Flood Control Dams Prove Worth in Record-Breaking Rainfall of 2013
Record-breaking rainfall and low summer temperatures in 2013 is quite a contrast from the drought and hot summer of 2012. But Oklahoma’s 2,107 flood control dams have proven their worth both years providing a total of $197 million in benefits from reduced flooding.
Oklahoma City received 45 inches of rain in the first eight months of 2013, which already makes it the fifth highest annual rainfall on record and on pace to be the wettest year on record. And it is not just the Oklahoma City area, high rainfall amounts have occurred in many parts of the state this year.
Even with high rainfall events, severe state-wide flooding has been limited thanks to Oklahoma’s 2,107 flood control dams. These dams held back water from heavy rains and slowly released it over a period of days or weeks reducing the flooding downstream. The flood control dams were constructed by local watershed project sponsors, mostly conservation districts, with assistance from the USDA Natural Resources Conservation Service (NRCS) Watershed Program. Conservation districts are governmental subdivisions of the state.
“If these dams were not on the landscape severe flooding would have occurred across the state this year,” said Mike Thralls, Oklahoma Conservation Commission Executive Director. “We know this by looking back at the severe flooding that occurred in the state prior to construction of the dams and by annual benefit reports from the USDA Natural Resources Conservation Service.”
Estimated benefits from the 2,107 flood control dams average $85 million annually. But, just in the first eight months of 2013, the dams have already provided $102.5 million in benefits, according to NRCS estimates. Over half of those benefits ($51.6 million) were realized from May through August. Benefits are determined by estimates of damages that would have occurred from flooding if the dams were not in place. It is also estimated that if the additional 300 flood control dams planned were already constructed they would have provided an additional $23 million in 2013 benefits through August.
Even though most parts of the state had below-normal rainfall in 2012, the dams still provided $94.5 million in benefits. “There are often high rainfall events in some part of the state even during years like 2012 where most of the state was in a severe drought situation,” said Robert Toole, Conservation Program Director for the Oklahoma Conservation Commission. “During the severe drought of the “Dust Bowl” period in 1934, part of Roger Mills County received 17 inches of rain in a few hours that caused flooding of the Washita River and resulted in the loss of 17 lives in Hammon.”
Flooding was a Common Occurrence across the State before the Dams Were Constructed
Before the flood control dams were constructed severe flooding occurred in many parts of the state costing thousands of dollars annually in damages to roads, bridges, farmland, livestock and homes. Just one high rainfall event in the Red Rock Creek Watershed in Noble and Garfield Counties in 1959 caused over one million dollars in damage. Since 50 flood control dams have been constructed in that watershed, landowners no longer experience that kind of flooding and damages. The dams provide over $645,000 in annual benefits from reduced flooding.
The 2,107 flood control dams were constructed primarily for flood control, but they also provide a myriad of other benefits including providing municipal water supplies, recreational areas, wildlife benefits, livestock and irrigation water and erosion control. They provide benefits for 1,439 bridges, 21,206 farms and ranches, and they reduce sedimentation in streams and rivers by 9,457,702 tons annually.
Flood Control Dams Require Operation and Maintenance
Oklahoma’s 2,107 flood control dams make up a $2 billion infrastructure that provides direct benefits to both urban and rural areas in 61 of the 77 Oklahoma Counties, and indirect benefits to all of Oklahoma. Like any infrastructure, the dams require operation and maintenance. Local conservation districts have this responsibility for the majority of the dams.
Most of the dams were constructed in the 1950s through the 1980s with a 50-year design life. Eight hundred and seven of the dams have already reached or exceeded that 50-year mark, and by 2015 that number will be 1,100. While these dams remain safe and are providing flood control, the older dams do require more maintenance. Maintenance work includes removing trees from the dam and auxiliary spillway; repairing eroded areas; clearing debris from the principal spillway inlet; fertilizing grass, mowing brush and spraying for weed control. Much of this work is labor-intensive and requires operators with machineries such as compact track loaders equipped with mowers, tree saws, and excavation attachments. “According to reports we receive from the conservation district project sponsors, it would require four million dollars annually to fully meet the operation and maintenance of the dams,” says Robert Toole.
Some Dams Need to be Rehabilitated
High hazard dams are those with homes or other structures downstream that may be flooded by a dam failure and lead to loss of life. Some need to be rehabilitated to bring them up to current state-mandated dam safety standards and ensure they remain safe. Most of the dams were originally constructed as low-hazard dams to protect rural agricultural land from flooding. After the dams were constructed, houses, businesses, roads and other structures were built downstream in the breach inundation area of some of the dams. These dams have been reclassified to high-hazard which means they no longer meet state dam safety standards.
An estimated $457 million will be required to rehabilitate the existing 172 high-hazard dams to comply with federal and state dam safety laws, according to Toole.
Oklahoma has rehabilitated 32 dams since the year 2000, and 18 more are in varying stages of planning, design or construction. Sixty-five percent of the rehabilitation funding comes from the NRCS provided there is a 35 percent state match by the project sponsors.
Flood Control Dams are a Valuable Assess to the State
“Most Oklahomans are not even aware that the 2,107 flood control dams exist,” said Mike Thralls. “Most of the dams are in rural areas on private land and not visible to the public. Oklahoma is fortunate that conservation districts had the foresight to work with NRCS to establish watershed projects and develop this infrastructure of flood control dams and associated conservation practices. But now the challenge is to keep these dams maintained to ensure they remain safe and continue to provide their many benefits.”