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 sewers 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

Stormwater Manual(Full manual: 17MB)

Traditional stormwater management strategies focused on conveyance and detention. Storm sewers were designed to move stormwater off urban landscapes to detention basins to reduce downstream flooding. The Iowa Stormwater Management Manual provides new stormwater management strategies that compliment the conveyance and flood control efforts of the past. The manual provides information on hydrologic 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 conveyance and flood control practices will make our stormwater management strategies more holistic and effective. 

Stormwater Manual(Full manual: 17MB)

Due to file size, various sections have been broken out and are available for individual download:
Chapter 1 - Specifications
Part 2A - General Information
Part 2B - Unified Sizing Criteria
Part 2C - Storm Water Hydrology
Part 2D - BMP Types and Applications
Part 2E - Infiltration Practices
Part 2F - Filtration Practices
Part 2G - Detention Practices
Part 2H - Storm Water Wetlands
Part 2I - Vegetated Swale Systems
Part 2J - Pavement Systems
Part 2K - Mechanical Systems
Part 2L - Coagulation and Flocculation
Part 2M - Storm Sewer Design
Part 2N - Design of Culverts
Part 2O - Open Channel Flow
Part 2P - Storm Water Easements
Part 2Q - References

Other Stormwater Resources

DNR Contacts
Storm water regulation issues:
Joe Griffin