Yates Center, Kansas
During a 2016 discharge event, the 84-year-old spillway failed for the second time in its history on Yates Center’s Woodson Lake. Large areas of scour and erosion resulted. A second high-flow event one month later caused additional erosion to the damaged spillway.
KDWPT in partnership with the Federal Emergency Management Agency contracted Water Resources Solutions to use hydrologic and hydraulic analysis to determine the cause of this most-recent failure of the lake’s terminal spillway structures, and to develop proposed improvements. WRS completed the hydraulic analysis using both numerical and physical models to fully understand the spillway hydraulics and erosion patterns. WRS first numerically modeled the existing conditions on the approximately 800-foot by 300-foot spillway using the one-dimensional U.S. Army Corps of Engineers HEC-RAS. HEC-HMS and HEC-ResSim were used to create stage/storage and pool-elevation curves to characterize spillway discharge. Next, to refine the numerical modeling to account for the unknowns associated with the hydraulics that have a direct impact on the performance of the spillway, WRS also constructed and tested a distorted-scale physical model.
The physical model allowed the design team to better understand the flow patterns, velocities and riprap sizes necessary to sufficiently control the unsuccessfully checked flow energy through past spillways. Physical modeling was used first to faithfully recreate and then fully record the failure mechanism that caused the spillway to erode and wash downstream. Once the physical model of the existing conditions and failures was complete, the physical model was then used to create and test the proposed improvements and to better analyze proposed spillway repairs. The initially proposed stepped spillway and baffled apron were constructed at model scale, and then the proposed options were modified to accommodate hydraulic conditions.
As a result of the physical modeling, the final proposed improvements include two 5-foot vertical wall concrete drop structures spanning the spillway width, incorporating a 100-foot wide concrete baffled apron, 45-degree wing walls, 10.5-foot walls along the baffled apron to protect the banks and a final row of below-grade baffles to guard the toe.