Loophole Cuts RV Park Detention Pond Capacity Requirement in Half
When examining the floodwater detention pond capacity for the Kingwood Area’s first RV park at 1355 LAUREL SPRINGS LANE, it seemed impossibly low. The park will build a pond with 7.68 acre feet of stormwater detention. That’s more than the required 6.675 acre feet, but about half of what the City of Houston (COH) would require under new guidelines that went into effect within 90 days of the plan’s approval.
Because of that 90-day grandfathering loophole, the RV park will escape current City and County requirements for floodwater detention.
Current Regs Would Require 13 Acre-Feet of Detention Pond Capacity
Under today’s requirements, a 20.032-acre RV Park would require 13 acre-feet of detention pond capacity (20 acres x .65 = 13 acre feet). That’s because the COH 2021 infrastructure design manual makes properties larger than 20 acres follow HCFCD guidelines (see below).
This requirement is based on NOAA’s new, higher Atlas-14 rainfall probability tables adopted in the wake of Harvey.
COH 2021 Infrastructure Design Manual Defers to HCFCD Regs for Lots This Size
The City’s Infrastructure Design Manual imposed new criteria in July 2021 that would have required developments greater than 20 acres to follow the HCFCD standard for detention pond capacity. See screen capture below which bridges two pages.
City’s 2020 Regulations Required Far Less Detention
However, the City’s 2021 standards also provided a 90-day grace period for plans initially submitted before July. That meant the City’s 2020 Infrastructure Design Manual applied. And those standards only required following HCFCD’s higher standards if the lot was larger than 50 acres – which this is not. It’s 20.032 acres. So the RV Park developer will get away with installing far less detention than current regs require.
Differences Between Old/New Versions of City/County Regs
Two primary differences exist between the City and County regs in 2020 and 2021.
The first is the basis for calculations. In both years:
- The County bases required detention pond capacity on the total size of the site.
- The City, except where it defers to HCFCD regs, bases detention pond capacity on the amount of impervious cover within the site.
The City also changed the minimum lot size required to follow HCFCD regulations between 2020 and 2021.
- Sites larger than 50 acres had to follow HCFCD guidelines in 2020.
- Sites larger than 20 acres had to follow HCFCD guidelines in 2021.
The 2020 requirements apply in this case because of when plans were first reviewed (January 2021). The 2020 Infrastructure Design Manual read as follows:
Developer Applied Before Detention Pond Capacity Increased
Using that formula, the developer planned a detention pond that holds 7.68 acre feet of storm water detention, an acre foot more than required at the time the plans were first submitted, even though they were finally approved four months after the new regs went into effect. But that’s still far less than the 13 acre-feet required under today’s regulations.
The City previously reviewed a version of the plans on 1/21/21 which were originally submitted in 12/20.
Impervious Cover Calculations Need Further Review
I question whether the amount of impervious cover above is correct. That’s because the developer’s permit allows 182 RV spaces, but the plans show 226 – about a 24% increase. However, the impervious cover shown on the plans before and after the permit approval did not increase. That could also affect detention pond capacity requirements.
Timing, Impervious Cover Issues Raise Public Safety Questions
Assuming the impervious cover calculations above are correct, and that’s a big assumption, the developer is providing more than the minimum amount of required detention under 2020 requirements. But if they are not correct, the developer would be short.
And if the 2021 requirements applied, the developer would have to provide virtually twice as much detention.
A half-sized detention pond would require the RV Park to pump water into Lakewood Cove’s drainage system sooner and faster than with a larger pond. And under severe conditions, when Lakewood Cove’s drainage is already stressed, the extra water could over-stress it.
No Drainage Impact Analysis
I’ve requested a drainage impact analysis from the City for the RV Park on at least two occasions and have not received one. I therefore deduce that one does not exist. Such an analysis would quantify the impact on Lakewood Cove, Edgewater Park and surrounding roads.
Bottom Line: Park Will Provide Half of Today’s Detention Requirement
If this developer, LS RV Resort, LP, submitted plans today, it would have to provide almost twice as much detention pond capacity.
- 2021 requirements call for .65 acre feet per acre times 20 total acres. That equals 13 acre feet of detention.
- 2020 requirements call for .5 times the claimed 13.349 acres of impervious cover. That equals 6.675 acre feet of detention.
And we wonder how floods happen! Remember this the next time you see water rising toward your home.
I wonder if investors in the RV Park will be notified of the potential liability in a prospectus. Undersized detention ponds based on a similar grandfathering loophole in Montgomery County regulations became the central issue in lawsuits by hundreds of Elm Grove residents against Perry Homes, its subsidiaries and its contractors. The defendants recently settled those lawsuits.
Posted by Bob Rehak on 11/13/2021
1537 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.
