Tag Archive for: May 7th

Mitigation Update: 3rd Anniversary of First Elm Grove Flood

Back in 2019, portions of Elm Grove and North Kingwood Forest Villages flooded twice. The first time occurred on May 7th. According to Harris County Flood Control District’s (HCFCD) report on the storm, “A 30-min rate of 2.9 inches was recorded at US 59 and the West Fork of the San Jacinto River and a 1 hour rate of 4.0 inches.”

“380 structures were flooded in the Elm Grove Village subdivision and other nearby subdivisions in the northern portions of Kingwood.”

Investigation by HCFCD the following day revealed that “… the flooding was potentially caused by development upstream in Montgomery County that sent large volumes of sheetflow into the subdivisions and Taylor Gully.” This video shows the sheetflow pouring out Perry Homes’ Woodridge Village property into homes along Village Springs Drive.

Perry contractors had clearcut 267 acres without installing the required detention ponds when the rain hit.

In the three years that followed, I posted 242 reports about every aspect of that flood and a second one during Imelda. The second flood affected two to three times more homes in the same areas.

The floods triggered multiple lawsuits which Perry Homes, its subsidiaries and contractors finally settled late in 2021.

What It Looked Like

Shady Maple the night of the May 7 2019 flood
Escape. In Elm Grove on Shady Maple the night of the May 7, 2019 flood.
High water rescue
Rustling Elms Bridge in Elm Grove underwater as school bus tries to cross it.
Water in Keith Stewart's home on Shady Maple after May 7th flood in 2019.
Water rising at night in Keith Stewart’s home on Shady Maple after May 7th flood in 2019.

Catalog of Flood Mitigation Efforts

Ever since the Elm Grove floods, Harris County, HCFCD, the City of Houston, Congressman Dan Crenshaw’s team and others have worked diligently to reduce future flood risk.

On this Mother’s Day weekend, it may bring flooded families comfort to understand how far we have come. Much remains to do, but much has already been done, or at least started.

Major Maintenance on Taylor Gully

Even before the second flood, HCFCD undertook a major maintenance project on Taylor Gully to remove accumulated sediment and restore channel conveyance.

The project began in 2019. Work extended downstream to the natural portion of the channel. It finished in 2021.

Taylor Gully maintenance
HCFCD working to remove sediment buildup in Taylor Gully near the Maple Bend Bridge in January of 2021. The work began upstream near Rustling Elms in July 2019.

Kingwood Area Drainage Analysis and Taylor Gully Study

In 2019-20, HCFCD, Lake Houston Redevelopment Authority (TIRZ 10), and City of Houston teamed up to conduct a drainage analysis for all streams in the Kingwood area. A recommendation to prioritize engineering of drainage improvements along Taylor Gully (including Woodridge) came out of that study.

The Flood Control District began preliminary engineering study on the Taylor Gully improvements in 2021. HCFCD anticipates presenting results during late summer or early fall this year.

Purchase of Woodridge Village By County and City

In early 2021, the Flood Control District and the City of Houston partnered to acquire the 267.35-acre Woodridge Village property for approximately $14 million.

They closed on the purchase of Woodridge Village in March 2021.

Houston Mayor Pro Tem Dave Martin lobbied the City to purchase about 70 acres of the property.

HCFCD will use the remaining 194.35 acres of the Woodridge site for stormwater detention. That will help reduce flood risk.

Crenshaw Earmarks

Congressman Dan Crenshaw secured an earmark for $1.6 million for engineering of flood mitigation improvements along Taylor Gully. The engineering should shrink the floodplain. That will effectively remove 387 structures from the floodplain and has the potential to remove another 62.

Crenshaw also has another earmark pending for $10 million to actually construct the improvements recommended by the study.

Local groups must spend earmarks during the fiscal year in which Congress approves them. So funding can’t get too far ahead of the engineering.

