To date, Montgomery County has resisted any mention of a subsidence metric in DFCs for the groundwater management area which includes 14 counties. All must abide by whatever metric the group adopts. The group has been arguing about this metric for years and they’re rapidly approaching a mandatory deadline set by the state.
The Lone Star Groundwater Conservation District (LSGCD) Board which regulates groundwater withdrawals in Montgomery County has favored unlimited groundwater pumping and denied that subsidence affects Montgomery County. Both the southern and northern parts have already seen measurable declines.
Sources close to the controversy do not expect GMA-14 members to reach agreement next week. However, John Martin, head of the management area says, “After we convene and discuss the summary reports submitted by each GCD (a summary of the comments received during the public comment period) the Group will have completed all of the necessary requirements that must be completed prior to the adoption of the DFCs. So, a “final” decision (for this round of planning) could be made at this meeting.”
The Army Corp’s public comment period for adding 1,000 feet of crest gates to the Lake Houston Dam ended on August 23rd. However, I have not yet found any recommendation from the Corps on their site.
The Coastal Water Authority discusses the project at its monthly board meetings.
Minutes from the September meeting have not yet been posted. However, directors did receive an update in their August 11 meeting. The minutes state that engineers presented their modifications of the spillway to support the gates. Next steps (at the time) were to focus on the cofferdam design and structural analysis of the spillway during demolition, interim construction, and post construction.
CWA has not yet responded to an inquiry about how the September meeting went.
Matt Barrett, SJRA’s flood-management director said, “We have not yet selected consultants for the Joint Ops project. My goal would be to start … joint ops by sometime next summer. We are coordinating with CWA/City of Houston on the joint ops schedule to ensure that the project merges as seamlessly and effectively as possible with their ongoing efforts related to the additional Lake Houston gates.”
Makes sense. While FEMA has approved construction of the gates in principle, FEMA has not yet approved the plans. Stephen Costello told a community meeting at the Kingwood Community Center on July 9 that he expects all plans and the environmental study to be completed by the summer of 2022.
The idea is to help people better understand how much water is moving down Winters Bayou, the East Fork, and Peach Creek by adding three gages, one on each at strategic locations.
Barrett says SJRA staff is handling most of this work in-house and has already started.
Locations at both Walnut Creek and Birch Creek have potential to provide flood-mitigation benefits to the watershed. But which to pursue? Here’s the scope of work.
This is another SJRA project. Barrett says, “We recently completed consultant selection and contract negotiation for the Spring Creek project and took the consultant contract to our Board last week (where it was approved). We are aiming for a mid-October start date.”
Location of MoCo projects in San Jacinto River Basin Master Drainage Study
Upper San Jacinto River Basin Sedimentation Study
This SJRA study is also an extension of work started in the San Jacinto River Basin Master Drainage Study. The application for this grant from the state’s Flood Infrastructure Fund states, “Any sedimentation reduction activity in the Upper San Jacinto River Basin (Lake Houston watershed) is anticipated to achieve some level of reduction of sediment load entering Lake Houston, which would in turn reduce storage reduction in the lake, which is the major water supply reservoir for the City of Houston and surrounding communities.”
It could also reduce Lake Houston Area dredging costs which Costello estimates will total $222 million. After taking years to dredge the West Fork, the City is now dredging its way to the East Fork.
Barrett has not yet selected a consultant for the sedimentation project. He hopes to get that started by Spring 2022. The Spring Creek and Joint Operations studies have much shorter timetables, so the SJRA started those first.
Potential vendors interested in developing a long-term dredging plan for Lake Houston had to submit their qualifications by September 23rd last week.
It’s not clear how many vendors responded or who they were. According to Stephen Costello, “It is my understanding that this information is not available due to the quiet period provisions of the city’s procurement process. The information will not be available until the consultant is selected/contract terms negotiated and the contract is on the city agenda for council action.”
That should happen sometime in November. Stay tuned.
