Tag Archive for: detention

Willow Creek Widening and Stormwater Detention Basins Improving Tomball Drainage

Harris County Flood Control District (HCFCD) has a large active construction project underway in Tomball. Phase I of the project stretches about two-thirds of a mile from SH249 to FM2920 on a tributary of Willow Creek as it arcs around a major shopping center near downtown Tomball and Lone Star College/Tomball. The project includes channel widening and deepening; dry and wet stormwater detention basins; and opportunities for recreational trails.

Limits of Phase 1 are within red oval. Additional improvements (M124-00-00-E002) will extend further south to Willow Creek itself as additional money becomes available.

Willow Creek: A Study in Contrasts

The Willow Creek watershed is located in northwest Harris County. It drains about half of the City of Tomball. The tributary highlighted above flows through densely developed shopping and medical center areas on the northern end to agricultural and oil and gas interests on the lower end.

Looking SW at southern limit of construction toward agricultural and rural areas beyond. FM2920 leads into distance.
Looking NE in opposite direction toward area of channel widening and detention basins. SH249 cuts left to right across top of frame. FM2920 cuts through upper right corner. Tomball in upper right.
HCFCD contractors were hard at work on Christmas Eve afternoon when I took these shots.
Closer shot of detention ponds north of shopping center out of frame on the right.

Willow Creek: Present and Future

Willow Creek flows into Spring Creek just upstream of where Spring Creek crosses under I-45. The Willow Creek watershed covers about 54 square miles. The downstream end of the watershed is within the floodplain of Spring Creek.

Willow Creek Watershed and current HCFCD projects in various stages of completion. This post is about the one near the top center of the frame ending in E001.

Willow Creek watershed is mostly undeveloped. Significant development is limited to the City of Tomball and a few residential subdivisions in the lower end. The development rate has not been very rapid. However, officials expect it to increase as the City of Tomball continues to expand and urbanization from Houston stretches northwest.

This project will directly benefit mostly areas on the northwest side of the county. However, it may provide some downstream benefit by holding back water in major floods.

Goal: Contain Runoff from 100-Year Event

Phase 1 of this project began construction activities in January 2021. As funding becomes available, future phases of the M124-00-00 project will continue channel conveyance improvements and construct several more stormwater detention basins from F.M. 2920 to the confluence with Willow Creek. Phase II will also deepen the channel improvements from Phase 1 that you see above.

The overall goal of the M124-00-00 project is to enable the channel to contain the 1-percent (100-year) storm event within the channel banks based on existing watershed conditions.


The total project focuses on conveyance improvements of stormwater in the area, as well as reducing flood risk through construction of stormwater detention basins. Stormwater detention basins reduce flooding risks by taking in and temporarily storing stormwater during heavy rain events and releasing the water back into the waterways when the threat of flooding has passed.

Multiple new detention basins along the M124-00-00 channel will add approximately 390 million gallons of storage capacity (an approximate 2,164 percent increase in current storage capacity) to benefit the Willow Creek watershed. That’s enough to contain a foot of water falling on 1200 acres.

Posted by Bob Rehak on 12/26/2021 based on info from HCFCD.org

1579 Days since Hurricane Harvey

Another Massive Detention Pond Going In Next to Halls Bayou

Construction has begun on another massive detention pond along Halls Bayou. It stretches south from Isom Street to the bayou between Chrisman and Aldine-Westfield Roads. It covers approximately 26 acres and when complete will hold 180-acre feet of stormwater to reduce the risk of flooding. This is just one of 11 projects comprising the Halls Implementation Program. Together they have a total current value of $212 million dollars.

Looking NNW across the new detention pond. Construction started in August 2021. HCFCD expects completion by March 2022.

Such basins take in excess stormwater during heavy rain events and then release it slowly back to the channel when the threat of flooding has passed. Part of the basin will have a wet bottom and another part will have a vegetated shelf. Yet another part will go in between Isom and Aldine Mail Route Road, although that portion has not yet begun construction. (See below).

Map on left shows current extent of construction work. Eventually, project will also include channel conveyance improvements (right) for a tributary that will be directed into the new pond.

Harris County Flood Control District (HCFCD) lists the project as C-25 on its website. But the Flood Bond Program ID is P518-11-00. Ultimately, this will become part of a much larger project area that includes P118-21-00. Together, they will improve drainage in a large part of east Aldine.

Each of these projects falls into Commissioner Adrian Garcia’s Precinct 2. The description that accompanies the project in the flood-bond spreadsheet says, “This project could reduce the risk of flooding for over 90 buildings and could reduce the 1% floodplain for over 100 acres.” The HCFCD spreadsheet and website indicate a total cost of more than $14 million.

But keep this in mind. Project C-25 will work in conjunction with two proposed Harris County Engineering Department projects: neighborhood drainage improvements in the Western Homes subdivision and proposed roadway and drainage improvements along Aldine Mail Route Road. The detention capacity in the pond you see here will accommodate drainage improvements in those areas without flooding other areas. Thus, the pond will really help more than 90 structures.

The project shown in these photos is P-518. P-118 is still in preliminary engineering review.

C-25 is a partnership project. HCFCD received an approximately $9.5 million Community Development Block Grant for Disaster Recovery (CDBG-DR) from the US Department of Housing and Urban Development (HUD). Approximately $5.4 million comes from local funding.

Photos of Work to Date

Looking NE from the SE corner of the construction. Halls Bayou, center, runs along the southern edge of the new basin. The detention basin in the top center was developed by TxDoT. Another phase of this project will expand north into those trees in the upper left.
Looking north from over Halls Bayou. A large part of this basin will have a wet bottom, which contractors are beginning to excavate now. Only detention capacity above the permanent waterline counts toward the total of 180 acre feet. So this pond will have a depth of 7-8 feet from the top of bank to the waterline.
Reverse shot looking SE from Isom Street. The TxDoT basin and Keith Weiss Park are in the upper left of this shot.
The scale of the workers in this shot shows the depth of excavation as of 10/13/21.

This HCFCD presentation explains more about the project, a related project (P118-21-00/C-28) and their benefits.

