The evolution of the modern Luanhe River delta, north China

The Luanhe River Delta is located at the northern coast of the Bohai Bay, which was an enclosed sea. In 1915, the Luanhe River changed course to its present position, and has since developed a typical fan-shaped delta under fluvial-wave interaction. Owing to the water conservancy projects constructed in the catchment, the sand load that the Luanhe River takes into the sea has decreased sharply since 1980. Hence, the evolution of the Luanhe River Delta can be divided into two phases: the delta constructing phase between 1915 and 1979, and the para-abandoned phase after 1979. In the different phases, the delta characteristics are not alike. The main features of the delta evolution are changes in the distribution and development of lagoons. It seems that with the increase in delta construction features there is an increase in lagoon areas. A decrease of lagoon areas indicates the delta dying. Along with further development, the delta flank lagoons expand and the delta tip lagoons tend to shrink. These trends are also present in the processes of the para-abandoned delta phase. In each different stage of development, the delta has a different geometric pattern. At the first stage, the prolate axis of the ellipse fitted to the delta plain outline was perpendicular to the coast, the delta tip had high curvature. Along with the deltaʹs further development, the delta tip curvature gradually decreased and the prolate axis of the ellipse turned to parallel the coast.