Taylor Gully Preliminary Engineering Study

The Taylor Gully study will look at Woodridge in conjunction with other potential Taylor Gully improvements. However, HCFCD must perform additional preliminary engineering to further evaluate specific alternatives for Woodridge and determine the best. 

During each study, HCFCD will hold Community Engagement Meetings to present alternatives and gather feedback.

Excavation & Removal Contract

In January 2022, HCFCD began work on a Woodridge Excavation and Removal (E&R) project.

Start of the new floodwater detention basin that could double the capacity on Woodridge Village.This pond should ultimately expand beyond the lone trees in the middle of the frame near the top. Photo taken 4/30/22.

E&R projects provide a head start on the excavation process and risk reduction. They can start before the design of a stormwater detention basin. Contractors excavate a set amount of material within an agreed-upon timeframe and general area.

The excavation can also potentially provide interim stormwater storage while awaiting the design and construction of the final stormwater detention basin.

As of April 30, 2022, 36,421 cubic yards of material has already been removed from the site. See photo above taken that day. The project will remove as much as 500,000 cubic yards of soil and other material.

Woodridge will remain an active construction zone for up to three years.

Have a Happy Mother’s Day this weekend.

Posted by Bob Rehak on 5/6/2022

1711 Days since Hurricane Harvey and 1096 Days since May 7, 2019

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.

One Year Ago: 415 Homes Flooded in All of Harris County; 380 of Those Bordered Woodridge Village

Harris County Flood Control District’s final report on the May 7, 2019, storm indicates that 415 homes flooded in all of Harris County. It also indicates that 380 of those bordered Perry Homes’ Woodridge Village development across the county line in Montgomery County.

That’s a whopping 91.5% of all flooded homes in the most populous county in the State. And the third most populous in the nation.

Report Cites Sheet Flow from Woodridge Village as Potential Cause

The heaviest rain that day fell on northeast Harris and southeast Montgomery Counties. However, the report also cited “large volumes of sheet flow” from Woodridge Village as the potential cause of flooding for those bordering the development. A jury in Harris County will decide the cause in two months.

At the time, Perry Homes’ contractors had clearcut virtually the entire 268-acre development but had only completed about 7% of the detention ponds.

High-water rescues in progress the night of May 7, 2019, on Shady Maple in Elm Grove Village, Kingwood. About one block south of Woodridge Village.

For official reports on this and other storms, see the Reports Page of this website. Click on the Major Storms tab.

Posted by Bob Rehak on 5/8/2020

983 Days after Hurricane Harvey and 367 Days after the May 7th Storm

One Year Ago Today, Streets of Elm Grove Turned into Rivers for First Time

May 7th is the anniversary of the first large-scale flood in Elm Grove history. On that day, more than 200 homes flooded on the streets south of Perry Homes’ Woodridge Village and the Montgomery County line. Homes that did not flood, even during Harvey.

Life After Harvey and Before May 7th

In the weeks leading up to May 7th:

Then The Rain Came

According to the gage at West Lake Houston Parkway and the West Fork, it started between 10 a.m. and 11 a.m. Then it picked up again between 11 a.m. and 12 p.m. when we got about 2.5 inches of rain. Then we got slammed between 3 p.m. and 5 p.m. when we got another 2.2 inches. Altogether, we got 5.64 inches before midnight.

Rainfall one year ago today.
Atlas 14 rainfall figures for Kingwood area.

The bulk of the rain, about 5.5 inches, fell in about a 12 hour period. That would make May 7th about a 5-year storm. The one-hour peaks during the storm never significantly surpassed the one-hour peaks during Harvey. Yet Elm Grove did NOT flood during Harvey and flooded disastrously on May 7th.

Act of God or Series of Missteps?

The Woodridge Village developer issued a terse statement saying that the flooding was an Act of God. But video showed sheet flow coming out of Woodridge Village.