Posted by Bob Rehak on 10/13/2021

1506 Days after Hurricane Harvey

New Caney ISD’s New West Fork High School Taking Shape

Between US59 and Sorters-McClellan Road, a few blocks south of Kingwood Drive, New Caney ISD High School #3 is finally taking shape. And it now has an official name: West Fork High High School.

On January 1, 2021, contractors were just starting to pour concrete for the foundations and parking lots. According to the New Caney ISD’s June update:

  • Site work storm drainage is 95 percent complete
  • Sanitary sewer system – 85 percent.
  • Electrical system – 98 percent.
  • Water system – 90 percent.
  • Building concrete slab – 90 percent.
  • Form and pour tilt-up panels – 99 percent.
  • Erect panels – 95 percent.
  • Structural steel – 55 percent.
  • Metal decking – 20 percent.
  • Concrete masonry unit (cinder block) masonry – 10 percent.

Aerial Photos Taken 7.12.21

Here’s how all that looked on the afternoon of July 12, 2021.

Looking NE from over Sorters-McClellan Road toward Kingwood Medical Center and Insperity (top center).
Looking east toward Field House and where playing fields will go just beyond it. US59 and Lowe’s in background.
Looking south at entire site. Sorters-McClellan Road on right. US59 on left and top.
A peak into New Caney ISD’s West Fork High School three-story structures
Looking north at entire site. Huge detention pond in foreground.
Looking North. Corrugated metal installed as base for roofing on four buildings.

Site Plan, Architectural Renderings for New Caney ISD West Fork High School

Here’s how it should all look when finished.

Architectural Rendering courtesy of New Caney ISD.
Architectural Rendering courtesy of New Caney ISD.
Architectural Rendering courtesy of New Caney ISD.
General plan for New Caney High School #3

New Caney ISD expects to finish construction on the 60-acre site in the summer of 2022. The site is in Montgomery County, but also the City of Houston’s Extra-Territorial Jurisdiction.

Detention Pond Requirements

The dry-bottom detention pond takes up approximately 5 of the 60 acres – or one twelfth of the site. Assuming it’s 12 feet deep, it would hold a foot of rain falling on the entire site. The new minimum recommendation for a site this size in Harris County and the City is .65 acre feet of detention per acre. That would be about 40 acre-feet of detention, which a pond 8 feet deep would hold.

Because the construction site is closed, and the plans I have don’t specify depth, it’s hard to say exactly how much capacity the detention pond has. But I’m guessing it’s deep enough to meet the new minimum requirements under Atlas 14. I say that judging by the height of the pond walls compared to the pipes leading into it.

I would expect no less from a public school system.

Posted by Bob Rehak on 7/12/2021

1413 Days after Hurricane Harvey

Perry Contractors Now Focusing on Finish Work for Detention Ponds

Perry Homes’ current contractors have excavated 3X more detention pond volume in ten weeks than the previous contractors did in virtually two years. During this past week, they finished excavating three ponds on the northern section of Woodridge Village. Together, they comprise 77% of the total detention volume for the whole site.

Excavation Done, but Finish Work Remains

That doesn’t mean they’re totally done with the ponds. Recent aerial photos show that they still have much finish work to do. That includes:

  • Shaping the sides
  • Creating backslope swales
  • Installing pipes to funnel water from the swales into the ponds and channels
  • Ensuring water can flow out of Adams Oaks in Porter on the west side of the subdivision into Taylor Gully as it previously did
  • Creating concrete “pilot channels” in the center of the ponds and larger channels
  • Planting grass along the sides of the slopes to reduce erosion
  • Installing outflow control in several places to hold back floodwaters
  • Building maintenance roads around the ponds

Elm Grove resident Jeff Miller, who monitors the progress of construction daily, says crews are already hard at work on many of those tasks.

Ponds NOT Expanded Beyond Initial Plans

Miller has compared the width and depth of ponds to the initial plans and verified that the ponds are being built to original specifications. Since the ponds were designed to meet pre-Atlas 14 rainfall requirements, that means the site will still hold 30-40% less runoff than needed to meet current regulations.

Still, surrounding residents in Porter, North Kingwood Forest and Elm Grove who flooded twice last year will find three large ponds on the northern section a welcome addition. They provide some measure of extra protection. Residents will have four times more upstream detention volume than they had during Imelda.

Racing Against Risk

With the peak of hurricane season now less than two months away, Perry Homes is in a race against risk. The company may regret the six months of virtual inactivity between the completion of pond S2 and the start of work on ponds N1, N2, and N3 in early April.

The faster pace of current construction puts pressure on Harris County and the City of Houston to complete an offer if an offer will be made. Elm Grove residents lobbied the City and County to purchase the property and build a regional flood detention facility. They center would also help protect downstream residents on the East Fork and Lake Houston.

However, at a Kingwood Town Hall Meeting in February, Mayor Pro Tem Dave Martin announced that the City would not participate in a deal. He said it was the County’s responsibility.

In April, the County announced that it would consider purchasing the land if the City contributed land in lieu of cash to cover half the purchase price.

Then in May, the County increased its demands. The County now wants the City to contribute land in lieu of cash to cover half the purchase AND construction costs for creating additional detention.

County and City Clamp Down on Communications

Since then, the County has clamped down on communications regarding this subject. Rumors suggest that all parties are still trying to make a deal happen. But the County has denied all FOIA requests and referred them to the Texas Attorney General for a ruling on their denials. That often happens when negotiations are in progress, according to a knowledgeable source.

What Happens Next?

At the contractor’s current rate of progress, it’s entirely possible that contractors will complete all work on detention ponds in July.

The City and County blew through a May 15 deadline that Perry put on the deal. But a “For Sale” sign at the Woodland Hills entrance remains on the property.

With approximately $14 million dollars invested in the property, with hurricane season here, with lawsuits pending, and knowing that the amount of detention is insufficient to hold a 100-year rain, Kathy Perry must be sweating bombshells.

Ms. Perry may be hoping for a City/County offer, but she can’t be counting on one. If she were, she could have sold the dirt coming out of those detention ponds. Instead, however, she’s building up land elsewhere on the site to keep her options open and develop the site if a deal falls through.

