Before human control  Natural rate of coastal progradation 4 m/y from 1000 B.C. to 1200A.D.  Seven points of discharge described by Plinio il Vecchio.

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Presentation transcript:

Before human control  Natural rate of coastal progradation 4 m/y from 1000 B.C. to 1200A.D.  Seven points of discharge described by Plinio il Vecchio

 abandonment of Po di Primaro  1152 AD a major natural avulsion  northward shifting of distridutary channels  Venice Republic is threatened by the potential infilling of the lagoon  1604 AD digging of a diversionary canal (Taglio di porto Viro) The artificial form of the modern delta

Po delta advanced in southeastern direction at 86m/y 1750 AD-1820 AD Po di Goro and Donzella advanced at 129m/y 19 th century Po di Tolle was the dominant distributary at 60m/y End of 19 th century natural tendency of the Po to shift its flow northward 1886 AD-1992 AD Po della Pila dominated and advanced 47m/y Taglio di porto Viro Beach ridges From Ciabatti, ‘66; Bondesan & Simeoni ‘83

River manipulation caused fast progradation and delta lobe switching Rapid accumulation of a large amount of sediment caused by confining the Po discharge to a small area The present delta is artificially held in position within context of the northern Adriatic oceanographic processes Natural and artificial subsidence are enhanced by levee construction, which prevents overbank sedimentation River-bed excavation and river damming in the drainage basin during the last 50 years led to a marked decrease in sediment supply Result of human changes to Po River mouth

October 2000 flood Despite the best intentions of humans...

An American Fiasco Loss of wetlands near mouth of Mississippi River has caused shrinkage of land surface and loss of protection for interior areas, including New Orleans

List of some things we did Dammed river – reduced sediment supply, 400 million t/y to 200 t/y Built artificial levees – reduced nourishment of flood plain Constrained flow to modern Balize delta – caused delta to build to shelf break, and lose sediment to continental slope Prevented lobe switching – eliminated sediment supply to other parts of delta plain Removed water and natural gas – accelerated consolidation of deltaic sediment and subsidence of land surface Dredged channel – created depressions that act as sediment traps