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Abstract: 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 ϕ TOTAL, 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 ϕ TOTAL by approximately 13%. In Nestos River mouth, the water column dynamics are highly affected by river damming, as ϕ TOTAL appeared reduced during November to July, by approximately 50.2%. [Copyright &y& Elsevier]

Summary: River flow forecasting consists one of the most important applications in modern hydrology, especially for the effective hydropower reservoir management. In this paper, an innovative non-linear time-series fitting and forecasting model is proposed, consisting of the following sub-modules: (a) the division of the time-series into generations, by identifying the structural change points, (b) the generation decomposition into linear trend, harmonic component and autoregressive component, consisting of several gene ARMA models, (c) the use of fuzzy methods to determine the relative weight of each gene model, and (d) the time-series expansion for the optimal forecasting. The method was applied to the mean monthly Nestos River discharge data for the 1966–2006 period, recorded at the Greek–Bulgarian border, serving as inflow to the Thissavros Hydropower Reservoir. The selected series was divided into five distinctive generations representing periods of gradual surface runoff reduction. It occurred that mean monthly discharge during the fifth generation was almost halved, compared to the corresponding value of the first generation. Harmonic decomposition produced periods in agreement with the large-scale atmospheric fluctuations, while ARIMA modeling performed on the residuals from a pre-defined gene model-base, produced satisfactory fitting to the measured flow series. Model expansion for the last 2 years (2005–2006) of the time-series illustrated reasonable good approximations. Model forecasts during 2005 followed closely the recorded variability, with MAPE and RMSE statistics indicating increased model accuracy. Overall, it is evident that the model slightly underpredicts Nestos River discharge, while slight overestimation occurs under high river flow conditions (winter 2006). Although current research proved model’s distinct capability and advantages in river flow fitting and medium-scale forecast, future improvement could facilitate the use of more elaborative models (ARCH, fuzzy, ANN), in the developed gene model-base. [Copyright &y& Elsevier]