Tag Archive for: Atlas 14

MoCo Updating Drainage Criteria Manual, Subdivision Rules

Montgomery County (MoCo) Commissioners voted on 8/23/22 to update the County’s Drainage Criteria Manual and its Subdivision Rules and Regulations. Precinct 2 Commissioner Charlie Riley made the motion (item 16.C on the 8/23/22 Commissioners Court agenda).

Montgomery County Commissioners Court discusses new drainage and subdivision manuals in 8/23/22 meeting.

See the discussion in the MoCo Commissioner’s Court video. Select Item 16. The discussion starts at 3:12.

The previous Drainage Criteria Manual posted on the MoCo Engineer’s site is dated 1989, but appears to have some minor updates from 2019. The Subdivision Rules and Regulations for new developments date even further back, to 1984, although they too had new amendments and addenda incorporated in July, 2021.

MoCo hired Halff Associates to do the updating. Their fee: $302,000.

Welcome News

This is welcome news for people in northern Harris County. Drainage and engineering standards in MoCo have lagged those in Harris. That has created adverse downstream impacts even though developers may technically meet MoCo requirements. But the lower standards enable them to claim “no adverse impacts” when, in fact, there may sometimes be some.

Changes Could Reduce Flooding in MoCo and Harris Counties

Since Harvey, the Harris County Engineering Department and Flood Control District have worked to get surrounding counties to adopt five minimum drainage standards. They include:

Scope of Content Updates

The Scope of Work approved by MoCo Commissions last week shows that Halff will examine most, if not all, of these issues and more. The effort will evaluate and potentially update, at a minimum:

  • Hydrologic methodology (this includes hydrographic timing but is broader)
  • Detention sizing and outfall design
  • Open channel design frequency and requirements
  • Floodplain analysis.

Process for Updates

The scope of work also defines the process that Halff will follow. It includes:

  • Coordination with County engineering staff
  • Evaluation of existing manuals
  • Identifying dated criteria/information
  • Comparisons with neighboring counties‘ practices (see below)
  • Revisions
  • Development of the new documentation
  • Stakeholder review and reporting
  • Presentation to Commissioners Court
  • Reporting approved changes to adjacent counties.

Work should take about a year.

Comparison with Regs in Other Entities

For the drainage Criteria Manual, Halff will compare criteria from TxDOT, Harris County, HCFCD, Waller County, Fort Bend County, and Brazoria County.

Halff will compare MoCo’s Subdivision Rules and Regulations to those in Harris, Waller, Fort Bend, and Walker Counties.

This is more good news for those in northern Harris County.

About Halff Associates

A source in the engineering community characterized Halff as a good company. He said, “The Montgomery County manual is in good hands….as long as they let Halff do the right things.”

Halff will work with the MoCo Engineer Jeff Johnson on the updates.

Subdivision Rules and Regulations

Neither the Scope of Work, nor Commissioners discussed specific recommendations for updates to Subdivision Rules and Regulations. But Commissioners did request an opportunity to discuss and review updates on both manuals before they came back to Commissioners Court for final approval.

Immediate Impact

One former MoCo employee said, “There is still the hurdle of the court adopting the updated standards. Expect a rush of drainage studies to be submitted in the next year so they can be grandfathered in.”

We saw this in the City of Houston (CoH), for instance, with the Laurel Springs RV Resort. The detention pond in that development is half the size required by new standards. CoH permitted it one day before the new standards went into effect.

Related News: MoCo Floodplain Administrator Office

At about 40 seconds into the video for Items 17 and 18 on the agenda, the Commissioners approved a motion to have Precinct 2 Commissioner Charlie Riley oversee MoCo’s Office of the Floodplain Administrator. Reasons for the change were not clear. Discussion happened in Executive Session.

All we have to go by is the outcome. And the outcome shows that MoCo is bringing the Office of the Floodplain Administrator – for the whole county – under the direct, political control of one precinct commissioner. Interesting.

Posted by Bob Rehak on 8/28/2022

1825 Days since Hurricane Harvey

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.

Giving Thanks to the Women and Men of Harris County Flood Control

A reader who visited a trade show recently in Las Vegas sent me several links to news stories about flash flooding there. 1.24 inches of rain caused widespread flooding, killed at least two people, and resulted in dozens of high water rescues!

