Unified sizing criteria section

A unified framework is presented for addressing stormwater sizing criteria in the context of the MPCA Construction General Permit (CGP) and local stormwater management requirements, if chosen by the local community. The unified approach addresses five different sizing criteria, as shown below.

• Recharge
• Water quality
• Channel protection
• Over bank flooding
• Extreme storms

In addition to these sizing criteria for regular waters, this Manual describes how sizing criteria can be adapted to provide greater protection for special and other sensitive waters of the state. The goal of the unified framework is to develop a consistent approach for sizing stormwater practices that can

• perform effectively: manage enough runoff volume to actually solve the stormwater problem it is intended to address;
• perform efficiently: manage just enough runoff volume to address the problem but not over-control it. More storage is not always better, and can greatly increase construction costs;
• be simple to administer: be understandable, relatively easy to calculate with current hydrologic models, and workable over a range of development conditions and intensities. In addition, criteria should be clear and straightforward to avoid needless disputes between design engineers and plan reviewers when they are applied to development sites, while also eliminating any competitive disadvantages that are created when uniform regulations do not exist;
• promote better site design: be structured in a manner so that property owners have real incentives to reduce storage volumes (and costs) by applying better site design techniques to receive stormwater credits; and
• be flexible to respond to special site and receiving water conditions: be expanded to adequately protect unique receiving waters, and to be reduced or eliminated in certain development situations where they are inappropriate or infeasible.

The individual articles comprising this section on Unified sizing criteria may be viewed as a single article.

1. Unified sizing criteria
2. Recharge and infiltration criterion (Vre)
3. Water quality criteria
4. Channel protection criteria (Vcp)
5. Overbank flood protection criteria (Vp10)
6. Extreme flood control criteria (Vp100)
7. Adapting stormwater criteria for receiving waters
8. References for Unified Sizing Criteria
9. Literature review summary for Unified Sizing Criteria
10. Stormwater sizing for redevelopment projects