The Little River Drainage District is comprised of 550,000 acres in Southeast Missouri. The District functions through a system of levees, canals, basins, and drainage ditches. During the 2011 flood event, the Caney Basin emergency spillway was activated and floodwaters discharging from the Basin’s spillway exceeded velocities of 25’ per second. After the water receded, it was discovered that significant scouring and erosion of bedrock occurred, undermining the concrete spillway. Additionally, these large flows flanked the spillway and eroded the adjacent bank. Klingner inspected and identified issues requiring repairs and slope protection. In addition to the undermining and erosion repairs, it was determined that significant energy dissipation was needed. Klingner’s solution was to backfill and cap the scour holes with reinforced concrete doweled into the underlying bedrock and to install four check dams with low flow orifices. The spillway modifications were analyzed in USACE’s HEC-RAS software to determine the approximate velocities resulting from the proposed project. The project was reviewed and accepted by the Missouri Department of Natural Resources.
Following construction of the Caney Basin, Klingner was subsequently retained by Little River to design a spillway for Jenkins Basin. Similar to the Caney Basin, the Jenkins Basin is utilized during highwater events as a detention basin to accommodate and allow for the crest of a highwater event to more effectively and efficiently pass without overwhelming the District’s canals and ditches. Klingner designed a cast-in-place, reinforced concrete spillway to route flow in a controlled manner. Therefore, Klingner designed a concrete stilling basin at the base of the existing spillway to dissipate the energy before passing the discharged water on to the receiving ditch. The spillway and stilling basin designs were modeled in the USACE’s HEC-RAS software to determine dimensions necessary to achieve the required velocity reductions.