Stormwater Problems & Impacts: Why All The Fuss?

Introduction Controlling stormwater runoff and its impacts is a serious issue facing many Stormwater local govern- Fact Sheet ment officials across North No. 1 Carolina and the nation. This fact sheet is No. 1 Citizens are of a four-part series for lo- complaining cal government officials on about flooding Local Governments Spend Millions Each Year Rectify- stormwater runoff problems caused by ing Flood Damage. and control strategies. The series covers: increased amounts of stormwater runoff, and the state and federal govern- 1) Stormwater Problems and Impacts ments are mandating local stormwater programs to control stormwater pollution. 2) Control Principles and Practices This series of fact sheets is designed to help local officials 3) Rules and Regulations better understand the problem and how it can be addressed. A Guidebook is also available for more detailed information and 4) Local Program Ele- ments and Funding assistance. Alternatives What Is Stormwater Runoff? Stormwater runoff is rainfall or snowmelt that runs off the ground or impervious surfaces like buildings, roads, parking lots, etc. and drains into natural or manmade drainage ways. In some cases, it drains directly into streams, rivers, lakes, sounds or the ocean. In other cases, particularily urbanized areas, it drains into streets and manmade drainage systems consisting of inlets and underground pipes commonly referred to as “storm sewers.” These sewers are not Land-Of-Sky Regional Council to be confused with sanitary sewers that transport human and indus- 25 Heritage Drive Asheville, NC 28806 trial wastewaters to a treatment plant before discharge to surface (704) 254-8131 waters. Stormwater entering storm sewers does not usually receive any treatment before it enters streams, lakes and other surface waters. 2 - Stormwater Problems & Impacts: Why All The Fuss?

What Is The Problem?

❏ 40% EVAPO- Increased Flows Cause Flooding TRANSPIRATION 38% EVAPO- 10% RUNOFF Stormwater runoff problems and impacts are 20% RUNOFF TRANSPIRATION most evident in areas where urbanization has 25% SHALLOW 25% 21% SHALLOW 21% DEEP occurred. Changes in land use have a major INFILTRATION DEEP INFILTRATION INFILTRATION INFILTRATION effect on both the quantity and quality of stormwater runoff. Urbanization, if not prop- NATURAL GROUND COVER 10% - 20% IMPERVIOUS SURFACE erly planned and managed, can dramatically 30% EVAPO- 35% EVAPO- TRANSPIRATION alter the natural hydrology of an area. In- TRANSPIRATION creased impervious cover decreases the amount 30% RUNOFF 55% RUNOFF of rainwater that can naturally infiltrate into the 20% SHALLOW 15% DEEP soil and increases the volume and rate of INFILTRATION INFILTRATION 10% SHALLOW INFILTRATION 5% DEEP stormwater runoff. These changes lead to more INFILTRATION frequent and severe flooding and potential 35% - 50% IMPERVIOUS SURFACE 75% - 100% IMPERVIOUS SURFACE damage to public and private property. Under natural conditions, typically 10% of Figure 1: Changes In Runoff Flows Resulting From Paved rainwater falling on a piece of property runs off Surfaces. (Source: Tourbier, et. al, 1981.) the land surface into streams, rivers or lakes. The remainder either evaporates into the air or PRE-DEVELOPMENT LARGE HIGHER AND MORE POST-DEVELOPMENT infiltrates into the soil replenishing groundwater STORM RAPID PEAK DISCHARGE supplies (Figure 1). Development of the site SMALL STORM MORE RUNOFF increases the percentage of impervious surfaces. VOLUME LOWER AND LESS As the percentage of impervious surfaces in- RAPID PEAK HIGHER GRADUAL creases, the percentage of runoff increases since BASEFLOW RECESSION there is less vegetated area to soak up the STREAMFLOW RATE rainwater. The rate of runoff and streamflow after a TIME storm event also shows dramatic increases under post versus predevelopment conditions Figure 2: Pre Versus Post Development Streamflow Rates (Figure 2). The higher and more rapid peak (Source: Schueler, 1987). discharge of runoff and streamflow can overload the capacity of the stream or river, causing and damage to bridges. When streambanks erode downstream flooding and streambank erosion. they clog stream channels, culverts, and pipes with Local governments spend millions of dollars sediment contributing to flooding problems. Sedi- each year rectifying damage to public and ment is washed into ponds, lakes and other im- private property caused by uncontrolled poundments reducing their capacity to store water stormwater runoff. In heavily developed areas, and requiring costly removal efforts. The increased damage to public and private property occurs volume and velocity of runoff and streamflow can during heavy rains. This damage includes road, also cause accelerated channel erosion and culvert and water and sewer line washouts, changes in streambed composition. This can flooded homes and yards, the deposition of destroy fish habitat and disrupt the natural ecol- sediment and debris on properties and roads, ogy of the stream or river. Stormwater Problems & Impacts: Why All The Fuss? - 3

