Tag Archive for: Drainage Criteria Manual

MoCo Development on Ben’s Branch Understates Current Detention Pond Requirement by 30%

Camcorp Management is building a new high-density development in Montgomery County called Brooklyn Trails on a tributary of Ben’s Branch upstream from Kingwood. The development’s detention pond is apparently 30% smaller than new Atlas-14 regulations would require for this area.

Brooklyn Trails
Most of Brooklyn Trails is still vacant...
…but time is running out to do something. High density homes are going up quickly.

The developer’s engineering company (A&S Enginners, Inc. at 10377 Stella Link in Houston) submitted its drainage analysis for approval on December 15, 2018, just days before new MoCo regulations went into effect on January 1, 2019. They would have required more detention capacity. And that would have meant fewer salable lots.

Even though plans were discussed, reviewed and revised after Atlas 14 went into effect, in Montgomery County the submission date determines which rainfall statistics apply.

Ben’s Branch cuts diagonally through Kingwood. It goes through three commercial areas: Northpark, Town Center and Kings Harbor. Bear Branch Elementary, Kingwood High School and the Humble ISD instructional center all border Ben’s Branch, not to mention hundreds of homes and St. Martha Catholic Church.

Atlas 14 Never Apparently Discussed

I filed a Freedom of Information Act request for the drainage analysis and correspondence relating thereto. The documents show that the subject of Atlas-14 apparently never arose as Montgomery County reviewed the plans.

Rainfall rates that A&S used to design drainage for Brooklyn Trails vary substantially from MoCo’s new rate and Atlas-14 rates for the Lake Houston Area.

Montgomery County bases its 100-year/24-hour rainfall rate on Conroe (the County seat). Despite variations within the county from north to south, adopting the Conroe rate makes it easier for developers to calculate detention requirements. Some parts of the county have no gages. However, the uniform rate also understates the detention needed for new developments in the fast growing southern part of the county, which receives more rain.

Differences Between Three Rates

The three different rates referenced above for the 24-hour 100-year rain break down as follows:

That means Brooklyn Trails is 25% short of MoCo’s new requirements and 30% short of NOAA’s.

NOAA Atlas 14 Rainfall Totals for the Lake Houston Area. Brooklyn Trails is 3 miles from Lake Houston but 20 miles from Conroe.

In fact, the rate A&S used (12.17 inches) corresponds to a 10- to 25-year rain by NOAA’s new standards, not a 100-year rain.

A&S Engineers Certify No Adverse Impact

A&S concluded on page 10 of its analysis that “…the proposed excavation/fill will cause no increase to the base flood elevation, and the proposed excavation/fill will have no adverse impact to the drainage on, from, or through adjacent properties.”

That may be true if you base all your calculations on rainfall that’s 30% less than NOAA’s best available statistics. Or even the new MoCo numbers. But, in fact, we get more rain.

Why do engineers whose first responsibility is protect the safety of the public do stuff like this! Because MoCo allowed it. And because increasing the size of the detention pond would likely have reduced the number of salable lots.

This is the same game that LJA Engineering played when it calculated detention requirements for Woodridge Village. Then hundreds of homes in Elm Grove flooded twice with sheet flow from Woodridge Village. Harris County Flood Control and the City of Houston have been mired in negotiations with Perry Homes for most of this year trying to buy the land. They want to put a regional floodwater detention facility on it to prevent further floods.

Potential Adverse Impacts

In my opinion, this drainage scheme could harm people downstream, adjoining property owners, and even homeowners within Brooklyn Trails.

Time to Fix is Running Out

Everyone who lives or works near Ben’s Branch should be concerned.

Camcorp the developer plans to put 414 homes with average size of .12 acres on this property. Such high density development will accelerate runoff.

To make matters worse, it’s unclear whether all the detention ponds downstream in Woodridge Forest are functional.

Both Montgomery County and City of Houston signed off on the A&S plans. The City signed in January before the Elm Grove floods. Montgomery County signed after the Elm Grove floods – on 10/1/19.

