Lecture by Dr. J. Kirk Cochran, SUNY Stony Brook

"Is Venice in Peril? Deciphering the impact of sea level rise on the Venice Lagoon"

Summary by Hahn-Ning Chou, MEM 2004

Dr. J. Kirk Cochran, GRD '79, Professor at the Marine Sciences Research Center, SUNY Stony Brook gave a presentation on the impact of sea level rise on the Venice Lagoon. The lecture was divided into four main parts: an introduction to Venice, the history of the region, stresses on the Venice Lagoon, and finally strategies to deal with sea level rise.

A photograph of a flooded Venice kicked off Dr. J. Kirk Cochran's lecture on the impact of sea level rise on the city. The acqua alta occurred in November 4, 1966, and called worldwide attention to the fragility of Venetian arts and architecture and jump-started the city to initiate the Instituto per lo Studio della Dinamica delle Grandi Masse to study lagoon processes.

The study area is Venice, a city on the northeastern coast of Italy, which is surrounded by the Venice Lagoon. Dr. Cochran stated that the Venice Lagoon is a water body with a surface area of approximately 500 km2 with an average depth of 0.6 m. There are three inlets for tidal exchange and the average flushing time of the lagoon by seawater is two days. From the map presented, we learn that there is one fish farm to the north of the city and one fish farm southwest of the city. There is one airport and one industrial district to the northwest and west of the city respectively. These are major exporters of nutrients or contaminants to the Venice Lagoon.

Dr. Cochran proceeded then by giving a historical perspective on the geography of the Venice Lagoon, and how it has changed over the past seven centuries. For example, he talked about anthropogenic influences on the seven rivers that entered the Lagoon when sediment loading became a serious issue in the 16th century. He continued by talking about sea level rise in the Venice Lagoon. Sea level rise in the Venice Lagoon is discussed in mean sea level rise (MSL) above the 1897 datum. The city today is currently 120 cm above the 1897 datum MSL, which is approximately 100 cm above present MSL. Sea level rise and ground subsidence have been attributed to groundwater extraction and eustatic sea level rise. Dr. Cochran lauded the Venetian government in recognizing that groundwater extraction has resulted in land subsidence. The city consequently banned groundwater extraction in 1970. The ban also means that the city's sea level rise is now solely related to uniform worldwide change in sea level, which is also known as eustatic sea level rise.

The lecture then focused on the stresses on the Venice Lagoon, which included eutrophication as a result of nutrient loading from Venice and the mainland in various forms of wastewater, surface runoff, and submarine groundwater discharge, and also from the fish farms from the northern lagoon. A discussion on the impact of wastewater and sludge dumping by the city into the canals ensued. However, Venice can rely on rapid flushing of canals due to its close proximity to the Lido inlet. Macroalgal bloom, which occurred in the Venice Lagoon during the 80s and then disappeared in the 90s, was also presented. The focus then shifted to brief discussions on using Thorium isotopes as indicators of scavenging rates in the Venice lagoon. This was followed by a talk on using lead-210 to determine accretion rates and chronology of salt marshes in the Venice Lagoon.

The final portion of the presentation was on the different strategies to cope with increasing sea level rise. There were two main strategies presented. The first one is to build up the city. An example is to raise the canal banks, but this has proven to be a formidable task since many historic buildings located at the banks are many centuries old. The other main strategy is to construct flood barriers to seal off the Venice Lagoon during high waters. An innovative method, the Experimental Electromechanical Module (MOSE), has been approved for construction. The two to three billion US dollar project that will be funded by the City of Venice, the Italian government, and the EU, is the construction of electromechanical underwater flood barriers that will be raised with sea level is projected to rise. Supporters of the project claim that it will effectively prevent floods from invading the city by successfully keeping the seawater out. The flood barriers will be raised approximately ten times a year depending on the sea level for one or two days each time. Opponents of the MOSE assert that it is not a long-term solution since the barriers will be raised over 100 times a year if MSL increases by 30 cm. Since flooding occurs mostly between October and January, the Venice Lagoon will be closed almost continuously during this period and the barriers will as a result affect the flushing of the Venice Lagoon.

Dr. Cochran concluded his presentation by offering his thoughts on environmental impacts that will be caused by MOSE. The barriers, with a lifetime projected of 50 to 100 years, will not significantly alter the basic character of the Venice Lagoons during it operating years. In the long run, however, the Venice Lagoon may become more lake-like. The MOSE is by no mean a permanent strategy and new ones will be required in the future.