Spatiotemporal change in the river network in rapidly urbanized plain regions of the Yangtze River Delta in China

Rapid urbanization has brought numerous aquatic problems to plain river network regions. We selected three categories (five indicators) of characteristics to describe the physical characteristics of river network systems, including quantitative, structural, and complex characteristics. Using the grid method and hierarchical clustering analysis (HCA), the spatiotemporal change pattern of one plain river network of the Yangtze River Delta was addressed from the 1960s to 2014 based on topographic maps. The results showed that the river density (D-R), water surface ratio (W-P), and box dimension (D-0) in over 82% of the area decreased. The spatial pattern of the water system is divided into four categories by HCA: urban areas, river network areas, mainstream areas, and lake areas. The categories of river network areas and lake areas decreased, while the categories of urban areas and mainstream areas increased from the 1960s to 2014 because of urbanization. There are approximately 12.8% grid cells that change from river network areas to mainstream areas, which is the most important change due to the reduction of tributaries and increase of main streams. These results indicate that river network distribution patterns have the tendency to simplify and remain mainstream. Our study suggests that water systems and river networks should be protected, which would provide support for water resource management in highly urbanized plain regions.