South Caspian River Mouth Configuration Under Human Impact and Sea level Fluctuations

Rivers that flow from the Iranian coast to the Caspian Sea encompass 135,000 km2 of that catchment’s basin and supply 40 million ton sediment to the Caspian coast annually. The dynamics of river mouths and deltas are studied using hydrological data of the rivers, air photos, satellite images and geological and geomorphological maps as well as field observations and sediment sampling. Results from this study show that the morphology of the river mouths and deltas are mainly controlled by marine (ware-induced currents and sea level changes) and fluvial processes. Among these factors, sea level and riparian sediment supply have great variability. Analysis of hydrological data revealed that, during the past few decades with increasing human activities, the sediment supply of the rivers reduced from 10 to 40 %. The Caspian sea level has changed over a range of 3 m during instrumental measurements. The rivers are classified into three groups based on the morphology of their mouths and the nature of river/sea dynamics: Type 1 is rivers that enter to the sea through lagoons and lowlands. They have gained an ephemeral nature due to increasing water consumption recently. Type 2 rivers have a normal flow into the Caspian Sea. They are common in steep slope coasts, where they are rarely affected by human activities and sea level changes. On moderately sloping coasts, they are slightly affected by long-shore currents of the sea. Some distributaries of the rivers enter into the sea independently. Some bars and lagoons are developed in the vicinity of the river's mouth, most commonly since the last sea level rise. Type 3 represents the great rivers with a significant sediment supply (Sefidrud River in the West andGorganrud River in the East), producing deltas and mouth bars. They have high sediment discharge into the sea and are more greatly affected both by human activities and sea level changes.