That dirt will have to be moved again at taxpayer expense if the county builds additional detention ponds.

Pictures of Site as of 6/19/2020

Here’s what the site looked like as of 6/19/2020.

Looking NW from over Taylor Gully toward Pond N2, the largest on the property.
The connecting channel between N1 at the top of the frame and N2 along the western edge of the property has been excavated. Note the pilot channel that contractors have started in the distance.
At Mace Street in Porter, contractors created a concrete face for the twin culverts on the upstream side, but not yet on the downstream side. Note the earthen dam holding water back while contractors complete the pilot channel running off the bottom of the frame.
Above Mace Street, contractors are still putting in pipes between the channel and backslope swales.
The Webb street entrance to the site has been removed to connect N1 (out of frame on the top) with N2 (out of frame on the lower left).
Looking SE at N1.
Looking South at N3, which runs down the eastern edge of the property.
More pipes are being put in to channel water from backslope swales to the pond so water won’t erode the face of the pond. Not the rills already cut in the dirt.
Looking SE. The southern half of N3 where it connects with Taylor Gully in the upper right.
N3’s connection to Taylor Gully is now wide open. It’s not clear how this connection will be completed to release the water at a slow controlled rate.
The two culverts under the bridge over Taylor Gully should slow the water from N2 (upper right) and N1 (out of frame) down.

Need for Grass if Deal Not Reached Quickly

Note how the grass on the southern side of the gully has all died. That raises a question. If Perry, the City and County do not complete a purchase agreement soon, will Perry plant grass on the northern section to slow runoff. Right now, it’s all hard-packed dirt.

Most of northern section is hard packed dirt which increases runoff rate.

Planting grass over an area this large would be a big investment and might get in the way of construction if Perry decides to develop the land. But it will reduce flood and legal risks.

Posted by Bob Rehak on 6/20/2020

726 Days after Hurricane Harvey and 275 after Imelda

What Went Wrong, Part III: Perry Homes’ Woodridge Village Detention Pond Catastrophe

Note: This is the third in a five part series about What Went Wrong in Woodridge Village that may have contributed to flooding in Elm Grove and North Kingwood Forest. It focuses on Detention Ponds.

Section 7 of the Montgomery County Drainage Criteria Manual cautions, “The introduction of impervious cover and improved runoff conveyance serves in many cases to increase flood peaks quite dramatically over those for existing conditions.” And that’s exactly what happened in Elm Grove and North Kingwood Forest in May and September of this year. Two subdivisions that had never flooded before were inundated with several feet of water from Woodridge Village.

Perry Homes failed to observe numerous regulations in the Drainage Criteria Manual including provisions for:

  • Erosion control measures such as pond linings, revegetation, backslope swales
  • Maintenance roads
  • Increases in downstream flooding
  • Geotechnical reports for detention ponds
  • Drainage of detention ponds

Critically, they also failed to construct all the detention ponds they promised.

Less than a Quarter of Detention Ponds Built

When listing factors that contributed to the flooding, the absence of several promised detention ponds should rank near the top.

  • Before the May flood, only one of five detention ponds (S1) was substantially complete and it provided only 7% of the promised detention capacity.
  • Before the September flood, contractors substantially completed a second detention pond (S2) that added another 16% of promised detention capacity.
  • Since then, no work has been done on additional excavation to protect against flooding.
While clearcutting ALL of the land, Perry Homes installed only PART of the detention.

According to LJA Engineering, Perry Homes was supposed to develop the project in two phases and clearcut only 30 acres in the northern section during Phase 1. However, something changed. Instead, Perry Homes clearcut the entire northern section. And they still haven’t excavated any of the three detention ponds there.

By May 2019, only S1 was substantially complete. By September, S2 was also substantially complete, but overwhelmed.

Had Perry Homes installed all the detention that it promised, the site should have detained a foot of rainfall. But it didn’t. When Imelda came along, it was like trying to pour 100 gallons of water into a 23 gallon jug. Water spilled out of the development into adjacent streets and homes.

Erosion Control Measures Missing for Detention Ponds

Section 7.2.7 of the Montgomery County Drainage Criteria Manual details Erosion Control Measures for Detention Facilities. It states:

“The erosion potential for a detention basin is similar to that of an open channel. For this reason the same types of erosion protection are necessary, including the use of backslope swales and drainage systems (as outlined In SECTION 6), proper revegetation and pond surface lining where necessary. Proper protection must especially be provided at pipe outfalls into the facility, pond outlet structures and overflow spillways where excessive turbulence and velocities will cause erosion.” (See page page 123 of pdf, numbered 113 in doc.)

Not much grass in S1 (right of the road) or the area that drains into it. All aerial photos below taken on 11/4/2019.
Not much grass on the slopes of S2 either, although Perry Homes did make an ineffective attempt to hydromulch the south (right) border.
No Protection for Overflow Spillway
Perry Homes quality! This spillway from Taylor Gully (right) was supposed to have a grass lining, but still does not. Picture taken 11/4/2019. As of 11/21/19 work still had not started on the lining. Perry Homes has done virtually no work on this pond for three months. However, they did start lining the channel on the right today.
Backslope Interceptor Swales?
The northern edge of the S2 pond has no backslope interceptor swale. As a consequence, water from Taylor Gully at the top of this frame flows over the edge of the pond and erodes it. This may not be a sustainable solution. In the long run, the Gully could erode its way into the pond from the north (top of the frame).

Maintenance Road Missing at Critical Point

Section 7.2.8 talks about Maintenance of Detention Facilities. It states, “A 30-foot wide access and maintenance easement shall be provided around the entire detention pond.” The most critical place in the entire chain of detention ponds, the final outflow culvert into Taylor Gully, has no room for a maintenance road. That’s because when they installed the required backslope interceptor swale, the only place left for it was the maintenance road. That’s planning for you!

S2 has no maintenance easement or road at final outfall into Taylor Gully. The backslope interceptor swale takes up that space.

No Increase in Downstream Flood Levels Allowed

Section 7.3 talks about DETENTION DESIGN PROCEDURES. It clearly lays out the design goal when it says…

No increase in downstream flow rates or flood levels will be allowed.

