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EarthCache

The breath of the Lagoon of Venice

A cache by Calico Team Send Message to Owner Message this owner
Hidden : 6/9/2009
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

The site is near the Punta Sabbioni lighthouse (1 m above sea level), located on an 300 m-long seawall near the Lido inlet. The cache site is totally public and free of access.

This earthcache is placed in the Lido inlet. This is one of the three “open doors” between the Adriatic Sea and the Lagoon of Venice.

The main educational goal of this earthcache is to tell you the history of the Lagoon, their environmental concerns and the importance of the inlets. If you love the nature, you may also visit the nearby natural area “Penisola del Cavallino”, a Site of Community Importance (SCI). Moreover, in this area you can see the “remains” of the original Venetian beach dune system. During the summer, you can also sunbathe on the nearby beach of Punta Sabbioni, or you can take the ship “vaporetto” to make an historical tour of Venice, Murano and Torcello islands.


Figure 1. Image from Wikipedia "http://en.wikipedia.org/wiki/Venetian_Lagoon"

The Lagoon of Venice is located along the north-western coast of the Adriatic Sea (approx 45°N; 12°E) and is the largest lagoon in the Mediterranean Sea. The Lagoon of Venice is today the most important survivor of a system of estuarine lagoons, which in Roman times extended from Ravenna to Trieste. It is a complex ecosystem, controlled by many natural factors and affected by several centuries of heavy human influence (see Figure 1). Today, the lagoon covers an area of about 550 km2; it has an extension of about 50 km along the coast and an average width of 15 km. The average depth is 1.2 m, with only the 5% of total surface deeper than 5 m and 75% shallower than 2 m [1,2]. About 140 km2 of the total lagoon surface is occupied by mud flats which form salt marshes (barene), emerging from the water only during low tide.
Some studies reported that the lagoon of Venice originated nearly 6–7 thousand years ago, during the Flandrian Transgression, during the last Ice Age. In this geological period, the rising sea flooded the Upper Adriatic Würmian paleo-plain and outlined the coast in approximately the present position [3]. The ancient lagoon was smaller than the present one, principally controlled by two main factors: i) the continuous sediment supply from several rivers originally flowing into the lagoon (e.g., Adige, Bacchiglione, Brenta, Sile and Piave); ii) the noticeable coastal nourishment coming from southward, due to the Po river, that led to a gradual silting-up of the tidal inlets. In this geological system, the sediments transported from the rivers compensated for the sinking coastal plain, and coastwise drift from the mouth of the Po tended to close tidal inlets. These two natural processes started unavoidably to the disappearing of the lagoon basin [3], however, in the subsequent centuries, the Venetians contributed significantly to modify the lagoon system with some hydraulic interventions. During the age of the Serenissima Republic (XV-XVI centuries), the Venetians, considering the lagoon a source of security against enemies, carried out several hydraulic works to preserve it.
Today, the lagoon appears as a salt-water estuary, protected from the Northern Adriatic Sea by some sandbars (Cavallino, Lido and Pellestrina) which are interrupted by three tidal inlets (Lido, Malamocco and Chioggia). The three inlets are not very wide, but they are extremely important, allowing the matter and energy exchange between sea and lagoon, driven by the tidal cycle. The tidal cycles can be considered as the “breath” of the lagoon, a fundamental process of water renewal between Adriatic Sea and lagoon, that is essential for the lagoon’s metabolism, i.e., salinity control, exchange of dissolved oxygen, nutrients and oligo-elements and… unfortunately, also the pollution.
At the present time, the Lagoon of Venice suffers from a series of environmental problems directly linked to: i) the presence of the city of Venice, with about 63,000 inhabitants; ii) the industrial zone of Porto Marghera, perturbing the air, the water and the sediments with heavy metal and organic pollution; iii) the commercial–industrial and private shipping, with some fishing vessels carrying out an intense -and in many cases illegal- clam harvesting and mechanical dredging of channels.
However, one of the most serious environmental problems affecting the Lagoon is the increasing of the high waters (“AcquaAlta”), due to the exceptional tide events. Venice is afflicted by high waters since ancient times, predominantly in autumn, winter and spring. Although the tide in the lagoon basin is lower than in other areas of the world where it may reach as high as 20 m, the phenomenon may become significant if associated with atmospheric and micro-meteorological factors, such as pressure and the action of the Bora wind blowing from Trieste or Sirocco wind coming from south-east, which push the waves into the gulf of Venice [4]. The recent increase in the frequency and intensity of high waters was associated with natural and artificial causes. The main “natural (?)” causes are the subsidence (sinking of the Earth’s surface in response to geologic or anthropogenic causes) and the eustatism (rise of the sea-level). In this way, during the 20th century, land in the lagoon dropped by 23 cm with respect to mean sea level. The main “human-made” cause is the erosive action of the water flows as a result of some of the measures taken by man to facilitate port activities (jetties, artificial canals) [2].
The MOSE Project (Italian acronym for Experimental Electromechanical Module) is a project started to protect the city of Venice from extreme events such as the high floods (see earthcache “AcquaAlta”) and from morphological degradation. It consists of some rows of submarine mobile gates, built to isolate the Venetian Lagoon from the Adriatic Sea when the tide reaches above the level of 110 cm. The construction of these mobile barriers was started on 2003, together with other complementary measures, i.e., coastal reinforcement, the raising of quaysides and paving and improvement of the lagoon environment. Today, you can see the works to build the barriers near the Lido inlet. You can read more information about the MOSE project from Wikipedia.

