Severn River Watershed Management Master Plan

Client: Anne Arundel County Department of Public Works

Location: Anne Arundel County, MD

Services: Public Involvement, Stream Assessment, Watershed Modeling, GIS

Severn River is one of Maryland’s Scenic Rivers, flowing through the Atlantic Coastal Plain until it meets the Chesapeake Bay as a tidal estuary. There are a wide variety of land uses in the 68-square mile watershed, from farmland and forest to suburban developments, to the City of Annapolis. The watershed is home to several unique ecosystems and species, such as the Atlantic White Cedars associated with freshwater bogs.

KCI assisted Anne Arundel County in preparing a Watershed Management Master Plan for the Severn River. The study characterized the watershed’s land use, natural resources, water quality and hydrologic conditions; assessed future conditions with computer models of drainage and water quality; identified and ranked problems; and recommended potential improvement projects. Improvements included structural measures such as SWM retrofits and bioretention and non-structural measures such as watershed protection zoning or pollution prevention.

Public Involvement. Identifying and involving watershed stakeholders were key tasks of the study. The KCI Team provided educational publications and a website, attended meetings of the Severn River Commission, and hosted public meetings to keep residents, stakeholders and other interested citizens informed. The project website can be found at www.severn-river-watershed.com.

Watershed Assessment. As the first step, the KCI Team analyzed earlier studies of the Severn River to determine their usefulness for characterizing the watershed and for developing and calibrating computer models. An extensive effort to update critical GIS data was undertaken, including revising the County’s land use layer from digital orthophotography to make it more useful for hydrologic modeling. Modeling was performed to provide the County with the information and forecasts needed for the assessment, and included TR-20 for hydrology, HEC-RAS for stream hydraulics, and PLOAD and GWLF for pollutant loading and water quality.

Stream Assessment. All 140 miles of perennial streams have been assessed for qualitative information documenting areas of bed and bank erosion, overall geomorphic stability, water quality, aquatic habitat, riparian habitat and buffer conditions, and other potential environmental concerns or constraints. Three subwatersheds will receive more detailed biological and physical assessment using MBSS and Rosgen Level II methods.

The data was collected using GPS connected to a handheld field computer. Custom data collection forms were developed within the field software to allow field crews to enter data in the field. Field data was downloaded and converted to ESRI’s shapefile format so data could be brought into ArcView for QA/QC.

GIS-Based Watershed Management Tool. KCI was part of a development team integrating the most innovative and unique aspect of the project – the development of a Watershed Management Tool, which will keep the study dynamic and usable for county staff in the future as changes occur in the watershed. The information and computer models developed during the project was combined into a Watershed Management Tool which will tie the GIS data used for model input with the models and link the output to the County’s existing internet GIS application for viewing the data. The tool will help County staff guide the direction of environmental protection programs, future development in the watershed, and planning of flood protection and stormwater management projects. Specifically, the County can Model hypothetical scenarios to determine the effects of rezoning and development on the watershed.

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