OAR 690-020-0037
Design Requirements for New Dams or to Increase Dam Height: Hydrology and Inflow Design Flood

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.

Source: Rule 690-020-0037 — Design Requirements for New Dams or to Increase Dam Height: Hydrology and Inflow Design Flood, https://secure.­sos.­state.­or.­us/oard/view.­action?ruleNumber=690-020-0037 (accessed May 26, 2025).

690–020–0000
Purpose and Applicability 690–020–0022
Definitions 690–020–0024
General Department Authorities and Intergovernmental Coordination 690–020–0026
Fees 690–020–0028
Preliminary Plans and Specifications for Construction of New Dams or to Increase Dam Height 690–020–0035
Minimum Engineering Requirements for Final Design of New Dams or to Increase Dam Height 690–020–0036
Design Requirements for New Dams or to Increase Dam Height: Site Suitability and Geotechnical Evaluation 690–020–0037
Design Requirements for New Dams or to Increase Dam Height: Hydrology and Inflow Design Flood 690–020–0038
Design Requirements for New Dams or to Increase Dam Height: Embankment Dam Structures 690–020–0041
Design Requirements for New Dams or to Increase Dam Height: Concrete Dam Structures 690–020–0042
Minimum Design Requirements for New Dams or to Increase Dam Height: Spillways 690–020–0043
Design Requirements for New Dams or to Increase Dam Height: Penetrating Conduit(s) and Control of Flow through Conduits 690–020–0044
Design Requirements for New Dams or to Increase Dam Height: Instrumentation for Monitoring 690–020–0047
Design Requirements for New Dams or to Increase Dam Height: Geosynthetics 690–020–0048
Exceptions to Standard Design Requirements 690–020–0055
Design Requirements for New Dams or to Increase Dam Height: Design Drawings 690–020–0060
Design Requirements for New Dams or to Increase Dam Height: Construction Specifications 690–020–0065
Plan Requirements for New Dams or to Increase Dam Height: Construction Administration 690–020–0068
Plan Requirements for New Dams or to Increase Dam Height: Operations and Maintenance Plan 690–020–0070
New Dams or to Increase Dam Height: Submittals and Notifications by the Engineer of Record 690–020–0080
New Dams, or to Increase Dam Height, Written Approval by State Engineer 690–020–0100
Hazard Rating of Dams 690–020–0120
Dam Breach Inundation Analysis 690–020–0140
Modification of Dams 690–020–0160
Removal 690–020–0180
Requirement of Owners to Provide Contact and Transfer of Title Information 690–020–0250
Maintenance of Dams 690–020–0260
Inspection of Dams 690–020–0310
Requirement to Address Maintenance Actions Need for High or Significant Hazard Dams 690–020–0340
Potentially Unsafe or Unsafe Conditions 690–020–0400
Emergency Action Plans (EAP) 690–020–0420
Immediate Action to Prevent Dam Failure 690–020–0460
Proposed Final Order, Request for Hearing, Contested Case Process 690–020–0600
Civil Penalty Assessment for Dam Safety

May 26, 2025

Rule 690-020-0037's source at or​.us