QUAYS & BREAKWATERS
Breakwaters at the entrances of the ports of the Venice lagoon - Italy  

Client:                         Venezia  Nuova  Consortium -  Ministry  of Public Works

Services:                    Ports entrance studies, hydrodynamic and wave propagation studies; assistance to model testing; 

                                     preliminary and detailed design; general supervision.

Period:                       1991 - 1997

Construction cost:  € 71,787,500

The project:

The construction of the six breakwaters at the entrances of the three ports of the Venice lagoon, Chioggia, Malamocco and Lido, which was carried out in the period  between the mid-nineteenth century to the early twentieth century, was motivated by the need to protect the lagoon's navigable access channels against filling with sediment. These works did in fact cause an increase in the depth of the access channels, but at the expense of the stability of the breakwaters which increased proportionally with the depth.

Technital was commissioned by the Venezia  Nuova  Consortium to:

• examine the reasons for the  continuous maintenance requirements;

• evaluate the feasibility of definitively rehabilitating the breakwaters, in relation to their present and future function;

• suggest the best type of intervention;

• perform  the  preliminary  and detailed design  of  the  proposed interventions.

The Preliminary Design, completed in 1991, included the examination and development of the types of intervention needed to make the breakwaters compatible with their present use and, above all, with their future function, when the flood control works (the fixed works for the mobile barriers) have been constructed. 

These interventions comprise:

• the creation of a filter in the lower part of each breakwater  which prevents the loss of fine materials, without removing all or part of the existing claddings and thus without creating hazardous conditions for the overall stability;

• the creation of a protection against erosion at the base of the breakwaters to combat further subsidence of the foundations;

• the  renovation  of the claddings exposed to current  and  wave motion action, using similar materials to the existing ones  the  restoration of the crown wall.

During 1992-1997 TECHNITAL developed the Detailed Design for all six breakwaters at the port entrances. The work defined by the design comprises:

• the installation of filters by the laying of 20-150 mm. crushed stone and  foundation berms for the cladding by laying 50-1000  kg. and 1-3 t. rubble for a total of 1,500,000 t.

• the restructuring  of  the protective  cladding  by installing 6.3 m3 tetrapods, with a total of 40,000 m3 of concrete, and of 2-5 t.  rubble for a total of about  300,000 t.
  
  This Project includes the reconstruction of 6 breakwaters at the 3 lagoon port entrances on depths varying from 9 to 19 m, for a significant wave height of 5,5 m, and for a total length of approx. 6,200 m.
   

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