Impact of river damming on coastal stratification-mixing processes: The cases of Strymon and Nestos Rivers, N. Greece

In this paper, the question of freshwater induced stratification at the mouth of two dam-controlled Greek rivers is addressed. Results from a monitoring program are presented along Strymon River estuary and Nestos River coastal zone, two of the most important freshwater suppliers in the North Aegean Sea. Strymon River flow is man-controlled through Kerkini Dam, while Nestos River discharge patterns depict significant alterations, due to the operation of two hydropower dams. Moreover, a stratification-mixing model was developed based on the water column potential energy ϕTOTAL, which accounted separately for the local contributions to stratification (solar heating and freshwater buoyancy) and mixing (wind and bottom shear stresses). The model was run under two different scenarios: a) the influence and the absence of Kerkini Dam for the case of Strymon River, and b) the presence and absence of the hydropower dams for the case of Nestos River. Results show that Kerkini Dam affects the stratification conditions in Strymon River mouth during spring and early summer (April to June), by reducing ϕTOTAL by approximately 13%. In Nestos River mouth, the water column dynamics are highly affected by river damming, as ϕTOTAL appeared reduced during November to July, by approximately 50.2%.