There’s time to fix this before the development is built out. But that window is rapidly closing.

Posted by Bob Rehak on 10/12/2020

1140 Days since Hurricane Harvey and 389 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.

Plaintiffs’ Engineer Alleges LJA Issued Misleading Studies, Followed Wrong Guidelines in Elm Grove Flooding Case

Fourteen documents filed with the Harris County District Clerk’s office on February 27, 2020, lay out the case of plaintiffs in the Elm Grove flooding case against LJA Engineering, Inc. Lawyers for the plaintiffs named LJA as an additional defendant in their most recent amended petition. Other defendants include Perry Homes’ subsidiaries and contractors: Figure Four Partners, LTD.; PSWA, Inc.; Rebel Contractors, Inc. (which recently changed its name); Double Oak Construction Inc.; and Texasite LLC.

Accusations Specific to LJA

The amended petition alleges LJA:

  • a. Failed to follow the correct drainage guidelines in Montgomery County;
  • b. Failed to provide adequate drainage in the Development;
  • c. Failed to adequately model the Development;
  • d. Failed to adequately report the modeling;
  • e. Removed drainage channels;
  • f. Caused post-development discharges and water surface elevation to increase downstream of the Development;
  • g. Failed to design detention ponds with adequate capabilities for rain events;
  • h. Failed to use the correct hydrology method;
  • i. Failed to design emergency overflows for the detention ponds;
  • j. Failed to notify the Developer Defendants and Contractor Defendants of the importance of the existing levee; and,
  • k. May be liable in other ways described in the consulting engineer’s report.

Consulting Engineer Says LJA Used Outdated Drainage Criteria Manual

The defendants’ consulting engineer, L. David Givler, MSCE, PE, provides the details that back up these claims. Givler is president of Givler Engineering, Inc. Givler’s firm is licensed in Texas to design drainage projects similar to Woodridge Village, which was designed by LJA. A “Certificate of Merit” filed with the court states Givler’s credentials and conclusions. Givler also provides thirteen more exhibits as part of his affidavit. (See links at bottom of post.)

Perhaps Givler’s most explosive finding: LJA based all of its conclusions on an outdated version of the Montgomery County Drainage Criteria Manual (DCM) developed in 1989. MoCo has since updated its DCM twice – in December 2014 and July 2019. Givler asserts that LJA should have used the 2014 version when it submitted its drainage analysis in 2018. The rainfall that MoCo requires engineering firms to design detention basins for have increased since 1989 (see below).

Givler asserts that the increases, along with other other errors and omissions outlined below critically skew modeling results. Ponds that might not overflow based on the 1989 rainfall depths do overflow with 2014 and 2019 rainfall statistics.

Critical Levee Removed, But LJA Did Not Model Effect of That

Givler says in his testimony that grading associated with the construction project removed a levee that had been constructed along the south side of Taylor Gully. “Prior to being removed, the levee had successfully protected the Elm Grove Village Subdivision from flooding,” said Givler. “However, removal of the levee increased the probability for Taylor Gully to overflow southward and to flood the Elm Grove Village Subdivision.”

Givler asserts that the levee successfully protected Elm Grove from flooding in previous extreme events such as Hurricane Harvey, which he characterized as a 330-year storm.

LJA Did Not Use MoCo’s Recommended Method For Modeling Runoff

Mr. Givler also found that LJA did not use Montgomery County’s recommended method for modeling runoff. LJA used something called the Clark’s Unit Hydrograph Method instead of the NRCS Hydrograph Method specified in the 2014 version of the County’s Drainage Criteria Manual. The latter shows significantly higher peak runoff rates, according to Givler. “LJA’s selection of an alternative method (The Clark Method) caused the underestimation of peak runoff rates,” said Givler. “LJA also used low, outdated rainfall depths in its model, which exacerbated the underestimating of the peak runoff rates.”

Givler modeled whether LJA’s designs for the Woodridge Detention Ponds would have successfully held the runoff from the updated drainage criteria manual.

