Annual runoff and flood regime trend analysis and the relation with reservoirs in the Sanchahe River Basin, China.

Over the past decade, intensive human activity, particularly dam construction, has resulted in altered runoff in the Sanchahe River region. In this study, the changes in runoff and flood regime were analyzed using Mann–Kendall trend analysis and linear regression analysis. The annual runoff coefficient (ARC) was selected as the primary index to verify the relationship between reservoirs and change in annual runoff at the outlets of upstream Sanchahe River Basin (Yangchang hydrologic station) and the entire basin (Yachihe hydrologic station). The results indicate that the construction of dams and the subsequent development of reservoirs have significantly influenced stream flow process in the Sanchahe River Basin. As reservoirs in the upstream part of the basin are small in both number and storage capacity, the annual runoff depth decreased only slightly from 1963 to 2012, and this trend was not significant at the 95% confidence level. Trend analyses on ARCs demonstrate that the consumption of water during reservoir construction is likely the cause of decreased runoff depth. In contrast, the annual runoff depth of the entire basin decreased significantly (∼4.01 mm/y). The basin-wide flood regime has been influenced by reservoir construction in the entire Sanchahe River Basin. The annual maximum peak flow (AMPF), annual maximum 3-day flood volume (AM3FV), and annual maximum 7-day flood volume (AM7FV) all decreased significantly at Yachihe station, especially after the construction of the Puding and Yinzidu Reservoir dams. Large floods seldom occurred after the 1990s, and since 2000, no flood cases with a recurrence period of more than 10 years have occurred at the basin outlet. [ABSTRACT FROM AUTHOR]