Quantifying the Positive Impact of Stormwater Retention Basins

Quantifying the Positive Impact of Stormwater Retention Basins

Pima County’s Flood Control Director Suzanne Shields (left) and hydrologist Jennifer Becker stand in front of a nearly dry retention basin as they await the monsoon rains arrival. (Photo By Lee Allen)

Interested in Stormwater?

Get Stormwater articles, news and videos right in your inbox! Sign up now.

Stormwater + Get Alerts

Acknowledging that it all flows downhill, engineers at the Keno Environmental Restoration Project in Southern Arizona recently decided to take what nature would offer and established an ecosystem within a flood-control basin that also provided both economic and recreational benefits.

And by including a diversion channel within the 155-acre multi-use site, first-flush flood potential has been mitigated by upwards of one-third. In one actual trial-by-raindrops, more than 16,000 gallons per second of angry, rapid-flowing stormwater was reduced to just over 10,000 gallons per second by detaining much of it in retention basins.

KERP can do even more during any 100-year storm, reducing peak flow rate from 85,000 gps to 35,000 gps. The efforts in flood-control infrastructure are credited with preventing mass flooding during a recent brief-but-ferocious storm that quickly dropped 2.54 inches of rain, averting what the county administrator says would have been “significant flood damage in the cities developed areas.”

The benefits are multiple — from the flood-control aspect to water harvesting to the uniqueness of capturing runoff from a stream channel rather than from open areas and retaining over 114 million gallons (350 acre-feet) that would normally disappear into the desert. 

“We decided to rethink what we did with stormwater and came up with a plan to store and reuse that stormwater in lieu of pumping groundwater or using reclaimed water or any other source,” says Pima County Flood Control Director Suzanne Shields, P.E.  “It has paid for itself in potable water dollar savings alone.

“We’ve been able to quantify what our retention basins accomplish during peak runoff and can show bottom line, there are tremendous savings" says Shields. "It’s built, it works and we can prove it. It gives you a water source you can control and it saves taxpayers money because in the last decade, we’ve used reclaimed water at the facility just twice.”


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.