Littoral

Introduction
It is the area of the Lido facing the sea. The "Lidi" are strips of land separating the lagoon from the sea and stretching for about 50 km: from the mouth of the Brenta to that of the Sile (From "I litorali sabbiosi del lungomare veneziano -part 2").
They are formed by a belt of high dunes made up of alluvial materials deposited mainly by two rivers: the Tagliamento and the Piave. The current, which in the Northern Adriatic Sea has a direction from northeast to southwest, has made these alluvial deposits parallel to the coast.
6000 years ago this zone used to belong to Veneto's plain and successively, with the rising of the sea level (eustacy) and the lowering of the soil (subsidence), it gave rise to longshore bars. Veneto's old plain, which, until 18.000 years ago reached the city of Pescara (from "La Laguna: Origine ed Evoluzione" in "La Laguna di Venezia") is made up of "caranto", a layer of very compact mineralised clay which forms the natural bed of the lagoon. On this lagoon bed the Venetians have set the stakes that support the buildings of the city.
The wide marshland, which had been confined behind that line, was initially a fresh water lagoon, but periodic breakthroughs of the tide let sea water enter, turning it into a brackish water lagoon (from "Guida alla natura nella laguna di Venezia - Itinerari, storia e informazioni naturalistiche", 1996).
These processes are still active and littorals are continuously involved by constructive phenomena as the deposit of sandy material coming from the sea (sedimentation) and by destructive phenomena as marine and eolian erosion.
The aspect of the littorals has changed during the centuries not only because of the natural evolution of this extremely dynamic environment, but also because of continuous human intervention, as in the case of the building of the "Murazzi", in the deflection of the tributaries from the Lagoon, and successively in the realisation of jetties and groynes.

Human Interventions
Man's relationship with the lagoon has been constantly characterised by interventions which began right from the time of the first settlings in this environment.
Until the 15th century interventions were restricted to a limited number of works of consolidation and embankment that did not modify the essential characteristics of the original lagoon.
Major works which influenced and started to modify the natural dynamisms began from the 18th century.
The first interventions date back to 1738, when the Republic of Venice realised along the littorals of Malamocco, Pellestrina and Sottomarina the so-called "Murazzi": sea defensive works made up of Istrian stone and "pozzolana". They are jetties whose aim was to create a barrier to prevent the sea from attacking and eroding the banks.
The idea of building these defensive works was conceived in 1716 by Father Vincenzo Coronelli. He sent the "Savi ed Esecutori alle Acque", main office in charge of civilian public works, his innovative project, in which he proposed to substitute the traditional sea defensive works made up of oak trunks and filling material with a real staircase made up of Istrian stone blocks.
But it was the Water, Rivers, and Lagoon supervisor Bernardino Zendrini who carried out this project thanks to the employ of "pozzolana", a recently discovered material, which solidifies when it is mixed to lime and if it comes in touch with water. This way the Istrian stone blocks "welded" with each other and made the "Murazzi" barrier even more effective.
ne more intervention that modified the aspect and the dynamisms of the lagoon was the deflection of the lagoon tributaries. Because of the sediments coming from the tributaries, which were not compensated by the erosive effect of the sea currents, the natural evolution of the lagoon environment would have meant its silting up.
The "Serenissima Republic" has always regarded the silting up of the lagoon as a problem because of the negative effect it could have had on the city of Venice, whose safety and prosperity were indissolubly linked to the existence of the lagoon around the city.
The first interventions on water-courses were first performed in the 12th century: the plain water-courses were embanked in order to limit the erosion and the consequent transport of sediments to the lagoon. These works did not bring the expected results and it was therefore decided to face the problem radically deflecting the rivers that flew into the lagoon.
The first river to be deflected was the Brenta, whose course was moved from Fusina to the sea in 1548. The silting up of the Lagoon was actually slowed down, but at the same time both the erosion and the withdrawing of the salt-marshes increased, a problem that has been discussed since 1600.
In the Lagoon there is still a well visible track of the old course of the Brenta: the Grand Canal, an old lagoon tract of that river.
In 1896 the Brenta, because of the difficult downflow and the consequent flooding caused by the winding course it was forced to follow to reach the sea, was newly deviated in the Lagoon. However, in the following 40 years the increase in the silting process led to the definite decision to deflect the river to the sea, in the bed of the Bacchiglione.
The Piave did not have such a troubled history as the Brenta had: it was first deflected to Cortellazzo, then to Santa Margherita, but in 1862 it flooded and went back to hold the river bed that leads to Cortellazzo.
The Sile, being a resurgence river, has always presented few problems of sediment transport and was deflected in 1680 in Piave's old river bed mainly for health problems.
The deflection of the tributaries to the sea caused the disappearance of the marsh belt, which formed a peculiar and important avifauna environment and to an increase in the level of the salinity of the salt marshes and of the lagoon beds.
Freshwater environments are currently reduced to small portions in the lagoon edge area and they are sometimes formed by artificial environments as deserted clay mines later transformed into in marshlands (e.g. Cave Gaggio).
During the 19th century interventions were carried out on fish farms building fixed frame embankments and jetties: these modifications started a process of substitution of lagoon environments with land environment. (From " Le problematiche naturalistiche nella progettazione e gestione degli interventi sulla Laguna”, 1997).
The jetties are hundreds of metres long and link the sea to the Lagoon allowing the ebb and flow of the tide.
They were built during three subsequent phases starting from 1805 at the Lagoon inlets of Malamocco, Lido and Chioggia in order to deepen the seabeds hindering the natural silting up of the canals and in order to allow big tonnage ships to enter the port of Venice.
By the narrowing of the section of the canals, the entrance speed of the current increased and so did the eroding force acting on the beds, whose depth indeed changed from the original 5-6 metres to the current 20 even 30 metres . This modified environment changed the natural current circultation causing downstreman at each jetty a loss in the sandy material and upstream an accumulation of the same material, as it can easily be observed comparing San Nicolò's littorals at the Lido and the littorals of Punta Sabbioni at the Cavallino.

