U.S. Department of the Interior

U.S. Geological Survey Printed on recycled paper

Fact Sheet 2009–3103

Prepared in cooperation with the Johnson County Stormwater Management Program

Stormwater Runoff: What it is and why it is important in Johnson 

County, Kansas

By Teresa J. Rasmussen1 and Heather C. Schmidt2

Stormwater runoff is a leading contributor to pollution in streams, 

rivers, and lakes in Johnson County, Kansas, and nationwide. Because 

stormwater runoff contains pollutants from many different sources, 

decreasing pollution from stormwater runoff is a challenging task. It 

requires cooperation from residents, businesses, and municipalities. An 

important step in protecting streams from stormwater pollution is understanding watershed processes, stormwater characteristics, and their 

combined effects on streams and water quality.

What is a watershed?

A watershed is the area of land where all of the water that falls in 

it and drains off of it goes into the same place. Watersheds range from a 

few acres draining to a neighborhood stream, to hundreds of thousands of 

square miles draining to a major river, such as the Missouri and Mississippi 

Rivers. Watersheds cross municipal, county, state, and national boundaries, 

so the actions of one community affect downstream neighbors.

What is stormwater runoff and why is it a problem?

During rainfall, part of the precipitation is captured by plants or 

infiltrates into the ground, and the remainder flows over the land surface as 

stormwater runoff to the nearest ditch or creek. In urban areas the percentage of precipitation that becomes stormwater runoff is much larger than 

in non-urban areas. Natural land cover that once absorbed rainfall has 

been replaced with impervious surfaces including streets, parking lots, and 

rooftops that prevent stormwater from soaking into the ground, and instead 

forces more water to flow at a faster rate into the storm drainage system 

(fig. 1). As it flows over the land surface, stormwater picks up potential pollutants that may include sediment, nutrients (from lawn fertilizers), bacteria 

(from animal and human waste), pesticides (from lawn and garden chemicals), metals (from rooftops and roadways), and petroleum by-products 

(from leaking vehicles). Pollution originating over a large land area without 

a single point of origin and generally carried by stormwater is considered 

non-point pollution. In contrast, point sources of pollution originate from 

a single point, such as a municipal or industrial discharge pipe. Polluted 

stormwater runoff can be harmful to plants, animals, and people.

What water-quality concerns exist in Johnson County and 

what causes them?

To better understand water-quality conditions in Johnson County 

streams, the U.S. Geological Survey, in cooperation with the Johnson 

County Stormwater Management Program, collected data on water and 

sediment chemistry and aquatic insect populations in the county’s five largest watersheds (Cedar, Indian, Kill, and Mill Creeks and the Blue River) 

and found that most water-quality concerns in county streams are related to 

excessive sediment, nutrients, and bacteria.

In large concentrations, sediment in streams reduces light penetration, smothers aquatic habitat, and transports and stores other 

1

 U.S. Geological Survey, Lawrence, Kansas.

2

 Johnson County Stormwater Management Program, Johnson County, Kansas.

Figure 1. Impervious surfaces such as streets, parking lots, 

and rooftops increase the amount of stormwater runoff in 

urban areas.

contaminants like nutrients and bacteria (fig. 2). Sediment can enter 

streams from surface erosion and streambank erosion. Surface erosion 

occurs when soil is disturbed and left exposed, which is common during construction of roads and buildings. A study of sediment in the Mill 

Creek watershed indicated that areas with the most construction activity 

contributed substantially more sediment to streams than established urban 

areas (Lee and others, 2009). Impervious surfaces increase the amount and 

rate of water flowing in a stream after intense rainfall and can cause stream 

banks to erode and the stream bed to shift. In 2005–06, about 90 percent of 

the total suspended sediment in streams was transported in less than 2 percent of the time, or about 7 days per year, and occurred during large storms 

that generated substantial runoff (Rasmussen and others, 2008). 

Streams and lakes need a certain level of nutrients (nitrogen and phosphorus) to support proper plant and animal growth; however, excessive nutrients 

can lead to excessive plant growth that disrupts natural ecosystems. When these 

plants die and decay it causes lower concentrations of dissolved oxygen in the 

streams and can lead to changes in plant and animal populations. Common 

sources of nutrients from stormwater runoff include fertilizers, animal waste, 

and soil erosion. 

Figure 2. Large amounts of sediment occur in Johnson County 

streams during stormwater runoff (Blue River near Kenneth Road). 
Bacteria such as Escherichia coli (E. coli) and fecal coliform commonly are used as indicators of the sanitary quality of streams and lakes for 

recreational use. Larger amounts of these bacteria indicate an increased risk 

that the water contains pathogens present in feces of warm-blooded animals. 

Potential urban non-point sources of bacteria include failing septic systems, 

leaking sewer lines, and pet and wildlife waste. As an example of how rapidly 

water-quality conditions in streams can change during storms, E. coli bacteria 

density in Kill Creek increased from about 180 col/100mL to about 100,000 

col/100mL in less than 12 hours when about 1.5 inches of rain fell over the 

Kill Creek watershed in May 2007 (Rasmussen, 2008).

How has stormwater runoff from urban areas affected the water 

quality of lakes, rivers, and streams in Johnson County?

Generally, as the population of an area increases, so does the amount of 

impervious surface area and non-point source pollutants available to stormwater runoff. These factors, in addition to loss of natural vegetation adjacent 

to streams, affect the ecology and overall quality of urban streams.

