Historical changes to the geomorphology of the Han River floodplain in central China caused by levees and polders

Keywords: Large river floodplain, river of power, landscape evolution,human modification, South-North Water Transfer
Abstract Type: Paper Abstract

Abstract

Over 2000 years the floodplain of the Han River in central China, historically renowned as Jianghan Plain, has been transformed from a series of lakes and swamps to an arable floodplain with confined meandering channels. This transformation was attributed largely to the extensive historical polder (a piece of land protected by enclosed levees) creation for reclaiming seasonally inundated land since the 14th Century. Yet the history of the human-made polder landscape across Jianghan Plain has not been revealed.
Thanks to the 63 historical topographic maps that became available recently, the artificial levee network during 1920s and 1940s across the 25,000 km2 Jianghan Plain could be fully mapped for the first time by manual delineation. The artificial levee network consisted of double or single side levees along river courses and 388 fully enclosed areas covering more about 55% of the floodplain with varying size and irregular shape. From the topographic maps, 646 polder names could be geographically located and traced with relevant records in historical gazetteers. In accordance with the downstream joining-up trend of fragmented river levees along the Han River, polder became densely distributed in the upper part of the floodplain earlier than the lower part. However, it did not mean that polder creation, as a river engineering and land management technique, travelled downstream only when levees along major rivers provided primary flood protection. Instead, polder had been created across a wide range of the Jianghan Plain even in the early stages in the 15th Century.