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Title: Sand transport in northern Venice Lagoon through the tidal inlet of Lido
Author: Helsby, Rachel
ISNI:       0000 0004 2668 245X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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The provenance and transport of sand has been investigated around Lido Inlet, the largest of three tidal inlets in Venice Lagoon, Italy. Morphological analysis has established the presence of an ebb-tidal delta extending from the mouth of Lido Inlet as well as other features typical of tidal inlets. The stability of the inlet, as well as the canals of Treporti and Burano, was determined through the application of the tidal prism/cross-sectional areas relationship theorized by O’Brien (1969). Whilst Lido Inlet and Treporti Canal have both remained in equilibrium in terms of this relationship, Treporti Canal has suffered erosion due to a fluctuating tidal prism. Lido Inlet is slightly flood dominant although grain trend analysis of bottom sediment reveals net export of sand. Treporti Canal is ebb dominant and is the source of this sand, but it is becoming increasingly flood dominant as average current speeds have reduced and ebb currents are weakening at a faster pace than flood currents. This is proposed as a reason to why the northern lagoon is accreting (0.44 cm yr−1), contrary to trends in the southern (-0.37 cm yr −1) and central lagoon (-0.23 cm yr−1). A sediment budget formulated for the whole lagoon has revealed that whilst the overall rate of erosion is reducing, the area subject to erosion is increasing and the rate of accretion is decreasing, resulting in no net change in the net sediment loss rate between 1930-1970 to 1970-2000 (-0.05 cm yr−1). Mineralogical analysis on bottom samples, beach and riverine samples confirmed that longshore transport is from north to south along the northern lagoon; carbonate grains are dominant in the north with proportions gradually replaced by quartz to the south. Lido Inlet proved to have similar mineralogy to the River Piave with a higher calcite/dolomite ratio than inner lagoon samples suggesting a less mature sediment and thus import of sediment. Conversion of ADCP backscatter into bedload transport rate, suspended sand, and suspended fines concentrations has shown that no sand is transported at velocities below ∼0.4 m s−1. 55% of sediment transported during an ebb flow was sand in suspension (peak: 527,000 kg hr−1), 37% was fines in suspension (peak: 283,000 kg hr−1), and the remaining 8% of sediment was transported as bedload (peak 68,700 kg hr−1).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: GC Oceanography