Sand transport in northern Venice Lagoon through the tidal inlet of Lido

The provenance and transport of sand has been investigated around Lido Inlet, the largest of<br/>three tidal inlets in Venice Lagoon, Italy. Morphological analysis has established the presence<br/>of an ebb-tidal delta extending from the mouth of Lido Inlet as well as other features typical<br/>of tidal inlets. The stability of the inlet, as well as the canals of Treporti and Burano,<br/>was determined through the application of the tidal prism/cross-sectional areas relationship<br/>theorized by O’Brien (1969). Whilst Lido Inlet and Treporti Canal have both remained<br/>in equilibrium in terms of this relationship, Treporti Canal has suffered erosion due to a<br/>fluctuating tidal prism. Lido Inlet is slightly flood dominant although grain trend analysis<br/>of bottom sediment reveals net export of sand. Treporti Canal is ebb dominant and is the<br/>source of this sand, but it is becoming increasingly flood dominant as average current speeds<br/>have reduced and ebb currents are weakening at a faster pace than flood currents. This is<br/>proposed as a reason to why the northern lagoon is accreting (0.44 cm yr?1), contrary to<br/>trends in the southern (-0.37 cm yr ?1) and central lagoon (-0.23 cm yr?1). A sediment<br/>budget formulated for the whole lagoon has revealed that whilst the overall rate of erosion<br/>is reducing, the area subject to erosion is increasing and the rate of accretion is decreasing,<br/>resulting in no net change in the net sediment loss rate between 1930-1970 to 1970-2000 (-0.05<br/>cm yr?1). Mineralogical analysis on bottom samples, beach and riverine samples confirmed<br/>that longshore transport is from north to south along the northern lagoon; carbonate grains<br/>are dominant in the north with proportions gradually replaced by quartz to the south. Lido<br/>Inlet proved to have similar mineralogy to the River Piave with a higher calcite/dolomite ratio<br/>than inner lagoon samples suggesting a less mature sediment and thus import of sediment.<br/>Conversion of ADCP backscatter into bedload transport rate, suspended sand, and suspended<br/>fines concentrations has shown that no sand is transported at velocities below ?0.4 m s?1.<br/>55% of sediment transported during an ebb flow was sand in suspension (peak: 527,000<br/>kg hr?1), 37% was fines in suspension (peak: 283,000 kg hr?1), and the remaining 8% of<br/>sediment was transported as bedload (peak 68,700 kg hr?1).

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Helsby, Rachel