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FLOW-3D CFD Modeling for Emergency Spillway Design

Reduced risk from extreme flood erosion

The original emergency spillway was comprised of a concrete gate structure with stanchion gates and a downstream channel that consisted of an earthen channel covered with vegetation. The downstream end of the spillway directs water into a common plunge pool with the dam’s service spillway. The client required engineering support to conduct an alternatives review and final design for the replacement of the emergency spillway to address dam safety inspection concerns with the susceptibility of the earthen channel for erosion when subjected to extreme flood conditions.

Kleinschmidt completed a preliminary options review for armoring of the spillway earthen channel, a geotechnical boring program, and preliminary hydraulic analyses using HEC-RAS, a 2D hydraulic modeling software, to determine baseline design parameters for the spillway to avoid erosion of the channel.

Due to the complexity of the spillway layout and the use of steps in the lower half of the spillway to dissipate energy, a more robust and detailed hydraulic analysis was required to have confidence in the design. Kleinschmidt developed a FLOW-3D CFD model of the spillway to determine velocities and flow depths along the spillway length, accounting for air entrainment and superelevation of flow caused by a bend in the spillway, including through the plunge pool area. The selected option for the spillway, a stepped, concrete structure, was chosen based on its ability to fit within the constraints of the site, dissipate energy, and minimize required wall heights to pass the design flood events.

Kleinschmidt’s use of FLOW-3D CFD modeling to inform the selection of and design of the new reinforced concrete spillway channel chute reduced the client’s project risks to the embankment dam and downstream damage caused by erosion when the spillway is subjected to extreme flood conditions. The model provided the design team with confidence about the performance of the spillway during flood events.