Iowa Stormwater Management Management Manual

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 stormwater 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, read more about the manual.

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 FormatOld ISWMM Format
1.01 Stormwater BasicsCh 1 Sec 1 General Information
1.02 Planning and Design PrinciplesCh 1 Sec 2 Planning and Design Principles
1.03 Stormwater Regulations and PermittingCh 1 Sec 3 Stormwater Regulations and Permitting
1.04 Stormwater Management CriteriaCh 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 file) (2021) 
Natural Resource Inventory Example Maps 
Storm Sewer Design Tables (2020) 
2.01 Overview of Stormwater HydrologyCh 3 Sec 1 General Information for Stormwater Hydrology
2.02 Rainfall and Runoff AnalysisCh 3 Sec 2 Rainfall and Runoff Analysis
2.03 Time of ConcentrationCh 3 Sec 3 Time of Concentration
2.04 Rational Method (abbreviated)Ch 3 Sec 4 Rational Method
2.05 NRCS TR-55 MethodologyCh 3 Sec 5 NRCS TR-55 Methodology
2.06 Runoff Hydrograph DeterminationCh 3 Sec 7 Runoff Hydrograph Determination
2.07 LID HydrologyCh 3 Sec 8 LID Hydrology
3.01 Unified Sizing Criteria (2019)Ch 2 Sec 1 Unified Sizing Criteria
3.02 Small Storm HydrologyCh 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 BMPsCh 4 Sec 2 Non-structural BMPs
4.03 Selecting Structural BMPsCh 4 Sec 3 Structural BMPs
5.01 Pretreatment PracticesNo previous chapter
5.02 Grass SwalesCh 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 StripCh 9 Sec 4 Vegetative Filter Strips
5.04 Sediment ForebayCh 3 Sec 11 Inlet Sediment Forebays
5.05 Hydrodynamic DevicesCh 11 Sec 1 General Information for Proprietary Mechanical Systems*
 Ch 11 Sec 2 Hydrodynamic Devices
5.06 Gravity SeparatorsCh 11 Sec 3 Gravity Separators
5.07 Catch Basin Sumps and InsertsCh 11 Sec 4 Catch Basin Sumps and Inserts
6.01 Rainfall Collection and Reuse BMPsNo previous chapter
6.02 Green RoofsCh 17 Green Roof Systems
6.03 Rainwater HarvestingNo previous chapter
7.01 Infiltration BMPsCh 5 Sec 1 General Information for Infiltration Practices
7.02 Soils Testing Requirements for Infiltration PracticesCh 5 Sec 8 Soils Testing Requirements for Infiltration Practices
7.03 Soil Quality Management and RestorationCh 5 Sec 6 Soil Quality Management and Restoration
7.04 Tree Filter SystemsNo previous chapter
7.05 Infiltration TrenchesCh 5 Sec 2 Infiltration Trenches
 Ch 5 Sec 4 Bioretention Systems
7.07 BioswalesCh 5 Sec 5 Bioswales
7.08 Infiltration BasinsCh 5 Sec 3 Infiltration Basins

Bioretention Design Checklists:

 
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**

Supporting Documentation Checklists:

 
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 (2021)Ch 3 Sec 12 Detention Basin Outlet Structure
9.05 Water Balance CalculationsCh 3 Sec 13 Water Balance Calculations
9.06 Channel RoutingCh 3 Sec 10 Channel and Reservoir Routing*
9.07 Downstream Hydrologic AssessmentCh 3 Sec 14 Downstream Hydrologic Assessment
9.08 Constructed Stormwater Wetlands (2021)Ch 8 Sec 1 General Info 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 DetentionNo previous chapter
9.14 Glossary (2021)No previous chapter

Design Review Checklists:

 
Supporting Documentation Checklist (2023) 
10.01 Sand Filter BMPsCh 6 Sec 1 Sand Filter
10.02 Surface and Perimeter Sand FilterCh 6 Sec 2 Design of Surface and Perimeter Sand Filter
10.03 Underground Sand FilterCh 6 Sec 3 Underground Sand Filter
11 Native LandscapingCh 5 Sec 7 Native Landscaping
12 Regenerative ConveyanceCh 15 Sec 1 Channel Types and Structures**
 Ch 15 Sec 2 Open Channel Flow**
13 ReferencesCh 18 References

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