Sediment management in reservoirs in order to reduce shoreline erosion: The case of Nestos River, Greece

Nestos River is the 71th biggest transboundary river in the world. At early nineties, two major hydroelectric reservoirs, at the locations “Thisavros” and “Platanovrysi”, in the Greek part of the considered river basin, were constructed. In a previous work, the authors have found that the construction of these reservoirs induced a dramatic reduction (more than 80%) in the sediment yield that reaches the outlet of Nestos River basin. This resulted to a major increase in the erosion rates at the river delta and the adjacent shorelines. In the present paper the effect of sediment dredging and flushing from the “Platanovrysi” dam downstream is investigated, in order to evaluate the increase in the sediment budget that reaches the outlet, which can contribute to the reduction of shoreline erosion. For this purpose a mathematical model is modified accordingly in order to take into account sediment dredging and flushing. A wide series of parametric simulation scenarios is performed, aiming to identify the optimum periods that dredging and flushing can be applied for maximizing the sediment amount that reaches the basin outlet. A definite classification of the months in “effective” and “ineffective” as well as to “consistent” and “inconsistent” with respect to the total amount of sediment that reaches the basin outlet is made. It is also found that the considered river has a maximum transport capacity regardless the further increase of the dredged and/or flushed sediment quantity from the identified limiting value. Finally, flushing is identified to be slightly more effective than dredging.