Recently, several droughts have negatively affected agricultural activities on the Padana plain
(Italy), causing scarcity of irrigation water and both extended (up to tens of kilometres) and
prolonged saltwater intrusion. The wetland system of Vallevecchia (Caorle, Venice) is based on a
700 hectares-wide drainage basin reclaimed during the sixties on the sand littoral zone of the
North-Western Adriatic Sea.The system, by means of several hydraulic works allowing the inside recirculation of rainwater and
drain water, has multiple pioneering goals: limiting saltwater intrusion, enhancing irrigation water
availability during droughts, and reducing the diffuse pollution from agriculture (i.e. the nutrient
loads discharged into the eutrophic Adriatic Sea) through phytoremediation. We have intensely
monitored the water quality of Vallevecchia since 2003. Ever since, the system was sensibly altered
by the construction (ended in 2005) of two hydraulic infrastructures in order to increase its
efficiency: a check-gate to control the outflow from the system and a basin for water storage. The
traditional functioning scheme of the system was based on pumping the water collected by the
Sbregavalle channel into the Canadare channel, by the Vallevecchia pumping station. In order to
allow water recirculation inside the basin, the abovementioned deep structural modifications were
realized: the water storage basin, characterized by an internal volume of about 200000 m3, was
created by excavation works and construction of surrounding levees. A check-gate was built in the
Sbregavalle channel, to allow water retention inside the channel itself, limiting water expulsion
through the Vallevecchia pumping station. In this way, water can be retained into the channel and
be pumped inside the storage basin by a new pumping station which was appositely designed for
this purpose. This pumping station contains three submersible pumps, and is well integrated in the
local environment thanks to its limited size. The storage basin is linked to the Vallo channel, which
flows along the sea border of the Vallevecchia basin, by a pipe line in which gravity flow realizes.
A tank interposed between the pipe line and the Vallo channel allows flow regulation. Water can be
distributed in the area between the Sbregavalle and the Vallo channels through some regulating
gates which allow water flowing inside first order and second order channels.
The following parameters have been monitored: ammonia nitrogen N-NH4, oxidate nitrogen NNOX,
dissolved organic nitrogen D.O.N., particulate nitrogen P.N., total nitrogen T.N.,
orthophosphate phosphorus P-PO4, soluble unreactive phosphorus S.U.P., particulate phosphorus
P.P., total phosphorus T.P. and total suspended solids T.S.S. The choice of these chemical
parameters has been made because they are of maximum interest to control the pollution in
drainage basins and in lagoons of the northern Adriatic area. The long-term monitoring dataset,
including nutrient concentrations, water flows and environmental data, has consequently allowed
the evaluation of the system performances both under varying environmental conditions and
different system configurations.
Monitoring data analysis shows that the two new hydraulic infrastructures have led to a markedly
increased within-system abatement of nutrients from 2006 to 2009 as compared to the 2003-2005
period. Strikingly, the reduction of discharged nutrient loads has been achieved with only a
minimal management effort, e.g. each year the water storage basin was filled once. Consequently,
our results indicate that the check-gate plays a fundamental role in increasing the system efficiency,
and suggest that starting a simple, routine management (e.g. of the check-gate position and of water
recirculation, to achieve a better exploitation of the wetland) would make the system functioning
remarkably more efficient