The controversial Laurel Springs RV Resort appears to have another problem with permit violations. The resort’s detention pond falls within the FAA regulatory limit and should remain “completely dry between storms.” But it’s not.
Screen Capture from C3.4 – Detention and Mitigation Plan – approved by City of Houston.
While FAA regulations give owners two days to drain ponds after storms, the Laurel Springs RV Resort pond has remained wet for more than two months. See a sampling of pictures below.
March 23, 2022March 28, 2022April 30, 2022Photo fromMay 3, 2022May 15, 2022May 25, 2022Photo taken on May 30, 2022. Two months later, still not completely dry.
Purpose of FAA Regulation
I looked up the FAA Advisory above to see exactly what it said. To summarize the relevant portions of the 28-page document, they prohibit the construction of wet-bottom, stormwater-retention ponds within a certain range of airports. The concern: the water could attract ducks and geese that create a hazard for aircraft taking off, landing or circling. The detention pond for the Laurel Springs RV Resort falls within the regulated range of Houston’s Bush Intercontinental Airport.
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.
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A best practice in the construction industry is to build detention ponds before you clear all the land. In Elm Grove and North Kingwood Forest, we saw what can happen when you don’t. Contractors cleared 277-acres before installing sufficient detention pond capacity. The result: hundreds of homes flooded needlessly. Twice. And silt poured into Taylor Gully which had to be excavated at public expense.
Staging Construction, Temporary Seeding, Mulching Not Used to Reduce Sedimentation
Harris County Stormwater Quality Management Regulations discourage clearcutting large sites all at once. See section 4.2.3.1, Stormwater Pollution Prevention (SWPPP) During Construction. The text states, “The clearing, grubbing and scalping (mass clearing or grading) of excessively large areas of land at one time promotes erosion and sedimentation problems. On the areas where disturbance takes place the site designer should consider staging construction [emphasis added], temporary seeding and/or temporary mulching as a technique to reduce erosion. Staging construction involves stabilizing one part of the site before disturbing another [emphasis added].“
But those rules don’t apply in Montgomery County. So you often see developers trying to build detention ponds as they build (or even after they build) the rest of the site.
Case in Point: Preserve at Woodridge
Such is the case at the Preserve at Woodridge…which promises “resort-style amenities.”
Preserve at Woodridge on 5/22/22. Eighty-five of 131 rental homes now under construction. That’s two thirds…before the detention pond is built.
Meanwhile, compare the detention ponds below. One is a white, chalky mess with dirt still piled around the edges. The other: pretty clean. Of course, residents pay to keep it that way.
Preserve at Woodridge is in bottom left and Woodridge Forest is in upper part of frame. Notice the difference in the water color in the detention ponds.Contractors have excavated additional dirt from the detention pond (mounded around edges and at left) to bring in clay to form a liner.
The sad part of this: downstream residents will pay the price. And because this is another development just north of the county line, that will be Kingwood. The last time, the developer pumped stormwater into the drainage ditch, the silt traveled miles down Ben’s Branch.
Why Bring In Clay?
I asked an expert in floodwater detention basin construction, why the developer would bring in clay? The answer: “To create a wet-bottom pond.” Developers sell those as residential amenities. I applaud that. But my point is this. Had they completed the detention pond first, it could have been growing grass to reduce sedimentation while they developed the rest of the property. That approach seemed to work well at the New Caney High School ISD West Fork High School.
The detention pond at the New Caney West Fork High School had already been mowed when they began pouring concrete. Photo from March 2021.
Lest you think I’m a MoCo basher, let me point out this. The detention pond above is also in MoCo.
Posted by Bob Rehak on 5/24/22
1729 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.
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Note: Updated 3/26/22 to correct drainage path from Peppervine to West Fork instead of Bens Branch.
Centex Homes, an affiliate of Pulte Homes, has cleared land for a new 47-acre development in Porter just north of Oakhurst. The developer will call the new development Peppervine and is targeting first-time homebuyers and young, budget-conscious homebuyers.
Few Details Available Yet About Homes
Centex doesn’t give many details about the homes yet. The company’s website contains only one page of high-level information. However, it does say that the builder will offer both one- and two-story homes. Their website shows a fairly traditional style that would fit in well with most homes in the Kingwood Area.