CBS Video posted on YouTube of Las Vegas Flooding

See also:

His comment: “Imagine if those types of videos were in Houston – for less than two inches of rainfall. You can’t, because it doesn’t happen.”

Why Houston Doesn’t Flood On Two Inches

While HCFCD employees take a lot of heat every time someone floods, we should remember that it takes far more rain for people to flood here. There are several reasons for that.

First, Harris County formed a flood control district in 1937. Clark County, Nevada (Las Vegas) didn’t start its until 1985. So, we had an almost 50-year head start on them.

But sadly, some fast-growing counties around Harris County STILL don’t have flood control districts! (We’ll save that discussion for the next legislative session.)

Second, our topography is different. Because Harris County is so flat, rainfall spreads out and starts soaking into the ground before flooding starts. Rainfall in Las Vegas is funneled by the rugged landscape. It picks up velocity, so it doesn’t have time to soak in. Concentrated rainfall turns into flash flooding. The Las Vegas Wash funnels a 1,879 square mile watershed toward a metro area of 2.29 million people.

From Flood Hazards and Flood Risk in Nevada’s Watersheds

I was almost killed by a flash flood in Tucson once. While hiking along a stream bed with friends in the desert, we saw rain in the distant mountains. They immediately suggested moving to higher ground. Minutes later, a wall of water 6-8 feet high came boiling down that stream bed!

Third, we build to different rainfall standards. Las Vegas averages 4.18 inches of rain each year. Harris County averages 51.84 inches.

In Harris County, new building codes and flood-mitigation standards currently use the 24-hour, 100-year amount shown in the Atlas-14 table below – 17.3 inches.

atlas 14 rainfall probabilities
Atlas-14 rainfall probabilities for northern Harris County now form the basis for building codes and flood-mitigation projects.

In other words, we build things to withstand more rain in a day than Las Vegas receives in FOUR YEARS.

That takes some talent. Especially when surrounding areas send ever-increasing amounts of floodwater downstream because of lack of comparable controls upstream. And that could be why flood control districts around the country try to recruit talented HCFCD employees.

Despite our occasional frustrations, we should never forget: They stand between us and disaster.

Posted by Bob Rehak on 8/13/2022

1810 Days since Hurricane Harvey

Despite Heavy Weekend Rains, Most Area Channels and Streams Stayed Within Banks

Despite heavy weekend rains, with a few exceptions, streams and channels stayed within their banks. There are several possible explanations.

  • Soil was dry before the rains.
  • Rainfall came in two waves separated by several hours, allowing the first peak to start working its way through the system before the second hit.
  • The amount of rainfall was within the designed capacity of most channels.
  • The heaviest storms occurred under relatively narrow bands of training supercells.
  • Harris County Flood Control has been actively working on channels!

Rainfall Map of Heavy Weekend Rains

In the image below, note how much higher the rainfall totals are near the red line compared to areas farther away. Most upstream areas received less than an inch or two, limiting the amount that traveled downstream.

Red line indicated path of supercells that tracked across the center of the county last weekend. Note how highest rainfall totals parallel line.

Heavy But Not Harvey

If you were under one of those supercells, you probably received 5-8 inches of rain between Saturday afternoon and Sunday morning – a little more than a 12-hour time span. Consulting NOAA’s Atlas-14 Rainfall Probability table for this area, you can see that those totals correspond to 2- to 10-year storms. Heavy! But not Harvey!

atlas 14 rainfall probabilities
NOAA’s Atlas-14 rainfall probabilities for the Lake Houston Area

Storms Tracked Perpendicular to Most Watersheds

In Harris County most watersheds track from NW to SE. But the storms tracked perpendicular to that. That limited the amount of water dumped in most watersheds. It might have been very different had the storms tracked parallel with bayous.

Here was the channel status report from Harris County Flood Control on Sunday shortly after noon. It shows that virtually all channels were well within their banks. Only the gage at Luce Bayou and SH321 in Liberty County indicated flooding was a possibility near Lake Houston (warning triangle in upper right).

Despite receiving the highest rainfall total in the area (8.56 inches)…

…Luce Bayou never did come out of its banks at that location. See below. As of today, Luce is falling.

