Flooding 6/19

[DMac]

good post, i was trying to explain this to some of my coworkers who were complaining. i like to bring up SoCal, where they're all from - considering a few inches there can cause havoc.

my question is, if this was a 100-year storm, and 5 years ago we had a 1000-year storm, should they back and change the definition, leading to changing the standards that we build to?

Both the 100 & 1000 year floods are engineering SWAG's

[HeightsGuy]

We could easily build a better flood control system...all it takes is $$$. Lots of $$$. Billions of $$$...and that's just for the City of Houston. HCFCD could also easily spend Billions of $$$ to try to help the situation.

Right now, the standard in Houston and Harris County is to design drainage systems (but not necessarily storm sewers) for the 100-year storm. That's a storm that statistically has a 1% chance of happening in any given year. Today's flooding is exacerbated by two issues: one, the rainfall at Gulfgate was greater than a 100-year storm, and two, drainage systems in our area have only been designed for the 100-year event since 1984, so there's a LOT of infrastructure that doesn't meet the current standard.

According to the Chronicle, up to 10.7 inches of rain fell in 3 hours. According to the National Weather Service Technical Paper 40, a 3-hour 100-year storm event is 7 inches. 10.7 inches in TWELVE hours would have been a 100-year storm event (for a 12-hr duration)...obviously 10.7 inches in 3 hours is well above a 100-year event.

HCFCD has been working pretty aggressively for a number of years now to improve flooding conditions in various watersheds. HCFCD has spent nearly $1 BILLION over the last 5 years in Capital Improvements, such as channel improvements, regional detention basins and other improvements.

That being said, the biggest issue is generally not bayou capacity, but local infrastructure capacity...that is, on the street level: storm sewers and curb inlets, as well as the street grades. In general, anything built in Harris County before 1984 is not up to snuff, and that's being conservative. In reality, it was several years after 1984 that the criteria was actually implemented, and that's only for unincorporated Harris County...the City of Houston is a different story. I'm not certain when storm water detention requirements were implemented in Houston, but it was certainly after Harris County implemented it.

Solving the local drainage infrastructure issue, on a street-by-street basis, will be massively expensive, as you can well imagine. HCFCD and the City of Houston are embarking on a drainage study right now to determine just how much drainage improvement that citizens are willing to pay for, and what level of service they expect (i.e., prevent all street flooding, or just prevent home flooding). Engineers can solve any problem...the question is, how much is our community willing to pay?

What you have said is true, but you have to be careful what you are asking for. There are two schools of thought, one is to get the water out as fast as possible (as you seem to be implying is the answer), the other is to allow water to back up locally to keep is from hitting the bayous all at once. If we "fix" local infrastructure capacity, that could in turn create huge flooding problems along bayou floodplains. Choose your poison. The way it stands now, localized street flooding with some houses and businesses with a few inches to a foot of water usually isn't a life-threatening scenario. The water in that scenario is calm. Having a raging bayou flooding streets and bridges in it's path is much more life-threatening IMHO.

What we in Houston have to accept is that if 10" of rain falls in your area in a few hours, you are at risk to get flooding whether you are in the 100 year flood plain or not.