Entrance to Peppervine. Looking east toward US59. As with Oakhurst to the south/right, a large stand of trees will shield residents from freeway noise.
However, the only other trees are in the northwest corner of the new subdivision to help shield residents from an RV park.
Looking SE toward 59. A small stand of trees will shield residents from an RV park (lower left). Oakhurst drainage ditch in lower right. Detention pond empties into ditch that cuts through upper right of frame.
Impact on Drainage
Of course, ReduceFlooding readers are concerned about the impact on drainage. While regrettable, the loss of more trees will be at least partially offset by a fairly large detention pond that occupies approximately 20% of the site. See above.
The Montgomery County Appraisal District shows the development, which comprises approximately 1.7 million square feet will have a detention pond that covers approximately 324,000 square feet.
The site will use Oakhurst’s drainage ditch which connects to the headwaters of Bens Branch. See Google Earth Pro image below.
Path of Drainage to West Fork
Peppervine in rectangle will drain through the Oakhurst drainage ditch to West Fork San Jacinto.Note even bigger area slated for development across freeway. It will drain into Bens Branch.Looking SE. Pepperdine’s detention pond will connect to the small drainage ditch in the upper right.Looking NE. The small drainage ditch will connect to Oakhurst’s larger ditch (lower left).Looking north.The site’s detention pond drains into the ditch in the foreground which connects to the Oakhurst Ditch on the left.
Homes Built Above Roads
Homebuyers will be pleased that the homes will be built up from the roadways.
Homes will be elevated above the roads, always a good practice.
Sizable Detention Pond Should Help Allay Concerns
During Harvey and Imelda, multiple homes flooded in Oakhurst. I’m sure Oakhurst residents must have concerns about yet another subdivision adding even more runoff to the ditches and stream. The good news here, though, is that Montgomery County required a rather sizable detention pond in this instance. The developer did not get to avoid detention with a beat-the-peak survey.
Posted by Bob Rehak on 3/24/2022
1668 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2022/03/20220310-DJI_0709.jpg?fit=1200%2C799&ssl=17991200adminadmin2022-03-24 17:50:052022-03-26 20:33:16Oakhurst Getting New Neighbor: Land Cleared for Peppervine
On Sunday morning, Jeff Miller, an Elm Grove resident who lives near Woodridge Village, reported 5.5 inches in his rain gage. That compares to a 6.24 inch rain that fell on Woodridge on May 7, 2019, when hundreds of homes in Elm Grove and North Kingwood Forest flooded. Also, Woodridge falls about 40% short of current Atlas-14 standards required to hold back floodwater from a 100-year storm.
Other important factors came into play last weekend that should relieve some of residents’ anxiety and help explain what happened.
First, remember that on May 7, 2019, Perry Homes’ contractors had clearcut 268 acres, but had barely begun work on detention ponds. Only one of five was complete.
Second, the intensity of the May 7, 2019 rain was higher than last weekend’s. On May 7, 6.24 inches fell in 5 hours. Last weekend, 5.5 inches fell in 9 hours.
Third, in 2019, the S2 detention area had been partially excavated but didn’t have any outflow control restrictions installed yet. So it didn’t really function as a detention pond.
Fourth, contractors had destroyed a berm between Elm Grove and Woodridge, and filled in a natural stream on Woodridge. Both have since been replaced.
I took the photos below Sunday morning between periodic sprinkles, several hours after heavy rain stopped. They show how the current Woodridge Village detention handled the storm. All ponds were well within their banks. One was empty.
The triangular pond on the left is N2. N1 is out of sight above it. The two ponds on the right are S1 (foreground) and S2 beyond it. N3 is out of sight at the top of the frame.
S2 was about halfway to two-thirds full.
The tail of S2 is already silting in but had plenty of room to spare.
N3 Pond on eastern edge of property was supposed to have had an outflow control device but never got one.
The Junction where water from all five ponds comes together before flowing into Taylor Gully. N3 is at top of frame.
Reverse angle shot of the Junction with Taylor Gully in the background. Note how high the detention ponds are compared to the gully.The areas that flooded so badly in 2019 are just beyond the ponds.
Water coming from the big trianglar N2 pond now has to go through these twin culverts which were almost completely inundated.
Wider shot shows volume of water backed up in N2.
