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Drainage & Sewer System
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Natural Drainage Systems
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Natural Drainage Overview
Goals and Objectives
The natural drainage systems (NDS) program has two goals:
1. Slow the flow and reduce the volume of stormwater runoff. Retrofit and redevelop public right-of-ways to improve water quality and imitate hydrologic processes that existed before development
2. Use a state-of-the-science approach to apply existing and new data in adjusting technical stormwater management design objectives.
NDS has three objectives for management of urban stormwater in areas of the city draining into creeks:
1. Protect Aquatic Organisms: Minimize the fluctuation of stream levels and disturbance of creek beds during storms that account for up to 90 percent of the total volume of rainfall in a given year.
Why? Creeks within urban areas receive too much stormwater flow too often, completely altering the sensitive equilibrium between storms and creek organisms.
How? Stormwater volumes entering our creeks as surface water will decrease by letting stormwater infiltrate into soils. Stormwater turns into ground water that seeps into creeks and keeps water at a level that is habitable for fish and other aquatic organisms.
2. Protect Creek Channels: Where possible, NDS will be used to reduce the disturbance of creek channels to pre-development levels.
Why? Prior to development, large rainstorms significantly changed the physical form of creek channels only once a year or less. The use of traditional drainage systems in developed areas increases the speed and volume of stormwater flows. Subsequently, the physical form of creek channels changes more frequently. This leads to the damage of wildlife habitat.
How? By infiltrating into soils, stormwater flows and volumes entering our creeks will decrease and the physical form of creek channels will change less frequently.
3. Improve Water Quality: Reduce pollutants reaching water bodies.
Why? Urban environments generate pollutants that are transported to creek systems by stormwater, impacting creek life and the food chain that includes humans.
How? Soils and vegetation absorb water and filter out or chemically break down many contaminants.
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