EVOLUTION ANALYSIS OF WATERCOURSE AND SHOALS OF THE XUNJIANG RIVER IN WUZHOU BASED ON TIME-SERIES REMOTE SENSING DATA
Wuzhou reach of Xunjiang River is the most valuable waterway in Guangxi. The research on the evolution of Xunjiang River in Wuzhou is of great practical significance in the aspects of river regulation and water conservancy construction. Based on Landsat images of normal water level in 1997, 2001, 2005, 2009, 2014 and 2018, this paper firstly conducts a quantitative analysis of evolution of the watercourse and shoals in Wuzhou section of Xunjiang River through using RS and GIS. Then the relationships between the changes of river course and sandbars of the research area and the annual rainfall and vegetation coverage of the upstream region are analyzed to determine the causes of the changes of watercourse and shoals of Xunjiang River in Wuzhou. The results show that the riverway contracted with a contraction amount of about 9.93 km 2 from 1997 to 2005, and the expansion volume of sandbars was about 12.21 km 2. From 2005 to 2014, the watercourse approximately expanded 12.33 km 2, and the shoals shrank about 12.49 km 2. From 2014 to 2018, the river course was a contraction trend, reducing about 1.57 km 2 in area; the sandbars showed an expanding trend, with an expanding amount of about 0.82 km 2. The changes of river channel and shoals are mainly influenced by the incoming water and silt from the upper reaches and are related to the annual rainfall and vegetation coverage of the upstream area. The correlation coefficient between watercourse area and upstream annual rainfall is 0.26, and that between riverway area and upstream vegetation coverage is 0.78. However, the correlations between the area of shoals and the annual rainfall and vegetation coverage of the upstream region are contrary to that of the river channel. The correlation coefficients between the area of shoals and the annual rainfall and vegetation coverage of the upstream district are −0.28 and −0.83 respectively.