A new 1700-acre development called Madera at FM1314 and SH242 claims it will have “no adverse impact” on surrounding areas. However, to determine this, the authors of the drainage impact analysis used a controversial technique permitted by Montgomery County drainage regulations. It’s called “hydrologic timing.” The technique doesn’t take into account drainage from other developments in surrounding areas. Nor did it factor in the destruction of wetlands.
The Problem with Hydrologic Timing
The theory behind hydrologic timing is that if you can get your water to the river before the peak of a flood arrives, then you aren’t adding to the peak. This might have “no adverse impact” if you were the only development in a watershed. But when you’re:
- Comparing peaks based on data last updated in the 1980s
- In one of the fastest growing areas of the country
- And dozens, if not hundreds of other developments are trying to beat the peak, too…
…everybody is racing to get their drainage to the river faster instead of slower. That could be shifting the peak for the entire watershed. A nearby 2,200-acre development called Artavia also used hydrologic timing to prove no adverse impact.
Example: Two Adjacent Developments Pile It On
Artavia, for instance, claimed that its drainage plan would get water to the West Fork 35 hours before upstream peaks arrived. Meanwhile, Madera (literally a few hundred feet away on the other side of SH242), claims it will get its peak to Crystal Creek 28 hours before that stream’s peak arrives. Crystal Creek empties into the West Fork just upstream from Artavia’s drainage.
So you could have potentially one peak on top of another and another, etc.
Now multiply that times a hundred or a thousand developments and you see the danger.
Several years ago, residents pleaded with MoCo Commissioners to outlaw such “beat the peak” analyses for this very reason. But commissioners refused.
Eliminating Nature’s Detention Ponds
The land in question is low. The US Fish & Wildlife Service shows its dotted with wetlands – nature’s detention ponds.
Even the Montgomery County Appraisal District website shows Madera covered with swamp symbols and ponds.
As far as I can see, the drainage impact analysis supplied by engineers makes no attempt to compare the amount of natural detention to man-made detention.
When Does Real Peak Happen and Why Does It Matter?
Engineers claim they aren’t adding to discharge; they’re just shifting the peak. But because of all the development in MoCo in the last 40 years, it’s not clear when that peak from outside the development will really happen.
In fairness, Madera plans do show a number of detention ponds. But even with those, Madera will still add 16,300 cubic feet per second to the West Fork in a 100-year storm. And that’s just for Phase 1 of the development! That’s why engineers say below, “will not likely have an impact on peak flows…”
To put that volume in perspective, during the peak of Harvey, the SJRA says the nearby West Fork carried 115,000 CFS. So Madera will contribute 14% of Harvey’s volume at that point on the West Fork. And most people consider Harvey far more than a 100-year storm.
Problem with Higher Peaks
The hydrograph below shows how the peak on Brays Bayou shifted over time with upstream development. On the West Fork, this may already be happening.
In the last 20 years, HCFCD and its partners have spent more than $700 million on flood mitigation in the Brays Bayou watershed.
The safest strategy is for new developments to “retain their rain” until the peak of a flood has passed and then release it slowly. “Retain Your Rain” is the motto of most floodplain managers. If everyone did that, there would really be “no adverse impact.”
Faster Runoff, Faster Erosion
As stormwater approaches Crystal Creek, it will encounter a steep drop that requires the use of check dams and other measures to slow water down.
Erosion during Harvey has already cost taxpayers more than $100 million in dredging costs and that total will go higher.
Aerial Photos Showing Work to Date
Land Consists Primarily of Wetlands
The hundreds of pages supplied by the Montgomery County Engineer’s Office in response to a FOIA Request show that this development tract consists “…primarily of evergreen and mixed forest and woody/herbaceous wetlands.” [Empasis added.] Yet the drainage analysis never again mentions that when it claims the development will have no adverse impact.
HCFCD Position on Hydrologic Timing
Harris County Flood Control has long lobbied to eliminate hydrologic timing in drainage analyses for the reasons mentioned above. However, Montgomery County Commissioners have not acted on the proposal.
Posted by Bob Rehak on 1/23/2022
1608 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.