Further down in this section, the regulations state: “The maximum 100-year water surface elevation in all detention facilities shall be a minimum of 1 foot below the minimum top of bank elevation of the basin.”

Judging from this video shot by Edy and Ricki Cogdill during the May 7th storm, I would say Perry Homes didn’t meet that objective. It reminds me of that slime show on Nickelodeon, but in this case, the innocent bystanders got slimed.

No Geotechnical Report for Groundwater Level at Pond Sites

Section 7.5 discusses GEOTECHNICAL INVESTIGATIONS. It says, “Before initiating final design of a detention pond, a detailed soils investigation by a geotechnical engineer should be undertaken.” Regulations state that the ground water investigation must be “at the proposed site.” Montgomery County has no record of such an investigation or report.

A company called Terracon prepared a Preliminary Geotechnical Report for Perry that addressed issues pertaining to utilities, road pavement and residential foundations. But it makes no mention of detention ponds.

The company took four widely spaced borings around the perimeter of the site that managed to miss all the detention pond locations. Significantly, they missed all the wetlands, too.

Page 17 of Terracon Report. Red lines added to improve visibility of locations.

MoCo Claims It Has No Further Geotechnical Reports

If Perry Homes did additional investigations into ground water on this site, Montgomery County says it doesn’t have them.

If no further investigations were conducted, this could be a fatal flaw affecting the economics of the entire development. Note the presence of standing water in the photo below.

S2 Pond (left), Taylor Gully (center), and area where N3 pond will go (right) all have standing water that will reduce their rated capacity.

The presence of standing water reduces the rated capacity of detention ponds and channels. Only the area above the standing water counts as capacity. Regulations say that these ponds should drain completely (see below).

Thus, S2 likely has lost a third of its designed capacity. N3, when eventually built, could fare worse. Note how close the water is to the surface in the small pond on the right.

If you can’t go deep to get your detention pond capacity, you have to go wide. And that will mean fewer homesites than the 896 they planned. This site might not even make economic sense for building homes.

Problems with Homes Built Over Wetlands

The presence of wetlands in the northern section, which the Terracon report never mentions, would also significantly reduce the site’s suitability for building homes.

This article describes the problems with homes built on wetlands. The title: “Caution: Building in a Wetland Can Be Hazardous to Your House.” A biologist for the US Fish and Wildlife service who investigated filled wetlands in Pennsylvania warned: “Build your house in a wetland, and you’ve got a hobby for the rest of your life. You will be fighting that water forever.” He discusses cracked foundations and also warns, “When wetlands are filled, the water that made them wet has to go somewhere. … the water likely is leaking into formerly dry homes of downstream property owners.”

I’m sure Perry Homes would divulge the presence of former wetlands to the future buyers of homes on this site. It’s the only ethical thing to do and Kathy Perry Britton, CEO, has standards to maintain.

Incomplete Drainage of Detention Ponds

Section 7.6 of the Drainage Criteria Manual addresses GENERAL REQUIREMENTS FOR DETENTION POND CONSTRUCTION. It states:
“A pilot channel shall be provided in detention facilities to insure that proper and complete drainage of the storage facility will occur.” (Emphasis added.)

Complete drainage will likely never occur in S2 and N3 because of the high water table.

To excavate S2 to the required design depth, contractors had to continuously pump water out of it as they worked. It still retains water to this day.

Photo by Jeff Miller on June 2, three days after contractors started digging to the final depth. No surface linings were ever added to this portion of the pond per Section 7.2.7 of the MoCo Drainage Criteria Manual.
Photo taken on June 3 shows contractors were pumping water out of pond as they continued excavating.

If Perry Homes continues its Woodridge Village venture using its current plans, chances are, the company will never provide enough detention capacity for real world conditions. When modeling, their engineers did NOT use the current Atlas-14 rainfall statistics from NOAA.

The new statistics would require 40% more capacity to ensure downstream safety.

Where Does Perry Homes Go from here?

After ignoring regulations, hundreds of homes flooded. And they will flood again. Owning this site is like hanging a millstone around one’s neck. It could drown the entire company in perpetual litigation and debt.

Future Posts in this series will look at:

  • Contradictions in Perry Homes’ Plans
  • The Dirt on Perry Homes’ Soil Test
  • The Floodplain that Wasn’t

Posted by Bob Rehak on 11/21/2019 with help from Jeff Miller

814 Days since Hurricane Harvey and 63 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.

Woodridge Village Detention Calculations Off by More Than 40% According to New Standard

Developers in Montgomery County try to avoid building detention ponds by beating the peak. They also have attempted to minimize the amount of detention ponds they must build by beating the clock.

Woodridge Plans Approved One Month Before NOAA Updates Flood Data

A year to the day after the peak of Hurricane Harvey on August 28, LJA Engineering submitted a hydrology report to Montgomery County. A table buried on page 32 of the PDF shows that they based their analysis on a 100-year storm that dropped 12.17 inches of rain in 24 hours.

From Page 2.1 of LJA Hydrology Report Addendum, 8/28/2018 (page 32 of pdf.)

Two weeks earlier, USGS had issued its report on peak streamflows and high water marks for Hurricane Harvey.

At this point, the world knew that flood maps would soon change radically. But the LJA report contains no mention of Harvey, USGS, or NOAA’s new Atlas 14 data. And in fact…

Less than one month after the LJA Engineering hydrology report, on September 27, NOAA issued new rainfall frequency values for Texas. Called Atlas 14, the NOAA analysis established significantly higher rainfall frequency values for this part of Texas.

New updated NOAA Atlas 14 data shows that a hundred-year rain for the Lake Houston area is now defined as 17.3 inches in 24 hours, up from 12.17 inches by the old standards.

NOAA redefined the amount of rainfall it takes to qualify as a 100-year or 1000-year event. They defined the new 100-year rain as 17.3 inches in 24-hours – a 42% increase. That means that to meet new 100-year standards, Perry would have had to increase its detention capacity by 42%. Instead of 271 acre feet, it would have needed 385.

Using Atlas 14 would have reduced the number of salable lots and the economic projections for the development to a substantial degree.

The one flood map in the 59-page LJA Engineering hydrology report shows flood plains magically stopping at the county line.

