Spatial distribution of water level fluctuating zones in the lower Jinsha River cascade reservoirs

The four power plants along the main stream of the Jinsha River, namely Wudongde, Baihetan, Xiluodu and Xiangjiaba, have formed a large area of water level fluctuating zones (WLFZ), and it is significant to clarify the spatial distribution characteristics of WLFZ for ecological protection and safe operation of the reservoirs. In this paper, the WLFZ of the four downstream reservoirs of the Jinsha River were studied. Meanwhile, based on the 12.5 m AlosDEM data combined with field investigation, the study integrated and analyzed the total area of water level fluctuating zones in the four reservoirs involving different counties, elevations, slopes, and main tributaries, by using ArcGIS hydrological and spatial analysis functions. The results indicate: ① the total surface area of water level fluctuating zone is 231.02 km², and the projected area is 202.88 km², including 142.12 km² for the main stream and 88.90 km² for the tributaries; the WLFZ surface areas of the four reservoirs are: 96.62 km² for Baihetan, 65.60 km² for Xiluodu, 56.29 km² for Wudongde, and 12.51 km² for Xiangjiaba. ② The WLFZ distribution involves 22 counties (districts) in 7 prefectures (cities) in Yunnan Province and Sichuan Province, among which, Qiaojia County of Yunnan Province has the largest WLFZ area. ③ In terms of elevation gradients, the WLFZ surface area in Wudongde Reservoir increases with the elevations, while the WLFZ areas in Baihetan Reservoir and Xiluodu Reservoir are evenly distributed at different elevations. ④ The WLFZ surface areas of Wudongde, Baihetan and Xiangjiaba Reservoirs at different slopes all decrease with slopes increasing, while the WFLZ of Xiluodu Reservoir is mainly distributed between slopes of 15° to 35°. The largest WFLZ area with slopes <15° in the four reservoirs is 76.68 km², accounting for about 33% of the total area.