Spillway Radial Gate Operating Procedures for Ice House Dam

In California, particularly in the Sierra Nevada, many earthfill and rockfill dams have gated spillway structures that consist of steel radial gates. Radial gates are typically installed on top of overflow spillways and are used to seasonally increase permanent water storage capacity by raising the water storage level above the fixed spillway crest. However, allowing the water storage level to rise above the fixed spillway crest results in an encroachment on the flood storage volume and a decrease in spillway discharge capacity. If a dam does not have adequate spillway discharge capacity, during a large storm event, there is an increased risk of dam failure by overtopping.
The California Department of Water Resources, Division of Safety of Dams
(DSOD) has historically required that spillway radial gates be held fully open to safely discharge large flood flows ·during the wet season of November 1 through April 1. Having the gates fully open enables the spillway structure to function at its full design discharge capacity and to provide adequate flood storage volume. During the spring and summer, when inflows into the reservoir consist mainly of snowmelt runoff, spillway gates are allowed to be lowered to their closed position to increase storage of water.