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Runoff Calculator

Roads, commercial buildings, and large public parking lots certainly generate a great deal of run-off, but so do our own residences.  At home, rooftops, driveways, patios and other hard surfaces prevent precipitation from absorbing into the ground.  This means that less rainfall is absorbed into the soil to become groundwater, and more rainfall becomes runoff. 

This excess runoff causes water to flow into waterways more quickly than would occur in a natural, undeveloped environment, increasing the risk and severity of flooding.  It also introduces more non-point source pollution into our waterways, as contaminants on the ground can get swept up with this water, enter our storm sewer system, and eventually discharge into surface waters. Even if the water was totally clean, the sheer volume of additional water creates "flashy" stream conditions with lower flow in dry weather and significantly higher flow during wet weather. This increases erosion of river banks, impacts biodiversity, and degrades overall stream health. 

Use this calculator to determine how much runoff your home produces based on its square footage. If you know it, add the area of your driveway as well. In Lansing, Michigan, the average annual rainfall is 32 inches. 

Interested in learning how to prevent this run-off from entering our waterways? Visit our rain garden resources page. Rain gardens and other green infrastructure solutions can help capture and infiltrate run-off on site!

For reference, Lansing, Michigan receives an average of 32 inches of rain fall per year.

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