Tag Archive for: ditches

Colony Ridge Drainage Reports Misrepresent Soil Types, Underestimate Runoff; Many Reports Missing

Drainage reports for the controversial Colony Ridge development in Liberty County misrepresent soil types in a way that underestimate runoff by as much as 6X to 9X. As a consequence, the massive development’s ditches and detention ponds are undersized. That contributes to downstream flooding. 

In addition, virtually all of the drainage reports supplied by the county in response to my FOIA (Freedom of Information Act) request were marked “preliminary” and many were missing. The Assistant County Attorney did not explain why. She said only that she had supplied all documents “responsive to” my request that the county had.

Let’s review soil types first.

USDA Findings Contradict LandPlan Engineering’s

U.S. Department of Agriculture (USDA) classifies soil into four groups (A, B, C, D) that represent rates of rainwater infiltration. Group A has the highest rate of infiltration and D has the lowest. Think gravelly sand vs. clays.

When USDA analyzed soils in the Colony Ridge area, it found less than 2% in Group A. However, virtually all  of LandPlan Engineering, PA reports used model inputs associated with soils in Group A. Hmmmm. Quite a contradiction. LandPlan is the engineering company for Colony Ridge that produced the drainage studies.

USDA says almost no Colony Ridge soils have the lowest rate of infiltration and LandPlan says almost all do.

Comparison of USDA Soil Survey and Landplan Engineering documents

Colony Ridge also has small percentages of soils in intermediate categories:

  • B = 2.3%
  • C = 1.2%

Finally, USDA shows some mixed soil types within Colony Ridge. For instance B/D or C/D. But a flood expert and professional engineer, who spoke on condition of anonymity, said that with mixed soil types, LandPlan should have classified them as Group D. “For all of the areas with B/D and C/D, you should assume that they are D because the soil is disturbed and probably compacted in some way.” So almost 95% of the soils should should be represented with a rate of infiltration equivalent to Group D.

Compacted soil on residential Colony Ridge lot. Note ponding water and damp soil at right. Note also the erosion under back fence next to ditch. Insufficient capacity of ditch contributed to erosion.

Soil Classification Consistently Off in One Direction

Liberty County supplied 39 drainage and construction documents in response to ReduceFlooding.com’s FOIA request. The soil classifications, as shown by the Curve Numbers in the reports all erred in one direction – the direction that favored the developer’s profits.

Almost 95% of the soils should be classified in the least porous group. But virtually all of the “curve numbers” reported by LandPlan Engineering are associated with the most porous group.

By classifying the soils as more porous than they actually are, the engineers could claim there was less runoff and therefore reduce the size of ditches. Likewise, they could reduce or eliminate detention ponds.

What Curve Numbers Mean

Curve Numbers (abbreviated as CN in drainage reports and construction docs) numerically represent the rate of rainwater infiltration. They correlate primarily to soil groups, but also land use and surface conditions. For instance, after soil is paved with concrete, the curve number goes up (indicating less infiltration).

Theoretically, CNs can range from 0 (100% rainfall infiltration) to 100 (totally impervious). In practice, however, the lowest CN is 30 and the maximum is 98, according to the USDA Natural Resources Conservation Service.

What Should Colony Ridge’s Real Curve Numbers Be?

TxDoT’s Online Hydraulic Design Manual shows curve numbers for residential developments (see Curve Number Loss Model section).

For 1/2 acre lots with average impervious cover of 25% (typical of Colony Ridge), USDA estimates the following Curve Numbers: 

  • Group A = 54
  • Group B = 70
  • Group C = 80
  • Group D = 85

LandPlan Engineering used Curve Numbers mostly associated with Group A. They should have used values mostly associated with Group D. See example below from the Drainage Report for Colony Ridge’s Bella Vista Subdivision Section 1.

Excerpt from Bella Vista Drainage Report. Note Curve Number for pre-existing conditions associated with Group A soils, i.e., those having the highest rate of infiltration.

