Storm Water

Permeable pavement in this parking lot helps rainwater soak into the ground instead of running off.Storm water runoff is the rainfall or snowmelt that runs off permeable surfaces or impervious surfaces like roads, buildings, sidewalks or compacted ground surfaces.

Storm water can flow directly to streams and lakes or it may be transported by municipal storm drain systems. Unlike sanitary sewers, storm drains do not lead to treatment plants, but drain directly into our streams and lakes. 

And according to a six year study conducted by EPA, urban storm water contains concentrations of pollutants that are equal to or larger than non-urban runoff.

As communities grow, they often experience more storm water runoff problems due to their increasing impervious surface areas. Rainfall and snowmelt that would normally infiltrate into the soil becomes runoff. This increases both the volume and rate of runoff, which leads to flooding, streambank erosion, and potential damages to public and private property and water quality.

The Iowa Department of Natural Resources is working in a variety of ways to improve storm water quality. Certain activities and specific municipalities and universities must obtain permits with requirements that are intended to reduce the impact of storm water on our lakes and streams. In addition, DNR and its partners have developed a number of storm water "tools" to assist developers, builders, cities and individual Iowans.

Financial Assistance



Manuals and Brochures


Stormwater Regulations and Permitting


Iowa Storm Water Manual
Traditional storm water management strategies focused on conveyance and detention. Storm drains were designed to move storm water off urban landscapes to detention basins to reduce downstream flooding. The Iowa Storm Water Management Manual provides storm water management strategies that compliment the storm drain network and flood control efforts of the past. The manual provides information on runoff and stream flow changes with urban development, uniform sizing criteria, low impact development alternatives and design guideline for practices that protect water quality and reduce stream corridor erosion.

Historically, 90 percent of annual rainfall has been from events that are less the 1.25 inches. A primary focus of the manual is to provide design guidelines for practices that infiltrate small runoff events to protect water quality. The manual also provides design guidelines for stream corridor protection, which is important because stream corridor erosion causes up to 70 percent of sediment loading in urban areas. These practices provide significant water quality benefits, and protect pipelines, sanitary sewers and other infrastructure. Adding water quality and channel protection practices to traditional storm drain network and flood control practices will make our storm water management strategies more holistic and effective.


Other Stormwater Resources


DNR Contacts
Storm water regulation issues:
Joe Griffin
515-725-8417
Joe.Griffin@dnr.iowa.gov