The Patuxent River Watershed in Montgomery County drains to the
two reservoir system maintained by Washington Suburban Sanitary
System (WSSC). These are the Triadelphia and Rocky Gorge Reservoirs.
The Patuxent River begins in Frederick and then flows through seven
counties: Howard, Montgomery, Prince George's, Anne Arundel, Charles,
Calvert, and St. Mary's Counties. It is a major tributary to the
Chesapeake Bay and has been the focus of inter-jurisdictional watershed
protection since the early 1980's. In Montgomery County, there are
three subwatersheds; the Upper Patuxent, Lower Patuxent, and Hawlings
River. The total drainage area of these watersheds is approximately
61 square miles, about 7% of the total Patuxent River basin. Principle
land use in the Patuxent Reservoirs watershed consists of agricultural
cropland, pasture, and large lot residential, with many large areas
of forested parkland. Since 1996, there has been a local, inter-jurisdictional
agreement to protect the resources of the reservoirs, tributaries,
and contributing drainage.
The Upper Patuxent watershed is largely rural and residential,
including portions of Damascus. The Upper Patuxent River supports
a naturally reproducing brown trout population and Maryland Department
of Natural Resources has designated this reach as a special catch
and release stream above Tridelphia Reservoir. The streams in this
watershed are generally of high-quality and many serve as reference
streams for the County's stream monitoring program.
The Hawlings River begins south of the intersection of Routes 108
and 650, and flows into the Rocky Gorge Reservoir. There are three
distinct land uses associated with the Hawlings. The headwaters
are characterized by rolling agricultural. The middle area has a
steep, narrow valley with a rocky grade where stream velocity increases
substantially, and is protected by the Rachel Carson Conservation
Area. The lower portion of the stream transitions into a sandy loam
floodplain. The transition in geology, combined with uncontrolled
storm flows from the Olney Mill tributary have resulted in severe
bank erosion and scour pools.
Of the three subwatersheds to the Patuxent Reservoirs, the Hawlings
has the most urban/suburban uses, including drainage from Olney
and Brookeville. There is also significant drainage from the closed
Oaks Landfill. Regional in-stream stormwater ponds were used in
several tributaries of Reddy Branch. This type of structure reduces
in-stream habitat upstream from the structure due to the need for
heavy bank armoring to prevent erosion. Restoration activities have
been undertaken in several areas to address some of the problems
associated with the high density development that has taken place
in these tributaries.
The Lower Patuxent Watershed consists of the drainage area downstream
of the Hawlings River and continues to the County line. This area
primarily receives drainage from areas of agricultural and large-lot
developments and flows into the Rocky Gorge Reservoir. The mainstem
and lower reaches of the main tributaries are protected by state
park lands and a forested buffer also protects the WSSC reservoir.
However, streams in the lower Patuxent tend to exhibit higher levels
of impairment than the upstream tributaries.
Watershed Implementation Plan
Montgomery County Patuxent Watershed Implementation Plan (PDF, 73 pp 4.79mb)
The Montgomery County Patuxent Watershed Implementation Plan prioritizes full implementation of high and low priority projects during the MS4 permit cycle through 2015. Far fewer opportunities exist overall compared to the Anacostia and Rock Creek. The Plan identifies a limited amount of ESD on private land and stream restoration. Outreach was targeted for pollutant load reduction (primarily nutrients) but not for impervious cover credit. Riparian reforestation was not targeted within the MS4 Permit area due to cost effectiveness concerns in the Rocky Gorge subwatershed and limited opportunities in the Triadelphia subwatershed. In future MS4 permit cycles, the Plan explores ESD on private and public land and stream restoration more substantially. A limited amount of riparian reforestation will achieve some impervious cover and pollutant load reduction. According to the model employed in the Countywide Coordinated Implementation Strategy, implementation of the Patuxent WIP will achieve the Rocky Gorge phosphorus WLA within the MS4 permit area. The model also found that the Tridelphia phosphorus WLA will also be met, but with a longer timeframe needed for compliance.
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