Formation of the Danube and Rioni deltas and their coasts  <B>Formation of the Danube and Rioni deltas and their coasts</B><P>M. Mikhailova</B><I><P> Water Problems Institute, Russian Academy of Sciences, Moscow, Russia.</I><P> Abstract<P> River mouths, including deltas, estuaries and an open nearshore, are the most changeable and ecologically vulnerable geographical objects. The investigations of delta processes are of a great scientific and practical interest in connection with use, protection and regulation of their abundant natural resources. The natural and anthropogenic changes in the river and sea regime result in the disturbance in the sediment balance at the river mouths and lead to the changes in the delta formation processes, deltaic morphology and ecology. The paper deals with the investigations of the deltas at the mouths of the Danube and Rioni Rivers. In the last 250 years the most intensive deposition of the Danube sediments took place at the mouth of the Chilia branch of the Danube delta. Here so called Chilia delta has been formed. The evolution of the Rioni delta included two periods: the old delta formation and the new delta formation. The new delta began to be formed in 1939 after the artificial diversion of the river flow in a new direction. The old delta began to be destroyed by the sea waves. The formation of the Chilia delta at the Danube mouth and the Rioni delta can be explained using the analysis of the sediment balance as the physical basis of the delta evolution. The coastal abrasion in several parts of the Danube delta and the old Rioni delta represents the serious problems for use and protection of natural resources of these deltas. The scientific basis of coastal protection measures is worked out.<P>