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Two-dimensional Habitat and Hydraulic Model of the Susquehanna River Below Conowingo Dam

As part of the Conowingo Hydroelectric Project’s FERC relicensing process, Gomez and Sullivan was given the opportunity by Exelon to build a two-dimensional (2-D) habitat and hydraulic model of the Susquehanna River below Conowingo Dam. Conowingo Dam, located on the main stem of the Susquehanna River in Maryland, is the largest and most downstream of several hydroelectric dams in the lower Susquehanna River before the river flows into Chesapeake Bay. The 4.5-mile study reach extended from the downstream face of Conowingo Dam to the river’s confluence with tidal waters. The model’s primary objective was to assess aquatic habitat downstream of Conowingo Dam for the Project’s normal operating flow range (3,500 cfs to 86,000 cfs).

The model required the compilation and input of several datasets, including combining recent topographic and bathymetric data, sediment survey results, and stakeholder-approved habitat suitability index (HSI) criteria. Target species included several life stages for American shad, striped bass, smallmouth bass, shortnose sturgeon, macroinvertebrates (mayfly, stonefly, caddisfly), and various other aquatic species. Several other datasets, including RTK-GPS-derived water surface elevations and ADCP-measured water velocities, were used to calibrate the model to within ±0.15 ft. of the observed water surface elevations.

After the model was calibrated, the results were used to estimate habitat for 23 distinct species, life stages, and habitat guilds over the entire study area. Model results were also used to provide data for a separate mussel habitat analysis. The model results were used to create flow versus habitat relationships, persistent habitat maps, and a habitat time series analysis. The model results were also used in several other relicensing studies requiring hydraulic data in the river, including a fish passage barrier analysis and sediment entrainment potential mapping. The model results will be used to better inform Exelon, resource agencies and other stakeholders’ future flow management decisions for the Conowingo Hydroelectric Project.