USDA’s soil report for Bella Vista Section 1 shows that the soils are Group C (69%) and Group D (31%). According to USDA and the flood expert/engineer above, the Curve Number used to calculate detention requirements for the “developed condition” should have been closer to 85. But the Curve Number on which the detention is based is 56 (see below) – a number associated with Group A soils. Note: this is a subset of the larger report for Colony Ridge discussed above.

Bella Vista Section 1 shows post-development Curve Number of only 56, associated with the highest rate of infiltration.

Importance of Accurate Curve Numbers

While Group A can absorb .3 to .45 inches of rainfall per hour, Group D absorbs only 0.00 to 0.05 inches per hour. Had LandPlan used the correct values, they would have had to accommodate 6X to 9X more rainfall.


That would have required building larger ditches and detention ponds. But by using the Group A numbers, they could claim:

  • Floodwaters were soaking in.
  • Their roadside ditches could hold runoff. 
  • No, fewer, or smaller detention ponds were necessary.
Loss rate for each soil group represents the amount of rainfall infiltration per hour. Infiltration for Group A is at least 6-9X higher than Group D. Source: TXDoThttp://onlinemanuals.txdot.gov/txdotmanuals/hyd/hydrograph_method.htm

This suggests that LandPlan altered model inputs to achieve the desired output. The flood expert above called LandPlan’s Curve Numbers, “just plain wrong.” “Soils like that just don’t exist in this area,” he said.

Developer’s Environmental Consultant Confirms USDA’s Accuracy

One of the developer’s own environmental consulting firms confirmed the accuracy of the USDA’s and flood expert’s soil observations. Berg-Oliver developed a wetland assessment for the developer in 2014. “The United States Department of Agriculture (USDA) Web Soil Survey of Liberty County, Texas, was, for the most part, reasonably accurate in identifying the basic soil types on the property…” says the report. However, nobody in Liberty County, according to the documents supplied, questioned or even noticed the conflict between LandPlan, Berg-Oliver and USDA.

The Berg-Oliver report was NOT one of the documents supplied by Liberty County. I found it attached to an affidavit by the former Liberty County Engineer in a lawsuit between the ex-Mayor of Plum Grove and the developer of Colony Ridge.

Role in Downstream Flooding, FM1010 Washout, Erosion

Plum Grove residents report increases in the severity and frequency of flooding since Colony Ridge started clearing land. Water accumulates faster and peaks higher, they say, because of the loss of trees and wetlands. But the extra runoff that engineers have not accounted for in their calculations makes those problems even worse. That’s because Colony Ridge ditches and detention ponds can’t retain the extra runoff.

Mischaracterization of soil types likely also played a role in the washout of FM1010.

During Harvey, Colony Ridge drainage ditches discharged so much water into Rocky Branch that the stream then overtopped and destroyed FM1010. The blowout worsened during Imelda. No one has repaired it yet.

Finally, the “tractive” force (power) of rapidly moving water through undersized ditches accelerated erosion. Downstream, the eroded sediment built up and forms sediment dams that back water up, flooding additional homes in Plum Grove, or near the San Jacinto East Fork and Luce Bayou.

“Preliminary” Plans

My Freedom of Information Act (FOIA) request to Liberty County asked for ALL drainage analyses/surveys and construction plans for Colony Ridge subdivisions. However…

  • Virtually all of the plans that Liberty County supplied were marked “preliminary.” 
  • None was marked final or approved. 
  • Many were missing altogether. 
  • NOT ONE bore the signature, stamp, or comments of the Liberty County engineer or his agent, LJA Engineering. 

The 39 reports/surveys and plans are too large to post here; they comprise 1.5 gigabytes.

Liberty County has yet to clarify why so many of the plans are named “preliminary” or were missing. However, the Assistant County Attorney did verify that she supplied all Colony Ridge documents that pertained to my request.