Halls Bayou near 45 briefly came out of its banks, but no structures were reported flooded. Same for Greens Bayou at 59. Water briefly got up to the feeder road there.

Brickhouse Gully, White Oak and Buffalo Bayous were also briefly in danger of coming out of banks in places, but receded quickly according to a HCFCD source. They were all back in banks before I could get there with a camera.

Photos of Area Streams and Bayous

At the East Fork and FM1485, I found a high water caution sign on the road Sunday afternoon. But again, the river was well within its banks. The closest it came to flooding was 2 feet from the top of bank three hours before I took this photo.

Here’s how some other local streams and channels fared in the heavy weekend rains.

A tributary channel of Bens Branch between Woodridge Forest and Northpark Drive next to Kingwood Park High School. That cleared area is the new Preserve at Woodridge that will offer 660 SF homes.
Bens Branch looking E (downstream toward Woodland Hills Drive. CVS on Northpark Drive (left). This was the highest part of the highest stream I found. Notice how it’s almost coming out on the left.
St. Martha’s School Parking lot flooded again a little farther downstream on Bens Branch.
Looking west at Bens Branch toward West Lake Houston Parkway. Note debris line on the left bank in the sun.
The debris line in Taylor Gully shows water never got more than halfway up the bank. Looking upstream from the Maple Bend bridge.
Kingwood Diversion Ditch north of Walnut Lane in distance just hours after tornado ripped through area.
Confluence of East Fork San Jacinto (right) and Caney Creek (left). Note docks still above water on right.

No Reports of Flooded Structures in Harris County

As of 8 PM Monday, Harris County Flood Control had not received any reports of structures flooding from the heavy weekend rains.

Storms of this magnitude are common in Houston, but not for January. Jeff Lindner, Harris County’s meteorologist remembered two in the last decade.

“We had comparable totals on 1-9-2012 in the Brays Bayou watershed (6.6 inches peak in 12 hours). On 1-18-2017, we also had several 4-7 inch gage readings on Brays and 7.0 inches in 12 hours on Lower White Oak Bayou.”

For now, most Harris County residents can chalk this one up in the “close-call” column. But let’s remember that people in Plum Grove DID flood. And pray for the tornado victims in Humble, Kingwood and Forest Cove.

Posted by Bob Rehak on 1/10/2021

1595 Days since Hurricane Harvey

Commissioners Vote Tuesday on Contract for Woodridge Village Detention Pond Excavation

Tuesday, 7.20.21, Harris County Commissioners will vote on a contract with Sprint Sand & Clay for excavation of a Woodridge Village detention basin. Item #21-3394 on the agenda is only for $1000, but it gives the contractor the right to enter the site and begin removing up to 500,000 cubic yards of dirt (at no cost to HCFCD) which it can then sell.

Backup provided to commissioners states that “This benefits the District because excavation and removal is always the highest cost of any stormwater detention basin that is constructed.”

Details of Proposed Contract

Here is the full text of the proposed agreement. Highlights include:

  • Amount of excavation TBD – somewhere between 20,000 and 500,000 cubic yards, depending on plans that HCFCD will deliver to the contractor based on the outcome on an engineering study currently underway.
  • The contractor must properly dispose of the spoils, which it is allowed to sell to make its money on the contract.
  • Contractor is liable for any materials that are disposed of improperly, i.e., within Base Flood Elevation or the 500-year flood plain and must identify all disposal locations.
  • Time allowed: 3 years.
  • Termination of contract possible if contractor fails to excavate a minimum average of 5,000 cubic yards every month.
  • Contractor responsible for environmental mitigation if necessary, excluding wetlands.
  • The contractor must provide an approved Stormwater Pollution Prevention Plan and abide by it.

The contract outline contains the map above but does not specify the exact size, depth or location of the proposed work within the outlined area – just that it will occur in Montgomery County. Engineers will supply additional details at a later date.

Making up for the 60% Solution

Assuming commissioners approve this, it is good news for the people who live who live in Elm Grove and North Kingwood Forest – indeed, for everyone who lives along Taylor Gully. The detention ponds installed by Perry Homes before they sold the land to Harris County were based on old rainfall statistics and will only hold about 60% of a new 100-year rain defined in Atlas-14.

