Last August, I posted about a loophole in Montgomery County Flood Plain regulations. It allowed all developers who could prove they were “beating the peak” of a flood to bypass the requirement for detention ponds. Montgomery County Commissioners decided to leave the loophole open. They said, “We don’t have a flooding problem.”
Giant Development Exploits Detention Loophole
It all seemed somewhat academic at the time – unless you previously flooded from upstream development. Then along came Imelda. The absence of functioning detention ponds on Perry Homes’ Woodridge Village property underscored the need for adequate detention for the second time in five months when hundreds of homes downstream in Kingwood flooded.
Now there’s a 2,200 acre development called Artavia going in upstream from the Lake Houston Area – without detention ponds.
Artavia straddles FM1314 south of 242.
The engineering company for the developer, Aliana, claims their calculations show that floodwater from Artavia will beat the peak of a flood to the West Fork by 35 hours. Dasa Crowell, PE, LJA’s Project Manager for Hydrology and Hydraulics, thus concluded, “This leads us to a conclusion that the peak flows generated by the runoff from project drainage area will have no impact on the WFSJR under proposed conditions, therefore detention is not required.” See page 56 of this PDF.
In fairness, the development does include a retention pond in Section 1 labeled as a detention/amenity pond. However, aerial photos show that it has only a few feet of excess storage capacity above its normal water surface elevation. See the plans here. It’s certainly not going to hold back a 100-year rain falling over 2200 acres.
Engineers seem to be relying on drainage channels to act as their detention basins, but as we will see, that comes with some risk. And one potentially bad assumption may invalidate the whole concept.
Problems with Beat the Peak
In an interview last July, MoCo Engineer Jeff Johnson argued for closing the “beat the peak” loophole. He said that the data developers use to calculate peaks is decades old; doesn’t reflect the current drainage picture; and that models should change every time a new development comes in, but they don’t.
Because detention costs money and limits the number of salable lots, developers try to get their water to the river as quickly as possible so they can “beat the peak.” Of course, racing to get water to the river in a flood is the exact opposite of what you want to happen if you are a downstream resident. Normally, you want developers to hold water back as long as practical so as not to overwhelm downstream channel capacity.
LJA developed the Artavia River Impact Analysis in 2014 (see page 60). Based on LJA’s assurances, Dan Wilds, then MoCo’s assistant county engineer issued a letter of “no objection.”
“No Impact” So No Detention Requirement
Wilds said in part, “The analysis … demonstrates that the peak flow from the developed tract will pass through the downstream cross-section approximately 35 hours prior to the peak flow from the upstream watershed. The report indicates that the 10-year, 25-year and 100-year events were analyzed and concludes that the runoff from the project drainage area will have no impact to the San Jacinto River under proposed conditions.”
“Based on this information, this office offers no objection to the analysis as presented. Storm water detention will not be required for this development as long as the developed flows up to and including the 100-year event can be adequately conveyed to the San Jacinto River.” For the full text, see page 51 of this PDF.
The Executive Summary of the most recent update of the drainage impact analysis for Artavia states, “The November 2014 memorandum documents the analysis supporting no detention requirement; this analysis provides calculations showing that the proposed Star Ridge Ranch development (as it was then called) drainage system will safely convey the rainfall runoff for rainfall events up to and including the one-percent annual chance (100-year) storm event.”
Similarities Between Woodridge Village and Artavia
Please note that both of these analyses base their conclusions on pre-Atlas-14 rainfall statistics and therefore may understate drainage requirements significantly by up to 40%. LJA did the same with Woodridge Village.
Also note two other similarities with the LJA analysis for Woodridge Village, Perry Homes’ disaster-movie-in-the-making project.
For its modeling, LJA used something called the Clark’s Unit Hydrograph. Their reports never mention the NRCS method specified in the current Montgomery County Drainage Criteria Manual. The use of Clark’s methodology, which minimizes runoff estimates, has become a bone of contention in the Elm Grove lawsuits.
Finally, LJA pushed both the Woodridge and Artavia plans through the MoCo Engineers office right before the drainage criteria manual was about to be updated again with more stringent requirements.
LJA submitted both drainage analyses for MoCo approval within approximately a year of Hurricane Harvey before flood maps, rainfall statistics, drainage criteria, and construction standards were updated.
LJA Engineering was not only playing beat the peak, it was playing beat the clock again. This will be the first of several posts on Artavia. More news to follow.
Posted by Bob Rehak on 3/17/2020
931 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.