Iowa Stormwater Management Manual (ISWMM)

The ISWMM has been assembled to provide guidance and resources to local jurisdictions (cities, counties, etc.) that adopt ordinances or policies which set requirements for storm water management. It also provides guidance on properly sizing and designing post construction practices for consultants and plan reviewers. The practices described in the manual are not requirements of the DNR. For more information about the manual, resources for jurisdictions, resources for designers and reviewers, and additional planning and design resources, please click here.

We are currently transitioning the ISWMM into a new format and table of contents. The new format may have new numbers and titles and are listed on the left side. The old format is shown on the right side. Sections will be linked to the most current version of the manual. The new and old corresponding sections will be aligned horizontally to each other.

New ISWMM Format Old ISWMM Format
1.01 Stormwater Basics Ch 1 Sec 1 General Information
1.02 Planning and Design Principles Ch 1 Sec 2 Planning and Design Principles
1.03 Stormwater Regulations and Permitting Ch 1 Sec 3 Stormwater Regulations and Permitting
1.04 Stormwater Management Criteria Ch 1 Sec 4 Stormwater Management Criteria
1.05 Stormwater Management Plan (2020) Ch 1 Sec 5 Project Drainage Report
Stormwater Management Plan Template (2020)  
Engineering Technical Documents (Word .doc file) (2021)  
Storm Sewer Design Tables (2020)  
Stormwater Plan and Supporting Document Checklist (Excel .xls file) (2020)  
2.01 Overview of Stormwater Hydrology Ch 3 Sec 1 General Information for Stormwater Hydrology
2.02 Rainfall and Runoff Analysis Ch 3 Sec 2 Rainfall and Runoff Analysis
2.03 Time of Concentration Ch 3 Sec 3 Time of Concentration
2.04 Rational Method (abbreviated) Ch 3 Sec 4 Rational Method
2.05 NRCS TR-55 Methodology Ch 3 Sec 5 NRCS TR-55 Methodology
2.06 Runoff Hydrograph Determination Ch 3 Sec 7 Runoff Hydrograph Determination
2.07 LID Hydrology Ch 3 Sec 8 LID Hydrology
3.01 Unified Sizing Criteria (2019) Ch 2 Sec 1 Unified Sizing Criteria
3.02 Small Storm Hydrology Ch 3 Sec 6 Small Storm Hydrology
4.01 Introduction to Best Management Practices (BMPs) Ch 4 Sec 1 General Information for BMPs
4.02 Non-structural BMPs Ch 4 Sec 2 Non-structural BMPs
4.03 Selecting Structural BMPs Ch 4 Sec 3 Structural BMPs
5.01 Pretreatment Practices No previous chapter
5.02 Grass Swales Ch 9 Sec 1 General Information for Vegetated Swale Systems**
  Ch 9 Sec 2 Grass Swales**
  Ch 9 Sec 3 Dry and Wet Swales**
5.03 Vegetative Filter Strip Ch 9 Sec 4 Vegetative Filter Strips
5.04 Sediment Forebay Ch 3 Sec 11 Inlet Sediment Forebays
5.05 Hydrodynamic Devices Ch 11 Sec 1 General Information for Proprietary Mechanical Systems*
  Ch 11 Sec 2 Hydrodynamic Devices
5.06 Gravity Separators Ch 11 Sec 3 Gravity Separators
5.07 Catch Basin Sumps and Inserts Ch 11 Sec 4 Catch Basin Sumps and Inserts
6.01 Rainfall Collection and Reuse BMPs No previous chapter
6.02 Green Roofs Ch 17 Green Roof Systems
6.03 Rainwater Harvesting No previous chapter
7.01 Infiltration BMPs Ch 5 Sec 1 General Information for Infiltration Practices
7.02 Soils Testing Requirements for Infiltration Practices Ch 5 Sec 8 Soils Testing Requirements for Infiltration Practices
7.03 Soil Quality Management and Restoration Ch 5 Sec 6 Soil Quality Management and Restoration
7.04 Tree Filter Systems No previous chapter
7.05 Infiltration Trenches Ch 5 Sec 2 Infiltration Trenches
7.06 Bioretention Systems Ch 5 Sec 4 Bioretention Systems (2020)
7.07 Bioswales Ch 5 Sec 5 Bioswales
7.08 Infiltration Basins Ch 5 Sec 3 Infiltration Basins
8 Permeable Pavement Systems (2020) Ch 10 Sec 1 General Information for Permeable Pavement Systems**
  Ch 10 Sec 2 Pervious Concrete Pavement**
  Ch 10 Sec 3 Porous Asphalt Pavement**
  Ch 10 Sec 4 Permeable Pavers**
Permeable Pavement Design Checklist (Excel .xls file) (2021)  
9.01 Stormwater Detention BMPs (2019) Ch 7 Sec 1 General Information for Detention Practices
9.02 Methods to Estimate Required Detention Storage (2019) Ch 3 Sec 9 Detention Storage Design
9.03 Storage Routing for Final Detention Design (2019) Ch 3 Sec 10 Channel and Reservoir Routing*
9.04 Design and Modeling of Outlet Controls (2020) Ch 3 Sec 12 Detention Basin Outlet Structures
9.05 Water Balance Calculations Ch 3 Sec 13 Water Balance Calculations
9.06 Channel Routing Ch 3 Sec 10 Channel and Reservoir Routing*
9.07 Downstream Hydrologic Assessment Ch 3 Sec 14 Downstream Hydrologic Assessment
9.08 Constructed Stormwater Wetlands (2020) Ch 8 Sec 1 General Information for Stormwater Wetlands**
  Ch 8 Sec 2 Design of Stormwater Wetlands**
9.09 Traditional Dry Detention (2019) Ch 7 Sec 2 Dry Detention*
9.10 Extended Dry Detention (2019) Ch 7 Sec 2 Dry Detention*
9.11 Wet Ponds (2019) Ch 7 Sec 3 Wet Detention
9.12 Detention Retrofits (2019) No previous chapter
9.13 Underground Detention No previous chapter
9.14 Glossary (2020) No previous chapter
Constructed Stormwater Wetland Design Checklist (Excel .xls file) (2020)  
Dry/Extended Dry Detention Design Checklist (Excel .xls file) (2020)  
Wet Pond Design Checklist (Excel .xls file) (2020)  
10.01 Sand Filter BMPs Ch 6 Sec 1 Sand Filter
10.02 Surface and Perimeter Sand Filter Ch 6 Sec 2 Design of Surface and Perimeter Sand Filter
10.03 Underground Sand Filter Ch 6 Sec 3 Underground Sand Filter
11 Native Landscaping Ch 5 Sec 7 Native Landscaping
12 Regenerative Conveyance Ch 15 Sec 1 Channel Types and Structures**
  Ch 15 Sec 2 Open Channel Flow**
13 References Ch 18 References

Specifications
Old Format Notations
* Old chapter to be split into separate chapters in new format
** Old chapters integrated into one chapter in new format