NRCS Structures Hold During Flooding

(from left) Indiana NRCS State Conservationist Jane Hardesty and Tech Team Leader William Elliott survey a flood damaged road (NRCS image -- click to enlarge)

This summer’s record rainfall and flooding in the southern half of Indiana caused hundreds of millions of dollars in damages in both rural and urban areas.  In rural parts of the State, many farms suffered flooding, erosion, or deposition damages…sometimes all three.  While there was no way to have controlled all the flood waters, the NRCS flood control structures held strong, which reduced flood damages to the rain soaked areas.

“NRCS field staff have been busy inspecting damages, measuring, designing, and estimating repair quantities and costs.  They have also been talking to landowners about what we can do for them since the June storms hit,” said Indiana NRCS State Conservationist Jane Hardisty.  “So far, we have focused on what the Emergency Watershed Protection Program can do to eliminate threats to people and property from situations that developed in the storm and subsequent flooding.  Now, we are turning our attention to longer term assistance that we can offer.”

“We also asked our field staff to take a look at flood prevention measures we designed and installed over the last 50 years to see how they held during the storms,” said Mike Cox, State Conservation Engineer for the agency.  “NRCS has 134 dams throughout central and southern Indiana that were built under the PL83-566 Flood Prevention Program.  Our first two dams were completed in 1959 in Washington County and our most recent addition was completed in 2004 in Clark County.  All of the dams were built for flood prevention, and many of them are multi-purpose structures adding water supply, recreation, and wildlife habitat in addition to their primary flood prevention purpose.  A majority of NRCS dams throughout Indiana can store nearly 13 inches of rainfall before storm water might overtop the dam.  Some structures, designed as ‘High Hazard dams,’ can store over 27 inches of rainfall before the dam would overtop.”

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As flood prevention structures, engineering design and specifications are of primary importance in these dams. With years of heavy rainfalls, the attention to detail and adherence to good construction methods has paid off in that none of the NRCS flood prevention dams in Indiana have failed.  Even at the point of overtopping, water flowing through the primary and auxiliary spillways in the NRCS flood protection dams is at full flow, quickly lowering storm water levels in the lake pool.  Dams are designed so that if overtopping takes place, the shallow water flows over a wide area, spreading out the possibility of any concentrated damage.  The auxiliary spillways are wide, flat earthen spillways covered in grasses or other vegetation to help stabilize them.

Even with the dramatic depth and force of flooding throughout central and southern Indiana, NRCS dams held strong.  They protected property, roads and bridges downstream of the dams, and reduced downstream flooding damages in their watershed.  Local conservancy districts are to be commended for carrying out their responsibilities in the maintenance of the dams and their structures.
Your contact is Indiana NRCS public affairs specialist Michael McGovern at 317-290-3200, ext. 324.