Said Barrett, “The Caney Creek project is on hold due to limitations of the CDBG-MIT funding program. Grants for a single project were limited to $100 million in the first round of applications (and the reservoir project as recommended in the San Jacinto Regional Watershed Master Drainage Plan was anticipated to be over $100 million by a decent amount).”
The Texas General Land Office (GLO), which coordinates HUD grants in Texas is committing most of the 2nd round funding to HCFCD after the uproar that followed Harris County’s snub in the first round. Barrett says he is coordinating with appropriate entities to determine how that funding will ultimately be distributed and whether SJRA would be eligible to receive any.
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/Project-Location-Map.jpg?fit=1238%2C1400&ssl=114001238adminadmin2021-09-30 19:04:282021-10-01 09:03:47Flood Mitigation Digest: Updates on Nine Lake Houston Area Efforts
Most of us have seen sinkholes. And most of us have probably given little thought to what causes them.
Retired engineer Chris Bloch, a local flood fighter, measured a 13-foot deep sinkhole near Taylor Gulley earlier this year that had become overgrown with vegetation. Working with the City of Houston and a local homeowner who first reported the problem, they found the sinkhole related to a nearby storm drain.
Bloch lowered this length of PVC pipe into the Taylor Gully sinkhole to measure the depth.Note how the hole had become overgrown with vegetation.
Other things can cause sinkholes, but in this area and in this part of the world, “storm drain gone bad” ranks high on the list of things to investigate.
Corrugated Pipe Commonly Used At Outfalls When Kingwood Built
According to Bloch, when Friendswood built Kingwood, they commonly used corrugated metal pipe (CMP) at storm sewer outfalls. CMP has an expected service life of approximately 35 years, says Bloch. And corrosion commonly causes failure at older outfalls constructed with such pipe.
For example, see the section of pipe below. This photo was taken on Ben’s Branch, not Taylor Gully, but it shows how the pipe rusted, bent, and crimped. Also look just to the right of the wooden posts, and you can even see a large hole in the pipe. It even tilts upward before it reaches the creek.
Bloch frequently walks ditches looking for sinkholes to report to the City. He says he’s aware of at least five right now.
The 72-inch outfall to Taylor Gully serviced drainage area G03408-00-OUT which encompasses all of Greenriver Valley Drive and Mountain Bluff Lane as well as portions of Appalachian Trail, Natural Bridge and Echo Falls Drives. That area comprises 33.4 acres. See below.
Service area for damaged outfall encompasses 33.4 acres where several homes flooded.
The transition from a 72-inch concrete storm sewer to the 72-inch CMP outfall is at a manhole on the edge of the Taylor Gully right of way. See below.
Over the years, the CMP at the connection to the manhole failed. The earth above the failed pipe washed into the outfall and then downstream where it helped reduce the conveyance of Taylor Gully.
Repairs Started But Not Complete
The City of Houston has already repaired several storm sewers with failed corrugated metal outfalls. At least five additional storm sewer outfalls with sinkholes have been identified that have not yet been repaired.
Vegetation frequently hides the presence of these sinkholes. In addition to posing a danger to citizens walking along the banks of the drainage channels, the soil that falls into the sewer can be held up by the corrugations of the metal pipe reducing the flow capacity of the sewer, says Bloch.
Even without obstruction from soil falling into a sewer outfall, the rough surface of the corrugated metal pipe generates greater friction than smooth concrete. The friction slows the flow of storm water and reduces flow capacity which becomes critical during high intensity rains that cause street flooding.
Bloch somehow convinced the City of Houston Public Works Department to replace the damaged CMP at Taylor Gully with concrete pipe. See below.
“This upgrade in the outfall piping will significantly improve the flow capacity of the storm sewer system,” says Bloch.
Concrete pipe replaced CMP at the location of the 13-foot sinkhole on Taylor Gully. Installed by City of Houston Public Works Departmentafter HCFCD repaired Gully.
