CS3B - Session 03B Spillway Hydraulic Modeling Tools: Suite-ly, Modeling a New Dam - Using a Variety of H&H Tools to Accomplish Multiple Tasks with Different Goals

Abstract Description: Hancock County and the City of Findlay, Ohio experience frequent and significant riverine flooding, impacting land, streets, homes, and businesses within the floodplain. Stantec was contracted by the Maumee Watershed Conservancy District to develop solutions to reduce the risk of flooding. Since 2017, the Eagle Creek Flood Basin has been planned, conceptualized, and designed – first Preliminarily, then through Final details! The Eagle Creek Flood Basin includes a 3.7-mile-long embankment and forms a dry-storage reservoir with a maximum storage capacity of 9,840 acre-feet. It is designed to have storage capacity for the 1% Annual Chance Exceedance (100-year) storm event on Eagle Creek with an Auxiliary Spillway designed to safely pass flood events of greater magnitude, up to the Probable Maximum Flood.

Drawings for a new dam are straightforward enough; containing plan views, profiles, sections, and details. But what did it take to get there? Throughout the process, a host of hydrologic and hydraulic modeling tools were used to achieve a project that has now been permitted through ODNR Dam Safety and is ready for construction. This presentation will discuss how SWMM, HEC-HMS, HY-8, HEC-RAS (1D, 2D, and hybrid 1D/2D), Flow3D and even Excel were used both independently and iteratively to accomplish the design of a safe, new dam and its many components. Specific goals of the modeling included the design of the Principal and Auxiliary Spillways, sediment transport, channel armoring, exterior drainage, fish passage facilities, development of stage discharge relationships, evaluation of downstream benefits and upstream impacts, and the analysis of potential dam breach inundation extents. Multiple models were developed for purposes of design, regulatory review, and dam safety approval.

Additionally, a 3D Computational Fluid Dynamics (CFD) Flow3D model of the hydraulic structures was created to confirm the empirical rating curve calculations and discharge coefficients available within HEC-RAS for the spillways, confirm energy dissipation performance, and verify that the fish passage criteria established for the project were being achieved with more fidelity than the 1D or 2D models. The CFD model was used in an iterative design process with the 1D and 2D modeling to overcome the inability of 1D and 2D models to accurately represent the complex hydraulic conditions in the spillway. This iterative design approach allowed the team to leverage the accuracy of CFD modeling and the speed of the 1D and 2D modeling to test alternative configurations rapidly, resulting in a more confident final design.