The expansion of cities and towns has caused a large amount of waters to be compressed,occupied or even disappeared,and the risk of floods in the region has increased sharply.This study is based on Hengyang,a typical city in midstream of Xiangjiang River.Based on expans...MORE The expansion of cities and towns has caused a large amount of waters to be compressed,occupied or even disappeared,and the risk of floods in the region has increased sharply.This study is based on Hengyang,a typical city in midstream of Xiangjiang River.Based on expansion speed index and intensity index of Xiangjiang mi...