Oregon Administrative Rules
Chapter 690 - WATER RESOURCES DEPARTMENT
Division 20 - DAM SAFETY
Section 690-020-0038 - Design Requirements for New Dams or to Increase Dam Height: Embankment Dam Structures

(a) Embankment Dams shall be designed to have stable slopes during construction, and under all conditions of reservoir operation;

(b) Standard slopes of 3:1 upstream and 2:1 downstream may be used at the discretion of the Engineer of Record for Low and Significant Hazard Dams as long as low strength materials are not used in the Embankment and conditions leading to elevated pore Water pressures are not present;

(c) For High Hazard Dams, an analysis of static and seismic slope stability, and of deformation. The State Engineer may require static and seismic slope stability analysis for Significant Hazard Dams. At a minimum, seismic analysis shall be based on full reservoir under steady state seepage conditions. Factors of safety shall be evaluated by slope stability analyses using appropriate strength parameters based on laboratory or in situ testing. For materials that can be reasonably tested either on site or in a laboratory, soil strength values may not be based on assumptions and must be made on strength testing of the appropriate soil or rock units;

(d) High Hazard Dams shall be designed for the maximum credible earthquake. If the State Engineer requires seismic analysis of a Significant Hazard Dam, deformation analysis shall be designed for the 0.2 percent Annual Exceedance Probability earthquake; and

(e) Abrupt changes in depth of compressible Foundation material shall be identified and where present, the design shall prevent significant differential settlement;

(a) Steady state seepage and internal drainage conditions beneath, around, and through the Dam shall be quantified for all High Hazard Dams, and may be required by the State Engineer for Significant Hazard Dams;

(b) A Core of low permeability material protected by a Soil Filter is required for all High Hazard Dams. A Core and Soil Filter is required for any Significant Hazard Dams where the Engineer of Record or State Engineer determines piping could potentially occur. All Core and filter zones must be of a configuration with dimensions that can be readily constructed;

(c) Internal drains and Soil Filters shall be used as needed to drain Water and prevent internal erosion of the Dam. Toe Drains shall be standard design practice for Water storage Dams, but not for most wastewater lagoons; and

(d) Internal drain pipes to collect and distribute seepage flows from internal filters and drains shall be comprised of material that is non-corrodible, designed to carry the overburden load, and be no smaller than six inches in diameter;

(a) The Crest shall be of sufficient width to be accessible by equipment and vehicles for emergency operations and maintenance, and shall have a road to allow Crest access during periods when the Spillway is flowing;

(b) The Crest shall have a camber sufficient to maintain the design Freeboard, based on the anticipated Crest settlement, and in no case shall the camber be less than 0.5 feet;

(c) Roads located on the Crest shall have appropriate surfacing to provide a stable base that resists rutting and provides adequate traction for access and safety in wet conditions; and

(d) The Crest shall have adequate cross slopes to prevent ponding;

(a) For reservoirs large enough to generate significant waves, the design shall include a determination of minimum Freeboard based on expected waves. The design shall also include slope protection for wave action if significant waves are likely; and

(b) The downstream slope shall be provided with non-woody vegetative cover, or a gravel or rock surface, to prevent surface erosion.