Missing Documents

Here is a list of NINETEEN missing documents:

Missing Drainage Plans/Analyses (16)
  • Bella Vista – Section 2
  • Camino Real – All Four Sections
  • Grand San Jacinto – All Five Sections
  • Montebello – All Four Sections
  • Sante Fe – Sections 1 and 2
Missing Construction Plans (3)
  • Camino Real – Sections 1 and 2
  • Grand San Jacinto – Section 2

The problems in the 39 documents that Liberty County DID supply make one wonder what’s in the 19 they DID NOT supply.

Fallacy of Government Oversight

Not only are many documents missing, the ones Liberty County does have appear to be based on false assumptions about soil types.

I’m told by reputable engineers and floodplain administrators that this problem is common. Developers can always find engineers willing to sell favorable opinions – much like junkies know how to find doctors willing to write prescriptions for oxycodone.

Most people don’t have the expertise to evaluate reports like LandPlan’s. The hired guns know it and count on it. Cities and counties could hire engineers to thoroughly check these plans, but they don’t … for several reasons:

  • Awareness of this problem is low.
  • There’s no public pressure for counties to hire plan-checking engineers.
  • Developers make huge political contributions.
  • Floods often happen years after buildout of subdivisions.

By the time people flood, it’s too late. The damage has already been done. And the people responsible are often long gone.

Posted by Bob Rehak on 12/26/2020

1215 days since Hurricane Harvey and 464 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.

City Quietly Cleaning Out Culverts Under Kingwood Drive Thanks to Local Activist

Chris Bloch, an engineer and Kingwood resident, has become a flood-control activist in his retirement. I often run into Chris inspecting ditches, streams and culverts for blockages and collapsed outfalls. Chris also works with the Bear Branch Trail Association which owns property along many of the channels and streams cutting through Kings Forest, Bear Branch, and Hunters Ridge.

Activist Extraordinaire

For the last several months, Chris has focused intensely on blocked channels that contributed to the flooding of 110 homes in Kings Forest during Harvey. Where the channels cross under Kingwood Drive, three had become almost totally blocked by vegetation and silt. That contributed to backing water up into homes. See below.

Ditch at Shady Run and Kingwood Drive before clean-out. Photo courtesy of Chris Bloch.

Chris meticulously photographed the problems, began researching which entities were responsible for which portions of the channels, and in the case above, contacted the City of Houston. The City has responsibility for the medians and sides of Kingwood Drive and other streets. His persistence paid off.

In October, the City began cleaning out the ditch near Shady Run and Kingwood Drive.

Vacuum truck photographed at same location on 10/3/2020

Here’s what that part of the channel looks like today.

Same ditch after clean-out. Photo courtesy of Chris Bloch.

End-to-End Inspections

Chris is tenacious, tireless, and wide ranging. He looks at ditches from end to end. In this case, he’s also trying to get the Flood Control District to escalate clean-out of the ditch south of Kingwood Drive. Reduced conveyance through that reach could also have contributed to flooding in Kingwood Lakes.

Bloch says he has also identified twenty storm-drain outfalls that need repair. “It doesn’t make any difference if the storm sewers are clear if the water in them can’t get to ditches and streams,” he says.

You Be an Activist, Too

Activists like Chris make Kingwood the great place it is. They help identify local problems for government and make the case for addressing them.

As you hike through our greenbelts and along channels, keep your eyes open for developing problems:

  • Collapsed outfalls into ditches
  • Eroded banks
  • Vegetation and silt blocking culverts
  • Developing sinkholes
  • Fallen trees damming streams

Be an activist like Chris. Take pictures and report them to the appropriate authorities. That will usually be the City or Flood Control.

You, too, can make a difference.

Posted by Bob Rehak on 11/15/2020

1174 Days since Hurricane Harvey

Top Priorities for Lake Houston Area Flood Mitigation

The fast-approaching Harris County Flood Bond referendum on August 25 is forcing people to focus on their top mitigation priorities.

Harris County Flood Control Bond Page at https://www.hcfcd.org/bond-program/.

Here is the current list of projects included in the Bond Proposal. Scroll down to page 7 to see those associated with the San Jacinto Watershed as of 6/1/18. Only one item from MY top four is currently on the County’s priority list.

