Oregon Administrative Rules › Chapter 690 - WATER RESOURCES DEPARTMENT › Division 20 - DAM SAFETY › Section 690-020-0042 - Minimum Design Requirements for New Dams or to Increase Dam Height: Spillways

Current through Register Vol. 63, No. 7, July 1, 2024
(1) Dams on
			 stream channels and all High Hazard Rated Dams must have a Spillway.
(2) Spillway(s) design to build a new Dam or
			 to increase Dam Height shall include the following minimum elements:
(a) Utilization of Inflow Design Flood.
			 Determination of Inflow Design Flood as described in OAR 690-020-0037  is
			 required to determine the required Spillway capacity;
(b) Hydraulic evaluation of flow through
			 control section. Flood flow through the control section must be calculated and
			 the minimum Freeboard at the Inflow Design Flood must be one foot for High
			 Hazard Dams and two feet for Significant and Low Hazard Dams;
(c) Optional low elevation Spillway. An
			 interior Spillway connected to the low level Conduit may be used for Low and
			 Significant Hazard Dams, and for High Hazard Dams only with specific approval
			 by the State Engineer. The capacity of the low elevation Spillway may be
			 considered in design of the overflow Spillway;
(d) Stable Spillway control section. The
			 Spillway control section must be hydraulically and structurally stable for the
			 Inflow Design Flood and have permanent features so that the control section is
			 identifiable for re-measurement of cross section during routine
			 inspections;
(e) Spillway channel
			 stability. Spillways shall be designed to be structurally adequate and stable
			 under all conditions of reservoir operation. Spillway structures of High Hazard
			 Dams shall be designed for earthquake ground motions per OAR
			 690-020-0036;
(f) Reinforced
			 concrete specifications for spillways. Structural elements of reinforced
			 concrete shall be designed for both strength and serviceability. The 28 day
			 strength of structural concrete shall be provided. The strength properties of
			 the reinforcing materials shall also be provided and contract drawings shall
			 clearly indicate the size, location, spacing, and cover requirements. Treatment
			 of construction joints and contraction/expansion joints shall be described and
			 special provisions for strength transfer and leakage prevention identified. Air
			 entrainment shall be provided in cast-in-place concrete if needed for
			 freeze-thaw protection, durability, and workability;
(g) Debris booms. For High and Significant
			 Hazard Dams, debris or log booms may be required. Where required, they shall be
			 designed for the Spillway approach where logs and other debris may block or
			 damage the Spillway structure. The design shall specify the necessary anchor
			 capacity, and the design of the anchors;
(h) Gates and Flashboards. Detailed drawings
			 and specifications are required for Spillway Gate structures or flashboards, if
			 present on the proposed Dam. Operations and maintenance plans are required for
			 any Dam with a Gated Spillway, or where flashboards or stop-logs are used in
			 the Spillway as per OAR 690-020-0068; and
(i) Energy dissipation. The design of
			 stilling basins for High Hazard Dams, and where required by the State Engineer
			 for Significant Hazard Dams, shall be based on calculated hydraulic forces and
			 designed to dissipate energy and minimize scour and erosion from the Inflow
			 Design Flood.