He found that the design for the ponds was “inadequate.” They overflowed. Significantly, Givler also found that LJA underestimated the volume of runoff sent downstream to Taylor Gully.

After May, Protection Not Implemented Against September Storm

“Even after the May 2019 flood, adequate measures had not been implemented to restore the pre­-development level of protection or to prevent a recurrence,” said Givler. “Under Woodrige Village pre­-development conditions, the Elm Grove Village subdivision was safe from flooding during the 330-year Hurricane Harvey rainfall. However, under construction conditions at Woodrige Village, Elm Grove Village was vulnerable to flooding in the 19-year and 92-year rainfall events.”

LJA Did Not Model Effect of Overflow Channel

Givler also noted that LJA’s plan claimed that the 100-year peak stage for the S2 detention pond would be 73.21. That would be high enough to cause water to backup into the grass-lined channel (bottom elevation 68.50) located at the northeast corner of the pond. “Since the highest adjoining ground elevation south and east of the grass-lined channel is approximately 72,” said Givler, “the peak 100-year stage would discharge to Taylor Gully downstream of the project and to the neighborhood east of pond S-2 [North Kingwood Forest]. Such discharges would increase flooding to the residential lots to the east…”

Figure 4 from Page 12 of Givler’s affidavit shows 100-year runoff overflowing Pond S-2 through the Grass-Lined Channel.
The grass-lined overflow spillway in the center of this photo is designed to funnel water from Taylor Gulley into the kite-shaped detention pond (S2) if the concrete channel overflows. But Givler says LJA did not model the opposite. In May and September 2019, water flowed from the gulley into the homes at the bottom left of the frame, as well as homes opposite them on the far side of the gully.

Emergency Overflow System Not Provided

Another problem that Givler found: Section 7.3.13 of the Montgomery County Drainage Criteria Manual (2014 version) requires an emergency overflow system shall be provided “…designed to carry the 100-year allowable detention basin discharge at full-bank conditions… The emergency overflow system shall direct flows into an outfall channel and prevent flow in the direction of developed areas.” (as quoted by Givler).

Even today, the project does not include such an overflow system.

Runoff During Construction More Severe than Ultimate Buildout Conditions

Givler modeled actual construction conditions after the May storm. He found that “…with the project site cleared and stripped of vegetation, runoff conditions were more severe than even the ultimate buildout condition. LJA’s analysis does not address this condition,” he says. His analysis showed that under construction conditions, LJA’s partially-constructed detention ponds were inadequate, unable to contain the May 2019 runoff and the 100-year runoff.”

The temporary construction conditions he says, “caused the ponds to overflow and to discharge runoff to the Elm Grove Village subdivision at a peak rate of approximately 2,110 cubic feet per second.”

Water running through North Kingwood Forest into Elm Grove (background) during Imelda as Keith Stewart evacuates his family.

“LJA Failed to Act as a Reasonably Prudent Engineering Firm”

In his conclusions, Givler alleges that “LJA failed to act as a reasonably prudent engineering firm.” He added, “…three professional engineers and the engineering firm were negligent in the provision of professional services that they rendered, and they committed various actions, errors, or omissions in providing professional services by violating standards required by Montgomery County.”

In Givler’s opinion, LJA failed to comply with Montgomery County standards by:

  • a. Using an alternate (Clark) hydrology method rather than the NRCS method recommended by Montgomery County, resulting in the underestimation of the amount of runoff that the watershed would discharge to the detention ponds.
  • b. Using rainfall depths in the hydrology models which are smaller than what was required by the applicable county standard (2014 DCM) and that are much smaller than recently adopted values (2019 DCM).
  • c. Designing detention ponds, which are too small to contain and too small to detain or attenuate the 100-year design flood.
  • d. Failing to design adequate freeboard for the detention ponds.
  • e. Failing to design adequate emergency overflows for the detention ponds.
  • f. Designing a project, which diverts runoff to properties of others in a harmful and detrimental manner.
  • g. Allowing peak runoff discharges downstream of the project to increase due to the impact of the project and due to the limited effectiveness of the detention ponds.
  • h. Allowing water surface elevations downstream of the project to increase due to the impact of the project and due to the limited effectiveness of the detention ponds.
  • i. Erroneously representing that the project had no impact on downstream areas.
  • j. Failing to notify the contractor of the importance of the existing levee.
  • k. Failing to guide the contractor in a logical construction sequence that would reduce the flood risk during construction.

