An integrated approach for water-quality investigation of Piediluco lake (Italy)

The study aims at investigating strategies to reduce the effect of the nutrients pollution in Piediluco lake, improving the water quality and limiting the eutrophication processes. In particular, managements options operating in the body of the reservoir are considered, i.e. the variation and/or repositioning of the main water inflow. Piediluco is the second largest lake of Umbria region (Central Italy) and is characterized by an extended and complex shape with several branches (approximately 1,7 km2 with an average and maximum depth, respectively, of 10 m and 20 m). Currently, the hydraulic regime of the lake is regulated by the downstream hydroelectric plants of Galleto and Monte Sant’Angelo: during the power generation, water from Piediluco lake is conveyed through Velino river into the hydroelectric plant; when the electric production is paused, the entire flow rate of Velino river is conveyed to the lake. Actually, the largest water supply is provided to the lake by the Medio-Nera channel, an artificial canal built in 1932 that has expanded the Piediluco basin area from 75 km2 to 2100 km2. The main idea is to move the position of the inlet in order to promote the movement and recirculation of water throughout the lake surface. Several field measurements, carried out from the first years of 1980s, have highlighted that the health of the lake has been constantly deteriorating: the increase of nutrients loading has negatively affected the ecosystem, progressively compromising the use of the lake and its resources, and, consequently, the local economy. A high eutrophication level of the lake, with algal bloom and, in extreme meteorological conditions, a significant water anoxia, in particular in the arms of the lake far from the inlet of Medio-Nera channel, have been observed. The work is based on an integrated approach: at first stage, remote sensing available data, coupled with the Google Earth Engine (GEE) platform, are used to analyse, in the last decade, the spatial distribution, the seasonal variations and the inter-annual variations of water quality parameters. Secondly, a two-dimensional model is developed, in order to simulate the sediment and pollutant transport connected with the hydrodynamic condition of the lake with different management scenarios. The model is calibrated and validated on the base of in situ monitoring data.