The one flood map that the LJA hydrology report does include (page 51 of PDF and above) shows flood zones stopping at the county line (the black diagonal) and the boundary of the Perry property (the maroon-bordered polygons). Pretty odd for a site partially covered by wetlands!

National Wetlands Inventory Map shows both sections of Woodridge Village contain wetlands.

Woodridge Plans Approved Even Before LJA Submitted Hydrology Report

Now here’s where it gets even more interesting. City of Houston approved the detention plans on 8/12/18 – two weeks BEFORE the LJA hydrology report on 8/28/18 and only a month BEFORE NOAA released the new Atlas 14 data. Hmmmm! Think they were in a hurry to get these approved? (Note: The approval date for MoCo is unreadable).

Signature block for City of Houston from Woodridge Village detention plans.

Perry Homes played a game of beat the clock and was winning … until May 7, 2019.

Future Flood Risk Remains Even with Planned Detention Ponds

Until now, I have been posting about the lack of detention ponds. Closer analysis reveals that this is only part of the problem. Even if Perry builds the remainder of the detention ponds as planned, they will be insufficient to meet the new NOAA standards and will pose a flood risk to people downstream.

After contributing to two floods in Elm Grove and North Kingwood Forest, the engineers and owners of Woodridge Village surely must realize how dangerous trying to Beat the Clock was.

Forty-two percent of a 100-year flood as defined by the new Atlas-14 data will overflow the banks of the detention ponds and add to the load on Taylor Gully or go into the streets of Elm Grove and North Kingwood Forest.

Facing west. This panoramic drone image by Chris Betz takes in most of the Woodridge Village constructions site. Note the ponding water 3.5 days after a two-inch rain.

This image taken Friday night at Sunset shows how impervious the Woodridge soil is. Water is still ponding three and a half days after a two-inch rain (October 28, 2019).

I wonder if the LJA engineers calculated the runoff coefficient accurately. Given some of the other problems in this report, perhaps an engineer would care to comment on their calculations.

Posted by Bob Rehak on 11/2/2019

795 Days after Hurricane Harvey and 45 after Imelda

The thoughts expressed 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.

One Week After Town Hall, Still No New Work on Woodridge Village Detention Ponds

A week after J. Carey Gray, a lawyer representing Perry Homes’ subsidiaries and contractors, promised the Mayor of Houston that his clients would move as quickly as possible to complete Woodridge detention ponds, there still has been no excavation activity at the job site. And in fact, according to Jeff Miller, an Elm Grove resident who visited the site today, much of the material and equipment that had been on site are now gone.

Lack of Detention Implicated in Two Floods

Twice in four months, Elm Grove and North Kingwood Forest flooded severely when water from Perry Homes’ troubled Woodridge Village development overflowed into the streets of those communities immediately south and east of Woodridge. 

  • Before the May flood, Perry had clearcut virtually the entire 268 acres, but installed only 7% of the detention. 
  • Before the September flood, they had substantially completed only one more pond, bringing the total to 23% of the planned detention. 
Percentage capacity of the five planned detention ponds on the Woodridge Village construction site as measured in acre feet. To date, only S1 and S2 are substantially complete.

So it’s not too surprising that the completed detention ponds overflowed in heavy rains. 

It was like trying to store 100 gallons of water in a 23 gallon container.

Excavation Work on Detention Ponds Stopped for Two Months

Where’s Larry the Cable Guy when you need him? He could “git-r-done.” 

As the pictures below show, there’s one piece of excavation equipment on the northern portion of the site and it hasn’t moved for about a month.

Looking west at northwestern section of Woodridge Village from helicopter more than a month ago, on 9/21/2019, two days after Imelda. Note the yellow excavator with its bucket resting on the ground in the middle of the frame toward the tree line on the right.
Note the same excavator in the same place in the same position at the left of the frame. Photo taken 10/16/2019 from opposite direction, looking east.The foreground is where detention pond N1 should be. But the pond has not yet been started. According to the LJA Engineering report, it should have been excavated as part of the first phase of development.

Eight days later, you can see the same equipment still in the same place. However, it appears that two other pieces are now parked with it.

Photo taken by Jeff Miller on 10/22/2019 shows excavator in same photo it was photographed in on 9/21/2019a month earlier.

Only Modest Repair Work on Ponds Since August

Resident Jeff Miller reported that an excavator removed some eroded sediment out of one completed pond (S1) after Imelda. Below is the photo he took on 10/6/2019. However, this was repair work, not new excavation work.

Photo of S1 Repair Work taken on 10/6/2019 by Jeff Miller. S1 was the first pond completed.

Four Detention Ponds Promised as Part of Phase 1

According to the LJA Engineering Drainage Impact Analysis, Table 3, Phase 1 of this development was to have FOUR detention ponds installed: N-1 and N-2 (regraded pilot channel) on the north, S-1 and S-2 on the South. 

However, no new detention capacity exists on the northern section which has the steepest slope and the largest surface area. It was to provide 77% of the total detention.

N-1 and N-2 should provide 62% of the detention capacity. However, N-1 doesn’t exist. N-2 is not fully excavated. And N-3, which will provide another 15% is only a distant dream.

Hundreds of Families Remain at Risk

The lack of progress on detention places hundreds of families at risk as we slog our way through another 5 weeks of hurricane season. The season ends on November 30. But flood-weary residents also remain wary of non-tropical storms, such as Tax Day, Memorial Day, and May 7th this year. In the moist, Gulf-coast region, heavy storms can strike any time of year.

J. Carey Gray’s Promise

Last week, J. Carey Gray, Attorney at Law, made a promise to the City of Houston’s top lawyer, Mayor Sylvester Turner. Gray said, “To the extent possible, we will attempt to begin each project as quickly as plans can be completed and approved.”

Now, there’s an iron-clad contract if I ever saw one! However, as of October 22, 2019, no residents that I consulted around the site had seen any workers recently. Mr. J. Carey Gray, Attorney at Law, dated his letter October 17th.

According to resident Nancy Vera who lives immediately south of the construction site, there has been no recent construction activity anywhere on the site that she or her family can see.

Gretchen Smith who can see the site from her front yard in Porter has seen no workers.