Concrete Better for New Atlas-14 Rainfall Intensities
When Friendswood Development installed stormwater sewers in Kingwood, they met standards which applied at that time. With new Atlas-14 rainfall projections, we now understand that we should expect more rainfall. Several homes along Appalachian Trial suffered flood damage during Tropical Storm Imelda.
How to Report Sinkholes When You Find Them
As they say, it takes a village to reduce flooding. Now that you know the story behind sinkholes…
If you jog or walk along drainage ditches, exercise caution. Look out for developing sinkholes. And report them to 3-1-1 when you find them. They can pose dangers to children and even grown adults. To put that in perspective, Bloch (shown in the first photo) is more than 6 feet tall, but the sinkhole dwarfs him.
This NBC News story on YouTube has some spectacular examples of sinkholes in Florida along with easy to understand animations that show how they form.
Another 7 minute YouTube video from a series called Practical Engineering focuses on how sinkholes form. It contains both real world examples and table-top experiments that bring the processes to life.
Posted by Bob Rehak based on information and photos provided by Chris Bloch
1492 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/09/Sinkhole-Depth-2-scaled.jpg?fit=1920%2C2560&ssl=125601920adminadmin2021-09-29 16:40:182021-09-30 15:53:15Sinkholes Often Sign of Damaged Storm Drains
The City of Houston Planning Commission was to have considered plat approval on September 30th for redevelopment of the old Kingwood Cove Golf Course acquired by Ron Holley and his FLOG Partners. However, I learned late today from District E Councilman Dave Martin’s office that Planning Commission staff is recommending postponing the public hearing until at least the next regularly scheduled meeting on October 14th.
The Planning Department Staff met with Houston Public Works staff. Reportedly, the applicant has not yet provided all the information necessary for Publics Works to review the application.
Drainage Study Reportedly Not Detailed Enough
According to Martin’s office, Holley’s people submitted a drainage study for the Kingwood Cove development. However…
“Public Works indicated that it needed a more detailed analysis.”
Spokesperson for District E Council Member Dave Martin
Therefore, Planning Department Staff will reportedly recommend to the Planning Commission that Commissioners postpone the public hearing. This will likely happen in the meeting itself when the agenda item is called. But a delay is not automatically guaranteed.
As of this afternoon, approval of the Kingwood Cove plats was still on the agenda.
If Delayed, October 14 Next Possible Date
If the applicant were to provide all required information immediately so that staff could review and provide recommendations, the earliest date for reconsideration would be October 14th (the next meeting following September 30).
The Planning Commission posted Holley’s current plans in two places:
A 24-page abbreviated version as part of the agenda
I haven’t had time to review the entire set of plans yet, so I’m including them all here for you to review. However, I did note several items that may explain why Public Works raised questions.
No HCFCD Check Off Yet
Apparently, no one from Harris County Flood Control District (HCFCD) has reviewed or signed the drainage plans yet. Note how the signature blocks are empty.
Beat-the-Peak Method Employed in Flood Calculations
The Kingwood Cove engineers apparently used the beat-the-peak hydrologic-timing method to support their claim of “no adverse impact.” They also based their calculations on profiles developed from 2001 LIDAR data and a 2012 model of the river basin.
FEMA’s National Flood Hazard Layer Viewer indicates that the boundary of the floodway shown above dates to 2008. Harris County Flood Control’s MAAPNext effort, however, is revising the flood maps. Floodways all over the county are expanding into the 100-year floodplain. So some or all of this detention pond could soon find itself within the floodway.
No Adverse Impact?
The Kingwood Cove engineers claim the detention pond would protect downstream residents in a 500-year storm, but the Harris County Flood Warning System shows, the pond would be under 9.5 feet of water in a 10-year storm. And 22 feet of water in a 500-year storm! I fail to see how the pond would be holding anything back in such situations.
Photo taken from helicopter on June 16, 2020 shows area in middle where Kingwood Cove detention pond would go. Looking SW.
A Grandfathering Play?
