Sawmill Creek Stream & Watershed Assessment
Anne Arundel County, MD
CLIENT: Anne Arundel County Department of Public Works
Prime: BayLand Consultants & Designers, Inc.
The Sawmill Creek Stream and Watershed Assessment project consists of the assessment of an 8.8 square mile watershed to identify stream restoration and stormwater management (SWM) retrofits to document water quality credit towards Anne Arundel County’s National Pollutant Discharge Elimination System (NPDES) municipal separate storm sewer system (MS4) permit restoration requirement, and assist in meeting the County’s wasteload allocation (WLA) towards the Chesapeake Bay Total Maximum Daily Load (TMDL). The project includes the assessment of 27,350 linear feet of stream, 52 adjacent SWM outfalls, and 8 SWM ponds to determine which reaches, outfalls and/or ponds are viable candidates for restoration and/or retrofit.
The Study Area included the Sawmill Creek main stem and three tributaries: Irving Branch, Ferndale Branch and Muddy Bridge Branch; as well as, the adjacent floodplain and floodplain terrace areas. Historic land use changes within the subwatershed, including extensive deforestation associated with the expansion of agriculture, followed by rapid commercial and residential development, have largely influenced watershed hydrology and channel morphology. Additionally, channel alterations associated with the implementation of utilities and roads have resulted in areas of channel incision, bank erosion and irregular planform geometry among other signs of instability.
Sawmill Creek, Irving Branch, Muddy Bridge Branch and Ferndale Branch were broken into 22 distinct study reaches for assessment and design efforts. A visual existing conditions assessment of each study reach was performed and later expanded upon using field collected geomorphic data.
A Watershed and Study Area Assessment Report (WSAAR) was prepared that summarized pertinent attributes of the Study Area including: physiography, soils, climate, existing and historical land use, jurisdictional wetlands and streams, historic wetlands, plant communities, rare, threatened and endangered species, and cultural resources. This report also summarizes the areas targeted for restoration and the proposed restoration approach. Multiple assessments and analyses were conducted to determine the areas proposed for restoration, including: a visual assessment, constraints analysis, hydrologic analysis, geomorphic assessment, biological assessment and a function based assessment. The function based assessment was conducted in accordance with the guidelines from A Function-Based Framework for Stream Assessments and Restoration Projects. A ranking system was then developed by BayLand to determine the priority for restoration for each reach by assigning scores to each existing function based assessment rating.
The WSAAR was completed in January 2017; schematic design for the proposed restoration reaches, outfalls and SWM BMPs is on-going.