Violation of Professional Standards and Ethics Also Alleged

Mr. Givler also alleges that LJA and three of its employees violated standards established by the State of Texas and the Texas Board of Professional Engineers in the Texas Engineering Practice Act. “This negligence caused and/or contributed to the endangerment of lives, health, safety, property and welfare of hundreds of people near the project,” he says. They did this, he asserts, “by issuing misleading reports, which failed to indicate the increase in flood potential.”

Questions Remain

“I recognize that additional documents may be produced,” said Givler, “which I will be asked to review and, therefore, reserve the right to add to or to modify this affidavit based on information that may be provided to me at a later time.”

Except for general denials, neither LJA, nor any of the other defendants in this case have responded publicly yet to Givler’s specific allegations.

When LJA and the other defendants make their positions public, I shall review them and give them “equal time.”

The big questions I have at this time are:

  • Why would a firm with LJA’s substantial reputation make the blunders that Givler asserts? Were they pressured into producing a favorable report that made the economics of the project “work”?
  • Five previous developers owned this land and, after studying it, decided not to develop it. That certainly should have raised red flags for LJA and Perry, and caused them to review this closely. There must have been scuttlebutt circulating among local professionals. One engineer I consulted said Friendswood walked away from this property decades ago because it would have been too hard to develop. However, Perry decided to move forward based on dubious studies and incomplete data. Why?
  • What did Concourse Development, Woodbridge 268, Reddy Partnership, Kingwood 575, Lennar Homes of Texas/Friendswood know that Perry Homes did not?

Supporting Documents

Check out the original text of Mr. Givler’s affidavit and exhibits for yourself to ensure I summarized them fairly. His affidavit includes his findings, professional opinions, conclusions and Exhibit 1, his resume.

Exhibit 2 includes the list of documents Givler reviewed in developing his affidavit.

Exhibit 3 includes topographic mapping for construction and pre-construction conditions.

Exhibit 4 includes a topographic map showing the location of the former levee.

Exhibit 5 includes the approval letter by Montgomery County.

Exhibit 6 includes the rainfall values used by LJA.

Exhibit 7 includes a meteorology report.

Exhibit 8 includes reported locations of flooded properties.

Exhibit 9 includes the drainage impact analysis submitted by LJA on March 26, of 2018.

Exhibit 10 includes the drainage impact analysis submitted by LJA on August 28, of 2018.

Exhibit 11 includes Givler’s hydrology model for pre-development conditions.

Exhibit 12 includes Givler’s hydrology model for construction conditions.

Exhibit 13 includes Givler’s hydrology model for post-development conditions.

Exhibit 14 includes LJA’s design for detention pond S2, the one north of Village Springs.

Posted by Bob Rehak on March 8, 2020 based on testimony from David Givler PE

922 Days since Hurricane Harvey and 171 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.

What Went Wrong, Part IV: Perry Homes Develops Flood Plain That Wasn’t

Chapter 9 of the Montgomery County Drainage Criteria Manual discusses development in flood plains. Perry Homes and LJA Engineering somehow “overlooked” many of the points in this chapter. A flood plain ran through the property, but FEMA had not yet mapped it. LJA used that as an excuse to claim none existed.

Notice how flood plain mapping stops at county line. Perry Homes has the undeveloped property along and above the county line. Color code: Cross-hatched = floodway; aqua = hundred year flood plain; brown = 500-year flood plain. Source: MoCo Maps

Unfortunately, physical boundaries of flood plains do not observe political boundaries. Taylor Gully bisects this property, if you look at the flood maps, it magically defies flooding on the MoCo side of the county line.

Montgomery County Regulations Affecting Flood Plains

Below are guidelines from the Montgomery County Drainage Criteria Manual that Perry Homes would have had to follow had the property been mapped.

