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When it rains, urban areas that are largely paved, like Baltimore City and many parts of Baltimore County, deliver a huge amount of water to nearby streams either directly or through storm drains. Called stormwater runoff, this rainwater can have many negative effects on the urban environment.
When it rains, water flows off impervious surfaces like roads, roofs, and parking lots very quickly causing erosion and flooding in nearby streams. As dirty surfaces are flushed by rainwater, oils, chemicals, pet waste, lawn fertilizers, and trash are transported into storm drains and streams. Urban stormwater is considered to be one of the largest untreated pollution sources in the country, and Baltimore is no exception.
Scientists have determined that there is a direct correlation between the amount of paving in an urban area and the degradation of local streams. Because it is hard if not impossible to dramatically reduce the amount of paving, other steps need to be taken to manage the flow of stormwater.
Regulators issue stormwater permits to major urban jurisdictions under the authority of the Clean Water Act. Baltimore has a stormwater permit, called an MS4 permit, which requires the city as well as the counties to reduce the amount and improve the quality of stormwater that gets into streams. This has proved to be a challenging requirement.
The Healthy Harbor plan includes many strategies for dealing with stormwater. Some are new, others are an expansion of techniques already in use. Strategies include storm drain retrofits; use of vacant lots and other public lands for installation of stormwater practices such as raingardens; implementation of new regulations for redevelopment to capture more stormwater; expanding urban greening practices; and restoring degraded stream channels.