Washington Beltway (I-495) at I-270 junction. Thomas Branch, a tributary of Cabin John Creek, parallels
the left edge of the roadway.
The Cabin John watershed is densely urbanized with residential and commercial development covering more than 90% of the land. Much of the development took place before environmental regulations for stream buffers, stormwater management, and sediment and erosion control came into effect in the 1970s. Montgomery County is working to address on-site stormwater controls in the watershed.
Impervious surfaces, such as buildings, roads, and parking lots, cover about 26 percent of the watershed. Stormwater runoff carries pollutants that wash off of roads, parking lots, sidewalks, and rooftops. These impervious surfaces concentrate and accelerate the velocity of runoff, which results in stream erosion. The runoff and erosion have been so extensive that sanitary sewer pipes are now exposed along the creek and its tributaries; these pipes were originally buried 10-20 feet under the streams. A county study has documented these problems.
Data from 2013 show that stream conditions in most of the Cabin John Creek watershed are fair or poor, while a small area in the western part of the watershed has good stream conditions.
Some Water Pollutants Exceed State Limits
In Maryland, when water bodies do not meet water quality standards, the state Department of Environmental Protection issues specific pollution limits to the county, which then has to create and implement a plan to reduce pollution loads so they fall below the limits. These limits have a technical name: Total Maximum Daily Loads (TMDLs).
In the Cabin John watershed, the state has issued limits for two pollutants: Fecal Bacteria and Sediment. Because Cabin John Creek does not meet water quality standards, it is known as an “impaired stream.”
Streambank erosion on Cabin John mainstem created
by excessive stormwater runoff
Cabin John Creek mainstem, north of MacArthur Boulevard
It’s All Connected to the Chesapeake Bay
Improving water quality in the watershed is part of the regional effort to clean up the Chesapeake Bay. Under the Environmental Protection Agency’s plan to clean up the bay, the State of Maryland issued TMDLs for impaired waters in each county in the Chesapeake Bay watershed. The Cabin John Creek Implementation Plan (2012) and Assessment Summary (2018) lays out the county’s approach to reducing pollution in the watershed.
How You Can Help
Homeowners can reduce the amount and impact of stormwater rushing off their property by soaking it up and slowing it down. The Montgomery County Rainscapes Program offers rebates to residents who install landscaping projects that reduce stormwater impacts. Visit our Stormwater Solutions webpage and the Rainscapes website for details about how to do the projects and qualify for a rebate.