Hydro-aesthetic improvement of St. Anthony Falls spillway at low flow

Abstract

The possible expansion of hydropower development at St. Anthony Falls on the Mississippi River within the City of Minneapolis is likely to generate questions on the future appearance of the St. Anthony Falls spillway when most of the riverflow is routed through the existing powerplant and a projected additional power station. In particular, it may be asked how the aesthetics of the St. Anthony Falls spillway can be enhanced when only a small (minimum) flow is discharged over the spillway. It is anticipated that minimum flow spillway discharge will occur for 10 months in an average year when the proposed hydropower facility becomes operational. To study this particular question, an experimental study was conducted at St. Anthony Falls Hydraulic Laboratory and small flow deflectors which can be attached to the spillway surface and generate a "roostertail-like" spray were devised to make the appearance of the spillway more pleasing. The methods used in the study and the recommended design modifications are described in this report. It was not the intent of this study to determine what the minimum flow over the spillway should be, but rather to determine the best aesthetic effects on the spillway that can be accomplished at a low flow.