COASTAL DEFENCE WORKS
Sea defences of ports and lagoon of Venice - Italy

Client:                          Venezia  Nuova  Consortium -  Ministry  of Public Works

Services:                    Hydrodynamic physical and mathematical model studies, Preliminary & Detailed Design of defence works

Period:                        1991 - 1997

Construction cost:   € 227,214,000

The Project:

In 1990 Technital drew up a General Plan for the interventions along  the littorals which separate the Venice lagoon from the sea (approximately 40 km.) including the organization and management of extensive measurement surveys; the examination of the coastal regimen using mathematical models of the hydrodynamic, wave motion and sediment transport phenomena; and the definition of the types of intervention for the four coastal sections of Sottomarina, Pellestrina, Lido and Cavallino. The principal type of intervention selected was artificial beach nourishment, contained by a groyne system and submerged breakwater.

The new interventions for the defence of the Pellestrina littoral started in 1990 with the design and construction of a submerged breakwater protecting the historic "murazzo" at the weakest point of the whole littoral belt. Technital performed the Preliminary and Detailed Design of the intervention and then co-ordinated a campaign for monitoring the evolution of the seabed, to obtain full knowledge of the local regimen of solid transport. The submerged breakwater, about 30 m long and with a summit level of -0.50 m., has proved to be effective in causing wave breaking though without modifying the physical appearance of a stretch of coast greatly admired for its landscape. The model study is considered among the most innovative and complete performed up to now in the field of coastal engineering: the continuous interaction among the four models created (2-D and 3-D mobile bottom physical models, mathematical models of longitudinal and transverse transport) allowed the examination of the efficacy of the various design alternatives in relation to the principal indicators selected.

The Detailed Design for the restructuring works to protect Cavallino littoral started in 1990 with a pilot intervention, consisting in the beach nourishment of a sample zone approximately 200 m. long, protected from the sea by a submerged barrier of sandbags located on the bottom about 2 metres deep. The ultimate works designed for the entire littoral included:

• artificial beach nourishment, for a length of approximately 11 km., by depositing about 2 million m3 of sand obtained at sea and contained laterally by 32 groynes at right angles to the shore;

• reshaping  of the existing sea wall, along a  length of about 3000 m., with a cladding of concrete blocks with a 2.5:1 gradient;

• an anti-syphoning/filtration diaphragm about 3500 m. long located behind the existing sea wall created by installing metal sheet piling or by jet-grouting;

• rehabilitation of the existing chain of dunes along a stretch of about 4000 m., to be achieved by depositing sand and planting suitable vegetation to stabilise the work.

The chosen solution for Lido littoral was again artificial beach nourishment, using sand taken from depths of about 20 m., to ensure the attainment of adequate safety standards, the restoration of the original morphological configuration of the island and the promotion of tourism. The newly replenished beach will be anchored using groynes of an unconventional structure, with the outer end submerged and a cladding of uniformly arranged blocks so as to favour tourist access and blending into the landscape.

In the case of Sottomarina the interventions include:

• the promulgation of legislative and environmental restriction measures to restore, in time, a certain recovery of the river sediment transport;

• restructuring of the two river outlets with breakwaters

• artificial beach nourishment;

• reconstruction of  some  areas of the dune belt  and  planting  of typical flora.

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