What is Stormwater?
Welcome
Stormwater means runoff during and following precipitation and snowmelt events, which
includes surface runoff, and interflow. An interflow is water traveling laterally or horizontally through the aeration zone during or immediately after a precipitation event that discharges to the Spokane River. To view some of the common pollutants found in stormwater runoff and the impact they have, please click here pollutant:
- Sediment:
This is often the largest pollutant load associated with stormwater runoff. The loadings have been shown to be exceptionally high in the case of construction activity. Sediment is associated with numerous impacts to surface waters, including increased turbidity, effects on aquatic and benthic habitat and reduction in capacity of impoundments. A number of other pollutants often attach to, and are carried by, sediment particles.
- Nutrients and Organic Matter:
Nutrients most often identified in stormwater runoff are phosphorus and nitrogen. In surface waters, these nutrient loads can lead to heavy algae growth, euthrophication (especially in impoundments) and low dissolved oxygen levels. Nutrients enter the storm sewer system in a variety of ways, including but not limited to landscaping particles (commercial and residential), car washing detergents and animal wastes. Decomposition of organic matter by organisms in surface waters results in depleted oxygen levels. Low levels of dissolved oxygen can impact water quality and life within surface waters. Sources of organic matter include leaking septic systems, garbage, yard wastes etc.
- Bacteria:
High bacteria levels may be found in stormwater runoff as a result of leaking systems, garbage, pet waste, etc. The impacts of bacterial on surface waters may pose health risks, affect recreation uses, and aquatic life.
- Oil and grease:
Numerous activities release oil, grease, and lubricating agents that are readily transported by stormwater. The intensity of activities, including vehicle traffic, maintenance and fueling activities, leaks and spills and manufacturing processes within the City of Spokane contribute the majority of these pollutants present in adjacent surface waters.
- Toxic Substances Including Heavy Metals:
Many toxic substances are potentially associated with stormwater including metals, pesticides, herbicides, and hydrocarbons. Toxic compounds may affect biological systems, and accumulate in bottom sediments of surface waters. Heavy metals such as cooper, lead, zinc, arsenic, chromium, and cadmium may be typically found in urban stormwater runoff. Metals in stormwater may be toxic to some aquatic life and may accumulate in aquatic animals.
- Temperature:
Stormwater runoff generally increases in temperature as it flows over impervious surfaces. In addition, water stored in shallow, unshaded ponds and impoundments can increase in temperature. Removal of natural vegetation (such as tree canopy) opens up water bodies to direct solar radiation. Elevated water temperatures can impact a water body's ability to hold dissolved oxygen to support fish and other aquatic organisms.
An illicit discharge is any discharge to a municipal separate storm sewer that is not composed entirely of stormwater; except for allowed non-stormwater discharges pursuant to the National Pollutant Discharge Elimination System (NPDES) permit and discharges resulting from emergency fire fighting activities. One goal of the stormwater permit is to eliminate illicit discharges. For some general tips you can use to help prevent illicit discharges please click here: preventing illicit discharges.
- Follow directions when applying lawn and garden chemicals and use them sparingly. This will help you save money.
- Properly dispose of household cleaners and recycle. Please visit http://spokanesolidwaste.org/default.asp for more information.
- Do not pollute bioinfiltration grass swales, other than stormwater.
- Store hazardous materials under cover or insde to prevent leaks and spills into storm drains.
- Compost leaves, grass-clippings and other wastes, or use City yard waste containers.
Please click on the link "Stormwater Brochure" to the left to view more detailed tips on preventing illicit discharges.
Bioinfiltration Grassy Swales
The purpose of grassy swales is to remove pollutants from stormwater
prior to infiltrating into the ground, helping to protect the Spokane
Valley-Rathdrum Prairie Aquifer. It is important to maintain grass swales
because they act as a biofiltration system for treating runoff.
Here are some tips to help with the longevity of your grassy swale. To view please click on the word maintenance.
Keep the inlets maintained by removing
sediment and debris that accumulate at the inlet of swales. Also keep
the grass and sediment low at the entry of the inlet; to allow the water
to enter the swale and percolate.
Remove accumulated trash and debris.
Maintain the grass and remove the glass clippings from mowing. Remove dead grass, rototill and re-seed or re-sod.
Use fertilizer as directed and sparingly.
Do not dispose of chemicals in swales.
Do not replace the grass with rocks.
Do not over water the grass. This slows or stops water movement through the soils
and will destroy the vegetation at the base of the swale.
Here are some examples of good/functioning swales: (click on image for a larger view)
Here are some examples of failing or bad inlets or swales: (click on image for a larger view)