Only N1 in the NW corner of Woodridge was totally dry. The outflow capacity is much greater than the inflow. So this pond provides no detention benefit whatsoever. Local resident Jeff Miller says he has NEVER seen standing water in this pond.
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.
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This is Part II in a series about how to find and verify flood-related information. Yesterday’s post focused on finding good information about flood vulnerabilities. This second part will focus on reviewing developers’ plans. The second can compound the first.
The very first sentence of the Texas Water Code § 11.086 begins with a warning not to flood your neighbors. It says, “No person may divert or impound the natural flow of surface waters in this state, or permit a diversion or impounding by him to continue, in a manner that damages the property of another by the overflow of the water diverted or impounded.”
The second sentence declares that a person injured by diverted water may sue to recover damages. Of course, at that point the damage has already been done. Lawsuits are expensive and take years. And the defendant, usually a developer, will always point to plans prepared by a professional engineer and approved by a government body. Suing them will require expert witnesses. And the defendant will likely claim that you wouldn’t have flooded except for an Act of God.
Lawsuits are tall, expensive mountains to climb. So concerned residents near new developments are better off closely scrutinizing plans before they’re built and closely monitoring construction to ensure developers follow the plans.
You can’t stop development. But you can ensure developers play by the rules.
But how do you find and verify their plans?
Need to Find and Verify Info
If you notice a large piece of property for sale near you, monitor it closely. Check with the listing agent. Also check Houston’s Plat Tracker website. It’s updated before every meeting of the Planning Commission and shows items on their agenda. Houston also maintains a map-based website that shows projects in various stages of approval throughout the City and its extra-territorial jurisdiction.
Leap into action if you find a potential cause for concern near you. The next step is to obtain the development’s plans, the drainage impact analysis and soil tests. The developer must prove “no adverse impact” to people and properties downstream.
How you obtain those plans and studies depends on the development’s location. If inside a municipality, check with your city council representative. If you live outside a municipality, your best starting point will probably be your county engineer or precinct commissioner.
The plans are public information and must be provided in response to Freedom of Information Act (FOIA) Requests.
Signed, Stamped, Approved and So Obviously Wrong
In every case I reviewed during the last four years where someone flooded because of a new development, something jumped out of the plans that should have raised concerns for reviewers, but didn’t.
For instance, after Colony Ridge engineers apparently mischaracterized soil types, Plum Grove flooded repeatedly. The engineer said soils would let more water soak in than actually could. That meant the developer didn’t have to build as many detention ponds and could sell more lots. But it also contributed to flooding homes downstream.
Concerned citizens must learn how to obtain and review such plans for potential problems or hire a consulting engineer.
Here are some things I’ve learned to look for.
Soil Tests
Are they accurate? Were the samples taken at representative points? Or did they conveniently ignore wetlands? Permeability of the soils will affect the amount of detention needed. The level of the water table could affect the amount of detention provided.
If plans call for a ten-foot deep detention pond, but the soil test encounters a shallower water table, that will compromise the pond’s capacity. Capacity should be calculated from the top of standing water, not the bottom of the pond. If the pond is already half full, that half shouldn’t count.
Floodplain maps in Harris County are currently being revised. That may not be the case in surrounding counties. The lack of updated flood maps endangers current residents, by letting developers build to old and ineffective standards.
Developers often try to beat the implementation of new requirements. This happened in the case of Woodridge Village. It’s also happening in the case of the Laurel Springs RV Park and Northpark South along Sorters-McClellan Road. The entrance to the Northpark development sits in a bowl. A quick check of the elevation profile on the USGS National Map confirmed that. During Harvey, local residents tell me that not even high-water rescue vehicles could get through that intersection. Put the Cajun Navy on standby now.
Wetland Issues
Filling wetlands requires an Army Corps permit for some, but not all wetlands. Whether they fall under the Corps’ jurisdiction depends on how far up in the branching structure of a watershed they are. Those near the main stem are jurisdictional. Three levels up may not be.
The US Fish and Wildlife service has thoroughly documented wetlands in this area. Check their National Wetlands Database and appeal to the Corps if you find a problem. At a minimum, the developer may be forced to buy mitigation credits somewhere nearby, which could help reduce flooding.
Drainage Issues
Is a new development’s detention pond capacity adequate? Is it based on the right percentage of impermeable cover? If the pond(s) fill up, where will the water go?
