Progradation, deltas

River water runoff is responsible for many hydrological features of river mouths and their parts - deltas, semi-enclosed coastal water bodies and open nearshore zone. Water runoff influences water levels in deltas, delta inundation, water salinity at the mouths, etc. Water runoff depresses action of the storm surges on the deltas. River sediments load determines channel processes, sedimentation in a delta and nearshore, delta formation processes, the rate of delta progradation into the sea. 

The relative steepness of these open nearshores can result in a decelerated progradation of deltas into the seas (even at constant sediment load) and the marked effect of sea waves. 

The effect of waves on the seashores, including the delta coasts, depends on the energy of waves. Waves are capable of destroying the deltaic deposits in the periods of low sediment load and to slow down the progradation of deltas into the sea, as well as to transport sandy sediments along the delta coastlines and to form beaches and sand coastal bars. In some cases, separate deltaic lobes were completely destroyed after the water and sediment input to the deltas had ceased (the deltas of the Danube, Rioni rivers). 

In modern times, the development of the protruding delta of the Rioni River has been as follows [15,28] the old55 delta was formed at the Rioni mouth before the diversion of river flow in 1939 (the data on the progradation of the old55 delta are very scarce) and a new55 delta was formed at the mouth of the Rioni-spillway after 1939 the old55 delta virtually inherited the distinctive hydrographic features of the ancient times (two branches, Northern and Southern), divided by the Bolshoy Island. 

In the last 30-35 years, delta coast has experienced abrasion. The retreat of the delta coastline has consisted of 3-5 myear-1. The main reasons of this process are reduction of the river sediment load after reservoir construction and sea level rise. Slight progradation of the delta is observed only near the mouths of the main branches. 

Stable sea level is characterized by neutral, depositional shorelines that prograde (extend) seaward, often at extremely rapid rates. The sediments are brought by rivers (deltas and estuaries), streams from nearby mountains (alluvial fans), glaciers (morainic outwash), and volcanoes (tephra beds and lava flows). In certain... 

Fjord environment with active prograding sandy deltas fed by glacial melt water. 

Detailed mineralogical and textural analysis of Ugnu Formation has been conducted by Mowatt et al. (1991) and Hallam et al. (1991). The sand bodies with good reservoir parameters in the Lower Ugnu Formation were deposited by the distributary channels of a prograding delta. The coarse channel sands are... 

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