Near the earthcache site you can see the natural area called “Penisola del Cavallino”. This is a Site of Community Importance (SCI), defined by the European Commission Habitats Directive (92/43/EEC) as a site contributing significantly to the maintenance or restoration at a favourable conservation status of a natural habitat type, and contributing significantly to the maintenance of biological diversity… a great place to make pictures of birds (birdwatching). Moreover, near the beach you can see the “remains” of the ancient dune system. Today, the dune system is almost-totally destroyed by human activities and urban/touristic infrastructures.

New question added!
To log this Cache you must go at the coordinates, in front of the Punta Sabbioni lighthouse (see Figure 2), and you have to answer four questions: 1) The lighthouse has 3 wall faces to the open sea. What is their color?; 2) How many doors have the lighthouse on the ground-floor? 3) How many inlets have the Lagoon of Venice? 4) In the 20th century, the land in the lagoon dropped some centimeters, with respect to mean sea level… How many centimeters?
Send me the correct answers using the geocaching mail (mauro78). If you want, you can make a photo of you, your GPS device and the Punta Sabbioni lighthouse!

Logs without correct answers will be extinguished by the owner regularly.


Lido inlet
Figure 2. Another lighthouse, near the cache.


References

[1] Ravera O., 2000. The Lagoon of Venice : the result of both natural factors and human influence. J. Limnol., 59(1): 19-30.
[2] Molinaroli E., Guerzoni S., Sarretta A., Masiol M., Pistolato M., 2009. Thirty-year changes (1970 to 2000) in bathymetry and sediment texture recorded in the Lagoon of Venice sub-basins, Italy. Mar. Geol., 258: 115–125.
[3] Brambati A., Carbognin L., Quaia T., Teatini P., Tosi L., 2003. The Lagoon of Venice: geological setting, evolution and land subsidence. Episodes, 26(3): 264-268.
[4] Wikipedia, http://en.wikipedia.org/wiki/MOSE_Project

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The lighthouse seawall and the earthcache location are accessible from 0 to 24h (all the day!). The area is totally public and free of access.
Reaching the cache location by foot: you may reach the final coordinates directly from the beach, or from the surrounding campings (e.g., Marina di Venezia, Miramare).
Reaching the cache location by car: you may park at the waypoint 1 coordinates. There is a big parking open 24h per day. Warning: since May 2009, parking costs 1 euro per hour. You have to pay from 0 to 24h. See parking fee by clicking here (tnx to Herp of Many Colours to this advice).

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Be careful in case of adverse weather: e.g., thunderstorms, seastorm, heavy seas, windy days.

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