Looking SE across Woodridge Village toward Elm Grove and North Kingwood Forest, areas where hundreds of homes flooded badly in 2019 – twice. Photo taken May 26, 2021.

Sprint Sand and Clay is a regular contractor for HCFCD. Currently, the company is excavating the massive Cutten Detention Basin near 290, Beltway 8 and Cutten Road.

Posted by Bob Rehak on 7/20/21

1421 Days since Hurricane Harvey

Valley Ranch Med Plaza and Shipping Complexes Planned

The Valley Ranch area in Porter near US 59 and SH 99 is developing rapidly these days. Signorelli Company calls Montgomery County the 18th fastest growing county in the US.

Medical Plaza Site Cleared

The developer has just cleared a 200+ acre site for a medical plaza in this area. Signorelli’s website says, “Envisioned as the ‘place of wellness’ for the region, the Medical District is a visionary mixed-use concept blending healthcare with restaurants, specialty services, hotels, and high-density residential, providing a broad range of health care services, from primary physicians to acute care and every specialist in between.”

Looking SW across US 59 in foreground. Photo taken on 5/3/21 after three inches of rain on April 30 and May 1. This area drains into the White Oak Creek Watershed.
Detention ponds, both in this picture and the developer’s website seem to be planned for the area back from the freeway. Photo taken 5/3/2021.

The Montgomery County Engineer’s office says it does not yet have construction, drainage plans, or an H&H analysis specifically for the medical plaza property. In response to my FOIA Request, the engineer’s office said, “This is all we have on file at this time.” Their drainage mitigation study they sent me was produced in 2014, long before Atlas 14. That means its runoff calculations are likely 40% short of the current standard. The study also does not isolate this portion of the overall development.

The study concludes, the entire development will have “no impact to adjacent properties” because of the timing of the runoff. Last year, the Montgomery County Engineer tried to get the MoCo Commissions Court to ban hydrograph-timing studies because of their limitations.

It’s unclear at this time whether Signorelli is planning to update its drainage mitigation study and incorporate Atlas-14 standards into its medical plaza drainage.

Amazon Distribution Complex Across Freeway

Right across the freeway from the Valley Ranch medical plaza, Amazon is building a distribution complex.

Looking NNW toward 59 and 99. Right across the freeway from the Signorelli development, a transportation hub is reportedly being built for Amazon. According to Community Impact, the company hopes to open the delivery center this year. Photo taken 5/3/2021.

That green area that snakes its way across 99 and then 59 from the top left to upper right is White Oak Creek. White Oak runs southeast through Porter then joins Taylor Gully and Mills Branch south of the Triple PG Sand Mine near Woodstream Forest. Ultimately, it joins Caney Creek near Dunnam Place and then the East Fork of the San Jacinto. See below.

From Harris County Flood Education Mapping Tool.

The Amazon facility did not require a H&H analysis because of its size.

Page 8 of Amazon Construction Plans shows site is covered with wetlands. Site borders floodway and part is in White Oak’s floodplain.

The Amazon site has a floodway/floodplain permit. For a high-res, printable version of the site plan above, click here.

Look out below!

Posted by Bob Rehak on May 10, 2021

1350 Days since Hurricane Harvey

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.

Interim Guidelines for Atlas-14 Implementation Until New Flood Maps Released

While reviewing the MAAPnext website today, I came across this 1-page PDF that outlines major changes to Harris County’s Policy Criteria & Procedure Manual (PCPM). It describes changes – based on new Atlas-14 Rainfall Statistics – that engineers and developers must follow when designing and constructing flood-control features as part of any development within Harris County.

Atlas 14 Updates Rainfall Frequency Estimates Developed in 1960s

Developers must now design detention and storm sewers around rainfall rates that increase 16-32% compared to the old standards for Harris County.

Data included in Atlas 14:

  • Replaces rainfall-depth information used since the 1960s
  • Provides estimates of the depth of rainfall for average recurrence intervals of 1 year through 1,000 years, and durations from 5 minutes to 60 days.

NOAA collected this data in Texas through December 2017, which includes rainfall from Hurricane Harvey.

