Sustainability evaluation of Mornos Lake/Reservoir, Greece.

The modern climate trend and population growth have dramatically increased the need for maximization of the net benefit from the existing storage space in freshwater reservoirs. However, sedimentation in reservoirs through physical deposition and/or slope failures is a major threat to their productivity and life expectancy. In this context, the sedimentation impact on the sustainability of Mornos Lake/Reservoir, which is exceptionally vital for the ~ 3.1 million inhabitants of Athens, had to be evaluated. Therefore, a meticulous geophysical survey of the reservoir bed was conducted in 2015 for the very first time. Bathymetric, sidescan sonar, and seismic profiling datasets, all integrated with real-time kinematic (RTK) positioning, were analyzed for a realistic evaluation of the storage capacity loss. Approximately 18.2 × 10 m of lacustrine sediments derived through physical wedge-type deposition process and ~ 800,000 m of material produced by slope failures have covered the bottom since reservoir commissioning in 1981. This configures an average storage capacity loss of ~ 0.07% per year, which, however, is one of the lowest rates worldwide. Moreover, the 108-m-deep reservoir basin can presently accommodate a maximum active water volume of ~ 740 × 10 m. The siltation pattern and sediment transport pathways in the reservoir are principally controlled by vigorous turbidity underflows, which deliver sediment mainly to the dam area (deposition thickness up to ~ 7 m) as well as to the pumping area (deposition thickness up to ~ 4 m) posing there a future risk; nevertheless, according to the predicted lake bathymetry, this risk will be negligible till 2045.