Note that Halff engineers submitted their Kingwood Cove drainage analysis on March 17, 2021, and the City implemented its .65 acre feet of detention per acre on March 31, 2021. Holley is just now seeking approval.
If he’s expecting to get a pass because he submitted the plans before a change in regulations, I would submit that we saw how dangerous that can be in the case of Woodridge Village and Elm Grove. Woodridge Village engineers calculated detention requirements based on pre-Atlas 14 data and got it grandfathered by MoCo even though everyone knew the requirements were changing.
There’s certainly lots to think about in these plans. They deserve more close scrutiny.
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/2021/09/20200616-RJR_4514.jpg?fit=1200%2C800&ssl=18001200adminadmin2021-09-27 19:48:112021-09-28 20:01:34CoH Public Works Asking for More Details on Kingwood Cove Golf Course Conversion
Flood Mitigation Digest: Updates on Nine Lake Houston Area Efforts
Here’s a digest of several efforts relating to flood mitigation in the Lake Houston Area and recent developments.
Subsidence
Groundwater Management Area 14 has another Discussion of Desired Future Conditions (DFCs) on the agenda for its upcoming October 5 meeting. Notice Item #7: “Discussion and possible action regarding the DFCs/Proposed DFCs and the path forward for GMA 14 to accomplish statutory mandates for Round 3 Joint Planning.”
To date, Montgomery County has resisted any mention of a subsidence metric in DFCs for the groundwater management area which includes 14 counties. All must abide by whatever metric the group adopts. The group has been arguing about this metric for years and they’re rapidly approaching a mandatory deadline set by the state.
The Lone Star Groundwater Conservation District (LSGCD) Board which regulates groundwater withdrawals in Montgomery County has favored unlimited groundwater pumping and denied that subsidence affects Montgomery County. Both the southern and northern parts have already seen measurable declines.
Here’s a paper that SJRA presented to the LSGCD board that corrects several LSGCD misstatements and misperceptions. It shows charts and graphs dramatizing the amount of measured subsidence.
Sources close to the controversy do not expect GMA-14 members to reach agreement next week. However, John Martin, head of the management area says, “After we convene and discuss the summary reports submitted by each GCD (a summary of the comments received during the public comment period) the Group will have completed all of the necessary requirements that must be completed prior to the adoption of the DFCs. So, a “final” decision (for this round of planning) could be made at this meeting.”
Projected future subsidence could tilt Lake Houston toward its headwaters because it would affect areas near the county line more than the Lake Houston Dam.
Follow this link to register to attend the meeting on the 5th. That’s next Tuesday from 9:30 AM to 12 PM. GMA 14 uses the GoToWebinar app.
Additional Gates for Lake Houston Dam
The Army Corp’s public comment period for adding 1,000 feet of crest gates to the Lake Houston Dam ended on August 23rd. However, I have not yet found any recommendation from the Corps on their site.
The Coastal Water Authority discusses the project at its monthly board meetings.
Minutes from the September meeting have not yet been posted. However, directors did receive an update in their August 11 meeting. The minutes state that engineers presented their modifications of the spillway to support the gates. Next steps (at the time) were to focus on the cofferdam design and structural analysis of the spillway during demolition, interim construction, and post construction.
CWA has not yet responded to an inquiry about how the September meeting went.
Joint Lake-Operation Plan Development
The SJRA received a grant to develop a joint operation plan for the dams at Lake Conroe and Lake Houston. This will involve the SJRA working with the Coastal Water Authority.
Matt Barrett, SJRA’s flood-management director said, “We have not yet selected consultants for the Joint Ops project. My goal would be to start … joint ops by sometime next summer. We are coordinating with CWA/City of Houston on the joint ops schedule to ensure that the project merges as seamlessly and effectively as possible with their ongoing efforts related to the additional Lake Houston gates.”
Makes sense. While FEMA has approved construction of the gates in principle, FEMA has not yet approved the plans. Stephen Costello told a community meeting at the Kingwood Community Center on July 9 that he expects all plans and the environmental study to be completed by the summer of 2022.