❏ Runoff Degrades Water Quality Stormwater Stormwater runoff is also a major source of water pollution. Various pollutants are deposited Pollutants on surfaces due to man’s activities and are & Sources washed off during storms into storm drains or directly into streams, rivers and Sediment – Construction sites, disturbed areas, streambank erosion and alterations lakes. Pollutant levels are typically much Nutrients – Fertilized lawns, roadsides, leaky sewers & septic tanks higher in the first inch Bacteria – Leaking sewers & septic tanks, pet of runoff commonly wastes referred to as the “first Oxygen Demanding Substances – Leaky sewers & flush.” Some studies septic tanks, organic matter, pet wastes have found that ap- Oil and Grease – Leaky automobiles, industrial proximately 90% of areas, illegal dumping the pollutant loading Photo By George Johnson. Courtesy Of Sea Grant Program. Trace Metals – Automobile wear and tear, exhaust, Lawn Chemicals Are One is contained in the industrial areas Source Of Toxics. first flush. Therefore, Road Salt – Applications to snow and ice effective water quality Toxic & Synthetic Chemicals – Pesticide applica- protection requires the treatment of the first tions, automobiles, accidental spills, illegal dumping flush through the use of various preventive and Thermal Impacts – Heated landscape/impervious control measures. In addition, some pollutants areas, tree removal, shallow ponds are dumped or discharged accidently or illegally into storm sewer systems. Stormwater pollutants Figure 3 and their sources are listed in Figure 3. Cumulative Impacts valuable property • Aesthetics - Dirty water, trash and debris, foul The cumulative effects of stormwater runoff on odors water bodies are evident across the state. Streams • Fish and Aquatic Life - Impairment/destruc- draining urbanized areas have fair to poor water tion quality due to stormwater runoff and leaking • Impaired Recreational Uses - Swimming, sewer lines. Some shellfish waters along North fishing, boating, etc. Carolina’s coast have been contaminated and • Threatens Public Health - Contamination of closed due to stormwater runoff and other pollu- drinking water, fish/shellfish tion sources. Uncontrolled stormwater runoff has • Threatens Public Safety - Drownings in flood many impacts on humans and the environment waters including: • Economic Impacts - Fisheries, shellfish, • Flooding - Damage to public and private tourism, recreation related businesses property, including infrastructure • Increased Cost of Water and Wastewater • Eroded Streambanks - Sediment clogs water- Treatment - Stormwater pollution increases raw ways, fills lakes, reservoirs water treatment costs and reduces the assimilative • Widened Stream Channels - Loss of capacity of waterbodies. 4 - Stormwater Problems & Impacts: Why All The Fuss?

For More Information

❏ Reference Documents • Stormwater Management in NC: A Guide For Local Officials, 1994 Land-of-Sky Regional Council. Tel. (704) 254-8131. • Stormwater Management Guidance Manual, 1994, NC Cooperative Extension Service and NC DEHNR. Tel. (919) 515-3723. • Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs, 1987, Metropolitan Washington Council of Governments. Tel. (202) 962-3256 Streambank Erosion Fills Streams With Sediment.

❏ Contacts Next Fact Sheet • EPA Stormwater Hotline - (703) 821-4823. Fact Sheet #2 describes the principles and practices to • NC DEM Stormwater Management Group - control stormwater runoff and prevent or minimize its (919) 733-5083. impacts.

LAND-OF-SKY REGIONAL COUNCIL 25 Heritage Drive • Asheville, NC 28806

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