Calculating detention capacity requires math skills most people don’t have. But you can check the basis for the calculations. Are plans based on new Atlas-14 requirements? Are plans meeting current Houston and Harris County requirements?
Current City of Houston and Harris County Requirements for Detention Pond Capacity
Also see where they’re routing excess water in case of an overflow.
In the case of the Laurel Springs RV Park, the developer said they would route the water to a detention pond near Hamblen and Laurel Springs in anything greater than a two year rain. See below.
Screen Capture from Laurel Springs RV Resort Drainage Impact Report shows that in anything greater than a 2-year rain, overflow water will could threaten homes in Lakewood Cove.
RV Park Site Outlined in White. Overflow described above would presumably follow red path.
Laurel Springs RV Park as of 11/29/21. Detention pond will go in foreground, but overflow will go into pond at top of frame according to text above.
Missing Details from Drainage Impact Analysis
I have requested additional details three times from the City but still have not received them. I suspect they may not exist. All other plan requests have been filled.
So what happens when the Lakewood Cove detention pond fills up? Or gets covered up in a flood? Overflow from the RV park will contribute to flooding someone downstream.
The developer also said excess capacity would get to the Lakewood Cove pond by overland sheet flow. That could threaten homes on the southwest corner of Lakewood Cove – visible in the middle of shot above.
But a City engineer reviewing the plans said overflow would follow the railroad tracks on the western side of the RV park. Hmmmm. Two engineers – one who developed the plans and another who approved them – 180 degrees apart. What’s a concerned citizen to do?
If the engineers who develop and review such plans were always right, no one would ever flood. But we do. So always find and verify those plans.
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.
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Valley Ranch, the new downtown of East Montgomery County, seems to be exploding with growth. The northwest quadrant of I-69 and the Grand Parkway developed first. Now the focus is shifting to the southwest quadrant where more than 500 acres are being cleared near the banks of White Oak Creek. People downstream from I-69 to Caney Creek have experienced flooding recently. This raises the questions, “Will the flood mitigation measures being put in place at Valley Ranch be enough?” and “In general, are we winning or losing the battle to reduce flooding?”
The Relentless Forces of Development vs. Battle to Reduce Flooding
Last week, I posted about the new Amazon distribution center, shown above at A. Today, I’d like to focus on four areas west of Amazon, shown as 1-4. All sizes below are approximate. I used the measuring tool in Google Earth.
Most of Area 1 just south of the Grand Parkway will be future retail space dubbed “Marketplace.”
Area 1 looking SW from over the Grand Parkway will contain retail. However, apartments are now going up in the far top left corner.What’s that soupy area in the middle? See below.US Fish and Wildlife Service (USFWS) Wetlands Mapper shows a wetland area that corresponds to the soupy area in photo above this one.Here it is again. Looking north toward the future Marketplace and the Grand Parkway. Closer shot of apartmentconstruction.
Area 2: Commercial District
Looking East from over Grand Parkway toward I-69. Commercial area is the clearing in the distance. White Oak Creek is the wooded area that runs diagonally through the frame.Closer shot of commercial area.From over White Oak Creek looking N toward Grand Parkway. I-69 on right.
Areas 3 and 4: Medical District
Medical District looking SW from over I-69.
You can tell by the amount of standing water on this property that drainage could be an issue. Note below how the standing water coincides with the former wetlands mapped by USFWS below.
Sediment control during clearing becomes a real issue for sites like this. Note the series of trenches channeling standing water toward the storm drain on the I-69 feeder road below.
Looking W from over I-69 across southern portion of Medical District. Note attempts to drain the site through the storm sewer in the foreground.
That basket of rocks is supposed to filter out sediment before it reaches the drain. But when I enlarged the image, look what I found.
Someone trenched around it! Reverse angle of same arealooking E toward I-69 shows two large detention ponds under construction on left.
We Need Regional Flood-Mitigation Scorecard
The pace of development seems to be faster than the pace of flood mitigation.
Certainly, responsible developers exist who retain their rain. This may be one. That remains yet to be seen. But other developers exist who do not retain their rain. The question is, “Are there more irresponsible developers than the responsible kind?
Posted by Bob Rehak on 11/9/2021
1533 days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/11/20211106-DJI_0785.jpg?fit=1200%2C799&ssl=17991200adminadmin2021-11-08 16:16:532021-11-08 16:27:27Are We Winning or Losing the Battle to Reduce Flooding?