From Section 9.1.1 Floodplain Regulations:

“No fill or encroachment is permitted within the 100-year floodway which will impair its ability to discharge the 100-year peak flow rate except where the effect on flood heights has been fully offset by stream improvements.” [Emphasis added.]

“Placement of fill material within the floodplain requires a permit from the County Drainage Administrator. Appropriate fill compaction data and hydrologic and hydraulic data are required before a permit will be issued.”

From Section 9.1.2 Floodplain Development Guidelines and Procedures

“Construction within the floodway is limited to structures which will not obstruct the 100-year flood flow unless fully offsetting conveyance capacity is provided.”

  • “The existing designated 100-year floodplain and floodway should be plotted on a map of the proposed development.”
  • “The effect of the proposed development and the encroachment into the flood plain area should be incorporated into the hydraulic model and the resulting flood plain determined.”
  • “Careful consideration should be given to providing an accurate modeling of effective flow areas taking into account the expansion and contraction of the flow.”
  • “Once it has been determined that the proposed improvements adequately offset the encroachment, a revised floodway for the stream must be computed and delineated.”
From Section 9.2 Downstream Impact Analysis

“Pursuant to the official policy for Montgomery County, development will not be allowed in a manner which will increase the frequency or severity of flooding in areas that are currently subject to flooding or which will cause areas to flood which were not previously subject to flooding.”

What LJA Said About Perry Homes’ Project

On Page 1-2 of its Drainage Analysis, LJA Engineering explicitly states, “As shown on Exhibit 3, the proposed development is outside the 100-year floodplain.”

Phyllis Mbewe, P.e., CFM, LJA Project Manager – Hydrology and Hydraulics
LJA Exhibit 3 shows the floodplain stopping at the county line. LJA also did its best to make the .2 percent risk area blend into the area of minimal flood risk. This visually minimizes the amount of floodplain bordering MoCo, so the abrupt stoppage at the county line becomes less visible. Source: LJA.

Ms. Mbewe then states in her conclusion, “Based on these findings, the proposed development of the 268-acre tract creates no adverse drainage impacts for events up to and including the 100-year event.” [Emphasis added.]

What Does “No Adverse Impact” Really Mean?

People often twist the definition of terms you think are self evident. Especially in legal, technical, and political contexts.

To me, “No Adverse Impact” should mean, “Downstream people who didn’t flood before won’t flood after development.” That’s what section 9.2 states explicitly.

But when I talked to a flood professional, I got a different answer. To that person, “no adverse impact” meant, “the amount of water flowing across the property did not increase after development.” Much narrower! And seemingly contradictory to the spirit of 9.2.

“Floodplain” Definition Shocked Me

But that person’s definition of floodplain really shocked me. To me, floodplain means “the area adjacent to a stream that fills with floodwater after a very heavy rain.” But the professional told me I was WRONG. To the professional, a floodplain was “an area on a map that FEMA designated a floodplain for insurance purposes.”

In that person’s mind, because FEMA had never mapped the area in question, a floodplain did NOT EXIST. Whether or not the area flooded!

To me, that’s like saying an apple is something you see in a Kroger’s flyer, not something you eat. We’re talking about the difference between a symbol of something and the reality of it.

This discussion proved once again that words and phrases have different meanings that depend on the social context of usage.

In the minimum compliance environment of Montgomery County, LJA and Perry Homes argued that there was no floodplain. They found someone in the county engineer’s office who agreed with them…or was told to agree with them.

FYI, the official FEMA definition says, “Any land area susceptible to being inundated by floodwaters from any source.”

Consequences of Overly Narrow Definition

So did Elm Grove flood because Perry Homes, LJA and Montgomery County did not enforce the floodplain regs in section 9.2 of the Drainage Criteria Manual?