New Atlas-14 Rainfall Frequency Estimates for the Lake Houston Area

Floodplain, Detention & Fill Restrictions

The amended policy manual adopts the increased precipitation rates. It also specifies more rigorous criteria for detention basins and fill within the floodplain.

Amendments anticipate that the future Atlas-14 1% (100-year) floodplain will equal the current 0.2% (500-year) floodplain.

Harris County Flood Control District

Therefore, these amendments are considered to be interim and will be reevaluated once new floodplains have been produced as part of HCFCD’s Modeling Assessment and Awareness Project (MAAPnext) in late 2021. You can find more information on MAAPnext at www.maapnext.org.

Zero Net Fill

The old guidelines prohibited developers from adding fill only within the 100-year floodplain. Now they’re prohibited from adding fill within the 500-year floodplain, too. The policy is called “zero net fill.” It means developers cannot bring fill into the floodplains. They can, however, excavate fill from one part of their property and use it to build up another part of their property.

Under new guidelines, developers cannot bring fill into either the 100-year or 500-year floodplains.

For a 20-acre development, the average volume of stormwater within detention basins will increase by about 20%, or about 32,500 additional gallons per acre.

Effort to Harmonize Floodplain Regs with Neighbors’

Harris County works with surrounding counties and municipalities to upgrade and harmonize their floodplain regs. However, the effort has not yet yielded much fruit.

Surrounding counties, such as Liberty and Montgomery, have not yet mirrored these restrictions. In fact, those counties still use their comparative lack of regulation as a competitive tool to attract new development. That, of course, makes it doubly difficult for residents of Harris County. They must not only contend with their own runoff, they must contend with their neighbors’.

Posted by Bob Rehak on 11/30/2020

1189 Days since Hurricane Harvey

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.

Perry Detention Ponds Pass First Modest Test, But Eroded Badly

The official rain gage at West Lake Houston Parkway and the West Fork San Jacinto recorded 2.32 inches of rain between 7 and 9 a.m. this morning. That was officially a 1-year rain. (See Atlas-14 chart below.) As rains go, it was not a severe test; it was more like a pop quiz.

After the rain subsided, Taylor Gully in Elm Grove was less than half full.

The good news: Taylor Gully was well within its banks and no one in Elm Grove or North Kingwood Forest flooded. The bad news: Perry’s detention ponds experienced severe erosion, enough to warrant repairs and perhaps delay the schedule.

The even worse news: Harris County’s meteorologist, Jeff Lindner predicts another one to two inches of rain tonight with isolated totals of three to four.

West Lake Houston Pkwy. Gage Showed 2.32 Inches In 2 Hours

24 hour rain totals for WLHP gage showed bulk fell in 2 hours.

2.32 inches in two hours qualifies as a one-year rain according to the new Atlas-14 rainfall precipitation frequency estimates. Even if you considered the entire 3.12 inches in 24 hours, it would still only be a one year rain.

Atlas 14 Precipitation Frequency Table for the Kingwood Area.

Aerial Images Show How Perry Detention Ponds Performed

These aerial images taken shortly after noon today when the rain stopped show that:

  • The detention ponds are starting to do their work and hold back water.
  • That kept the level in Taylor Gully manageable
  • The overflow spillway between S2 and the concrete-lined channel was apparently not needed.

However, the images also show that:

  • Portions of the detention pond walls severely eroded and appear to have collapsed in places.
  • The water in the N1 pond overcame temporary dirt barricades sending water and silt down to N2.
  • The newly excavated N2 was entirely covered with water for the first time. It also received a significant amount of erosion.
  • N3 merges with Taylor Gully to form one large detention pond that holds water all the way from the northern end of the pond to the county line.
  • Rain has halted construction for the last two days and could delay it into next week.
Expanded, giant N2 detention pond was covered entirely with water for first time. Looking West toward western border of Woodridge Village.
However, erosion re-deposited large amounts of soil within the pond. Looking North along Western Border of Woodridge Village.
Rainwater entering the site from Joseph street in Porter (center left) shows by comparison how much silt the Perry water held. Looking north along western border of Woodridge Village.
Still looking north, but farther up western border, you can see silt slumping into ditch.
Looking SE toward Elm Grove and North Kingwood Forest from the NW corner of site. Water coming in N1 pond from left exited right, down the western border. Water washed out a temporary dirt barrier that appeared designed to hold water in the pond.
Looking east. Note erosion from former utility corridor on left that has turned into a new drainage ditch along northern edge of property.
Looking at western wall of N3 which runs along eastern border of Woodridge Village.
Another portion of the western wall of N3 shows severe erosion.
Standing water from rest of property is slowly making its way into detention ponds.
Looking South along eastern border toward Taylor Gully. At present, N3 (bottom left) simply merges with the concrete channel by S2 (top right). It appears to have nothing to control the outflow.
Looking north along eastern border. Silt fences prove inadequate at stopping erosion. In fact, most of site has no silt fences.