Natural evolution
From what has been said so far it can be easily understood that littoral environment is continuously evolving both from a morphological and a functional point of view.
Besides the changes that have been taking place on wide spatial scales, one can also notice the continuous evolution characterising the littoral environment.
sea current in the shape of heaps of algae and dead phanerogamae, enable the vegetal and animal population to evolve and settle in an environment which apprently seems so inhospitable and without resources (from “Un ambiente naturale unico – Le spiagge e le dune della penisola del Cavallino”, 1992).
Each vegetal and animal "presence" helps to create the right environment for the settling of other organisms in a dynamic process of close relations that takes place in a restricted belt stretching from the seashore to the littoral wood.
The organisms living in this environment had to adapt to difficult life conditions, adopting some devices enabling them to survive.
Some plants as the Russian thistle (Salsola kali), try to reduce as much as possible potential water losses due to transpiration by reducing the leaf surface exposed to sunbeams: this way they can accumulate water in the tissues and employ it in case of drought (From "Un ambiente naturale unico – Le spiagge e le dune della penisola del Cavallino").
The plants in this environment have succulent leaves to reduce the loss of water due to evaporation, a quick vital cycle to exploit as much as possible the most favourable periods and an elevated seed production to enable at least some individuals to take root (From "Un ambiente naturale unico – Le spiagge e le dune della penisola del Cavallino").
The plants suitable to live at some distance from the sea are grouped in strips parallel to the seashore line forming vegetal associations whose characteristics reflect the variations of the environmental characteristics from the seashore to the most inland environments.
The first plants that can be met moving away from the seawater are the so-called "pioneer plants", that means that they are the first plants to colonise an inhospitable environment and that they prepare the soil for more exigent species.
The sand transported by the wind and the materials brought by sea currents are deposited at the basis of these plants, thanks to which the first belt of dunes is made up (From "Un ambiente naturale unico – Le spiagge e le dune della penisola del Cavallino").