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December 09, 2005
Someone! Venice’s sinking! Do Something.
Not only is Venice sinking, but it’s surrounding land is sinking as well. Though this is not new news, there are some interesting tactics being considered to save this international treasure. Are these innovative approaches worth the risk of possible destruction in a historical city?
The current anthropogenic subsidence of the land in the Zennare Basin surrounding Venice city is 1.5 to 2 cm per year. (Gambolati et. al 2005) This is largely due to bio-oxidation of organic rich peat layers, which naturally decompose at a rate that is increased with agricultural nutrification and water level increase from agricultural drainage. Venice currently has sunk about one foot in the last 300 years and is in jeopardy of flooding from high tides and floods which threaten to drown the landmark city. (U.S. Water News)
The current approach to remediation of these issues is a $5.2 billion project attempting to build large gates which will act as a flood barrier for high tide conditions.(U.S. Water News) Though this approach was approved in 2003 a new approach to directly save Venice from its current condition is being proposed. Project head Giuseppe Gambolati and his group of engineers are “considering injecting seawater under Venice to raise the waterlogged Italian city by one foot to rescue it from the tides and floods.”(Gambolati et. al 2005) This extreme hydrological alteration may have large impacts on both the hydrology and the geology of the city and the local area. The current approach to slow the subsidence of the Zennare Basin is to implement conservation soil practices for agricultural land use, implement cover crops in times of bare soils, and manage the level of the water table to keep the levels low and the bio-oxidation at a manageable rate.
Currently, professional dispute of the effectiveness in the seawater injection results exists. Professor of geotechnic engineering at Turin Polytechnic, Michele Jamiolkowski, fears that only half of the projected height gain will be obtained and the possibility of uneven rise as well as other unknown repercussions may tear the city apart.
Difficulties with water table regulation due to fluxes in precipitation are also current concerns about effectively regulating the Zennare Basin drainage discharge.
The approaches being considered for these problems shows innovation as well as solid scientific principal. The largest question is the possibilities of implementation problems such as uneven distribution of the water and uneven land elevation. Agricultural conservation has little possibility of undesired alterations to height levels, but water table management should be done with great care. The risks to the city of Venice should be studied carefully before any action is taken. A mistake on this magnitude would doubtfully be acceptable to any historical preservation entity.
Reference
Gambolati G., Putii M., Teatini P., Camporese M., Ferraris S., Gasparetto G., Nicoletti V., Silvestri S., Rizzetto F., and Tosi, L.(2005) Peat Land Oxidation Enhances Subsidence in the Venice Watershed: EOS Vol. 86, Numb. 23, June 7 pg. 217
U.S. Water News Online (Nov. 2005) New idea proposes to inject seawater to raise Venice: http://www.uswaternews.com/archives/arcglobal/5newxidea11.html
Posted by Jason Carlson at December 9, 2005 01:39 AM | 4. Land Use and Land Management