  • They certainly did not offset peak flows with stream improvements.
  • They did not plot the REAL-WORLD floodway and floodplain on a map of the proposed development (see above).
  • LJA did not incorporate encroachment into the floodplain in its hydraulic modeling, because they denied a floodplain existed.
  • Neither did LJA provide “an accurate modeling of effective flow areas taking into account the expansion and contraction of the flow.”
  • Finally, LJA did not compute, revise and delineate the floodway for the stream.

Had they done all these things, perhaps people would have seen that downstream homes that had never flooded were now subject to greater flood risk. But that’s really something for the jury to decide. And it would require FEMA to model the floodplain after the fact.

But like the narrow definition of floodplain, this whole discussion symbolizes a bigger problem.

How Do You Fix a Permissive, Minimum-Compliance Environment?

LJA had an obligation to its client and a higher one to the public that it ignored in my opinion.

Perry Homes could have demanded honest answers from its engineers, not the ones they wanted to hear.

FEMA could label areas like Woodridge Village “UNMAPPED”. This would send a signal to potential home buyers if sellers tell them they’re NOT in a floodplain. That might make developers think twice.

Home buyers need to demand integrity in this process. They need to ask better questions. They need to learn more about flooding.

But at the end of the day, Montgomery County Commissioners must define the kind of future they want. Do they want constant flooding? Or not. Because right now, they’re competing with other areas for new development on the basis of willful blindness and self-serving definitions.

Thirty years down the road, when it’s too late to fix the infrastructure problems they ignore today, MOCO residents will be paying the price. Some, who have flooded repeatedly, might argue they already are.

Posted by Bob Rehak on 8/26/2019 with help from Jeff Miller

820 Days after Harvey and 69 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.

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.

What Went Wrong, Part II: Lack of Erosion and Sediment Control Worsen Elm Grove Flooding

On May 7th and September 19th, sediment-laden runoff from Perry Homes’ Woodridge Village development in Montgomery County flooded the streets and homes of Elm Grove Village and North Kingwood Forest. On September 26, the City of Houston wrote a cease and desist letter to Perry Homes, its subsidiaries and contractors. The letter alleged that runoff damaged the City’s sewer system and residents’ homes. It demanded that Perry Homes’ proxies stop sending sediment into the City.

After Imelda, Abel Versa had to grab his car to avoid slipping in ankle-deep sediment on Village Springs. The sediment came from Woodridge Village right behind him.

Sediment Control Measures Not Followed in Subdivision Rules and Regs

If Perry Homes and its contractors had followed all the construction regulations affecting drainage, the flooding of Elm Grove would not have happened and the letter would not have been necessary. So what went wrong? I previously reviewed the sediment control measures in the Montgomery County Subdivision Rules and Regulations. Perry Homes received seven strikes. Among the worst apparent violations:

  • They clearcut 268 acres when the rules say no more than 10.
  • They are supposed to plant temporary vegetation but haven’t.
  • They were supposed to make provisions for increased runoff during construction, but didn’t.

In fact, they have substantially completed only 23% of the permanent detention ponds for the whole subdivision despite clearcutting all 268 acres.

The southern section of Woodridge Village has been cleared, filled and graded since last summer. Grass could have reduced the runoff during Imelda. Photo taken on 11/4/2019.
The northern section has also been mostly cleared for months, though workers are still removing piles of dead trees. This shows the area where they filled wetlands. Because no detention exist for the northern section, runoff from 188 acres is supposed to funnel through a 3′ pipe. That’s not working well in heavy rains. You can see how much loose sediment is exposed to floodwaters.

More Regulations in Drainage Criteria Manual Not Followed

Perry Homes also overlooked many provisions in the Montgomery County Drainage Criteria Manual. Twenty-two of the 175 pages also discuss erosion and sediment control (see Section 6 starting on page 85). Among the more serious omissions:

Channel Slopes Severely Eroding

Section 6.2.1 on Grass Establishment states that: “A good grass cover must be established on all areas within the right-of-way (except the channel bottom) disturbed by channel improvements or by any type of construction. An adequate grass stand on the banks helps stabilize the channel and minimize erosion caused by overbank flow and high velocities in the channel. Establishing a good grass cover requires preparing the seedbed, seeding properly. keeping the seed in place, fertilizing, and watering regularly.

