Trend Analysis of At-a-station Hydraulic Geometry Relations on the Loess Plateau of China

Empirical at-a-station hydraulic geometry (AHG) power function relations have been widely used to depict relationships between flow width (W), flow depth (D), mean flow velocity (V) and discharge rate (Q) for natural rivers and streams. However, it has seldom been considered whether AHG relations hold true for describing hydraulic relations at watershed outlet channels. In this study, observed data from three experimental watersheds of different sizes (1-100 km(2)) in the past three decades were used to verify stability of AHG at watershed outlet channels on the Loess Plateau in China. Trend analysis via the sequential Mann-Kendall test was used to detect the stability and abrupt changes in AHG during the study course. The results suggested strong stability in AHG exponents and significant decline in coefficients (P < 0.05). The abrupt decline for coefficients was found to be influenced by human activities such as land use changes. This study could provide some useful aids for watershed hydrology management.