Batumi coastal protection: facing decreasing river discharges of gravel and canyons traps

Maria Di Leo

Chair(s): dr. Vojinovic

Tuesday 30 june 2015

14:50 - 15:05h at Central America (level 0)

Themes: (T) Special session, (ST) Coasts at threat in Europe

Parallel session: 6H. Special session: Coasts at threat in Europe

The beaches of Batumi coast are formed by gravel sediment carried by the Chorokhi River. Two submarine canyons stretch from the far depths to Batumi coast: one reaches Batumi Cape in the north, the other one lies directly opposite the mouth of river Chorokhi in the south. Previous studies have shown that part of the pebbles from the river flow into this canyon, hence failing to feed the beaches downdrift. Furthermore human interventions on the river (sediment mining, water flow regulation) have reduced in time the amount of sediment available to the beach, and further reduction is expected due to planned construction of new dams along the river. As a result the beach is suffering erosion in the southern stretch. In addition, geotechnical instability processes have been identified involving the canyon in the Northern area of Batumi coast. Here two different instabilities coexist: the main instability process, which led to a massive landslide observed in 1999, and a secondary instability process, which is independent from to the main one and involves smaller soil volumes. Both these processes can be related to the high sedimentation rate in the area. From a geotechnical point of view, especially with reference to the main landslide, the reduction in the sedimentation rate or better its halt could prevent any further instability phenomenon. The design process, developed with support of Deltares, has gone through different steps. At first, dominant natural mechanisms governing the transport of beach material and acting upon the coast of Batumi have been identified and quantified. Secondly, different design options have been evaluated considering the development of different coastal functions, both based on a technical and cost-benefit analysis. State-of-the-art numerical models have been used extensively in the study of the reference situation and in the evaluation of the different options.

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