As rain washes urban surfaces, it collects all kinds of pollution from trash and debris to motor oil, lawn fertilizers, and animal feces. Pollutants that would be filtered by soil and vegetation pour into storm drains and ditches, creeks and rivers, and eventually the Chesapeake Bay. A severe storm may cause sewage treatment overflow or septic system failure. Construction sites where there is no plant cover can add silt which will later need to be dredged.
Issues: flooding, storm water management, legal regulations, costs & funding
Virginia's Water Budget Analysis in million gallons per day:
INFLOW: Precipitation 79,800 + Surface water inflow 1,770 = 81,570
OUTFLOW: Evapotranspiration 52,600 + Surface water outflow 28,700 = 81,570
Safe Drain lists ways of controlling storm water runoff at http://www.safedrain.com/stormwater-bmp
- Bio retention areas - land devoted to using either soil or plants to filter runoff from developed sites. The storm water flows into the area, ponds on the surface, and gradually seeps into the soil bed.
- Wet Detention (Ponds and Lakes) - natural or man made ponds that can remove water soluble pollutants up to 90% of suspended solids, up to 80% of metals and up to 40% of biochemical compounds through the natural sedimentation process.
- Dry Detention Basin – a pond planted with durable grass that can withstand large amounts of water. The basin collects and hold storm water runoff and will completely empty within 48 hours. It also uses the natural sedimentation process to remove pollutants.
- Filter Strips - densely planted strips of ground used primarily to contain runoff from paved areas such as roadways, small parking lots, play grounds, etc.
- Grassed Swales – a shallow channel or depression commonly used in highly developed areas. The storm runoff collects in the swale and natural sedimentation removes the pollutants.
- Green Roofs – rooftops that have been spread with top soil and planted with vegetation to reduce the amount of runoff from roof tops. They use natural sedimentation to filter pollutants.
- Infiltration Basin – man made basins planted with hardy vegetation that collects storm water and uses natural sedimentation to remove pollutants. These are commonly seen in parks and other recreation areas. The water will normally drain with 24 to 48 hours.
- Infiltration Planters – man made raised areas planted with vegetation to act as strip filters for parking lots, sidewalks and other paved urban areas. They are commonly seen around large buildings.
- Infiltration Trenches – man made excavations that are lined with filter material. The trench holds and filters the storm water until it eventually seeps into the surrounding soil. These are used in areas when the natural soil doesn’t drain quickly.
- Natural/Native Vegetation – plantings of natural grasses and other vegetation usually on higher ground adjacent to lowlands to reduce and slow runoff and trap sediment. They are normally used in areas where oil, grease and chemical pollution are not present.
- Pervious Pavement - porous pavement which, when properly maintained to make sure holes aren't clogged, can remove from 65% to 95% of pollutants and sediments. These can be used a strips in a parking lot where vehicles can drive over them.
- Rain Barrels and Cisterns – used to prevent runoff from roofs entering the storm drain system and can provide water for gardens, lawns and flower beds. These methods do not remove pollutants and sediments will have to be removed periodically from the barrel or cistern.
- Rain Garden - a small residential depression planted with native wetland and prairie vegetation designed to collect street runoff. They are a small scale version of bio retention areas.
- Wetland – man made wetlands designed to filer runoff and improve downstream water quality. These are commonly built on the outskirts of large cities as barriers for natural waterways.
http://www.hampton.gov/publicworks/stormwater/ditch_maintenance_plan.html Tentative Major Outfall Ditch Maintenance Schedule
http://www.hampton.gov/floodplain/local_flood_hazard.html The Local Flood Hazard
http://www.hampton.gov/publicworks/stormwater/ Storm Water
http://www.hampton.gov/publicworks/stormwater/storm_water_billing.html Stormwater Billing FAQ
http://www.wetlandswatch.org/sea_level/norfolk_city_flooding_pres_2010.pdf Flooding, Norfolk and the Region [p20 begins diagrams of mitigation possibilities p33]
http://hamptonroads.com/2010/12/feds-threaten-tougher-rules-stormwater-runoff Feds threaten tougher rules on stormwater runoff
http://www.wydaily.com/local-news/5462-clean-bay-or-leave-it-either-way-youll-pay.html Clean Bay or Leave it, Either Way You'll Pay
http://www.cbf.org/Document.Doc?id=591 The Economic Argument for Cleaning Up the Bay and Its Rivers
http://water.usgs.gov/wid/html/chesbay.html Chesapeake Bay: Measuring Pollution Reduction
http://www.deq.state.va.us/vanaturally/guide/water.html Virginia's Water Resources
http://www.cbf.org/Document.Doc?id=242 York River Fact Sheet
http://www.cbf.org/Document.Doc?id=233 Lower James Fact Sheet
http://www.oasisdesign.net/water/quality/coliform.htm Fecal Coliform Bacteria Counts: What They Really Mean About Water Quality
BMP stands for Best Management Practices and has become public works jargon for good storm water management.
Effluent is typically waste water or sewage, though it literally means anything flowing out. http://water.epa.gov/scitech/wastetech/guide/index.cfm
"Nonpoint source" is defined to mean any source of water pollution that does not meet the legal definition of "point source" in section 502(14) of the Clean Water Act. NPS pollution is caused by rainfall or snowmelt moving over and through the ground... As the runoff moves, it picks up and carries away natural and human-made pollutants.” http://water.epa.gov/polwaste/nps/whatis.cfm
“Point source" means any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged.” Section 502(14) of the Clean Water Act
Tailwater occurs when storm water in pipes and ditches encounters seawater, particularly at high tide or during storm surge. http://www.wetlandswatch.org/sea_level/norfolk_city_flooding_pres_2010.pdf
Total Maximum Daily Load (TMDL) gives the hard limits on how much nitrogen, phosphorus and sediment will be allowed in the Chesapeake Bay in the EPA’s “pollution diet.”