Calculated model and application of ice-free length of diversion channel for pumping well water to melt ice at high altitude and cold regions

Abstract: Pumping well water to melt ice is an effective method to solve the ice problem for diversion channel at high altitude and cold regions, which is widely used in Hongshanzui hydropower station, Jingou river hydropower station, Youth hydropower station of Xinjiang and Xiangjia hydropower station of Qinghai Province. According to the local hydrological and natural conditions and the characteristics of hydropower projects, pumping well water to melt ice is a method to pump high temperature underground well water into the diversion channel to increase water temperature, which makes the ice in the channel melted. In order to solve the calculation problem of ice-free length for pumping well water to melt ice, the calculation formula of ice-free length was proposed theoretically based on water heat balance theory. The influences of hydraulic, thermal and climatic conditions on ice-free length were considered in above formula, which was verified by using the values of ice-free length of diversion channels in Hongshanzui and Jingouhe hydropower station of Manas River, Xinjiang. The results show that calculated results are in agreement with measured values of the ice-free length for the diversion channel of the Hydropower station with the minimum and maximum errors of 6.2% and 29.5%, respectively, which confirmed the reliability of deduced formula. In this study, the second diversion channel of Hongshanzui hydropower station in Manas River of Xinjiang was selected as the study area, and the values of ice-free length were calculated under different hydraulic, thermal and climatic conditions. The calculated results indicate that the ice-free length is proportional to discharges of channel and well water, temperature of well water, atmospheric temperature and daily solar radiation, and it is inversely proportional to wind speed, atmospheric saturation deficiency and daily snowfall. Firstly, the value of ice-free length is increased by only 200 m with the channel discharges being increased from 0 to 20 m3/s under the conditions of atmospheric temperature of -20 ℃ and well water discharge of 0.16 m3/s, which indicates that the influence of channel discharge on ice-free length is little. Secondly, the value of ice-free length can be increased by 400 m with well water discharge being increased by 0.02 m3/s under the condition of atmospheric temperature of -20 ℃. In practical engineering, the increase of well water discharge is a direct and effective way to increase the mixed water temperature of channel, and to increase the ice-free length. Thirdly, the values of ice-free length can be decreased by 16.1%-31.3% with atmospheric temperature being decreased by 5 ℃, which shows that the influence of atmospheric temperature on the ice-free length is also significant. Finally, the values of ice-free length can be decreased by 4.30%-53.0% with wind speed being increased from 0.5 to 6.0 m/s under the condition of atmospheric temperature of -20 ℃. Above results indicate the influences of well water discharge, atmospheric temperature and wind speed on ice-free length are significant. This study can provide valuable information for preventing ice hazards of diversion channel of diversion power station at high altitude and cold regions.