Jeff Miller visits the site almost daily to check progress or non-progress of work. He had not seen any workers lately either. Moreover, he said that much of the materials and heavy equipment that had been stored on site appear to be gone.

Maybe Mr. Gray needs to consult with Larry, the Cable Guy.

Posted by Bob Rehak on 10/23/2019, with help from Jeff Miller, Nancy Vera, and Gretchen Dunlap-Smith

785 Days since Hurricane Harvey and 34 since Imelda

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.

Elm Grove Has 2-3X More Damage Than After May 7th, Much of It Foreseeable and Preventable

Many homes flooded in Elm Grove this week that did not flood on May 7th, or ever before. Estimates from the homeowner’s association range from 2 to 3 times the number that flooded on May 7th. The shocking part: most of the flooding was preventable.

History of Problems with Woodridge Village

On May 7th, floodwater from a new development in Montgomery County contributed to the flooding of almost 200 homes in Elm Grove Village.

On May 8th, Montgomery County Commissioners should have known they had a problem with the development (Woodridge Village). What did they do? They let the developer’s engineering company (LJA Engineering) investigate itself.

The basic problem: Perry Homes, its subsidiaries and contractors had clearcut approximately 268 acres. They filled in natural streams and wetlands without installing needed detention ponds. Runoff from the development then went straight into Elm Grove.

In the weeks that followed, hundreds of Elm Grove residents filed lawsuits against the developer and contractors. In the months that followed:

The Perry gang, managed to complete less than 25% of the needed detention pond capacity, despite ideal construction weather, and then they apparently stopped work altogether.

They finished only two ponds on the southern section and ignored three on the northern. Work came to a virtual standstill almost three weeks ago.

For a breakdown on detention pond capacity and how much had been built before Imelda, click here.

Drone Footage Shows Huge Clearcut Area Where Three Detention Ponds Should Have Been

As work came to a standstill, residents became concerned. Last Sunday, Matt Swint flew his drone over the development to document the status of work on detention ponds. Just four days later, Imelda struck.

Swint captured all three of the images immediately below on 9/15/2019. They show that no progress was made on ANY of the detention ponds planned for the northern section.

Woodridge N1 Detention Pond should have gone here.
Woodridge N2 Detention Pond should have gone here. It was supposed to be the largest pond on the site, but the only work done on it was between 2006 and 2008 by Montgomery County.
N3 Pond should have gone here.

No Work Ever Done on Northern Detention Ponds Despite Area Having Been Clearcut for Months

They could have hired extra crews to build those northern detention ponds. But no. Why be aggressive when you’re months behind schedule and have ideal construction weather?

Their lawyers were, however, working overtime, blocking discovery in the court case against the developer and contractors.

A judge failed to recognize the dire threat that Elm Grove residents still lived under. She may have unwittingly contributed to this mess. With no sense of urgency, she tolerated deliberate delays and set a trial date a year away.

Meanwhile, at an August 27th meeting, MoCo commissioners considered a motion to close a loophole that allowed developers to get away without installing detention ponds. Commissioners chose to table the motion. They insisted that Montgomery County didn’t have a flooding problem. They worried that closing the loophole could change the economics of work in progress and harm developers.

Then came Imelda. The storm dumped almost 12 inches of rain on a development that was designed to retain exactly 12 inches of rain (see page ES-1). But because less than a quarter of the planned detention pond capacity was functional, the plans failed.

The Harris County Flood Warning System shows that the USGS gage at US59 recorded 11.56 inches of rain on 9/19/19, most of it during the late morning.

Second Verse, Worse than the First

On September 19, Elm Grove flooded again. Worse than on May 7th. Much worse. Beth Guide of the Elm Grove Homeowners Association and numerous homeowners estimate that the water was at least a foot to eighteen inches deeper. The additional water involved twice as many streets, and affected as many as two to three times more homeowners. Now they, too, get to join the lawsuit and battle institutional indifference. (Note: many streets are so congested that it is virtually impossible to get an exact count at this time. That number could change.)

Scenes from Elm Grove, One Day after Second Flood in Four Months

Today, I:

  • Witnessed men and women weeping openly as they hauled belongings to the curb for the second time in four months.
  • Watched kids discarding Christmas and birthday presents in trash piles that sometimes reached rafters.
  • Talked with a family that had just finished installing replacement cabinets from the May 7th flood.
  • Saw desperation in the eyes of young couples who feared bankruptcy.
  • Met the grown children of elderly people there to help salvage what they could for parents.

Defendants’ Responses to Plaintiffs’ Questions

As this tsunami of heartbreak unfolded in front of me, I could not get the defendants’ responses to the plaintiffs’ simple requests out of my mind.

For instance:

  • Request: Identify the entity or individual in charge on May 7, 2019.
  • Response: “Defendant objects to this Request for Production on the grounds it is vague, ambiguous, unclear and overly broad with respect to the requesting party’s use of the phrase ‘in charge…'”

Or how about this one:

  • Request: Identify the person in charge of permit compliance.
  • Response: “Defendant objects to this Request for Production on the grounds that such Request is vague, overly broad, and fails to specify and/or describe with reasonable particularity – as is required by Rule 196.1(b) of the Texas Rules of Civil Procedure — the documents and/or things to be produced. Defendant further objects to this Request for Production on the grounds that such Request is argumentative and assumes the truth of matters which are not in evidence, and which may be in dispute, to the extent that such Request suggests and/or assumes that one specific individual was “… in charge of compliance …” by this Defendant as to the terms and conditions of TPDES General Permit TXR150000.”

Whew! That lawyer must be getting paid by the word. I know some people that could have communicated the same meaning with a finger gesture.

The defendants produced 61 pages of such responses. If you ever need to boil your blood, read it. They use the word “vague” 27 times in response to clear and pointed questions,.

Hearing on Monday

The judge in this case will hear a motion to compel responses on Monday, September 23rd in the 234th Judicial District Court of Harris County. I hope she puts a stop to this nonsense. It’s time somebody did…with the rain train spread out across the Atlantic during the worst part of hurricane season.