Data indicated that several stream contaminants are more common in 

urban areas than in rural areas. E. coli bacteria densities are larger in more 

urban watersheds (Lee and others, 2005). Sediment concentrations are nearly 

always largest in Mill Creek, which is Johnson County’s most rapidly developing watershed (Rasmussen and others, 2008). Chloride concentrations in urban 

streams are elevated during winter as a result of runoff from road salt application (Rasmussen and others, 2008). Also, the biological quality of Johnson 

County streams, determined using aquatic insect data, generally decreased as 

urbanization increased (fig. 3; Poulton and others, 2007). Aquatic insect populations in more urban streams generally have shifted from a diverse population 

of insect species that are intolerant of pollution (such as mayflies, stoneflies 

and caddisflies), to fewer different species that are more tolerant of pollution 

(such as midges, leeches, and worms).

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400

500

600

700

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1,000

0 5 10 15 20 25 30 35 40

10-METRIC AQUATIC INSECT SCORE

PERCENTAGE IMPERVIOUS SURFACE

Figure 3. Percentage of impervious surface (a general measure of 

urbanization) compared to a 10-metric aquatic insect score (a measure of 

overall stream health) at stream sites in Johnson County, Kansas, indicated that 

as urbanization increased stream health decreased (Poulton and others, 2007).

What practices are being implemented to manage stormwater 

and protect water quality in Johnson County?

As the focus of the federally mandated Clean Water Act has shifted 

from point to non-point source pollution (U.S. Environmental Protection 

Agency, 2005), stormwater quality has become increasingly important to local 

governments. In Johnson County, the Stormwater Management Program is a 

department of the county’s government that coordinates with the 20 cities in the 

county through the Johnson County Stormwater Management Advisory Council as well as other cities, counties, and agencies in the Kansas City metropolitan 

region to address stormwater management issues.

City and county governments in urbanized areas are responsible for 

minimizing pollution in stormwater runoff. To achieve this, local governments have passed laws to reduce the amount of sediment entering the 

waterways from construction activities; to prevent illegal dumping of pollutants (such as used motor oil, paint, and chlorinated pool water) into the 

storm drain system; and to require treatment of stormwater runoff from new 

developments through best management practices such as preserving open 

space and incorporating systems to treat stormwater runoff.

References Cited

Lee, C.J., Mau, D.P., and Rasmussen, T.J., 2005, Effects of nonpoint and 

selected point contaminant sources on Johnson County streams, northeastern 

Kansas, October 2002 through June 2004: U.S. Geological Survey Scientific 

Investigations Report 2005–5144, 186 p., accessed September 2009 at http://pubs.

usgs.gov/sir/2005/5144/.

Lee, C.J., Rasmussen, P.P., Ziegler, A.C., and Fuller, C.C., 2009, Transport 

and sources of suspended sediment in the Mill Creek watershed, Johnson County, 

northeast Kansas, 2006–07: U.S. Geological Survey Scientific Investigations 

Report 2009–5001, 52 p., accessed September 2009 at http://pubs.usgs.gov/

sir/2009/5001/pdf/sir2009-5001.pdf

Poulton, B.C., Rasmussen, T.J., and Lee, C.J. 2007, Assessment of biological conditions at selected stream sites in Johnson County, Kansas and Cass and 

Jackson Counties, Missouri, 2003 and 2004: U.S. Geological Survey Scientific 

Investigations Report 2007–5108, 68 p., accessed September 2009 at http://pubs.

usgs.gov/sir/2007/5108/.

Rasmussen, T.J., 2008, Water quality of streams in Johnson County, Kansas, 

2002–07: U.S. Geological Survey Fact Sheet 2008–3090, 4 p., accessed September 2009 at http://pubs.usgs.gov/fs/2008/3090/.

Rasmussen, T.J., Lee, C.J., and Ziegler, A.C., 2008, Estimation of constituent concentrations, densities, loads, and yields in streams in Johnson County, 

Northeastern Kansas, using regression models and continuous water-quality monitoring, October 2002 through December 2006: U.S. Geological Survey Scientific 

Investigations Report 2008–5014, 103 p., accessed September 2009 at http://pubs.

usgs.gov/sir/2008/5014/.

U.S. Environmental Protection Agency, 2005, National management 

measures to control nonpoint source pollution in urban areas: U.S. Environmental 

Protection Agency Office of Water, EPA–841–B–05–004, accessed September 

2009 at http://www.epa.gov/nps/urbanmm/pdf/urban_guidance.pdf

What can Johnson County residents do to help protect 

streams?

The Johnson County Stormwater Management Program 

recommends the following actions to help protect streams from the 

damaging effects of stormwater runoff:

• Never dump anything down a storm drain or any 

waterway, and properly dispose of trash and yard waste. 

In Johnson County, report stormwater pollution by calling the Stormwater Hotline 913–715–6969 or online 

at http://stormwater.jocogov.org/stormwaterpollution/

reportpollution.shtml

• Have soil tested to determine what treatment is needed for 

lawns and gardens. Use lawn chemicals sparingly. 

• Clean up pet waste and dispose of it in the trash or other 

appropriate location. 

• Purchase only chemicals that are needed and dispose of 

household hazardous waste properly. In Johnson County 

call 913–715–6900 to schedule an appointment to drop 

off household hazardous waste. 

• Repair and contain vehicle fluid leaks.

• Have onsite wastewater treatment (septic) systems 

inspected and maintained regularly. 

• Reduce runoff by re-directing roof drains away from pavement and toward vegetated areas. Consider using native 

plants and rain gardens to capture and infiltrate stormwater 

on your property. Use pervious stones or pavement for driveways. Use rain barrels or cisterns to capture rainwater from 

downspouts and use it to water plants.

For additional information, visit:

http://ks.water.usgs.gov

http://stormwater.jocogov.org

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