The LJA Engineering report never mentions erosion or sediment control by those words. However, it does mention grass-lined and concrete-lined channels and spillways. Only one problem. The channels are not grass lined and most of the areas designated for concrete lining have yet to be lined.

The banks of detention ponds should be lined with grass. They are not. As a result, sediment is slumping to the bottom of the ponds where it is carried downstream by floodwaters.
This closeup shows how severe the erosion is.

Channel Turns Not Protected

Section 6.2.3 on Minimum Erosion Protection Requirements for Bends specifies that bends in drainage ditches must be protected from erosion by grass, rip-rap, or concrete. The material depends on the radius of the curve, the type of soil, average water velocity and maximum water velocity.

Despite funneling 188 acres of sheet flow into Taylor Gulley, which narrows down into a 3-foot pipe, Perry Homes has done little to increase the channel capacity or detention for that area. Worse, the channel design which may have been adequate for forested wetlands, can no longer handle high volume overland sheet flow.

The most obvious needs are on the eastern side of the development. There, Taylor Gully makes a 120-degree turn, then two quick 90 degree turns and two 45-degree turns, all within two hundred yards. Getting dizzy? The floodwater turns 390 degrees in this area!

At each turn the banks take a beating. The full force of the floodwater slams against the far bank and erodes it.

Photo taken on 11/4/2019 along eastern boundary of the southern section of Woodridge Village. That’s North Kingwood Forest on the right and Elm Grove on the bottom. Little wonder that this was the area hardest hit by flooding in May and September.
Where the channel on the right narrows down into the black 3-foot pipe, contractors built an overflow channel into the detention pond on the left but still have not lined it with concrete. Note the severe erosion. Also note the erosion and sediment coming into the pond on the left just below the flow-constricting device in Taylor Gully. Clearly, there isn’t enough channel capacity to handle the volume of water. Photo taken on 11/4/2019, looking north.

Straight Drop Spillway Not Installed

Section states that a straight-drop spillway should be installed in drainage channels to adjust channel gradients which are too steep for design conditions. 

LJA specifies one between where detention pond N3 will be and the 120-degree turn shown above. However, neither the detention pond, nor the spillway have yet been installed. So water from the north comes barreling down the ditch on the right unchecked. The high velocity increases erosion. Here’s what it looked like after May 7th.

Same area shown above but from ground level and looking south toward Elm Grove. Rain did a lot of the excavating for Perry Homes. But unfortunately, the sediment wound up in flood victims’ homes and the City storm drains.

Yesterday I posted about how Perry Homes was supposed to cut only 30 acres of trees on the northern section but cut 188. Still to come in this “What Went Wrong” Series:

  • More Things Perry Homes Didn’t Do in the Montgomery County Drainage Manual
  • Contradictions in Perry Homes’ Plans
  • The Dirt on Perry Homes’ Soil Test
  • The Floodplain that Wasn’t

Posted by Bob Rehak on 11/20/2019 with help from Jeff Miller

813 Days since Hurricane Harvey and 62 since Imelda

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Provisions for Off-Site Overland Sheet Flow in Montgomery County Drainage Criteria Manual Warned Perry Homes of Dangers to Elm Grove

Section 5.3.5 of the Montgomery County Drainage Criteria Manual (Pages 83-84) specifically address flooding of established subdivisions by land under development. For example when Elm Grove was flooded from clearcut land in Woodridge Village. Had Perry Homes, its subsidiaries and contractors followed the requirements in the Manual, Elm Grove might not have flooded.

Provisions Adequate for Ultimate Development Can Be Severely Deficient for Intermediate Stages

The section on Offsite Overland Flow starts out by saying, “Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a localized flood hazard by overloading street inlets and/or flooding individual lots.” This is exactly what happened to Elm Grove Village and North Kingwood Forest in May and September of this year. City of Houston storm drains already taxed to the max became overloaded when water broke out of Woodridge Village and started flowing down the streets of Elm Grove and North Kingwood Forest.