Flood Early Warning System
The SJRA also applied for and received a grant to develop a Flood Early Warning System for San Jacinto County.
The idea is to help people better understand how much water is moving down Winters Bayou, the East Fork, and Peach Creek by adding three gages, one on each at strategic locations.
Barrett says SJRA staff is handling most of this work in-house and has already started.
Spring Creek Flood-Control Reservoir
The purpose of this project is to perform a conceptual engineering feasibility study of two potential dams/reservoirs within the Spring Creek watershed. This is a the next phase of the Spring Creek Siting Study which came out of the San Jacinto River Basin Master Drainage Study.
Locations at both Walnut Creek and Birch Creek have potential to provide flood-mitigation benefits to the watershed. But which to pursue? Here’s the scope of work.
This is another SJRA project. Barrett says, “We recently completed consultant selection and contract negotiation for the Spring Creek project and took the consultant contract to our Board last week (where it was approved). We are aiming for a mid-October start date.”
Upper San Jacinto River Basin Sedimentation Study
This SJRA study is also an extension of work started in the San Jacinto River Basin Master Drainage Study. The application for this grant from the state’s Flood Infrastructure Fund states, “Any sedimentation reduction activity in the Upper San Jacinto River Basin (Lake Houston watershed) is anticipated to achieve some level of reduction of sediment load entering Lake Houston, which would in turn reduce storage reduction in the lake, which is the major water supply reservoir for the City of Houston and surrounding communities.”
It could also reduce Lake Houston Area dredging costs which Costello estimates will total $222 million. After taking years to dredge the West Fork, the City is now dredging its way to the East Fork.
Barrett has not yet selected a consultant for the sedimentation project. He hopes to get that started by Spring 2022. The Spring Creek and Joint Operations studies have much shorter timetables, so the SJRA started those first.
The grant application states that this study could take up to four years, though the SJRA hopes to complete it faster.
Long-Term Dredging Plan Development
Potential vendors interested in developing a long-term dredging plan for Lake Houston had to submit their qualifications by September 23rd last week.
It’s not clear how many vendors responded or who they were. According to Stephen Costello, “It is my understanding that this information is not available due to the quiet period provisions of the city’s procurement process. The information will not be available until the consultant is selected/contract terms negotiated and the contract is on the city agenda for council action.”
That should happen sometime in November. Stay tuned.
SJRA CDBG-MIT Caney Creek Grant
The SJRA also applied for a HUD Community Development Block Grant for Mitigation from the US Department of Housing and Urban Development (HUD). The purpose was to develop a Caney Creek Reservoir Upstream of FM 1097.
Said Barrett, “The Caney Creek project is on hold due to limitations of the CDBG-MIT funding program. Grants for a single project were limited to $100 million in the first round of applications (and the reservoir project as recommended in the San Jacinto Regional Watershed Master Drainage Plan was anticipated to be over $100 million by a decent amount).”
The Texas General Land Office (GLO), which coordinates HUD grants in Texas is committing most of the 2nd round funding to HCFCD after the uproar that followed Harris County’s snub in the first round. Barrett says he is coordinating with appropriate entities to determine how that funding will ultimately be distributed and whether SJRA would be eligible to receive any.
Forest Cove Golf Course Redevelopment
This doesn’t exactly fall into the category of flood mitigation efforts, but Ron Holley today reportedly withdraw his application to the CoH Planning Commission to replat the Kingwood Cove Golf for single family homes. The City of Houston Public Works department requested more details on the drainage analysis which raised many questions.
Posted by Bob Rehak on 9/30/2021
1493 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.
Sinkholes Often Sign of Damaged Storm Drains
Most of us have seen sinkholes. And most of us have probably given little thought to what causes them.
Retired engineer Chris Bloch, a local flood fighter, measured a 13-foot deep sinkhole near Taylor Gulley earlier this year that had become overgrown with vegetation. Working with the City of Houston and a local homeowner who first reported the problem, they found the sinkhole related to a nearby storm drain.
