by Don Barker

One of the most visited tourist centers in the world is today threatened by the very element that makes it famous. The canals of Venice can no longer hold back the rise of the tidal waters.

Of major architectural significance in the sinking city and one of the lowest areas of the island is the Piazza San Marco. The plaza now becomes fully immersed during the highest tides of autumn and winter.

With high tides of more than a meter, the city streets become blocked with water, and raised wooden walkways must be placed along established pedestrian thoroughfares. In addition to disrupting the lives of the inhabitants, the high water is causing considerable damage to their architectural heritage.

The Problem

Is Venice sinking? Or is the water level rising? The answer is complex but "yes" to both questions. The mean level of the land has lowered by 9 inches (23 centimeters) relative to sea level. Tapping the underground water supply has caused a reduction in pressure in the subsoil and, therefore, a contraction of the ground itself, with a subsequent lowering of structures above.

At the same time, the tidal level has increased by some 3 inches (8 centimeters) for several reasons, including organic structure growth on the barrier reef in the lagoon basin and changes in atmospheric pressure and wind action on the Adriatic Sea.

Eustasy, or the global variation in sea level, is tied to changes in the world's climate. During the last century, the eustatic rise for the city of Venice, independent of its subsidence, was on the average 0.05 inches (1.27 milimeter) per year.

The Grand Canal of Venice, as seen from the Academia Bridge looking toward the San Marco basin. Photo: Don Barker Showing the signs of previous high tides on Venice's internal waterways. Photo: Don Barker   Click on thumbnail images to view full-size pictures.