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Rules & Design Standards
About the Rules of the Washtenaw County Water Resources Commissioner
The Rules embody a shift in stormwater management philosophy. Where in the past these rules have governed stormwater management from a flood control perspective, they have been revised to include design standards that provide more sophisticated quantity control, and directly address water quality.
These revisions are based upon the most current body of knowledge concerning stormwater management from across the state and country, modified as appropriate for application in Washtenaw County. A Technical Advisory Committee, representing both public and private interests within the County, contributed extensively to the content of these rules throughout the revision process.
These rules were issued pursuant to Section 105(c) of Act 591 of the Public Acts of Michigan of 1996, as Amended and The Michigan Drain Code Public Act of 1956, as Amended.
- Evan N. Pratt
Washtenaw County Water Resources Commissioner
Thoughtful planning and integration of stormwater management requirements in the design phase helps maximize the benefits green infrastructure can offer to any site. Unlike piped systems below the surface, infiltration systems can work with the natural landscape and land uses to become an asset to a site.
Preserving natural features, reducing disturbance, and minimizing impervious surface area will help reduce the total amount of stormwater a site will need to manage. This can result in smaller stormwater management facilities and reduced costs.
Review the Hierarchy of Preferred Best Management Practices (BMPs) before you begin site design.
Procedures & Design Criteria for Stormwater Management Systems (Section III revised 01/01/23)
- Rules and Guidelines - Procedures and Design Criteria for Stormwater Management Systems (2023)
- I Introduction (PDF)
- II Plat and Plan Submission and Review Procedures (PDF)
- III Permit Requirements and Review Fees (2023)
- IV Computational Requirements for Stormwater Management Systems (PDF)
- V Design Requirements for Stormwater Management Systems (PDF)
- VI Areas of Special Concern (PDF)
- VII Soil Erosion, Sedimentation and Pollution Control (PDF)
- VIII Appendix (PDF)
- Appendix A Glossary (PDF)
- Appendix B Major Categories of Non-Point Source Pollutants and Associated Impacts (PDF)
- Appendix C Stormwater Pollutant Hotspots (PDF)
- Appendix D Wastewater Treatment Systems, Community Drain Fields and Other Sanitary Facilities Under Michigan Drain Code (PDF)
- Appendix E Engineers Certificate of Consultation (PDF)
- Appendix F Example Three Stage Outlet Design (PDF)
- Appendix G Rainfall Precipitation Data (PDF)
- Appendix H Hydrologic Soil Groups for Washtenaw County (PDF)
- Appendix I Required Easement and District Language for Chapter 18 Drainage Districts (PDF)
- Appendix J Sample Agreement Form (PDF)
- Appendix K Maintenance Plan and Budget (PDF)
- Appendix L Engineers Certificate of Outlet (PDF)
- Appendix M General Guide to Native Plant Species (PDF)
- Appendix N Legal Opinion Regarding Need for Easements Downstream of Drainage District Outlets (PDF)
- Appendix O Order of Adoption of Rules (PDF)
- Appendix P Outlet Design Examples 2-Stage and 3-Stage (PDF)
- Appendix Q Index (PDF)