Reasons of changes sediment movement near the Rioni river estuary

Rioni river, which joins the Black Sea in the territory of Western Georgia, has undergone hydrological changes many times as a result of artificial intervention. Close to its estuary to the south is the port of the city of Poti, whose breakwater was extended by 1.8 km and approached closer to the estuary of the river Rioni.

The article discusses the influence of the construction of a breakwater at the mouth of the northern channel of the river Rioni on the movement of sediments along the shore.

The constancy of sediment mass balance condition was used to study the sediment transport rates in the coastal zone and the change in the topography of the seabed, based on this the equation of water depth change was obtained. The finite element method and Crank-Nicolson schemes are used to solve the developed equations. The seacoast near the Rioni Nabada delta is taken as the research area.

Based on the resulting equations, the numerical experiments are conducted using the values of the known hydrological and hydrometric parameters of the Rioni river and the sea coast.

The overbank and bank-directed sediment transport rates are determined. The amount of beach-forming sediment imported by the Rioni river is about 4 million m³ per year.

Numerical analysis shows that after the construction of the new port breakwater, the impact of southwesterly waves will be weakened to the north, the movement of sediment in the southern direction will be completely blocked, and 0.85 mln m³ volume of solid sediment will begin to settle in the north of the new Breakwater. In the case of the current hydrological and hydrometric parameters of the Rioni River, the accumulation of a large amount of sediment over time will lead to the blocking of the southern branch of the Nabada channel. Accordingly, the total flow of water from the channel will be shifted to the northern branch and the formation of a new delta will begin there.

All movement of fine sediments in this direction will be stopped, and solid sediments will begin to settle to the north of the new breakwater after the new breakwater is built. Ultimately, this will lead to the blocking of the southern branch of the Nabada channel. The entire flow of water from the Nabada channel will be diverted to the northern arm, and the formation of a new delta will begin there. The canyon is currently in equilibrium. A reduction in the supply of sediment may cause it to move towards the shore, which will interfere with the normal operation of the harbor.