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Engineering and Environment Glossary of Terms

Cleaning and lining. A process by which the inside surfaces of water mains are cleaned of accumulated build-up and are then resurfaced and prepared for re-use.

Erosion. The wearing away of earth along stream banks and channel bottoms, leading to collapse of stream banks.

Impervious areas. Surfaces which prevent runoff from soaking into the ground, such as rooftops, parking lots, and roads.

Infiltration and inflow. Any non-sewage water entering into the sewer system, such as stormwater or ground water (sewer and storm drain systems are intended to be separate).

Runoff. Rainfall which flows across land or paved areas to enter storm drains or stream channels, carrying pollutants such as sediment, fertilizers, oil, and pet waste into streams.

Sedimentation. The carrying off and resettling of earth, sand, or dirt in urban runoff and in streams. Sources of sediment include construction sites, local erosion, and winter road sanding.

Sewershed. A drainage area in which sources of sewerage flow by either gravity or pumping to reach a common collection point.

Storm drainage. A system of underground pipes that carry runoff to stormwater management facilities or directly to streams.

Stormwater management (SWM). Stormwater management includes measures designed to manage, control, and/or mitigate surface runoff from storms, including but not limited to stormwater management facilities and non-structural stormwater management practices. Methods include ponds, wetland marshes, and filtering facilities.

As the City has developed over the years, land previously occupied by trees, shrubs, and porous soil has been replaced by structures such as streets, houses, buildings, parking lots, and sidewalks which are all impervious to water. Rainwater, then, courses rapidly over and off these structures with a quantity and velocity which, if unchecked, can have and has had damaging effects to streams and stream banks unable to handle it. Moreover, this flowing water runoff takes with it a volume of sediment and a variety of pollutants including fertilizers, oil, and pet waste which have their own deleterious effects.  The combination of storm drainage systems and stormwater management is designed to manage and reduce these consequences of urban runoff.

Stream restoration. Efforts to repair stream and stream bank damage due to urban runoff, to apply techniques to stabilize eroded areas, and to rebuild aquatic habitats.

Watershed. From the EPA : "A watershed, also called a drainage basin, is the area in which all water, sediments, and dissolved materials flow or drain from the land into a common river, lake, ocean, or other body of water." The City of Rockville lies over three watersheds, the Cabin John Creek Watershed, the Rock Creek Watershed, and the Watts Branch Watershed.