Innovative Spillway Design

Rutledge, John Lee; Tullis, J. Paul; ,

Innovative Spillway Design

by John Lee Rutledge, Freese and Nichols, Inc., Fort Worth, United States,
J. Paul Tullis, Freese and Nichols, Inc., Fort Worth, United States,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering

Abstract:

The Lake Alan Henry Dam, near Lubbock, Texas, will consist of an earth filled embankment, a service spillway and an emergency spillway. The service spillway is designed to handle flows up to and slightly above the 100-year flood. Once the reservoir rises above the 100-year flood level, the emergency spillway activates, after which the contribution of the service spillway is minimal. The peak discharge for the 100-year flood is about 10,000 cfs. The peak PMF discharge is approximately 368,000 cfs. The service spillway consists of a 40-foot wide uncontrolled ogee crest. As originally planned, the maximum service spillway flow at the PMF would have been 35,500 cfs (about 890 cfs per foot). This large unit discharge created design difficulties with the stilling basin. An innovative concept was tested by a hydraulic model study and found to be effective in reducing the service spillway capacity once the emergency spillway had been enacted. The new design consisted of placing a fixed gate across the spillway such that at flows above the 100-year flood, control shifts from critical flow at the ogee crest to orifice flow at the gate. With the gate, the maximum service spillway discharge was reduced to about 15,600 cfs, for a unit discharge of 390 cfs/ft. This reduction in total flow made it possible to significantly reduce the size of the stilling basin, and produce a total cost savings of more than $800,000.

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