Urban Effects on Streams
Increased Runoff: With urban development comes more impervious (hard) surfaces like parking lots, rooftops and roads. Since water cannot be absorbed by these surfaces (unlike soil), the runoff velocity of this water is increased. The development of land can increase runoff to 600% of what would occur naturally in it's absence.
When water infiltrates into soil, the soil can act as a filter for certain pollutants. In urban areas, water runs off directly into storm sewers, which outlet directly into streams or other water bodies. Any pollutants carried with this water runoff enters that stream or water body. Potential pollutants can be sediment from soil erosion, nutrients from improper fertilizer use, pesticides from lawn applications, oil from vehicles and salt used on roads in winter months.
Increased sediment: In developing areas, significant soil erosion occurs, and off-site damages from sediment occur. These off-site damages can include sediment on streets and in storm sewers, more sediment entering streams, more nutrients (like nitrogen and phosphorus) and other soil-carried pollutants entering streams.
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Clockwise from upper left: Sediment leaves construction sties, enters streets and culverts and eventually ends up in lakes or streams.
How to Reduce Water Runoff and Sediment
Nutrients: Nutrients can come from several sources, but come mostly from the overuse and misapplication of lawn fertilizers. High amounts of nutrients produce excessive growth of algae and other aquatic plants. These aquatic plants decrease the dissolved oxygen content of the water, thus negatively affecting habitat for fish and other aquatic organisms.
Overuse of lawn fertilizers is the major cause of water pollution.
Algae growth caused by excessive nutrients in lake
Algae growth reduces the dissolved oxygen content of water & decreases water
quality.
Pesticide Use: The improper use and storage of pesticides can pollute water supplies and kill aquatic organisms. According to the US Geological Survey, common pesticides found in streams in urban areas are diazinon, carbaryl, chlorpyrifos, malathion, atrazine, metochlor, simazine, prometon and 2,4,-D.
Dead fish in stream as a result of improper pesticide use.
Yard Waste Disposal: Leaves, grass clippings and other yard refuse placed along stream banks can worsen stream bank erosion. Existing vegetation and stabilizing roots are killed. When combined with an increase in runoff, the bank soils become unstable and begin to erode. Loss of land will eventually occur as more of the bank erodes. Yard waste washed into streams also causes water quality problems related to high nutrient levels and organic loadings (again, reducing the dissolved oxygen content of the water).
Leaves and grass clippings placed along this stream bank have
killed existing vegetation.
Protecting Streams from Litter & Debris
Litter & Debris: Healthy streams provide effective rainwater conveyance and fish habitat. Often, debris blockages occur, reducing channel capacity to carry water downstream, causing flooding and reduced aeration in the water. Debris can also deflect stream flows into banks causing increased erosion as well as pollute the water.
Trash in streams is not just unsightly, but degrades water
quality and can cause bank erosion. Debris blockages at right can reduce
channel capacity and deflect stream flows.