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Howard Duckett Dam Drainage Area Study
AMT provided hydrologic and hydraulic modeling support for this WSSC project, to assess spillway operations and downstream impacts from releases at the Rocky Gorge Dam. Services included hydrologic modeling using GIS-Hydro and HEC-1 for a 367 square mile watershed on the Patuxent River. The study included areas around the Town of Laurel (nearest the dam) and continuing downstream to the Town of Bowie, Maryland. This study area includes the Brighton Dam / Tridelphia Reservoir, Rocky Gorge Dam / T. Howard Duckett Reservoir and several waterway tributaries including the Little Patuxent River, Hawlings River, Cattail Creek, Cabin Branch, and the Middle Patuxent River. Modeling was first developed using the 100-Year Event as an update to the 1999 hydrologic modeling provided by WSSC, and then was refined using current land use plans, GIS-Hydro output, and modeling techniques structured to simplify future modeling updates to land use conditions. The 100-Year Model was then developed into modeling of the Probable Maximum Flood (PMF) Event using rainfall data developed in HMR-52 for worst case flooding at the Rocky Gorge Dam.
The resulting hydrologic modeling was then used to develop GIS-based mapping for flood inundation limits for the PMF Event and for dam-break analysis of the potential flooding limits. These models were converted from the 1999 HEC-2 data to current HEC-RAS models and more than 7-miles of additional river length was added downstream to incorporate the confluence with the Little Patuxent River and to provide a more comprehensive assessment of potential downstream impacts. The resulting modeling was utilized as appendices to the 2006 report update which AMT helped prepare, and the draft report is under review by WSSC. AMT will continue with the modeling as necessary to finalize the study and provide a basis for decisions by WSSC as to dam releases and downstream impacts for the watershed.
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