More Rain Likely Tonight

Jeff Lindner, Harris County meteorologist, says that today’s wet pattern should remain in place through the weekend, contrary to earlier predictions that saw rain chances ending by Friday.

Storms currently in the Gulf near Corpus Christi are tracking toward Houston late tonight and Friday morning. They will probably not be as severe as this morning’s storms. With that said…the air mass remains tropical over the region and excessive rainfall rates of 2-3 inches per hour will be possible, warns Lindner.

As of 6 p.m. Thursday, the National Weather Service decided NOT to issue another flash flood watch for tonight, but stay alert to see if a more significant threat may develop.

Expect rainfall amounts of generally 1-2 inches tonight with isolated totals of 3-4 inches.

To Get Up-to-the-Minute Forecasts and Stream Alerts

You can always find up to the minute weather forecasts at this National Weather Service page.

To check on rising rivers and major streams, visit the Harris County Flood Warning System, and click on channels and channel status simultaneously. To see further upstream, click on All Gages. That will show you the status of gages operated by the SJRA in Montgomery County.

Posted by Bob Rehak on 6/25/2020

1031 Days since Hurricane Harvey and 280 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.

Street Flooding: Causes and Cures

What causes street flooding? At the risk of clarifying the obvious, rain accumulates faster than storm sewers and drainage ditches can carry it away.

A Lack-Of-Capacity Issue

Most streets are actually designed to be part of the flood retention system in any community. That’s because most storm sewers can only handle a two-year rain (about 2 inches per hour). When we get more than that – say a 10-, 25-, 50- or 100-year rain – water is stored in the street until capacity opens up in the storm sewers, ditches and creeks.

As you can see from the new Atlas-14 rainfall chart below, a 2-year rain in this area is 2.23 inches/hour; a 25-year rain 3.88 inches/hour; and a 100-year rain 4.88.

New Atlas-14 Rainfall Data for Lake Houston area from NOAA

When evaluating rainfalls, look at the storm totals AND shorter intervals, such as 15, 30 and 60 minutes.

Street flooding usually results from short, high-intensity downpours caused by slow-moving or training thunderstorms.

From a street-flooding perspective, getting 4 inches of rain in one day is not the same as getting 4 inches in one hour.

If you get 2 inches of rain in 30 minutes, you’re already at a 5-year rain. That’s well beyond the design capacity of storm sewers. You can expect water to back up into the street at that point, even if there are no blockages in the storm sewers.

That’s why builders elevate most homes several feet above street level and above the 100-year flood plain. It gives you an additional margin of safety.

How To Determine Intensity of Rainfalls

If you flooded from your street, first determine whether the cause was simply overwhelming rainfall or whether complicating factors existed.

How can you determine how much rain you got in any given time interval during a storm? Follow these simple steps:

  • Go to HarrisCountyFWS.org. (Harris County’s Flood Warning System)
  • Click on the gage nearest you. (For me, that’s Gage #755 at the San Jacinto West Fork and West Lake Houston Parkway. I will use that in the example below.)
  • In the pop-up window, click on the “For More Information” button.
  • At the top of the next window, select date and time intervals. The Time Interval varies from One Hour to One Year. I selected September 19, 2019 (the day of Imelda) and 24 hours. That shows me 24 1-hour intervals. From this and the table above, you can see that we had three very intense hours in a row during Imelda.
HarrisCountyFWS.org shows we got almost 11 inches during Imelda, the vast majority of it in three hours. Note: selecting other time intervals displays other time increments. For instance the system breaks hours down into 5-minute increments, years into months, etc.