Since my last update, Kingwood Middle School (KMS) reconstruction has progressed nicely despite heavy rains and a tropical storm in the last month. My rain gage, a few blocks away recorded more than 11 inches of rain in the last 30 days – almost triple the average for September.
My last update on August 20 showed that contractors had erected most of the structural steel, but large parts of superstructure were still open. Today, almost the entire roof is on and most of the structure has been walled or glassed in.
Photos Showing Status of KMS Reconstruction as of 10/3/21
Here are pictures of KMS reconstruction taken this afternoon with a drone.
KMS reconstruction as of 10.3.21. Looking SE from over Woodland Hills Blvd.
Looking N across roof of old KMS. Woodland Hills Blvd on left. Note how left (western) part of building is already bricked in. When new KMS is complete, the old one will be torn down.
Plans call for reconstructing the athletic fields on the site of the old school and building a permanent, larger detention pond where the circular drive in the foreground is.
It’s hard to tell from this angle, but temporary detention pond had barely emptied from yesterday’s deluge.Only one small section in lower left remains without roof. The new KMS will go up instead of out to create the needed capacity for studentsAs construction moves in phases from NW to SE, you see different degrees of finish.
Shortly after Imelda, I posted about Lovett Commercial’s Kingwood Docks development. At the time, Lovett said it would be ready for occupancy in fall of 2019. A year and a half later, two 14,000 square foot buildings still sit empty. Certainly, this has to be one of the more bizarre retail developments around. I’ve never seen a detention pond comprise a higher percentage of a property, although I’m sure one must exist somewhere. Regardless, don’t park here in a flood.
Massive Detention Pond Occupies Approximately Three Fourths of Property
If all developments devoted this much area to detention, we probably wouldn’t have a flooding problem. That said, we do have a flooding problem and the commercial developments to the east, anchored by Memorial Hermann and H-E-B, are both higher than this.
During Harvey, many people who lived between Kingwood Drive and the West Fork parked their cars in the H-E-B and Memorial Hermann lots thinking they would be safe. They weren’t. Hundreds of vehicles flooded.
Lovett Commercial’s Kingwood Docks development is dwarfed by its detention pond. Note the manholes sticking up far above the level of the property.
Everything in the background flooded during Harvey. Memorial Hermann facility is in upper right.
Looking west from the Kingwood Docks detention pond. Memorial Hermann and its parking lot sit on much higher ground than the Docks project.
It’s unclear whether the Kingwood Docks buildings sit high enough to survive another Harvey. The water reached 7 feet in Torchy’s just a few hundred feet to the east. And Torchy’s sits on higher ground. But it is clear that your car won’t survive if you park it here during the next big flood. The entire property sits in the 100-year flood plain.
Aqua = 100-year floodplain. Tan = 500-year. Docks proper is the pie-shaped wedge under the City of Houston lettering.
Posted by Bob Rehak on 3/1/2021
1280 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.
Understand also that regulations vary widely from county to county and city to city. Some may not allow the type of study that the engineer above performed. But Liberty County does. And so does Montgomery County for developments under 650 acres.
To see whether a new development near you accurately reflects soil types in its drainage analysis , follow these steps.
High-Level Outline
You will need to:
Obtain the developer’s drainage analysis and construction plans.
Look up soils in the development via the USDA’s Web Soil Survey.
Compare the “Curve Numbers” used by engineers in Step 1 to Soil Groups in the development from Step 2.
Curve Numbers represent the rate of rainwater infiltration numerically. But USDA estimates infiltration by grouping soils alphabetically. So comparing them requires translation. Not to worry. Just look them up in the tables below.
Your Goal: To see if the developer accurately depicted the soils in his development.
Engineers can alter inputs to provide the desired outputs. And this is one of the main ways they can do it if they’re going to cheat on the volume of detention ponds necessary. See more below.
Background
Different soils absorb water at different rates. What doesn’t soak in runs off. And under developed conditions, it can run off quickly. That’s why developers build detention ponds. But detention ponds cost time and money. They also reduce the amount of salable land.
