WAESS (West Arm Exchange Enhancement System) Project: for the restoration of the Lake Como First Basin

The WAEES Project aims at the installation of a propeller system designed to increase the flushing rate of the southernmost region of the Lake Como West Arm (the so-called First Basin) characterized by high residence time due to the absence of a natural outflow.
The first phase of the project (2006-2007) saw IRSA-CNR and the Centre for Water Research (CWR) of the University of Western Australia jointly work with the Centro di Cultura Scientifica A. Volta (the project manager).
WAEES developed a high-tech real time measurement system consisting of three limonological mooring stations (Lake Dyagnostic System) for the detection of the principal meteorological drivers and of the lake thermal structure and of two gauges system to detect the inflowing volumes from the two principal point sources of the western basin (Cosia and Breggia streams). The real time measurement system transfers the information remotely and provides the input data for a hydrodynamic-ecological model (ELCOM-CAEDYM) developed by CWR and tailored for the Lake Como by CWR and IRSA-CNR.
During the first phase of the project the data from the real time equipments were integrated with data from a pilot field experiment and an intensive field campaign, conducted in October 2006 and October-November 2007 respectively. The first experiment was performed, jointly by CWR and IRSA-CNR with the logistic support of Centro Volta, in the Como bay in order to verify the dynamic of the functioning of a pilot propeller. The propeller consisted of a blade with a diameter of 2.5 m positioned under the water surface and powered by an electric motor. Once switched on the propeller draws the surface waters and generates a descending flux that enters the thermocline as a horizontal intrusion. The overall effect of the propeller action is to draw the surface nutrient-rich waters of the Como bay and to spread them into the lake interior using the entire assimilative capacity of the ecosystem to mitigate the nutrient load on the First Basin. The thermocline flow detected during the pilot experiment (25-30 m3 s-1) was around 30 times higher than the discharge of the Cosia stream and 10 times higher than that of the Breggia stream. This allows pointing out a high efficiency of the propeller in flushing the surface waters of the Como bay. A subsequent modeling study showed that a number of 6 impellers, properly distributed in the bay of Como, would be sufficient to double the natural flushing rate of the bay, enhancing the assimilative capacity of the lake.
The intensive water quality campaign was conducted by IRSA-CNR in 2007 with the principal aim to define the nutrient and phytoplankton distribution in the western basin. Measurements were conducted with an unprecedented detail in spatial resolution. The water quality campaign showed a consistent nutrients gradient that feeds the higher level of algal production and the recurrent algal blooms. Within the phytoplankton population a consistent contribution of the potentially toxic cyanobacterium Planktothrix rubescens (that may compromise the use of the water resource for bathing and drinking supply) was also detected. The data collected during the intensive campaign joined to the historical data from the Regional Authority for Environmental Protection (ARPA Lombardia) are currently being used for the calibration of the hydrodynamic-ecological model that will be applied, to manage the propeller system and to guide the nutrient reduction policies, in the second phase of the project. From this point of view the analysis of point and non-point nutrient sources distributed in the catchment of the Lake Como west arm underlined that the major effects of the nutrient reduction policies will be gained from 2016, thus confirming the value of the WAEES Project and the goodness of the management approach undertaken by the local authorities that integrates long-term structural measures with a local and short-term action designed to mitigate the nutrient loads from the residual pollutant sources.
The research proposal for the second phase project is currently under revision before to be submitted at the supporting institutions. The installation of the propellers system is expected for spring 2009.