From the two charts above, correlate the actual precipitation with the recurrence intervals. You can see that…

We had a 10-year rain, followed by a 5-year rain, followed by a 2-year rain – all in three hours!

Every single one of those hours met or exceeded the maximum capacity of the storm sewers. So it’s easy to see WHY we had street flooding.

When Street Flooding Turns into Home Flooding

In a small percentage of cases, street flooding turns into HOME flooding – when there simply isn’t enough backup capacity in the streets. (In the following discussion, I’m EXCLUDING homes that flooded from rivers, streams, or overland sheet flow during Imelda, i.e., Ben’s Branch, Elm Grove, etc.).

Extreme events reveal the weaknesses in any system. If your home was:

  • At a low point on the street…
  • Near a clogged storm drain…
  • A foot or two lower than surrounding homes…
  • At the bottom of a hill…
  • In an area where water collected or converged…
  • Near an outfall pipe that collapsed or was blocked…
  • Upstream from a ditch that was blocked…

…you may have flooded.

And then there are the bizarre cases.

I visited one man in Trailwood at the bottom of a hill that had NO storm drains. Inexplicably, someone placed the nearest drain in the middle of the hill – about half a block ABOVE his home.

Another man called me who lived near Village Park Drive next to a tributary of Ben’s Branch. The Community Association had erected a fence between the end of the street and the tributary. They built the fence so low to the ground that it became clogged with weeds and grass clippings during Imelda and formed a dam. In the heavy rain, water could not get under it and backed up into his home.

What Can You Do?

Short of praying or digging up every street in Houston to enlarge the storm sewers, homeowners DO have some remedies.

  • Keep storm drains clear. Keep yard waste out of them.
  • Participate in the City’s Adopt-A-Drain program.
  • Call 311 for a storm-drain inspection if you suspect yours have become clogged. The City is currently inspecting ALL drains in Kingwood subdivisions that had street flooding last year.
  • Inspect outfall pipes where your storm drains enter the nearest ditch to ensure they have not collapsed or become blocked.
  • Look out for new construction, such as the fence above, that may back water up. Remove or elevate the horizontal rot board if it blocks the overflow of water from your street.
  • If the problem recurs in less extreme events, consider flood proofing or elevating your home.
  • Make sure you have flood insurance; that it’s up to date; and that it reflects the true replacement value of your home.
Wide shot from farther up the block of fence shown above. Gap under fence did not exist at time of Imelda.
Note how rot board has NOW been elevated to allow water collecting in street to get into creek beyond fence.

Great Options Where Possible

If your area floods repeatedly, you may also be interested in lobbying the City or County to build an overflow spillway or detention pond between your street and the nearest drainage channel. Obviously, geographic circumstances may rule this possibility out for many. But if you have a vacant lot in your neighborhood and a nearby ditch…

Example of community detention pond with overflow channel to Taylor Gully (beyond fence). This wasn’t enough to protect North Kingwood Forest in Imelda, but their problem was complicated by sheet flow from Woodridge Village.

Posted by Bob Rehak on 2/22/2020

907 Days after Hurricane Harvey and 156 after Imelda

Perry Homes’ Woodridge Village Investment Could Be Costliest Ever

Usually when you make an investment, the worst thing that could happen is that you lose all your principle. But Perry Homes could loose a hundred times more than they paid for Woodridge Village land. That takes special talent.

Out-of-Pocket Costs

The land that Woodridge Village sits on didn’t cost much; much of it was wetlands and many streams converged there. Regardless, a Perry Homes subsidiary, Figure Four Partners, bought the land. Montgomery County Appraisal District values the two main parcels at less than a million dollars. Together they comprise more than 80% of the 268-acre project. (See screen captures below from Montgomery County Appraisal District website.)

Real Costs Could Be 100X Greater

Now let’s look at the real costs to Perry. Just to screw up the land, they paid for:

  • An engineering study that underestimated drainage needs by at least 40%
  • Clearcutting and grading 268 acres
  • Filling in natural drainage
  • Excavating two detention ponds (out of five they promised)
  • Soil tests and a geotechnical report
  • A mile of pavement to the middle of nowhere
  • Two large box culverts
  • Storm drains

Let’s say that cost another five million.

