Natural and Beneficial Functions

Floodplains should be seen in their natural appearance.  They are more than just hazardous areas for development.  Open and natural areas, like the Vulcan Property off Rangeline Road and the Wetlands off Grand Avenue, absorb much more rain and floodwater than urbanized areas, reducing flood flows on downstream properties.  Wetland plants filter stormwater runoff, making it cleaner for those downstream.  These floodprone areas are used by a variety of wildlife and provide habitat for various species of animals.

It is important that we preserve such natural areas and wetlands.  While some development is allowed, local, state, and Federal regulations ensure that natural benefit areas remain by creating or improving natural habitats nearby.

Another concern is water quality.  Increasing population and expanding economy are placing unprecedented pressure on its land.  Urban sprawl, particularly the paving of large segments of the landscape, can have significant and usually negative impacts on water resources.  This can lead to significant degradation of streams and loss of aquatic life.  Most people realize that construction of any type impacts water quality.

Storm drains carry untreated stormwater runoff directly to our streams and river during heavy rain events.  Rains wash the oils from the roads, and debris into the storm drains which impacts our environment.  Oil, anti-freeze, paint, fertilizer and pesticides pollute the water, destroy plants, and endanger wildlife.

What Happens When It Rains?

When it rains, most of the rain infiltrates into the soil, where it eventually either is used by growing plants or percolates down to the ground water.  Ground water flows slowly into streams, usually over a period of months, providing steady base flow that fish and other aquatic life need.  By contrast, most rain that falls on a parking lot runs off immediately, often draining into storm sewers.

The following example is a “model” showing typical runoff from a 4 inch rainfall for four different land uses.  This 4 inch rainfall “model” represents a 10 year, 24 hour storm for much of Indiana.  (This means that there is a 10% chance of receiving four or more inches of rain in a single storm in any year.)  On a forest, meadow, or good quality turf grass, less than 1 inch or rain runs off (out of the 4 inch rainfall).  On a cropped field, the runoff is 2 inches, representing approximately half the rainfall.  On roofs or pavement, the runoff is 3.9 inches, which is about 97% of the rainfall.  (The other 3% gets caught in puddles or depressions and evaporates.)

*Assumptions:  NRCS “Curve Number” method of estimation; Hydrologic soil group; Row crops (corn/soybeans) have 30% residue coverage; Soil moisture before storm is average.

What’s Wrong With More Runoff?

Some of the results of increased runoff are:

• Increased frequency and severity of flooding.  If the runoff from a storm is greater, the chance of the flow exceeding the channel capacity and causing flooding increases as well.
• Reduced ground water recharge.  Water that runs off, particularly if it is channeled through storm sewers, never has a chance to recharge ground water.  This could be cause for concern, because 60% of drinking water in Indiana is provided from ground water, and ground water provides base flow to streams throughout the year.
• Decreased base flow in streams.  Base flow is the water that flows even during dry periods.  Most people prefer to look at a stream that has water throughout the year rather than one that is periodically dry.  More importantly, continuous base flow is vital to the health of aquatic life in the stream.
• Negative impact on stream health.  Streamflow varies even under natural conditions and most aquatic life is adapted to this.  But increased streambank erosion due to high peak flows, and periods of very low flow due to the decreased base flow add stress for man organisms.
• Reduced natural filtration of the water.  The process of passing through the soil is one of the most important purifiers of water.  Many pollutants are filtered, absorbed to soil particles, or eaten by microbes as water passes through the soil.
• Increased erosion.  Stream channel erosion is an important source of sediment in channels.  Erosion is very dependent on flow – doubling of he flow of the flow may cause the streambank erosion to increase by a factor of 4 or more.

What Can Be Done?

Strategies such as the following can minimize the effects of development on water quality:

• Minimize impervious areas.  Impervious areas can be reduced by incorporating open spaces into open areas, reducing road width, planning subdivisions so that driveways are smaller, reducing parking requirements, and using permeable alternatives to pavement such as gravel or porous pavement.
• Slow stormwater.  Avoiding direct connections from impervious areas to streams has an important effect on runoff.  Examples of eliminating direct connections include spreading rooftop runoff over pervious areas, and routing road or parking lot runoff to grassy swales rather than to storm drains.  The most common way stormwater is slowed, however, is by requiring stormwater basins (also known as retention/detention ponds).
• Reduce pollutant sources.  Many contaminates can be prevented from getting into stormwater through good management practices such as encouraging proper disposal of pet wastes; reducing fertilizer and pesticide runoff from lawns, gardens, cemeteries, and golf courses; and community hazardous waste and waste oil recycling centers.
• Protect critical areas such as buffer areas around streams.  The riparian areas along the edges of streams and waterways have a particularly important effect.  Buffer zones or “green belts” along streams can improve water quality while providing recreational areas for residents.  Buffer zones are particularly effective at reducing streambank erosion, filtering out sediment and sediment-bound contaminates, and promoting infiltration, and if the primary pathway followed by runoff water is over land (rather than through pipes) they will reduce dissolved contaminates.
• Plan development on a watershed basis.  Subdivisions require approval by the Planning Department, and a detailed drainage or water management plan for the proposed development is required as part of the approval process.  In most cases a drainage plan for the site itself is all that is considered, rather than how the development affects the entire watershed.  In order to protect streams and watersheds, a broader approach is needed.  A watershed approach would require an analysis of the watershed in which the proposed development fits into the cumulative development impacts in watershed.

The Future

Stormwater runoff is one of the leading causes of water quality problems in the United States.  Many cities have already been required to respond to stormwater runoff rules which required that they obtain Clean Water Act (NPDES) discharge permits.  Also, stormwater regulations expand control of stormwater runoff to cover small construction sites (under five acres).

There is no doubt that it is easier to plan for good stormwater management before development takes place rather than retrofitting existing development to reduce stormwater impacts.  Balancing the needs of growth and protection of the environment, (particularly streams, rivers and lakes) requires planning and commitment, but it is well worth the effort.  All citizens benefit when clean steams with healthy aquatic life flow in and around their communities.

References

Land Use and Water Quality – Jane Frankenberger, Department of Agricultural and Biological Engineering (6/23/99)