What 23% Retention Contributed To

This video shows what the people of Elm Grove faced during Imelda from Woodridge Village and what they will continue to face. With only 23% of the detention capacity in place, it overflowed when the design limits were tested. See video below.

On September 19, 2019, Woodridge Village detention pond S2 overflowed directly into Village Springs in Elm Grove. This matches the video shot by Edy Cogdill from the same location on May 7. Video shot by Allyssa Harris, a resident on Village Springs.

It’s kind of like expecting a car with one tire to work as well as a car with four.

At 10:10:09 a.m. on 9/19/19, Jeff Miller’s security camera captured a cloud of silty water invading clear rain water that had been filling Forest Springs Drive (four blocks west of Taylor Gully) all morning. Miller believes that Woodridge Village’s S2 detention pond overflowed minutes earlier. See photo below.

One Day After the Latest Storm

Silt fence pushed toward Taylor Gully adjacent to Woodridge S2 detention pond. This indicates two things: There was not enough detention capacity; it overflowed. And water from the development did not follow the route it should have, i.e., through the outflow control device to the left. Photo by Jeff Miller.
Bent silt fencing above Village Springs Drive failed to stop the flow of sediment toward Elm Grove.
Abel and Nancy Vera burned out two power washers trying to get Woodridge muck off their driveway after Imelda.
Abel Vera had to grab his car to avoid slipping in slippery, ankle-deep sediment on Village Springs. Rainwater alone would not have deposited so much muck.
Nancy Vera says that her home had more than a foot of water in it before Taylor Gully overflowed. The water contained thick sediment from Woodridge just north of her house. It made a dangerous, syrupy mess.
Flood debris lodged in the wheel well of Allyssa Harris’ vehicle which took on water up to the door handles despite being parked in her drive on higher ground.
Bill King, candidate for Mayor of Houston, spent the day after Imelda investigating the causes of Elm Grove flooding. Woodridge is in the background.
King also visited with homeowners who lost everything for the second time in four months.
Another Elm Grove debris pile from Imelda flood. There are hundreds of similar piles.
The joys and fun of children were dragged to the curb, too.
New furniture. Old Story. Another Imelda debris pile in Elm Grove.
For block after block, people were tossing flooded items.
A masking-tape sign on a discarded headboard on Shady Maple in Elm Grove provided the only ray of hope.

Posted by Bob Rehak on 9/20/2019, with images from Matt Swint, Allyssa Harris, Jeff Miller

752 Days after Harvey and One Day after Imelda

All thoughts expressed in this post are my opinions on matters of public opinion and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP statute of the Great State of Texas.

Study Suggests Large Cities Like Houston Can Intensify Rainfall and Runoff From Hurricanes

A November 2018 article appearing in the peer-reviewed scientific journal Nature found that urban growth can intensify both rainfall and runoff from hurricanes. Further, urban growth can increase the risk of flooding and shift the location of flooding. The article specifically studied the effects of Hurricane Harvey on Houston and found that urban growth increased the probability of such an extreme flood across the basin by 21X.

A sister publication, Scientific American, reviewed the article the same month and helped explain the findings in Nature.

The Nature study looks at two distinct effects of urbanization. The first is the impact of impervious surface on RUNOFF. The second is the impact of the urban landscape’s surface roughness on RAINFALL.

The Runoff Component

Numerous studies have looked at the relationship between percentage of impervious cover, runoff, and flooding – a well documented phenomenon. Impervious cover accelerates transport of rainfall from neighborhoods to rivers. That raises peak flows rather than spreading them out over time. Dr. William Dupre, professor emeritus from the University of Houston visualized the relationship this way.

Effect of Urbanization on Peak Stream Flows” by Dr. William Dupre, professor emeritus from the University of Houston.

Rainfall Component Much Less Studied

However, the effect of urban growth and a city’s surface topography on RAINFALL from hurricanes is much less studied. The authors say in Nature that, “Urbanization led to an amplification of the total rainfall along with a shift in the location of the maximum rainfall.” (Page 386).

“Much less is known regarding the urban effects on the organized tropical rainfall of a hurricane, in particular during one like hurricane Harvey, which stalled for several days.” They continue, “…experiments (with computer models) clearly show a large increase in rainfall arising from urbanization over the eastern part of the Houston area.”

The authors compared present and past urban landscapes and also modeled a scenario in which the entire region was cropland.

Mechanisms Responsible for Increase Rainfall

To understand the physical mechanisms responsible for the heavier rainfall, they analyzed the vertical convergence of winds and wind fields.

Kingwood Greens Evacuation During Harvey by Jay Muscat
Evacuation During Harvey. Photo courtesy of Jay Muscat.

“The enhanced rainfall … and the shift of rainfall … are tied to the storm system’s drag induced by large surface roughness,” say the authors.

Scientific American explains in more detail. Kerry Emanuel, an atmospheric scientist at Massachusetts Institute of Technology, who did not work on the study said, “We know cyclones are sensitive to characteristics of the surface—mountains, streams, marshland. This new twist is that cities have become big enough to tangibly alter the storm.” Said Gabriele Villarini, an environmental engineer at The University of Iowa and an author on the study, “We removed the urban areas from Houston and replaced them with cropland.”

“The presence of urban areas enhanced all the things you need to get heavy precipitation,” Villarini, one of the study’s authors says. “A stronger drag on the storm winds, associated with a larger surface roughness length” contributed to the increased rainfall.

Emanuel explained, “First, the artificial ruggedness of an urban area slows air down. Whenever air slows in a hurricane, he says, it gets shunted toward the center of the storm and up into the sky. That increases rainfall everywhere [in a metropolitan area].” He added, “A storm moves particularly slowly over downtown areas where buildings are tallest, but the winds bearing down from outside the city are still moving quickly. So, [the storm] is piling up on the city.”

Impact on and Implications for Houston

This increase in urban growth in flat terrain creates problems from a flood perspective, despite mitigation measures already in place.

Urbanization has increased the probability of an event like the flooding associated with Hurricane Harvey by about 21 times, say the authors in Nature on page 388.

The authors make several high-level recommendations.

