A leading reservoir followed by diversion cascades which can make full use of the waterhead is very common in the small mountain rivers, due to it’s large gradient ratio. To understand the water temperature cumulative effects of a leading reservoir followed by diversion cascades, a field observation in a small mountain river of southwest China was performed to collect the water temperature data, both inflow and outflow, of each cascade reservoir. The results indicated that the leading reservoir had a large capacity of heat regulation. Since there was significant water temperature stratification, the gradient of water temperature was 0.15℃/m, in spring. The water intake in front of the dam can suck water from upper layer of the reservoir and the suction height was about 8m. The difference between the outflow water temperature and the water temperature in the middle of water intake was 1.3℃. When compared the outflow water temperature process with the natural temperature process, one month of delay was observed, presenting as colder water in March to April and warmmer water in September to December, with the biggest difference reaching up to -1.7℃ and 2.8℃, respectively. In addition, the data showed no difference between the inflow and outflow water temperature in the diversion cascade. Connected diversion cascades leaved no space for the low temperature water discharged from the leading reservoir to recover, and the low temperature water phenomenon was more severe in the downstream in spring, but the high temperature water phenomenon was weakened in the downstream in autumn.