So developers and their engineers have a large incentive to avoid building detention ponds…if they can. By misrepresenting soils, unscrupulous engineers can make it look like more rainwater is soaking in, so they have less runoff to handle. Most people don’t have the expertise to challenge engineers and the engineers know it. So here’s one way to check their work before hiring your own consulting engineer.
Ask for the Drainage Analysis AND Construction Plans for ALL parts of the development.
To speed up the process, request electronic delivery.
By law, the city or county has ten days to comply.
When you get the plans, check the construction docs to see if they have any detention ponds included.
Then look at the drainage analysis. It should contain a discussion about soils.
Also look for numbers on both the Drainage Analysis and Construction Plans preceded by “CN.” CN stands for Curve Number. That’s a numeric representation of the rate of infiltration for soil groups that engineers use in their runoff calculations. Note the curve numbers for future reference.
Step Two: Look Up Developer’s Soil Types Via USDA
USDA has surveyed soils of every county in Texas. They make it easy to see what kinds of soils are present in any development. USDA groups them via rate of infiltration, but assigns LETTERS to groups, not CURVE NUMBERS. (You will translate those in the next step.)
Click on AREA OF INTEREST (AOI) tab. Then NAVIGATE to the development in question.
Over the map, you’ll see the words AOI in two red buttons, one rectangular, the other a polygon. Pick one and click on it. The cursor will then turn into a plus sign.
DRAG the plus sign over the Area of Interest to DEFINE the AOI. A cross-hatched area should appear.
Click on the SOIL MAP tab. A white box will appear on the left showing all soils in the AOI, their acreage, and the percent of the AOI that they comprise. Contours will appear on the map showing soil-type locations.
Click on the SOIL DATA EXPLORER tab.
In the row under it, click the SOIL PROPERTIES AND QUALITIES tab.
From submenu, click on SOIL QUALITIES AND FEATURES.
From the next submenu, click on HYDROLOGIC SOIL GROUP.
Click VIEW DESCRIPTION to learn about differences between soil groups, then…
Click VIEW RATING. Your map should turn into colored groups. Underneath the map, a list of all the soils in the AOI will appear with their Group (A, B, C or D). Group A soils have the highest rate of infiltration; Group D the lowest. Most important, you can see the PERCENT of the AOI that each soil in various groups comprises.
For future reference, click PRINTABLE VERSION in the upper right. This lets you save your findings as a PDF or printout. The file will include: the MAP, a LEGEND, SOIL GROUPS, each group’s PERCENT OF THE AOI, and a SUMMARY of what the different groups mean.
Screen capture for newly developing part of Colony Ridge shows that only 3.2% of the soils should be classified lower than Rating Group D. See comment below about mixed groups after development. This represents undeveloped land.
After you do this once, the second time should take less than five minutes. Next…
Step 3: Compare USDA’s Soil List with Developer’s Curve Numbers
Now you need a way to compare the developer’s Curve Numbers with USDA’s soil groups. TXDoT does the “translation” for you in the two tables below taken from this page.
Table 4-17 shows infiltration rates by soil group in inches per hour. They range from a high of .45 inches to a low of 0.
Table 4-18 shows Curve Numbers for Development Type and Soil Group. Note how many houses per acre there are from the construction plans. Then look up the corresponding Curve Numbers under each Soil Group.
Create a weighted average of your findings. For soil groups A/D, B/D and C/D, use the curve numbers that correspond to D. That’s because, after development, soil will be compressed, reducing the rate of infiltration. AND note the last line: “Developing urban areas: Newly Graded.” Group D has a curve number of 94, close to the theoretical upper limit for runoff.
Curve numbers ALL erred in the direction that favored the developer’s profits.
If you find errors like that, demand explanations. Keep the system honest. Let people know you’re checking. Your home could be the next one to flood. In egregious cases, you may want to hire a consulting engineer to verify whether the rest of the analysis is valid and meets local regulations.
Posted by Bob Rehak on 12/29/2020
1218 Days after 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/12/Screen-Shot-2020-12-29-at-12.52.40-PM.png?fit=1256%2C1150&ssl=111501256adminadmin2020-12-29 13:44:482020-12-30 08:48:55When Developers Claim No Detention Ponds are Necessary…
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. GroupA 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 allof 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).
Excerpt from Bella Vista Drainage Report. Note Curve Number for pre-existing conditionsassociated 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.
Texdot
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.
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.
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.