Other things can cause sinkholes, but in this area and in this part of the world, “storm drain gone bad” ranks high on the list of things to investigate.
Corrugated Pipe Commonly Used At Outfalls When Kingwood Built
According to Bloch, when Friendswood built Kingwood, they commonly used corrugated metal pipe (CMP) at storm sewer outfalls. CMP has an expected service life of approximately 35 years, says Bloch. And corrosion commonly causes failure at older outfalls constructed with such pipe.
For example, see the section of pipe below. This photo was taken on Ben’s Branch, not Taylor Gully, but it shows how the pipe rusted, bent, and crimped. Also look just to the right of the wooden posts, and you can even see a large hole in the pipe. It even tilts upward before it reaches the creek.
Taylor Gully Sinkhole One of Many In Area
Bloch frequently walks ditches looking for sinkholes to report to the City. He says he’s aware of at least five right now.
The 72-inch outfall to Taylor Gully serviced drainage area G03408-00-OUT which encompasses all of Greenriver Valley Drive and Mountain Bluff Lane as well as portions of Appalachian Trail, Natural Bridge and Echo Falls Drives. That area comprises 33.4 acres. See below.
The transition from a 72-inch concrete storm sewer to the 72-inch CMP outfall is at a manhole on the edge of the Taylor Gully right of way. See below.
Repairs Started But Not Complete
The City of Houston has already repaired several storm sewers with failed corrugated metal outfalls. At least five additional storm sewer outfalls with sinkholes have been identified that have not yet been repaired.
Vegetation frequently hides the presence of these sinkholes. In addition to posing a danger to citizens walking along the banks of the drainage channels, the soil that falls into the sewer can be held up by the corrugations of the metal pipe reducing the flow capacity of the sewer, says Bloch.
Even without obstruction from soil falling into a sewer outfall, the rough surface of the corrugated metal pipe generates greater friction than smooth concrete. The friction slows the flow of storm water and reduces flow capacity which becomes critical during high intensity rains that cause street flooding.
Bloch somehow convinced the City of Houston Public Works Department to replace the damaged CMP at Taylor Gully with concrete pipe. See below.
“This upgrade in the outfall piping will significantly improve the flow capacity of the storm sewer system,” says Bloch.
Concrete Better for New Atlas-14 Rainfall Intensities
When Friendswood Development installed stormwater sewers in Kingwood, they met standards which applied at that time. With new Atlas-14 rainfall projections, we now understand that we should expect more rainfall. Several homes along Appalachian Trial suffered flood damage during Tropical Storm Imelda.
How to Report Sinkholes When You Find Them
As they say, it takes a village to reduce flooding. Now that you know the story behind sinkholes…
If you jog or walk along drainage ditches, exercise caution. Look out for developing sinkholes. And report them to 3-1-1 when you find them. They can pose dangers to children and even grown adults. To put that in perspective, Bloch (shown in the first photo) is more than 6 feet tall, but the sinkhole dwarfs him.
For More Information about Sinkholes
I highly recommend:
The US Geological Survey has an in-depth discussion of different types of sinkholes in different parts of the country and how each forms. This is geared toward students in science classes.
This NBC News story on YouTube has some spectacular examples of sinkholes in Florida along with easy to understand animations that show how they form.
Another 7 minute YouTube video from a series called Practical Engineering focuses on how sinkholes form. It contains both real world examples and table-top experiments that bring the processes to life.
Posted by Bob Rehak based on information and photos provided by Chris Bloch
1492 Days since Hurricane Harvey
CoH Public Works Asking for More Details on Kingwood Cove Golf Course Conversion
The City of Houston Planning Commission was to have considered plat approval on September 30th for redevelopment of the old Kingwood Cove Golf Course acquired by Ron Holley and his FLOG Partners. However, I learned late today from District E Councilman Dave Martin’s office that Planning Commission staff is recommending postponing the public hearing until at least the next regularly scheduled meeting on October 14th.
