WANAPUM SPILLWAY FLOOD STABILITY REVIEW

摘要

Wanapum Dam is located in the State of Washington on the Columbia River approximately four miles downstream of 1-90 and the town of Vantage. The project, completed in 1964, consists of an earthen embankment on the left abutment, left gravity section with fish facilities, a powerhouse with ten generation units, six future unit intakes, twelve spillway monoliths with large radial gates, right gravity section with fish facilities, and another earthen embankment on the right abutment. Based on the recommendations of the FERC Part 12D safety inspection Hatch Acres was assigned the task to review the Wanapum Dam spillway stability under load conditions that included the Probable Maximum Flood (PMF). Initial review of previous analyses revealed that the earlier flood stability analyses may have under estimated crest forces. Hydrodynamic forces acting on a spillway and apron during flood conditions result from the change in the speed and direction of the water as it passes over the spillway. The most recent edition of the FERC's engineering guidelines for gravity dams includes a revision to the manner in which hydrodynamic forces on the spillway are to be evaluated for flows greater than the design discharge. With recent developments in computational fluid dynamics (CFD), numerical models now offer a cost effective means to model the spillway nappe forces for a number of flow regimes including the PMF. Evaluation of a range of flows allows confirmation of which flow condition is critical to the stability of the structure. This paper presents a review of stability analyses performed for the Wanapum Dam spillway monoliths based on CFD generated pressures. The paper also explores the influence of drain efficiencies and uplift assumptions including the effect of the downstream apron.