Flood plains not always a good indicator of flood risk 1

[ACtrafficengr]

I thought this may be of interest:

…. a new report by the Chicago-based Center for Neighborhood Technology that amassed an impressive database of 177,000 local flood insurance claims, worth a total of $660 million over the five-year span, covering 96 percent of the zip codes in Cook County (this represents a flood claim for one in every six properties in the county). The analysis found no correlation between damage payouts and floodplains ...

http://www.theatlanticcities.com/neighborhoods/2013/05/way-we-build-cities-making-them-flood/5590/

 

[ACtrafficengr]

I guess I may have misworded my title. They're not saying that being in a floodplain doesn't increase risk. They are saying impervious surface creates risk over a much wider area, and you can't say that just because your're above the 100 year flood, that flooding is not a risk.

Looking at the maps in the article, floodplains are a small percentage of the study area, so the effect of impervious surface drowns out the effect of floodplains when looking at a county-wide or city-wide data set.

As for me, I live on top of a hill of Type A soil. I think I'm good.

 

[beej67]

The Way We Build Cities Is Making Them Flood

That might be more accurately titled "The Way Chicago Builds Cities is Making Them Flood."

Anyone familiar with stormwater management rules and regs for Chicago? Do they require detention at all? If so, how much of it was built before those regulations came into effect?

I would be interested to see a similar analysis for other metro areas. I suspect the regions of Atlanta that are undetained and on CSO, which are older developments on older infrastructure, are more prone to flooding. I suspect that flooding in the newer developed areas is much less common.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[Drew08]

I have two comments to this:

1. It should read, "no correlation to FEMA mapped floodplains." Looking at the map, the hottest area for claims is void of any streams. Historically, there were streams in the area; before it was Chicago, it was swamp land after all. So where are the historic streams? Under people's living rooms, that's where. FEMA has no methodology for mapping floodplains for streams under living rooms, but that doesn't mean they're not there. The outcome of the study might be very different if claims were matched geographically to the floodplains in the area in 1800.
2. This actually says a lot for the effectiveness of FEMA’s floodplain program, because the point is not only to predict who will be flooded, but to prevent development in the highest risk areas to begin with. No development = No risk = no corrolation.

 

[eea]

Chicagoland is actually one of the more rigid storm water management regions in the state, Q(100) zero impact. Downstate rural areas can have none and most Illinois cities have a Q(10) 15min or Q(2)/Q(25) 24hr approach. I think the article raises some excellent points about collective impervious areas and needing to view this as a larger regional problem. I believe that unless agencies band together through a larger intergovernmental agreement, the term "collective or regional" often stops at the city limits or county line rather than the hydrologic basin.