Oregon Administrative Rules
Chapter 690 - WATER RESOURCES DEPARTMENT
Division 20 - DAM SAFETY
Section 690-020-0037 - Design Requirements for New Dams or to Increase Dam Height: Hydrology and Inflow Design Flood

Universal Citation: OR Admin Rules 690-020-0037

Current through Register Vol. 63, No. 9, September 1, 2024

The design to build a new Dam or to increase Dam Height shall characterize flow into and through the reservoir and the Dam and shall include the following elements:

(1) A topographic map delineating the drainage area contributing to the Dam, with the drainage area size labeled in square miles and showing the specific location of the proposed Dam;

(2) For Dams on stream channels, the name of the stream where the Dam is located, the name of the principal watershed, and a determination of average annual inflow into reservoir and potential to fill the reservoir;

(3) The Inflow Design Flood that is the basis of hydraulic design for the Dam shall be determined based on the Hazard Rating of the Dam as follows:

(a) The Inflow Design Flood for a High Hazard Dam is the Probable Maximum Flood (PMF) unless the Engineer of Record proposes to determine an Inflow Design Flood based on a quantitative analysis of risk to people;

(b) The minimum Inflow Design Flood for a Significant Hazard Dam is the 0.2 percent Annual Exceedance Probability Flow;

(c) The minimum Inflow Design Flood for a Low Hazard Dam is a 1.0 percent Annual Exceedance Probability Flow;

(d) The Inflow Design Flood for a lagoon or off channel reservoir is the maximum capacity of inflow pumps or ditches plus the maximum local storm precipitation over the lagoon; and

(e) For watersheds under 30 square miles, the Engineer of Record may consider just the 24-hour storm to help determine the PMF, while for larger basins the Engineer of Record shall utilize at least a 72-hour storm for calculating the PMF for a general storm;

(4) Designs shall include a description of all hydrologic parameters and the method used to determine the Inflow Design Flood hydrograph and the volume of the Inflow Design Flood, which is to be determined considering basin size and other factors as appropriate to the watershed above the Dam; and

(5) The design report must include the information used to develop the stage and storage capacity curve for the reservoir, including the capacity with and without excavation for construction.

Statutory/Other Authority: ORS 536.027, 540.488

Statutes/Other Implemented: ORS 540.449, 540.488

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