i) The wearing away of the land surface by rain or irrigation water, wind, ice, or other natural or anthropogenic agents that abrade, detach and remove geologic parent material or soil from one point on the earth's surface and deposit it elsewhere, including such processes as gravitational creep and so-called tillage erosion; (ii) The detachment and movement of soil or rock by water, wind, ice, or gravity. It is the opposite process of sedimentation and tends to be more common in the Venice lagoon. This phenomenon removes sediments and sand from the lagoon beds, lowering them, and causing the disappearance of all those vegetation and animal communities that live there. The phenomenon was stressed by building large navigation canals, as S. Leonardo’s Canal, and the moles at the inlets. Wave motion caused by the boats and the employment of fishing techniques with a strong impact as idraulic dredges and trawling cause severe damages not only to the lagoon beds, but also to the surface of the salt-marshes and mud flats, whose surface is diminishing year after year. There is therefore an annual loss in the sediment of about 1 million cube metres that is leading towards a decrease in the height of the salt marshes and at the same time to an increase in the height of the bottoms of the canals.
Source: Taken from Soil Science Society of America