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Impacts of Urban Development on Waterways

Steve Tonn, Douglas/Sarpy Counties Extension Educator

Urban development has a profound influence on the quality of the Omaha metro area’s waters. As the City spreads outward, more and more streams, especially small creeks feeding directly in to rivers, are transformed into urban streams. These natural areas are perhaps the most neglected watercourses.

An urban creek may experience many things on its journey from its headwaters in the upper watershed to its mouth at the confluence of a larger creek, stream, or river. It may pass through a park or residential area in one reach, then flow past a shopping mall or industrial park in the next. In a small, steep, wooded draw behind a residential area, it may become a convenient place to dump grass clippings or garbage. It may pass through vacant lots, becoming lost among the discarded appliances, shopping carts, and tires. It may flow through an over-fertilized golf course. It may flow for long distances inside a culvert underground. It may receive stormwater runoff from oily roads, parking lots, and factory drainage ditches. Uninformed neighbors may even dump used motor oil or antifreeze into storm drains that empty directly into the stream.

The situation worsens after construction. Roof tops, roads, parking lots, driveways and other impervious surfaces no longer allow rainfall to soak into the ground. Consequently, most rainfall is converted directly to runoff. The increase in stormwater can be too much for the existing natural drainage system to handle. As a result, the natural drainage system is often altered to rapidly collect runoff and convey it away (using curb and gutter, enclosed storm sewers, and lined channels). The stormwater runoff is subsequently discharged to downstream waters such as streams or lakes.

Once buildings and pavement are introduced, less water is able to penetrate the soil to be filtered of contaminants such as automobile by-products, pesticides, fertilizers, and excess sediment. Not only is the land less able to filter contaminants, but increasing numbers of people produce a greater pollutant load.

There are countless threats to water quality and wildlife habitat due to urbanization. The urban environment contributes 11.8% of nonpoint source pollution into the nation’s waters. Impacts result from residential, transportation, commercial, and industrial uses. Specific impacts include toxic substances that enter the food chain, petroleum products that are harmful to plants, fish and wildlife; excessive nutrients that increase algal blooms; and a reduction in water quality.

Sediment, fertilizer, pesticides, trash, automotive products, oil, paints, solvents, pet waste, gasoline, household chemicals are all examples of nonpoint source pollution. Stormwater management practices help to control nonpoint source pollution through the use of nonstructural and/or structural techniques to intercept surface runoff from developed areas, filter and treat this runoff, and then discharge it at a controlled rate. The overriding condition that governs the quantity of stormwater runoff is the amount of impervious surfaces located on your property (driveways, roofs, carports, sidewalks, etc.) Stormwater quality, however, is governed by the accumulation of pollutants on the entire surface area, regardless of whether it is grassed or paved. As the use of chemicals around the home such as fertilizers, pesticides, engine oils, deicing materials, and similar products increases, the more degraded the stormwater runoff from your property will be. Although the effect of one property on the quality and quantity of stormwater runoff may seem insignificant, the cumulative impact from hundreds of thousands of yards across the Omaha metropolitan area continues to be destructive to our water quality.

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