Steve Stewart, 410-887-4488 Baltimore County EPS
- Watershed Assessments
- Stream Classification
- Stream Restoration
CRI conducted detailed Rosgen stream assessments and classifications and helped develop regional relationships for the Lower Gunpowder Water Quality Management Plan in Baltimore County, MD. Developing this management plan entailed a comprehensive and extensive assessment of stream conditions throughout 41-square mile Lower Gunpowder River watershed. The final plan will rely on water quality modeling and the results of extensive field investigations. CRI’s first task was completing a Rosgen Level I mapping of the entire watershed. We used available reference information to review geology and soils, relief, landforms, dominant land uses, and valley morphology. Approximately 1,400 stream reaches were classified using the Rosgen stream classification methodology, aerial photography, and topographic mapping. Reaches were classified as A through G channel types depending on slope, sinuosity, channel width, valley width, adjacent land use, and riparian buffer condition. A database of all reaches was developed to allow consistent data entry throughout subsequent phases of the project. The Level I mapping was a valuable task that provided a thorough overview of the range of existing stream types and a basis for prioritizing areas for evaluation in later tasks.
CRI also calibrated several USGS stream gages in Baltimore County in order to verify the bankfull channel dimensions and discharges of different stream types based on local watershed conditions. The gage calibrations required very detailed cross sectional and longitudinal channel surveys at the stream reaches where a gages were located.
Consistent field bankfull indicators were identified along the stream reach and plotted. The field bankfull elevation was then compared to the elevation from the USGS stream gage records to verify that the observed bankfull discharge had a return period of 1 to 2 years, depending on degree of upstream development. Data from the gage calibrations were plotted on regional curves published by Dunne and Leopold. Hydraulic relationships were developed and plotted based on the past operating records of the gage. The stream classification of the reach was provided. This task supplemented an ongoing effort by DEPRM to develop improved regional relationships based on physiographic province and degree of urbanization for use in ungaged watersheds in Maryland. Based on the Rosgen Level I mapping and USGS gage calibrations, CRI established representative reaches at various locations throughout the watershed. Representative reach locations were selected to denote the range of channel types identified in the Level I mapping. At least one representative reach was established for each channel type and substrate type. In several cases, more than one reach was established in order to represent the different degrees of forest cover or urbanization present in the watershed. The locations of the representative reaches were monumented and recorded with a global positioning system (GPS). Detailed Rosgen Level II geomorphic assessment and stream classification and Level III stability analyses were performed at each representative reach. Data extrapolated from the results of the representative reach assessment were used to analyze an additional 70 miles of stream length to Level II and Level III degree of detail. Remote sensing was used to evaluate an additional 129 miles of stream length to a Rosgen Level II classification. The watershed characteristics and the stream stability assessment were integrated into a comprehensive evaluation of the existing and potential water quality problems in the Lower Gunpowder River watershed. Water quality problems were ranked on a comparative subwatershed basis according to their impacts and relative magnitude of contribution to the overall water quality deterioration in the entire watershed. Management measures, capital improvement projects, alternatives, controls, and strategies were developed for reducing and preventing water quality problems in the watersheds and streams.