And that helped trigger hundreds of lawsuits. Over the next year, hundreds of posts would piece together a series of missteps by the developer that turned a heavy rain into a disaster. Contributing factors included:

All of these factors would come into play when Elm Grove flooded again during Tropical Storm Imelda on September 19.

The judge in the lawsuits set a trail date for July 13, 2020. But COVID may delay that. Meanwhile, Harris County is trying to buy Woodridge Village from Perry Homes with the help of the City. We should have a final answer on that within two weeks.

Images from That Awful Day

While we wait, here are some pictures of that awful day and the immediate aftermath.

High-water evacuation in middle of night on Shady Maple Drive
HFD High-Water Rescue
Humble ISD school bus attempting to return kids home as sun started to set.
Erosion where S2 detention pond should have gone.
Log spearing warning sign at north end of Village Springs in Elm Grove
Dumpsters filled driveways for blocks as people gutted their homes.
Keyframe from Jim Zura drone video showing where S2 detention pond should be. Instead, only a muddy river.
Families carted precious belongings to the curb.
Keith Jennings bewildered dog as flood waters rose in his kitchen.

Encore Performance Just as People Moving Back Into Homes

As tragic as all these images are, the whole scene would repeat itself again in September, just as many people were moving back in to repaired homes. Except in September, 2x-3x more homes flooded.

Since then, many people have waited to repair their homes a second time until they can be sure that the source of the flooding has been fixed.

The hearts and prayers of the entire community go out to those who flooded so needlessly.

Posted by Bob Rehak on May 7, 2020 with images from flood victims

982 Days since Hurricane Harvey and 366 since last May 7th

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.

Part II: When Is A Detention Pond Not A Detention Pond?

Q: When is a detention pond not a detention pond?
A: When it’s just a wide spot on a stream.

The defining characteristic of a detention pond is an “outfall” smaller than the inlet. The pond holds back rain in a storm and releases it later at an acceptable rate. This reduces downstream flooding.

From the Montgomery County Drainage Criterial Manual

That’s the theory, at least. In practice, sometimes things don’t always work out that way. It often depends on maintenance.

Unrestricted Outfalls

On 2/13/2020, I reported on one Woodridge Forest detention pond on Ben’s Branch that had an outfall LARGER than its inlet. Harvey and Imelda blew out the pond’s outfall.

This week, I discovered that a second pond immediately upstream also apparently has an unrestricted outfall.

Two tributaries of Ben’s Branch come together in the foreground pond. The pond also collects runoff from surrounding commercial and residential areas. Photo taken 2/13/2020.
Water flows toward exit in upper right. Photo taken 2/13/2020.
Note height and width of exit. Photo taken 2/13/2020.

The low area in the picture above measures more than 200 feet wide in Google Earth. That’s far wider than the combined inlets. Net: this pond provides little if any detention capability.

Same Problem with Second Pond

Neither does pond beyond it that I highlighted last week provide much detention capacity.

Note how Ben’s Branch flows both through and around the next pond. Direction of flow is from bottom to top of frame. Photo taken 2/13/2020.
Reverse angle looking NW. Direction of flow is now toward camera. Note how the outfall (foreground) is larger than the inlet. Also note how runoff from residential streets (upper right) is channeled outside the pond. Photo taken 2/13/2020.

Both Ponds Provide Little Detention Benefit, If Any

Both of these ponds provide little detention benefit, if any.

Neither pond has a maintenance road around it, even though Section 7.2.8 of the Montgomery County Drainage Criteria Manual specifies that “A 30-foot wide access and maintenance easement shall be provided around the entire detention pond.”

Sometimes, what looks like a detention pond is really just a pond. Or a wide spot in a stream.

Recent Surge in Downstream Flooding

During the May 7th and Imelda floods in 2019, water flowing through these ponds then flowed over Northpark Drive and flooded homes in North Woodland Hills. It also flooded numerous homes and businesses downstream on Ben’s Branch between Woodland Hills Drive and the San Jacinto River West Fork.

