Development Standards - Design Methodologies

Stormwater Design Methodologies

Simplified Method

Facilities designed in accordance with the simplified approach are presumed to comply with the City’s pollution reduction and flow control requirements. 
  
  Form SIM
  
Presumptive Method

The presumptive design approach is used for particular facility types that do not lend themselves well to the simplified sizing. More detailed hydrologic calculations must be performed to adequately design the facility to achieve the desired goal. The presumptive approach also presents sizing methodologies that meet the requirements of one particular goal (pollution reduction, flow control, or destination), rather than multiple goals.
In addition to detailed construction drawings and details shown on permit drawings, all applicants using the presumptive approach for stormwater management are required to submit a detailed stormwater report.

Performance Method

The performance approach requires detailed engineering design and calculations, as well as documented evidence of the proposed design’s performance. The City will accept the proposed design for meeting pollution reduction requirements if the design professional demonstrates that it:

Will perform at the required efficiency and capture and treat 80 percent of the average annual rainfall. See Eugene’s Stormwater Management Manual Appendix B: Vendor Submission Guidance for Evaluating Stormwater Treatment Technologies, which is actually a function of influent concentration. Also see Appendix B for required testing protocol, related definitions, and additional requirements. Documented performance is required and shall include published data, with supporting cited research, demonstrating removal of target pollutants at required levels.

Can be maintained to perform at the maintenance level set forth in Eugene’s Stormwater Management Manual.

In addition to detailed construction drawings and details shown on permit drawings, all applicants using the presumptive approach for stormwater management are required to submit a detailed stormwater report.