But all of that contributed to the flooding of approximately 200 homes in May and 350 in September. Let’s assume the damage to each home totaled $100,000. That comes to about $55,000,000.

Furniture, appliances, rugs, window coverings and other contents? Let’s assume an average of $40,000. That would total another $22,000,000.

Let’s also assume that 300 cars flooded. Average cost – $30,000. Bingo. $9 million.

Now let’s estimate the reduced marketability of homes that flooded. To do this, let’s assume an average price of $200,000 per home and a 20% reduction. That would cost homeowners $40,000 each in the market value of their homes. That’s another $22,000,000.

And we haven’t even factored in the legal fees of J. Carey Gray, counselor extraordinaire.

If juries rule in favor of the flood victims, that million dollar investment could add up to more than $100 million in potential liabilities…before any penalties for negligence and/or gross negligence kick in.

Corps Now Investigating Wetland Violations

Perry Homes bought wetlands and must have thought that no one would notice when they filled them in. They didn’t even bother to request a jurisdictional determination from the Corps for the wetlands. That reduced costs even more. It’s a proven formula in business; minimize costs to maximize profits.

But perhaps Perry Homes went too far. People did notice. The wetlands that they conveniently ignored fall under the jurisdiction of the Army Corps. And the Corps is now investigating potential violations of Section 404 of the Clean Water Act. That could get expensive all by itself.

Like Building Homes at the End of a Gunnery Range

It just keeps getting worse for Perry. This was kind of like buying land to build homes at the end of a gunnery range. A little risky.

But it’s too late to rethink that decision. No one will ever want to buy a home on this site. It’s less marketable than swampland near Chernobyl.

There’s another rule of thumb in business. When you find yourself in a hole, stop digging. And that’s exactly what Perry has done. They have stopped work on the site for months. Work on detention ponds that would help protect people downstream from future flooding is going undone.

That means the numbers above could balloon with the next big rain. Or a negligence ruling by a jury. Yep, we’re in double Jeopardy now.

Career-Limiting Moves

Whoever made the decision to develop Woodridge Village definitely made a CLM (career-limiting move). At this point, even Perry Homes employees not associated with the decision must worry about their Christmas turkeys. Few careers or companies survive blunders that become case studies for how not to do something.

Eroding Profit Margins

Because of faulty assumptions and corner cutting, Perry Homes put itself between a rock and a hard place. They’ve managed to turn a million dollar investment into a potential $100 million liability. They can’t develop this property profitably now. And they can’t sell it. Who would want to buy this land and inherit the liability every time a storm cloud floats by?

To protect downstream homes from flooding, they would have to expand the detention ponds by at least 40%. And that would eliminate so many homesites that costs could exceed income. I say “at least” because the issue is not just Atlas-14 compliance. While digging the S2 detention pond, contractors hit water that’s not going away.

The S2 Detention Pond has lost about 20-30% of its capacity. The bottom 3-5 feet have been filled with ground water since contractors started digging to the target depth.

That means they can’t achieve their detention goals by going deeper; they’ll have to go wider. And that will cut into marketable land even more.

Toxic for Perry Homes

Let’s face it. When Perry Homes bought this property, Kathy Perry Britton swallowed a poison pill. Woodridge Village now has a toxic reputation that will infect the rest of Perry Homes. No one will ever be able to trust anything Perry Homes says again.

Just imagine how bad this could get for Perry Homes if Montgomery County and the City of Houston really started scrutinizing their permit applications in the future.

But what to do with this land? If you’re Kathy Perry Britton trying to spit shine the legacy of dear old dad, you can’t keep it. And you can’t sell it. You can’t even give it away. No land conservancy organization would take it until the damage done to wetlands and streams was remediated. That could take decades.

The Real Value of Wetlands

However, there are two pieces of good news in this mess.

  • If Perry Homes implodes, it won’t take a lot of investors with it; the company is private.
  • Perry Homes may serve as a lesson to other developers and teach them that the real value of wetlands is their downstream legal costs.

Time To Be Decisive

Just remember, Ms. Britton. Historically, 85% of Houston floods are non-tropical. So if you think you have eight more months to figure this out, think again.

Posted by Bob Rehak on 11/15/2019

808 Days after Hurricane Harvey and 57 after Imelda

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