets too complex everything can go wrong.” And it did.
Of course, it was complicated by the facts that:
- Most of S2 had not yet been excavated.
- The grassy-lined channel to convey water from the upper part of Taylor Gulley into S2 had also not yet been excavated.
- A reinforced concrete box culvert had been installed to reduce the outflow into the lower part of Taylor Gully. That backed water up.
- A second reinforced concrete box culvert had not yet been installed farther up the ditch that might have held back some of the water that flowed into Elm Grove.
Critical Corner of Chaos
Jeff Miller, an Elm Grove resident who came within inches of flooding dubbed this corner of the development the “Critical Corner of Chaos.”
Photographs of debris patterns left in grass near the diagonal part of Taylor Gully show that water started overflowing the banks as far west as the road that crosses the ditch. From there, it headed straight south toward Elm Grove.
Also, when water started to make that 120 degree turn at the top of Miller’s diagram, it overflowed the banks into North Kingwood Forest. Part of the water also split off on the other side of the ditch and headed toward Elm Grove. The constrictions caused by:
- Flowing from a large ditch into a smaller ditch
- Flowing from the small ditch into a 3-foot pipe
- Not enough detention excavated
- Restricted outflow at the box culvert
…all forced water to flow into surrounding neighborhoods and down streets. Overland sheet flow added to street flooding already present raised the level of the water enough to enter at least 196 homes. The main paths that the water took looked something like this.
Current and Future Concerns
It’s been three weeks since the flooding. As the site continues to take shape, and as we officially enter hurricane season this week, several things should concern residents.
- Rebel Contractors is far from having all the detention ponds excavated.
- The dirt they have excavated is being used to elevate Woodridge above Elm Grove.
- The drainage scheme LJA envisioned at the southeastern corner of the subdivision may not be sufficient in future heavy rains to prevent flooding in neighboring communities.
- Taylor Gulley in Kingwood may not have sufficient conveyance to handle the volume of water coming from upstream development.
I mention this last point because older subdivisions in Porter along the western edge of Woodridge also flooded. Apparently, Woodridge blocked, at least partially drainage flowing from those areas. Therefore, less water came from that area than normal. Had it been added to the May 7th flood, things in Elm Grove and North Kingwood Forest could have been even worse.
Before all of Woodridge Village becomes set in concrete, we need the best engineers in town to re-evaluate the LJA plans independently, especially at the “critical corner of chaos.” Then I hope the developer hires additional resources to ensure a verified or improved plan is executed before we hit the peak of hurricane season in August and September.
All thoughts in this post represent my opinions on matters of public policy and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP statute of the great State of Texas.
Posted by Bob Rehak on 5/28/2019 with help from Jeff Miller
637 Days since Hurricane Harvey