The influence of water level hydrodynamics on potential changes in the morphology of a mountain reservoir shore zone

This study evaluates the influence of water level fluctuations in a mountain reservoir on potential changes in the morphology of its shore zone. The analysis was carried out in the Czorsztyn reservoir on the upper Dunajec river (located in the upper Vistula Basin within the Polish Carpathians). The spatio-temporal distribution of water levels in the Czorsztyn reservoir was analysed using Fourier spectral analysis, Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), and predictive models. The results indicate that the actual range of water levels in a mountain dam reservoir that can have an impact on the morphology of the shore zone is much narrower than its theoretical range. Over the multi-year distribution of daily water levels in the reservoir, four quasiperiodic, overlapping cycles were identified (0.5-year, 1-year, 1.9-year, and 3.8-year cycles); these cycles are expected to have the greatest impact on the intensity of changes to the morphology of the reservoir’s shore zone. Predictions of water levels in the reservoir were carried out using STLForecaster, TBATS, ThetaForecaster, ExponentialSmoothing, and EnsembleForecaster models. The forecasting results suggest that the reservoir will be subjected to slight but statistically significant changes in its water levels in the following years. Furthermore, the frequency of high water levels close to normal water levels is expected to increase, that may consequently lead to morphological changes of the shore zone and instability of the reservoir slopes. The results of the study can be useful in predicting the effects of environmental changes within dam reservoirs as important elements of infrastructure for effective water resources management.