Or. Admin. Code § 690-020-0043 - Design Requirements for New Dams or to Increase Dam Height: Penetrating Conduit(s) and Control of Flow through Conduits

New Dams on stream channels must have a low level Conduit. All other new Dams and Dams with increases to Dam Height must have a low level Conduit or other means to safely drain the reservoir. The Conduit and related control structures must be designed to meet the following criteria:

(1) Ability to lower the reservoir. The minimum diameter of the Conduit should be determined through analysis of the time required to drain the Dam at average annual inflow;

(a) The Conduits for High Hazard Dams shall be capable of releasing the amount of Water which could be stored in the top five feet of the reservoir in five days;

(b) The Conduits for Significant and Low Hazard Dams must be able to release the amount of Water which could be stored in the top five feet of the reservoir in ten days;

(c) All Conduits must be of sufficient size to allow passage of inflows as needed;

(d) In no case shall Conduits be smaller than eight inches in diameter;

(2) Durable and water-tight Conduits. Conduits must be made of medium to heavy gage durable materials. Pipe joints must be designed to seal and prevent leakage. Corrugated metal culverts are only acceptable for Low Hazard Dams, and only when the Conduits are encased in concrete. Encasement of Conduits in concrete may be used to assist in the design of a durable Conduit and to reduce the potential for seepage and erosion adjacent to the Conduit;

(a) Diaphragms using materials designed as an effective Soil Filter are required for any Conduits not designed as encased in concrete, and are required regardless of encasement for all High Hazard Dams;

(b) Seepage collars may not be used;

(3) Control Mechanisms. The design for the control mechanism must be sturdy and durable. The control mechanism must allow for air venting when needed, and allow manual operation to drain the reservoir if hydraulic or other power controls are inoperable. Hydraulic or other power controls must have redundancy if control relies on any submerged hydraulic or pneumatic hoses or electrical conduits. Intake structures for outlet works must have trash racks unless the Engineer of Record shows trash racks are unnecessary, or not safe to construct due to conditions at the Dam site. For High and Significant Hazard Dams, measures to prevent unauthorized use of the control mechanism must be included in this design;

(4) Outlet structure. The outlet structure must not be submerged when the inlet control Gate or Valve is fully closed. The outlet structure must be designed to protect the Conduit from mechanical damage and convey Water to the stream channel without channel erosion and cavitation near the Gate structure; and

(5) Pressurized operation. Conduits must be specified as suitable for pressurized operation if they are to be operated with controls other than at the inlet of the Conduit. Dams with Pressurized Conduits shall have a guard Gate installed at the upstream end of the Conduit. Operations and maintenance plans are required for any Dam designed for pressurized operation as per OAR 690-020-0068.

Notes

Or. Admin. Code § 690-020-0043

WRD 2-2015, f. & cert. ef. 3/17/2015; WRD 3-2020, amend filed 06/29/2020, effective 7/1/2020; WRD 6-2020, minor correction filed 12/14/2020, effective 12/14/2020

Statutory/Other Authority: ORS 536.027, 540.488

Statutes/Other Implemented: ORS 540.449, 540.488