Streets of Elm Grove during May 7th Flood show danger of not planning for runoff during intermediate stages of development.

The text in the Drainage Manual then continues. “Any drainage plan for a proposed subdlvision submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.” [Emphasis added.]

The LJA Drainage Analysis claimed Woodridge would create “No adverse impacts to neighboring developments or Taylor Gully.” However, the LJA analysis did not:

  • Discuss the drainage of adjacent lands, such as Elm Grove.
  • Discuss intermediate conditions of development; they focus only on fully developed Phase 1 and Phase 2 Conditions.
  • Mention the phrase “sheet flow” once.
  • Make provisions to divert 100-year sheet flows.

No Swales to Redirect Sheet Flow

The next paragraph of the Montgomery County Drainage Criteria Manual starts, “Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision.” Perry Homes built no such swales … at least not adequate ones.

No Berms to Block Sheet Flow

Later in that same paragraph, the Manual talks about building berms between the swales and adjoining neighborhoods to prevent the flow from overrunning the swale. Unfortunately, on May 7th, no such berms existed. They did for Imelda, but they proved inadequate to divert the sheet flow and they had gaps in them.

No Additional Storm Sewer Capacity

The next paragraph talks about building “additional inlet and storm sewer capacity … to prevent prolonged street ponding in the (neighboring) subdivision resulting from flow from the undeveloped area.” That didn’t happen either.

No Planning for Rain Before Detention Ponds Fully Built

Perry Homes took none of these precautions. LJA never planned for them (as far as I can see from publicly available documents). Reading LJA’s drainage analysis, one gets the impression that no one ever even conceived of rainfall before they could build all the detention ponds for Woodridge Village. That turned out to be yet another fatal assumption. Despite all the warnings and mitigation advice in Montgomery County’s Drainage Criteria Manual.

Add this to a long and growing list of other things they ignored, underestimated, or mischaracterized.

Stay Tuned for More

The list goes on and on. I have barely started. This series could last for weeks. The MoCo Drainage Manual goes on for almost 200 pages. And Woodridge Village is far from the only Perry Homes Development.

Perhaps the biggest question in all of this is for the Montgomery County Judge and Commissioners. How do plans like this get approved?

Posted by Bob Rehak on 11/12/2019 with thanks to Jeff Miller

806 Days since Hurricane Harvey and 55 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.

For those who are interested, I have reprinted verbatim the full text of Section 5.3.5 from the Montgomery County Drainage Criteria Manual below.

Section 5.3.5 Off-Site Overland Flow from the Montgomery County Drainage Criteria Manual (See Pages 83 and 84)

Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a locallzed flood hazard by overloading street inlets and/or flooding individual lots. Any drainage plan for a proposed subdlviston submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.

Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision. As the adjacent area develops to the point at which the street system can effectlvely handle the sheet flow condition, the temporary drainage swales and easements may be abandoned.. The drainage swales should be relatively shallow, with the excavation spoiled continuously along the subdivision side of the swale to prevent flow from overrunnmg the swale. The swale should have sufficient grade to avoid standing water, but not enough to create erosion problems. Generally, a minimum. grade of 0.1% should be maintained with the maximum grade strongly dependent on local soil conditions.

Such temporary drainage swales may be directed to inlets in the storm sewer system or, preferably, to the appropriate primary outfall channel. lf an undeveloped area is to be drained to a storm sewer, additional inlet and storm sewer capacity must be provided to prevent prolonged street ponding In the subdivision resulting from flow from the undeveloped area. Provisions for this flow must also be included in the design of the street drainage overflow system. The design of temporary drainage swales directed to Montgomery County drainage channels must include adequate pro­visions to drop the flow into the channel through an approved structure in order to avoid excessive erosion of the channel banks.

Outfalling the temporary swale into the backslope drainage system for the channel is unacceptable because the backslope drainage interceptor structures are not adequate to convey flow from an off-site swale. A typical approved structure is shown in Figure 6.3, With the exception of the pipe dimension. The pipe must be sized to handle the 100-year flow from the off-site area.