cedimento moli foranei

Manifestation
Causes
Consequences

The jetties, built between the mid-nineteenth century and the first decades of the twentieth century, were unable to withstand the major physical changes that were taking place. Over the years, regular maintenance work has coped with immediate damage, but it has not tackled the problem at its source. In order to remedy this situation the Venice Water Authority - Consorzio Venezia Nuova carried out a general intervention reconstruction programme which has recently been completed.

Manifestations

The jetties are located on either side of the lagoon inlets and extend hundreds of metres out to sea. As years went by, the jetties narrowed the inlets, causing an increase in the speed of the currents and thus a deepening of the beds, which fell to as much as twice their original depth.

		Because the depth of the inlet canal kept increasing, the jetties continue to settle and crack. Deterioration occurred in a continual and gradual way, causing fracturing and breaks in the jetty structure and paving.
		Gli effetti delle mareggiate e dei cedimenti sul Malamocco north jetty. The damages caused by sea storms and cracking

Causes

With the passing of time, the materials and technologies used to build the jetties have proved inadequate and unable to withstand the major physical changes that were taking place. The jetties increased the depth of the inlet canals, but this increase in depth inturn damaged the structure of the jetties. Large rocks were infact deposited directly onto sea beds without an intermediate layer of smaller rocks acting as a filter and, thereafter, the structure continued to sink and to suffer severe deterioration and cracking.

The example of Malamocco. The cross sections show the condition of the canal bed when the jetties were first built and before restoration. The inlet canal bed was 6 m deep when the jetties were built. Today the average depth of beds is 15 m, or even 19 m at the foot of the jetties, and at some points along the beds, trenches have been created

Consequences

		With time the jetties became more and more unstable and vulnerable to wave motion with a considerable reduction in their stability . Repeated maintenance was always in the form of emergency measures and did not stop the further deterioration of the jetties.
		Malamocco north jetty. Damages caused by the sea storm of November 4, 1966