URBAN RUNOFF AND STORMWATER
When rain falls in a city like Los Angeles, where rooftops, freeways, and paving comprise such a large proportion of the surface area, excess water is abundant. Runoff channels first into catch basins, then into overflow systems called storm drains. Besides rain, other sources of stormwater can include water from gardens, streets, car washing, and swimming pools. As flows merge, they collect in our storm drain system and are eventually dumped at a common point called an outfall site which releases the flow into a lake, bay or ocean. This makes it important not to leave materials where they might be swept or channelled into a catch basin. Pollution entering storm drains can include: fertilizers, cigarette butts, trash, pesticides, chlorine, automotive fluids, used oil, paint, chemicals, animal waste, and decomposing organic matter. Since most urban stormwater is not allowed to penetrate into the soil and re-enter the natural hydrologic cycle, stormwater systems bypass the organic decomposition of pollutants that occurs naturally in topsoil. When compared to a natural system, storm drains deliver more volume, and more pollution, into our oceans and lakes.
What about household water?
There are two separate systems of drainage: the Wastewater System (also called the sanitary sewage system) and the Storm Drain System. The sanitary sewage system is designed to handle water from sinks, washers, toilets, etc. Wastewater flows first through a home's plumbing system, then into an underground sewer pipe. This system terminates at a wastewater treatment plant and is processed before it is released at an outfall site.
What happens with stormwater?
Stormwater either infiltrates the soil, is conveyed over the soil surface, or it is detained by an impermeable material at the surface. Natural chemical and bacteriological processes that occur in the top few inches of soil break down oils and chemicals to help prevent the surface runoff from contaminating the groundwater. In places like cities where limited permeable surfaces exist, special infiltration basin structures may be built alone or as the base courses to pavement.
Ponds and wetlands function like natural treatment plants because they allow particles to settle out, and chemicals to be absorbed and decomposed in the bottom sediment. Because extended infiltration is a treatment process that relies on the physical properties of nature like sunlight, air, soil and microorganisms, it can also be much less expensive than mechanical treatment.
Sometimes, when ponding occurs over long periods, heavy peat begins to form which makes the soil even less permeable. This can become a problem when the water harbors pests like mosquitos or becomes stagnant
What about rivers and streams?
In cases where natural streams have been required to carry urban stormwater flow, stream erosion, channelization, and ultimately the destruction of natural habitat were common results. Before urbanization, soft bottomed natural channels only needed to carry a small percentage of the water that currently flows into storm drains.
You can help reduce stormwater by investigating the design and installation of permeable paving materials at home and in your community greening projects. Landscape practices such as hillside planting and terracing can help reduce runoff and assist in infiltration. Preventing wastewater and pollutants from entering storm drains is another way to help. You can report spills and abandoned waste by calling the L.A. Stormwater Hotline at 800/974-9794. Urban stormwater management is a dynamic process that must be constantly monitored in order to improve current practices. To find out the latest information on stormwater, you can check the L.A. City Watershed Protection's home page at http://www.LAstormwater.org.
Info on TMDLs and other stormwater issues.
Pollution prevention, NPDES compliance, education for businesses and the g
eneral public on helping to keep our waterways and ocean clean.
20 Year Wastewater Master Plan for the City, intergrating water recycling,
conservation and stormwater runoff diversion.