Draining basin of the Venice Lagoon - Venice province
The case study is located in the draining basin of the Venice Lagoon. It is characterized by intensive agriculture and by a web of drainage channels discharging into the rivers. This case study, in particular, includes measures on the drainage channels discharging into the Dese river, one of the main water bodies of the Venice Lagoon basin.
The Veneto Region, through the “Plan for diffuse pollution prevention and restoration of water in the draining basins of the Venice Lagoon” financed measures of re-calibration of riverbeds aimed at the renaturation of the hydraulic web, to increase the time of permanence of water and phytodepuration processes in the draining basin. In this framework, the Consorzio Acque Risorgive implemented a series of extended interventions on the area under its responsibility. This case study was implemented as part of these interventions.
In particular, it aimed at re-structuring the effluents of the mid course of the Dese river (Rio S. Martino, Rio S. Ambrogio and Scolo Desolino). Such effluents are mostly draining channels, draining water from agricultural fields to the Dese river. The primary objective was the reduction of the amount of N and P reaching the Venice lagoon through phytodepuration. However, at the same time the project carried out the restoration of the draining channel web aimed at reducing flooding issues affecting the area. Over the years, the area has in fact been subject to massive urban development (new residential and industrial areas), with consequent soil sealing and culverted effluents: this had a devastating effect on the hydrological system. The strong floods of 2006 and 2007 on the city of Mestre, for example, were a consequence of this.
The following measures were implemented: (i) Riparian buffer zones; (ii) Creation of wetlands; (iii) River bed enlargement; (iv) Creation and reconnection of floodplain and new buffer strips; and (v) Channel naturalization, creation of new meandering channel.
The ability of the measures to address two pressing environmental issues in the area was a key success factor. The measures proved in fact very effective in reducing nitrogen loads in effluents and, ultimately, into the Venice Lagoon, as well as mitigating flood risk in the area. During the implementation phase, some residents complained for the annoyance (e.g. the dust lifted by the machinery). However, during the first intense precipitation, the rivers/ channels did not overflow (they would have before implementation), so residents understood the key role of measures for flood mitigation. Furthermore, the overall decrease of N levels in the Venice lagoon, which followed the implementation of these and other similar measures in several sites within the draining basin, contributed to gain a positive public perception of these measures.