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On-Call Water Quality Restoration, Montgomery County, MD
A. Morton Thomas and Associates has provided water quality restoration engineering and design services in support of Montgomery County's Watershed Planning, Management and Improvements program for a number of years. Projects have included evaluating drainage areas for 80 acres to 20 square miles; reviewing existing studies/data; evaluating existing land use and topography as well as watershed characterization in terms of both stormwater management and channel condition, watershed pollutants, aquatic habitat, soil conditions, site limitations, and wetlands; preparing GIS mapping; developing concepts and design for innovative water quality measures for regional watersheds including peat/sand filters, wetland marshes and extended detention facilities; and participating in public outreach/relations campaigns.
Representative task assignments have included:
- Sligo Golf Course Pond - Project consisted of a dam embankment and excavation to create a permanent pool to provide stormwater quantity and quality control. The pond was also designed to provide extended detention for the first flush storm runoff and 2-year flood control.
- Hollywood Branch Peat/Sand Filter - This was the first project in Maryland to utilize an underground peat/sand filter for stormwater quality purposes. Other unique aspects of the project included a flow splitter to divert the "first flush" runoff and a permanent pool stilling basin to allow for the settlement of sediments.
- Dickerson Forebays - Project included TR-20 modeling of three watersheds and three existing compost water quality ponds, design of pretreatment forebays to meet NPDES requirements, wetland delineation and permitting through MCDPS, MDNR, USACOE and MDE.
- Northwood Stream Restoration - Project services included design of erosion control and streambank protection measures as well as in-stream and riparian habitat improvements using bioengineering techniques such as vernal pools and wetland enhancements. Provided field surveys; cross sections of the stream channel; NRI/FSD and wetland delineation for jurisdictional determination; and design to improve storm flow access to the floodplain, reduce velocity, and provide water quality treatment at storm drain outfalls.
- Watts Branch Watershed Restoration Study - Provided assessment and prioritization of stormwater management and stream enhancements for Watts Branch. Services included prioritization of subwatersheds, identification of retrofit and new SWM opportunities, hydrologic modeling of the 1, 2, 10, and 100 year storms, development of SWM concept designs, investigation and ranking of 10 miles of stream restoration opportunities, and preparation of stream restoration concept design. (Study on-going)For both of the previous projects TR 20 analyses were performed to determine the 1-, 2-, 10-, 50-, and 100-year storm event discharges. A HEC-2 model was developed for each stream, using the computed discharges for each stream, to determine the 100-year floodplain, velocities and shear stresses for the existing condition and improved condition of the stream. The hydrologic discharges and bank full elevations and geomorphic analogies were used to determine the proposed streambank protection measures and stream meanders as necessary. The HEC–2 cross sections in the model were then modified from existing to proposed conditions to include the modification improvements in the streams to determine any impacts due to the proposed improvements. Permits for NRI/FSD, Erosion and Sediment Control, Non-Tidal Wetlands, and access were obtained. Community participation was encouraged and Community meetings were held to summarize the process of the design and construction activities.
Other Environmental Services Projects
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