Effect of Water Withdrawal on the Appearance and Sound Level of Waterfalls

摘要

For rivers or streams with waterfalls, water withdrawal for multiple uses can lead to potential conflicts of interest. The question arises to what extent water withdrawal impairs the appearance and acoustics of waterfalls. A data set was analyzed of 15 waterfalls of different morphological types in Switzerland, Austria, and Norway. It comprises discharge measurements as well as photo imaging and sound level measurements. The variations of waterfall appearance and sound level decreased after reaching a threshold discharge value for all investigated morphological waterfall types. For low discharges, visible and acoustics changes were more significant compared to higher discharges. Acoustics changes were less pronounced than visual changes. The acoustics and visual extent of a water withdrawal can be calculated with a novel assessment equation using a normalized discharge. Based on an impact intensity, which is a function of the extent of the water withdrawal and the nonmonetary waterfall value, the selected residual discharge can be evaluated. In addition, a software tool was developed to enable a sensitivity analysis of the required residual discharge to maintain a certain waterfall appearance.