The response of river mouths to large-scale variations in sea level and river runoff: Case study of rivers flowing into the Caspian Sea

Regularities in the response of the mouths of major rivers, flowing into the Caspian Sea, to large-scale variations in its level and river water runoff and sediment yield are considered. Changes in the morphological structure and hydrological regime of the Volga, Terek, Sulak, Ural, and Kura mouths have been analyzed in both geological past and separately for three modern periods: a considerable drop in Caspian Sea level before 1978, its abrupt rise in 1978–1995, and a relative stabilization in the subsequent years. Specific features were identified in the hydrological-morphological processes in different mouths, caused by the differences in river sediment yields, and the slopes of delta surface and mouth nearshore beds. Some theoretical and methodological approaches were verified in the analysis and evaluation of the processes under consideration. The obtained results of studies of the mouths of rivers flowing into the Caspian Sea can be regarded as examples and analogues in the assessment of processes, which take place at the mouths of other Russian and world rivers at present and can take place in the future under anticipated natural and anthropogenic variations in sea level and river runoff.