Radar Based Hydrologic Modeling and Site-Specific Storm Analyses: A Case Study in Ohio

Flood risk mitigation projects (dams, levees, flood diversion channels, etc.) were once most often designed for the flood of record or the expected response from a single estimated extreme design event, such as a 100-year 24-hour storm. The engineering design process today is rapidly evolving and multiple events with varied probabilities and durations are often considered. Other variables like spatial and temporal storm patterns and area-based precipitation depth reductions are being incorporated into grid-based numerical models and simulations to allow for more complex risk informed decisions related to various aspects of the design. The result is a design that’s more robust, more cost effective, more resilient, and ultimately a better solution.

A case-study for one such project on the Blanchard River, in Findlay, Ohio will be presented. A large flood diversion project had been proposed to reduce impacts to Findlay during extreme flood events. Stantec developed more detailed grid-based hydrologic modeling and 2D hydraulic modeling of the watershed and used the models to consider multiple objectives related to flood risk reduction. Applied Weather Associates was contracted to analyze regional trends in spatial and temporal storm patterns to develop a more realistic representation of hydrologic risk in the project area based on actual extreme storm events. Stantec’s hydrologic and hydraulic models were calibrated using ground-truthed radar data and stream gage data for several historic events. The models were then used to evaluate a series of synthetic storms with varying return periods, durations, and spatial patterns under Existing and several Proposed configurations. The end result was a more cost-effective set of recommendations that better reduced flood risks using channel modifications and a series of in-line dry detention storage basins. A general overview of the design process, results, and potential future applications is presented.