Committee studies flood control measures on Dry Creek

The ditches on both sides of the 110,000 miles of Iowa roads can and should be part of flood control efforts, Palo infrastructure administrator Tom Watson said Thursday at a meeting of the Dry Creek watershed committee.

The ditches are public property with tremendous water storage capacity that could be used to control runoff after heavy rains, Watson told the group of about 15 meeting at Wickiup Hill nature center near Toddville.

Witold Krajewski of the Iowa Flood Center at the University of Iowa in Iowa City, while not directly supporting a network of roadside ditch reservoirs, said the flood center advocates active management of stored water, which would release water in some areas while holding it back in others, in a coordinated effort to minimize flood impacts.

Even though Palo is at the “bottom of the bowl,” in a low flat area that collects storm runoff, the community is implementing practices such as rain gardens and absorption fields to slow and store runoff, Watson said.

The committee wants to push those efforts farther out into the watershed of Dry Creek, which combined with the Cedar River two years ago to inundate Palo.

Dry Creek, which drains 17,450 acres in Linn and Benton counties, is a minute part of the Cedar River watershed, but it added greatly to Palo's devastation when it carried in floodwaters from the west just as the Cedar was cresting on the town's east edge.

The effort to reduce Dry Creek flooding will be boosted by state I-Jobs grants totaling more than $400,000.

About $105,000 will be available for urban mitigation practices such as bioswales, pervious concrete, rain gardens and soil quality improvement in Palo and Atkins, said John Bruene, a district conservationist with the Natural Resources Conservation Service.

About $302,000 will be available for rural mitigation practices such as ponds, sediment basins, grassed waterways, no-till farming practices and grade stabilization structures, his NRCS colleague, Jim Brown, said.

Applications for the grants, which provide 75 percent of the cost of qualifying projects, are available at the Linn County Soil and Water Conservation Office.

Palo residents had begun organizing an informal Dry Creek watershed improvement committee before the June 2008 flood that swamped more than 90 percent of the homes in the Linn County town of 900.

An NRCS study of Dry Creek last year found that a so-called two-year frequency storm of 3.1 inches of rain in 24 hours would swell the creek flow to 1.545 cubic feet of water pre second – well above the channel capacity of 400 cfs, said Dave Beck, assistant state conservationist with the NRCS.

The construction of 25 farm pond-size dams within the watershed would reduce the flow from that same two-year-frequency rain to 627 cfs, he said.