One wonders whether those damages could have been averted if the ponds had detained water.

As Harris County Flood Control conducts the Kingwood Area Drainage Study, engineers must consider the possibility that this area may be dumping more water downstream than planned.

The Woodridge Municipal Utility District apparently is responsible for these ponds.

Posted by Bob Rehak on 2/16/2020

901 Days after Hurricane Harvey and 150 after 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.

Why Some People Flooded on May 7th or September 19th, But Not During Harvey

After May 7th and September 19th storms, reports started pouring in about homes that flooded that had not flooded during Harvey. How could that be? Harvey dumped more rain than any storm in history of the continental U.S. The short answer: When you look closely at the rainfall statistics, its comes down to totals versus intensities. Even though Harvey brought more rain, its peak intensity never came close to the other storms’. Those higher peaks can create street flooding miles from any river. And they did.

Those looking for a more detailed explanation can read below.

Let’s start by looking at three local rainfall gages on the West and East Forks. Then we’ll compare statistics.

Where To Find Statistics

Using the Harris County Flood Warning System, you can find historical rainfall data for any date or gage in the region. Here’s what I found for three local gages and three storms.

Comparison of Storm Totals, Peak Intensities and Durations

During Harvey, we received:

  • 33.04 inches at the West Fork/US59, with a peak 2.36 inches in one hour.
  • 27.44 inches at the East Fork/FM1485, with a peak 1.4 inches in one hour.
  • East Fork/FM2090 – no data reported.

On May 7th, we received:

  • 6.76 inches at the West Fork/US59 with a peak 3.64 inches in one hour
  • 9.84 inches at the East Fork/FM1485 with a peak 3.16 inches in one hour
  • 6.76 inches at the East Fork/FM2090 with a peak 1.6 inches in one hour

On September 19th, we received:

  • 11.56 inches at the West Fork/US59 with a peak 4.56 inches in one hour
  • 18.88 inches at the East Fork/FM1485, with a peak 9.4 inches in three hours.
  • 19.68 inches at the East Fork/FM2090, with the peak of 3.24 inches in one hour.

Comparing Totals and Intensities

From this data, several things become immediately apparent.

  • Harvey dropped the most rain, but had the lowest peak intensity.
  • Compared to May 7th, the September 19th storm dropped roughly 2-3X more rain at each gage.
  • Comparing gage locations, you can also see tremendous variability over just a few miles for any given storm. For instance, on September 19th, 63% more rain fell on New Caney than the Humble/Kingwood area.

Comparing All 3 Storms to Precipitation Frequency Estimates

The next question: How do these numbers compare to the hypothetical 100- and 500-year rainfall events? Here are the updated precipitation frequency estimates for this area from NOAA Atlas 14.

Take the totals and peak intensities from the gage information above. Then locate them in the table below. Here’s what you find.

Frequency Estimates for Harvey – August 25-30, 2017

US59 at West Fork during Harvey
  • 500-year event based on 5-day total
  • 2- to 5- year event based on peak hour.
FM1485 At East Fork during Harvey
  • 200-year event based on 5-day total
  • 1-year event based on peak hour.
FM2090 at East Fork during Harvey
  • No data available

Frequency Estimates for May 7 Storm

US59 Gage on May 7
  • 5-year storm based on 24-hour totals
  • 25-year storm based on the 1-hour peak

Street and minor yard flooding in an event like this is normal. But it should not have entered your house if the house is above the 100-year flood plain. (Most homes are at least two feet above.)

If you’re near this gage and your home flooded on May 7th, it probably wasn’t because of the peak rainfall intensity or total. You should be looking for clogged or broken storm drains, fallen trees/sediment blocking ditches, or upstream development, like Woodridge Village, that overtaxed the capacity of drainage systems.

FM1485 Gage on May 7
  • 25-year storm based on rainfall total
  • 10-year storm based on peak intensity (1-hour rate).

Again, this should be well within the capacity of infrastructure to handle. If your home flooded, look for other causes like those above.

