Depositional Characterisytics and Models of the Modern Anastomosing River in China

The anastomosing fluvial system was considered as the same term of the braided fluvial system, but the anastomsing stream is distinct from the well-known meandering and braided river. Smith described the anastomosing fluvial system as low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate islands. Many Chinese rivers have anastomosing reaches, including some large rivers such as Changjiang River, Heilongjiang River, Zhujiang River and some middle-small rivers as Neijiang and Ganjiang River. Based on their physical geography and structural background, they can be divided into four types: plain anastomosing river, vale anastomosing river, lacustrine deltaic plain anastomosing river, marine deltaic plain anastomosing river. Three anastomosed river systems are described. They are anastomosing river in Qiqihaer section of Neijiang River, Ganjiang deltaplain anastomosing river and Zhujiang deltaplain anastomosing river. These rivers contain low gradient, high aggradation rates, multiple channel and large-area wetland between the channels. Channels, natural levees, crevasse-splay, floodplain, lakes, marshes and eolian dunes are important morphological and sedimentary units. Anastomosing channel-filling sediments are mainly composed of pebbly sand and medium to fine sands. Internally channel sandbody consist mainly of trough cross-bedding and oblique bedding. The other morphological units are mainly composed of fine-grained sediments. Some basic characteristics are as follows: climate and geography are not controlling factors of anastomosis; Low gradient is an essential condition for developing anastomosed river systems; Stable multiple channels are different from meandering and braided river; Wetland is major sedimentary unit; Primary factor of channel stabality is dense vegetation on the nature levees and high cohesiveness; Modern examples of anastomosed river systems are not common