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AN EVALUATION OF STREAM RESTORATION EFFECTIVENESS IN AN URBAN WATERSHED
Citation:
STRIZ, E. A., P. M. MAYER, P. M. GROFFMAN, AND E. DOHENY. AN EVALUATION OF STREAM RESTORATION EFFECTIVENESS IN AN URBAN WATERSHED. Presented at Mid-Atlantic Stream Restoration Workshop, Berkeley Springs, WV, November 08 - 09, 2005.
Impact/Purpose:
To inform the public
Description:
The USEPA ORD Ground Water and Ecosystems Restoration Division has been conducting a before and after stream restoration evaluation of Mine Bank Run, a highly degraded stream in an urban watershed at Towson, MD. Mine Bank Run is being progressively restored from the headwaters down by Baltimore County. The objectives of the study are to 1) assess geomorphic benefits of restoration, 2) identify stream restoration techniques that enhance ground water/surface water interaction (GSI), 3) identify stream restoration methods that enhance denitrification, 4) develop guidelines for effective stream restoration. The study began in 2002 on a five hundred foot unrestored stream reach. Three monitoring transects composed of piezometer nests in the stream and stream banks and flood plain wells were installed. The piezometers and wells were instrumented with continuous data loggers to measure water level and temperature to define the ground water flow field. A continuous stream gage and rain gage were installed to capture surface water hydrology. Cross sections were monumented and evaluated to determine sediment transport. The wells and stream were sampled every two weeks for DOC, bioreactive nitrogen and cation/anion suites. This chemistry was collected to identify limits to microbial denitrification, a natural process occurring in soils and groundwater that removes significant amounts of bioreactive nitrogen. Two monitoring transects were also installed in the older headwater restored reach. The stream study reach was restored in 2005 using various techniques including reshaping stream banks, modifying the stream channel, armoring eroded banks, reconstructing stream meander features and riffle zones, and re-establishing riparian plant communities. Well transects were reinstalled, instrumented and the post-restoration monitoring phase began in fall 2005. The major pre-restoration findings show limited near stream and flood plain GSI interaction under base flow conditions. Storm events create the greatest water exchange in near stream sediments. Significant denitrification activity is occurring in the stream channel and ground water, especially where carbon concentration is high and the stream is connected with the floodplain. Bioreactive nitrogen is lower in the older restored stream reach than in the degraded reach likely due to enhanced carbon supply and reconnection of the stream and floodplain. The geomorphic stability of the older restored stream is greatly improved and far less sediment is being transported. These results appear to show restoration to be a potentially sustainable means of improving water quality through sediment transport reduction and the enhancement of the conditions necessary for denitrification, such as reestablishing near stream and flood plain water supply and/or increasing carbon availability to microbes. The continuing post-restoration evaluation should identify those stream features and restoration techniques which produce significant GSI, high denitrification activity, geomorphic stability and thus provide a BMP for addressing impaired streams.