Historically, when it rained on the prairie, the majority of rainfall soaked into the organic rich soils.  Our streams were fed mainly through groundwater recharge.  As soil surfaces in our communities are paved over or built upon, the rainfall has few areas to infiltrate into the soil and instead moves as runoff to local streams.  This runoff is called stormwater runoff, which is rainfall and snowmelt that drains off impervious surfaces such as streets, parking lots, driveways, roof tops and compacted soils.  It eventually drains into a storm drain in the street that enters an underground storm sewer system that discharges in most communities directly into local waterways such as rivers, streams, creeks and lakes.  The concern with stormwater, is how it is managed locally for water quality and quantity or flood control.  Most stormwater is released directly into local bodies without any treatment.  Some communities use detention (dry basins) and retention (wet basins) to temporarily hold back stormwater during major rainfall events and release it more slowly to a local waterbody to minimize flooding impacts.

Once 10% of a given watershed (drainage basin) has been converted to impervious surfaces, significant ecological damage occurs as an increase in stormwater runoff from urban development is quickly collected and discharged into the storm sewer drainage system. The following impacts occur:

1. Groundwater is no longer recharged
2. Surface water becomes polluted
3. Streambanks and channels are degraded
4. Flooding occurs

The slow infiltration of rainfall into the surface of the soil and downward percolation through the soil profile is essential for replenishing groundwater that is water stored underground.   When urban development occurs it creates impervious surfaces such as streets, buildings, and driveways that prevents rainwater from infiltrating into the soil and decreases groundwater recharge rates.  Most Iowan’s depend on groundwater as a source of drinking water, so it’s important to replenish groundwater supplies when possible.

Urban development increases the amount of water draining to the closest stream, lake or river due to impervious surfaces (rooftops, sidewalks, streets & parking lots) generating greater runoff volumes and storm drains delivering it more rapidly to a stream. Streams are historically sized to handle only so much water – when more water is generated than a stream channel can handle the water spills out into the adjacent floodplain, the areas bordering streams and rivers.  This is called an “overbank” flood and can damage property and downstream drainage structures.  Urban areas are especially prone to “flash” floods, as the water comes and goes quickly, and can be as destructive to structures and aquatic life in streams. 

Operationally, the floodplain is usually defined as the land area within the limits of the 100-year storm flow water elevation. The 100-year storm has a 1% chance of occurring in any given year. In Iowa, a 100-year flood occurs after seven inches of rainfall in a 24-hour period (which is a storm that has a 10% chance of occurring in any given year – not one that occurs every 100 years, i.e., the 100-year storm).   As a consequence of water draining faster and in larger quantities off the land surface than before development, the elevation of a stream’s 100-year floodplain becomes higher, and the boundaries of its floodplain expand.  In some instances, property and structures that had not previously been subject to flooding are now at risk.

“Rainscaping” is a concept promoting infiltration-based stormwater management practices on a statewide basis. “Rainscapes” are stormwater practices that can be installed on both residential and commercial properties.

Rainscapes look like regular landscapes at a glance. However, one major difference exists: rainscapes are designed to retain and infiltrate a known quantity of runoff generated from a certain area, such as a rooftop, driveway, parking lot, or street. Rainscapes prevent rain from becoming polluted stormwater runoff.

Rainscaping and Green Infrastructure Practices

Stormwater best management practices, or BMPs, can fall into one of two categories – the Basic Rainscape or the Engineered Rainscape, also known as “Green Infrastructure.” Rainscapes mirror traditional landscape, but their commonalities end with plants and mulch. A great deal of work below ground ensures that a 1.25″ rain infiltrates, or .78 gallons per square foot of area are managed by the practice.

Bioswales	Bioretention Cells	Constructed Wetlands
Rain Gardens	Soil Quality Restoration	Native Landscaping

• Park/Dry Pond 
• Green Infrastructure
• Green Roofs
• Make Your Own Compost
• Native Garden Layout Brochure
• Permeable Pavers
• Rainwater Harvesting
• Soil Quality Restoration
• Stormwater Education Brochure
• Stormwater Management Strategies
• Stormwater Strategies for the Community
• Street to Stream - English
• Street to Stream - Spanish
• Tree Boxes
• Urban Prairie Strips
• Urban Stormwater Drainage