Here are four things that I think would make the biggest impact for this area. Do you agree?

Top Priorities

  1. More river dredging. We must restore the velocity and carrying capacity of the entire river, not just a small portion of the West Fork and not just to pre-Harvey conditions.  The Army Corps of Engineers is restoring a 2-mile stretch to pre-Harvey conditions. But we need to dredge deeper and further. And we need to do it on a regular basis. In 2000, Brown & Root recommended dredging and periodic maintenance as the best option they examined to mitigate flooding. Neither was ever done. That’s a huge part of the reason why we face increased flood risk today. Personally, I’d like to see the East and West Forks restored to their 2000 condition.
  2. More floodgates on Lake Houston. Freese and Nichols found that 14 additional gates could have lowered the flood level during Harvey by up to 1.9 feet. That could help reduce flooding both upstream and downstream from the dam. It could also help reduce flooding downstream. By releasing water before a storm hits in a gradual, controlled fashion, you can create more capacity within the lake so you can discharge water at a lower rate as the reservoir fills back up.
  3. More upstream detention. Offset Lake Conroe releases by capturing and holding water elsewhere. Everybody from here to Waller County seems to be lobbying for this. Small dams along the streams and bayous could temporarily hold back flood waters before they reach highly populated areas. Spring and Cypress Creeks are popular candidates. Lake Creek has also been mentioned. Finally, TACA pointed out that sand mines could make excellent detention ponds – my favorite alternative.
  4. Better ditch maintenance. Before Harvey, many of our drainage ditches became silted and clogged with fallen trees. Some, like Ben’s Branch, near the public library, still have islands and standing water in them. Keeping these ditches clear and free flowing should be a high priority at all times to eliminate internal flooding.

Consensus Starting to Emerge

Monday, at separate meetings of the Lake Houston Area Grass Roots Flood Prevention Initiative and the Recover Lake Houston Task Fork, I saw consensus emerging around these flood mitigation measures. Together, these top priorities seem to have the best chance of actually reducing flooding in the Lake Houston area.

What are your top priorities? Whether you agree or disagree with these, please communicate your thoughts to Harris County Flood Control ASAP. The County is actively soliciting ideas for the bond proposal right now.

According to Community Impact, Judge Ed Emmett said the county hopes to have a final list of projects to share with the public by Aug. 1. Early voting will begin on Aug. 8. Thus, we have only six weeks to influence the project list.

Leveraging Local Dollars

County bond money can be used to leverage Federal matching funds from FEMA and HUD grants. These grants usually operate on a 75/25 or 90/10 basis, returning $3 to $9 for every dollar put up. If voters approve the$2.5 billion referendum, it could potentially bring in tens of billions of additional dollars. This flow chart explains how the Flood Control District’s funding works.

Federal dollars for Harvey flood mitigation efforts are available now, but may go elsewhere if we don’t act. So it’s important that we:

  • Make sure the language in the proposed bond accommodates our needs
  • Pass the bond
  • Focus the money where it will do the most good

Here is where the proposed bond language stands as of this date. See BondLanguageAsOf6.13.18.  It will most likely be modified before voting begins, based on what officials hear from citizens at a series of meetings being held in all 22 watersheds throughout Harris County.

Give the County Your Thoughts

Remember, according the Greater Houston Flood Mitigation Consortium, the Lake Houston area historically has received 0% of the region’s flood mitigation dollars, but sustained 14% of the region’s damage during Harvey. Let’s make sure we get our fair share of flood control dollars this time around.

Call 713-684-4107 or mail comments to 9900 Northwest Freeway, Houston, Texas 77092, ATTN: Bond Program Communications.

Come to the meeting with Judge Ed Emmett at the Kingwood Community Center on July 10 from 6 to 8 pm. Learn more about bond proposal and give the Judge your feedback directly.

Posted by Bob Rehak 6/13/2018

288 days since Hurricane Harvey