Modeling the Effect of Water Diversion on the Temperature of Mountain Streams

Abstract

Water diversion for hydroelectric power generation impacts the temperature of mountain streams. Such changes are estimated by using a coupled one-dimensional dead-zone heat balance model. In very steep river sections, the dissipation of kinetic energy is the dominant heat source. For such streams, water diversion has only a minor effect on water temperature, because dissipation-induced temperature changes are independent of discharge. In contrast, in river sections of gradual slope, the influence by solar radiation, long-wave radiation, and heat exchange with the streambed is stronger. In such cases, a discharge reduction can lead to significant temperature changes. For a small stream in the southern Swiss Alps, model results show that diversion increases temperature by about 3.7 (±0.9)°C in a 21 km long river section under high solar radiation during summer. During a cold winter episode, water temperature is estimated to be about 1.8 (±0.8)°C lower compared to natural conditions. This heat balance model can also be used to simulate the effect of different measures to reduce water temperature changes in affected streams.