More on What Went Wrong Near Elm Grove and How to Help Protect Residents from Future Flooding

Map by LJA Engineering shows natural drainage. Purple outline shows boundaries of Figure Four Partners’ Woodridge Development. Dark gray outline shows extent of drainage area for Taylor Gully. All drainage in A-E flows to F.

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:

Red labels and circle have been added to approved drainage plan to make it easier to follow this discussion. Small black arrows indicate direction of flow. The 29-acre triangular area labeled N2 actually belongs to Montgomery County, which started cleared most of the land between 2006 and 2008.

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.

Note two u-turns made by the water within the space of 200 feet.

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.”

Jeff Miller schematic showing series of problems near area that flooded. To his list, I would add the culvert across the ditch by the road that did not yet exist.

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.

Debris from flood caught in grass high above ditch indicates that water went out of banks near the proposed street that connects the north and south sections of Woodridge. From here, the water headed overland toward Elm Grove in the background.

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.

The red line shows the location of the buried 3′ pipe. Blue lines indicate the MAIN flow of water. Note, it also spilled out onto other side streets. This map shows the main flow, not the extent of flooding.

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.

Dirt excavated from S2 Detention Pond is being used to raise elevation of land elsewhere in development. Homes along Needham Road in Porter are in background by cell tower.
Jeff Miller, who helped with this analysis, stands on the original level of the land next to a street that will be about three feet above the elevation of Elm Grove. Miller stands 6′ tall. Note the fire plug at his eye level.

Urgent Recommendations

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