To Step or Not to Step! – Using SpillwayPro to Evaluate Increased Discharge or Design Head

ABSTRACT ONLY - Several Reclamation projects have aimed to increase the discharge capacity of existing spillways or maintain spillway functionality with increased reservoir storage and head. A common consideration is adding steps to existing chutes to increase energy dissipation. This presentation will consider some example cases and highlight the utility of Reclamation’s SpillwayPro water surface profile tool for analyzing existing conditions and new design options, with comparisons where possible to CFD or physical modeling. The case studies span the spectrum from a no-action result to a complete spillway modification recommendation.
SpillwayPro was developed over several decades at the Bureau of Reclamation [1]. The program began as a FORTRAN-based standard-step water surface profile calculator with features that supported the analysis of aerated open channel flow [2]. Further improvements supported cavitation-related design needs (aerators, controlled-pressure spillway profiles, and the estimation of damage indices for extended operational periods) [3]. The most recent version is an Excel-based spreadsheet with improved aerated flow analysis and the capability to evaluate flow in stepped chutes [4]. SpillwayPro offers a full-featured ability to analyze many of the most important aspects of spillway hydraulics incorporating robust equations suited to steep-slope situations that exceed the limits of traditional hydraulic analysis tools such as HEC-RAS. In most cases, the analysis can be completed more rapidly than with physical or computational fluid dynamics (CFD) models. The spreadsheet is available for free download by the public [5].