Applicability and Requirements

Development and redevelopment proposals must comply with this manual if they include at least 2,500 square feet of new or replaced impervious surface within Grants Pass city limits.

Best Management Practices (BMPs) must manage runoff from all landscaped and hardscaped areas for the project site.

Single family residential improvements that are not part of a new subdivision are exempt from these requirements.

BMP Sizing Methods

To design stormwater facilities, select either the Simplified Sizing Approach or the Engineered Design Approach. Each has a unique process to review and approve plans. Final selection of an approach is subject to City approval. The City may require a different approach upon review.

Some stormwater facilities require a specific approach. A combination of approaches may be used for a single project, but review and submittal requirements will be for the more intensive approach.

Simplified Sizing Approach

This approach is for projects with less than 10,000 square feet (0.23 acre) of total new or redeveloped impervious area on private property, including but not limited to roofs, concrete, asphalt, pavers, compacted gravel, compacted clay, plastic liners and clogged landscape fabric. The landowner or any other qualified, licensed professional or contractor may perform the sizing.

This approach is most appropriate for small-scale residential development, typically with limited professional design services. It is not allowed for:

  • Large, complex projects
  • Projects with multiple catchments totaling more than 10,000 square feet of new or redeveloped impervious area
  • Projects that include a public right of way or are a Public Improvement (Municipal Code).

BMPs using this approach may require the Engineered Design Approach upon review by the City.

Engineered Design Approach

When any of the conditions for the Simplified Sizing Approach are not met, use the Engineered Design Approach. This approach may also be required as determined by the City Engineer. It requires a licensed engineer to design BMP based on the criteria in Sections “Stormwater Management: Water Quality” and “Stormwater Management: Flow Control.” Submission of the Chapter 5 LID forms is not required with this approach.

Selecting an Approach

On this page is a "Sizing Methods" logic tree for selecting a sizing approach.

First determine if the manual applies based on the footprint of new or replaced impervious surface area. If the manual applies, select an approach.

If all the conditions in the “Simplified Sizing Approach” section and Chapter 2 requirements are met, the Simplified Sizing Approach may be used at the discretion of the City Engineer. Otherwise, use the Engineered Design Approach.

Simplistic vs Engineered Approach Flowchart

Simplistic vs Engineered Approach Flowchart