FM2090 Gage on May 7
  • 5-year storm based on rainfall total
  • 1-year storm based on peak intensity.

Infrastructure should have handled that easily. If your home flooded, look for one of the possible causes listed above.

Frequency Estimates for September 19 Storm

US59 Gage on September 19
  • 25-year storm based on 24-hour total
  • 100-year storm based on peak intensity.

Storm drains are designed to handle about 2 inches per hour, but when we got 4.56 inches between 9 and 10 a.m., we clearly pushed infrastructure capacity to the limit. It’s no accident that Jeff Miller’s security camera witnessed a huge surge of muddy water from Woodridge Village coming down his street at 10:10 a.m.

Most infrastructure, homes, and businesses are built to handle a hundred-year rain event. Even homes surrounded by 100-year flood plains are usually raised above them.

If you flooded in this event, it may have been because of the extreme rainfall or because your slab wasn’t elevated two feet above the 100 year flood plain like most building regs require.

Other causes may have factored in also. When there’s little margin for error, a partially clogged storm drain or ditch, or upstream development could have made the difference between flooding and not flooding.

A massive 268-acre, clear cut area with only 25% of the detention installed immediately upstream from you would quickly turn a marginal situation hopeless.

FM1485 Gage on September 19
  • 100- to 200-year storm based on 24-hour totals.
  • 100- to 200-year storm based on 3-hour peak intensity.

It easily surpassed the design capacity of infrastructure. Events like this make a good case for flood insurance if you don’t have it.

FM2090 Gage on September 19
  • 200-year event based on 24 hour total
  • 10-year event based on peak intensity.

Again, think flood insurance. You’re way past the design capacity of infrastructure.

River Flooding Vs. Street Flooding

Peak intensity usually affects streets first. Storm totals usually affect rivers later.

From the frequency estimates above we can see that Harvey was extreme in its totality, but did not reach the peak intensity that either the May 7th or September 19th storms did. In fact…

The highest one-hour total for the May 7th and September 19th storms at all three gages exceeded the highest one-hour measurement during Harvey.

The real story of Harvey: how much rain KEPT falling for days and days. And how much water was released from the Lake Conroe Dam at the peak of the storm. Harvey was not about street flooding. It was about river flooding.

River Flooding Versus Street Flooding

Rainfall totals, intensities and durations affect flooding differently.

Street Flooding

Intense bursts of rain like we saw on September 19th create street flooding. Short bursts quickly exceed storm drain capacity, and the storage capacity of sewers and streets. Water comes up in the streets quickly and goes down quickly. This could be miles from a river, long before river flooding. Rainfall just can’t get out of the neighborhood quickly enough.

River Flooding

It can take days for water to migrate to a river and for large rainfall totals to force the river out of its banks. River flooding usually happens long AFTER street flooding, when the storm totals exceed the conveyance capacity of the river.

Importance of Location

During Imelda, New Caney received 20 inches of rain, while Lake Conroe received only 2. So there was no need to release water from Lake Conroe. For the most part, West Fork flooding was minor. But it was a totally different event on the East Fork where heavy rain piled up for two days.

Harvey – Classic River Flooding

During Harvey, the rainfall intensity only briefly surpassed the carrying capacity of infrastructure. But when the rain piled up in rivers for days and the SJRA released 80,000 cubic feet per second from Lake Conroe, tens of thousands of people flooded.

  • As the river rose, the water in ditches had nowhere to go.
  • As the ditches rose, the water in storm drains had nowhere to go.
  • As the water in storm drains backed up, the water in streets had nowhere to go.
  • And when the rain kept coming…you know the rest.


I hope this helps explain why some people flooded on May 7th and/or September 19th and not during Harvey. Different intensities and different durations produced different types of flooding.

Posted by Bob Rehak on 9/27/19 and dedicated to my old friend David Lyday

759 Days since Hurricane Harvey