River sinuosity in tidal plain and its response to rapid urbanization

River sinuosity is an important indicator of channel planform. The city of Shanghai is a typical tidal plain and chosen as the study area in this paper. Sinuosity values in the 1950 were studied for the city centre region with dense river networks. The impacts of rapid urbanization on river sinuosity are diagnosed for the period after 1960. The result shows that the density of river networks in the city centre region has been reduced by 67.22% due to intense human activities since 1950, which resulted in Horton laws of drainage composition no longer holds. The tidal plain is seen as a representation of developing regions on straight rivers. The latter can account for 85.4% of the total number of rivers in the city centre region in the 1950. A further analysis of sinuosity reveals that those straight rivers with sinuosity values less than 1.1 can be as high as 70.57% at the time. The number of destroyed straight rivers in the city centre region was 12 times more than those with higher sinuosity in the past 60 years. We thus propose the adaptation of the index of weighted average river sinuosity for the study of the influence of river network shrinking on river sinuosity. Finally, it is found that in the practice of the comprehensive treatment of Shanghai river system, the tendency is to use engineering-oriented measures rather than replying to natural meandering channels as the curving cut-off measure has been applied to 60.9% river projects.