  • Urban planning must take into account the compounded nature of the risk now recognized.
  • Flood mitigation strategies must recognize the effect of urbanization on hurricanes.
  • Weather and climate models must incorporate the effects of urbanization to increase forecast accuracy on local and regional levels.

“It is critical for the next generations of global climate models to be able to resolve the urban areas and their associated processes,” conclude the authors.

About the Authors and Models

The authors are:

  • Wei Zhang and Gabriele Villarini from the Department of Hydroscience & Engineering, The University of Iowa, Iowa City, IA
  • Gabriel A. Vecchi from the Department of Geosciences, Princeton University and the Princeton Environmental Institute, of Princeton, NJ
  • James A. Smith from the Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ.

This presentation explains the Noah Model that the authors used to calculate air/ground interactions.

Local Questions Raised by Study

To date, the role of a city in altering rainfall during tropical cyclones has received very little attention. Houston has had the largest urban growth and the fifth-largest population growth in the United States in the period from 2001–2011. Much of that growth is now on the periphery of the city. The two fastest growing parts of the region are Fort Bend and Montgomery Counties.

As the city grows, we need mitigation measures that can offset the impact of that growth. That’s why the meeting of the Montgomery County Commissions on August 27th is so important. They will vote on whether to close a loophole that allows developers to avoid building onsite detention ponds. Closing that loophole is important. It will help protect hundreds of thousands of downstream residents as well as those in Montgomery County.

Also, the new NOAA Atlas-14 (rainfall measurements updated after Harvey) does not consider forward-looking urban growth effects. The precipitation frequency data in NOAA Atlas 14 was determined by a statistical analysis of historical rainfall, a key input for FEMA Flood Insurance Rate Map (FIRM) modeling. With all that uncertainty, we need to err on the side of caution in flood planning.

For more about Atlas 14, see this link.

Posted by Bob Rehak on 8/18/2019

618 Days after Hurricane Harvey

MoCo Will Consider Requiring More Detention for New Developments in August 27 Meeting

Montgomery County commissioners will consider changing flood mitigation requirements for new developments at their regular August 27 meeting. Commissioners will hear public testimony and consider approving a revision to the Montgomery County Drainage Criteria Manual. The change would close a loophole that allows developers to substitute “flood routing studies” for detention ponds in new Montgomery County developments. 

How Developers Use Flood Routing Studies

Flood routing studies calculate when runoff from a new development will hit a river during a major rain event. If results show that the runoff will reach the river before the crest of a flood, developers may not need to build detention ponds. The idea: it’s not adding to the peak, so why run up costs needlessly?

Why Flood Routing Studies are Inadequate

In principle, that sounds good. However, routing studies almost always contain flawed assumptions according to Jeff Johnson, Montgomery County’s Engineer.

First, they don’t consider the cumulative effects of other developments. Second, they are almost always based on outdated hydrologic models. And third, they assume “ideal” storm conditions.

“If you start with a brand new hydrologic model,” says Johnson, “the modeling a developer does could theoretically be accurate.” But his/her runoff changes the model. That runoff rarely gets incorporated into the model that the next developer uses. “So the next developer is dealing with outdated assumptions,” says Johnson. Same way with the third and fourth developers, etc. They all keep going back to the original model, even though they know it has been changed by previous developments. Said another way, additional runoff is not added to the model on which subsequent developers base their calculations. So they all show no consequences when the cumulative effects can be large.

Another problem. They all base calculations on ideal assumptions. Johnson estimated that only a small percentage of storms conformed with ideal conditions. For one example, calculations are valid only if rain stops before the flood reaches its peak.

Shortage of Detention Leads to Downstream Flooding

As a result, there’s not enough detention upstream to protect downstream residents during a major storm.

Many developers like the flawed assumptions behind the routing studies. They justify building less detention, which costs developers time and money. And with less detention, they can develop and sell more lots per acre. So they reduce costs and increase income.

But when that happens, somebody downstream pays the price. “They’re not being responsible,” said Johnson. “This is a public safety issue.”

One flood expert that I interviewed for this article said, “Only good things come from more detention.”

City of Houston Public Works Director Agrees

As if to punctuate Johnson’s point, shortly after my interview with him, I attended a talk by City of Houston Publics Work Director Carol Haddock. Haddock emphasized that flooding today largely stems from problems inherited from legacy infrastructure. “We’re living with infrastructure developed before we knew what we now know about flooding,” said Haddock.

Haddock argued for both higher drainage and detention capacity. They will help accommodate future floods and future development – while protecting people and property downstream, she argued.

Projected MoCo Growth Underscores Need to Close Development Loophole

Getting drainage and detention right is crucial, not just for families downstream in northern Harris County, but also for families in Montgomery County itself. The New Caney ISD (NCISD) is projected to grow substantially in the next few years. The NCISD just completed a demographic update from Population and Survey Analysts (PASA). (Caution: 58 meg download.) Page 6 of the study shows that the District expects to grow by more than 19,000 housing units in the next 10 years. That’s almost as large as Kingwood. And it doesn’t even include commercial space.

A graphic from a Caldwell Brokerage brochure shows some of the major current and planned developments in the area between the Woodlands and Kingwood with the number of homes.

In the previous 5 years, the NCISD had the second highest percent change in school district enrollment in the region at a whopping 30.3%. Only Alvin had a higher increase at 31.6%.

PASA graphic comparing 5-year growth rates in area school district enrollments.

PASA predicts the new commercial area near 45 and 99 will have as much square footage as downtown Austin. And, further upstream, Conroe was the fastest growing City in America in 2017.

Fortunately, the new San Jacinto River Basin Survey will update hydrologic models. But with projected growth like this, they will become outdated as soon as they are complete. All the more reason to move away from the flood routing paradigm of development and require more on-site detention. ASAP.

Register Your Opinion

Expect developers to testify against closing the “flood routing study” loophole. You can testify for closing it, however. Montgomery County Commissioners will hear public testimony at their regular meeting on August 27th. The meeting starts at 9:30. Montgomery County has special sign-up procedures for citizens who wish to testify; make sure you sign up beforehand. Check the agenda beforehand to plan your time. You can also register your opinion with county commissioners via phone or email.

Posted by Bob Rehak on 7/31/2019

701 Days since Hurricane Harvey