The Planning Department Staff met with Houston Public Works staff. Reportedly, the applicant has not yet provided all the information necessary for Publics Works to review the application.
Drainage Study Reportedly Not Detailed Enough
According to Martin’s office, Holley’s people submitted a drainage study for the Kingwood Cove development. However…
Therefore, Planning Department Staff will reportedly recommend to the Planning Commission that Commissioners postpone the public hearing. This will likely happen in the meeting itself when the agenda item is called. But a delay is not automatically guaranteed.
As of this afternoon, approval of the Kingwood Cove plats was still on the agenda.
If Delayed, October 14 Next Possible Date
If the applicant were to provide all required information immediately so that staff could review and provide recommendations, the earliest date for reconsideration would be October 14th (the next meeting following September 30).
The Planning Commission posted Holley’s current plans in two places:
Holley’s plans are #133 on the Agenda. I’ve extracted the 24 relevant pages to make file size manageable (2.5 megs).
The full submission is much larger but I compressed the file size from 75 megs to 50 megs. It includes the drainage analysis.
I haven’t had time to review the entire set of plans yet, so I’m including them all here for you to review. However, I did note several items that may explain why Public Works raised questions.
No HCFCD Check Off Yet
Apparently, no one from Harris County Flood Control District (HCFCD) has reviewed or signed the drainage plans yet. Note how the signature blocks are empty.
No Public Works Check Off Yet
Beat-the-Peak Method Employed in Flood Calculations
The Kingwood Cove engineers apparently used the beat-the-peak hydrologic-timing method to support their claim of “no adverse impact.” They also based their calculations on profiles developed from 2001 LIDAR data and a 2012 model of the river basin.
Harris County and City of Houston have been urging upstream counties to abandon the beat-the-peak methodology for years now, in part because it does not take into account upstream developments since the last models were developed. It also allows developers to understate the amount of runoff subject to detention requirements.
Wrong Detention Ratios Apparently Used
The project engineers say on page 52 of the 238-page PDF that they based their conclusion of “no adverse impact” on a floodwater detention ratio of .55 acre feet of detention per acre. But the City requires .65 acre feet per acre. So does HCFCD. Thus, the capacity of the detention pond appears to be understated.
Detention Pond Just 2.5 Feet Above Normal River Level
According to the Kingwood Cove plans (page 47 of full set) the water surface of the detention pond would be at 47 feet. That’s just 2.5 feet above the normal river level and six feet below the parking lot for the golf course (according to the USGS National Map elevation profiler). It’s also 2.3 feet below the level where West Fork flooding becomes likely, according to the gage data at US59.
Floodway Boundary Will Likely Soon Change
FEMA’s National Flood Hazard Layer Viewer indicates that the boundary of the floodway shown above dates to 2008. Harris County Flood Control’s MAAPNext effort, however, is revising the flood maps. Floodways all over the county are expanding into the 100-year floodplain. So some or all of this detention pond could soon find itself within the floodway.
No Adverse Impact?
The Kingwood Cove engineers claim the detention pond would protect downstream residents in a 500-year storm, but the Harris County Flood Warning System shows, the pond would be under 9.5 feet of water in a 10-year storm. And 22 feet of water in a 500-year storm! I fail to see how the pond would be holding anything back in such situations.
A Grandfathering Play?
Note that Halff engineers submitted their Kingwood Cove drainage analysis on March 17, 2021, and the City implemented its .65 acre feet of detention per acre on March 31, 2021. Holley is just now seeking approval.
If he’s expecting to get a pass because he submitted the plans before a change in regulations, I would submit that we saw how dangerous that can be in the case of Woodridge Village and Elm Grove. Woodridge Village engineers calculated detention requirements based on pre-Atlas 14 data and got it grandfathered by MoCo even though everyone knew the requirements were changing.
There’s certainly lots to think about in these plans. They deserve more close scrutiny.
Posted by Bob Rehak on 9/27/2021 based on documents downloaded from the City Planning Commission website.
1490 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.