8/12/2019 Sheet 10 - Runoff

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Drought Fact Sheet #10

Contaminants in Runoff Can Taint Our Water SupplyContaminants in Runoff Can Taint Our Water SupplyContaminants in Runoff Can Taint Our Water Supply

How Does Runoff AffectOur Water Supply?

sediment worsen the impact. There are alsodissolved contaminants in surface flow that areindependent of the sediment. These can includesalts as well as various residential and farmchemicals. Any runoff that flows directly into awaterway will carry with it some of thesechemicals. In addition, when runoff is diverted intodrainage systems that route water directly to thenearest river or stream, the water does not soak intothe ground and is lost to groundwater recharge.

How Can We Mitigate the Effects of Runoff?From the perspective of drought planning there aretwo primary effects that need to be addressed. Thefirst is the impact of the pollutants on the surfacewater and its degradation as a water source in theevent of a drought. The second is loss of rechargewater through the direct discharge of runoff.One effective strategy is the development ofundisturbed vegetated buffers along the edges of

What Do We Mean When We Talk About Runoff?Runoff is surface water that flows across the land inorder to get to a body of water such as a stream,lake, or wetland. Runoff often transportscontaminants to these water bodies, reducing theirusefulness as a source of water in the event of adrought. Because drought preparedness is

concerned with decreased water quality and the lossof groundwater reserves, there is interest in all kindsof runoff, regardless of regulatory jurisdiction.Consequently, for the purposes of this discussion,runoff includes both stormwater and agriculturalrunoff.

Stormwater runoff carries with it the contaminantsthat accumulate on roadways, in green space and onopen storage areas. These can include sediment, oilsand greases, pet waste, trace metals, and fertilizersand chemicals from lawns. Another potential source

of stormwater runoff is found at construction sites.In areas where excavation has taken place, thenatural soil surface is disturbed and easily eroded bya significant storm event (see Fact Sheet #6).

Agricultural runoff can contain sediment, chemicals,and livestock waste. Possible sources includeagricultural tillage, which can reduce ground coverand increase sediment release, livestock grazing,which can bring livestock waste directly orindirectly in contact with the waterway, andirrigation practices that release contaminant-ladenwater back into waterways.

How Does Runoff Impact Our Water Supply?Believe it or not, increased runoff, can actually causea stream to become drier in the long run (see FactSheet #8). Another key concern is that runofftransports sediment and dissolved contaminants tothe waterway. The sediment itself is a seriouslydegrading factor, but the chemicals, bacteria andother contaminants that attach themselves to the

Stormwater runoff carries contaminants that accumulate

on roadways, in green space and on open storage areas.

8/12/2019 Sheet 10 - Runoff

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March, 2006

streams and waterways to control runoff. Thesebuffer areas can effectively intercept the runoff andfilter sediment and the attached contaminants fromthe water through a number of natural processes thatinclude vegetative uptake, chemical breakdown,uptake in the soil, and biodegradation. Additional

details about these processes and an introduction toseveral helpful agencies and documents can be foundat www.epa.gov/nps/agriculture.htmlAn excellentpaper that discusses agricultural runoff can be foundat www.forester.net/sw_0305_impact.html

The use of detention basins has gained widespreaduse in providing a way to increase stormwaterrecovery for groundwater recharge. The principleused in these basins involves holding the water longenough for sediment to settle out, and allowing asubstantial portion of the stormwater to infiltrate into

the groundwater supply after it is filtered andcleaned by the soil profile. An excellent source ofadditional stormwater information can be found athttp://cfpub1.epa.gov/npdes/pubs.cfm?program_id=6An excellent text that compares the various optionsfor stormwater control can be found athttp://www.epa.gov/npdes/pubs/usw_c.pdf

Constructed wetlands provide another method todetain and treat stormwater or agricultural runoffbefore it continues through the hydrologic cycle.

Constructed wetlands are different than natural

wetlands in that they are designed with watertreatment and detention in mind. They rely on thesame treatment processes as the other methodsdiscussed above, and can include the use of aquaticwildlife, and emergent vegetation to provideadditional treatment. Existing natural wetlands(jurisdictional wetlands) cannot be used to treatrunoff.

Stormwater detention basins, grassed waterways,riparian buffers, and constructed wetlands are alleffective ways to prevent runoff from entering anddegrading surface water that we depend on for helpin the event of a drought. Designs that prevent the

direct flow of runoff into waterways and provide away for this detained water to be filtered throughthe natural soil to recharge the groundwater willhave the greatest benefit to the prevention ofdrought.

How does Runoff Impact Drought Planning?Increased surface water runoff effectively shortcircuits the natural processes that ensure watertreatment and groundwater recharge. EveryDrought Plan needs to carefully consider measuresfor the restoration of these natural systems.Encouraging local policy decisions that supportmeasures to minimize runoff and encourage naturalinfiltration is an important step in the long-rangepreparation for a drought event. Remember, thegroundwater beneath your community is yourwater savings account. It is what recharges your

streams during the dry season. It is what you willbe counting on when a drought event occurs (seeFact Sheet #2).The NARC&DC would like to thank the USDAsNatural Resources Conservation Service for theirassistance in the development of this fact sheet.

Constructed wetlands provide another method todetain and treat stormwater or agricultural runoff.