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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Ritmare: WP4.A5 - Hydrodynamic and morphodynamic modelling of lagoon systems

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Ritmare is an Italian National programme of scientific and technological marine research. The University of Southampton is involved through a long term partnership studying Venice Lagoon between Prof Carl Amos and colleagues at the Institute of Marine Science – namely the numerical modelling group led by Prof Georg Umgiesser. Two field campaigns were undertaken under the framework of Ritmare, through the WP4.A5 on hydrodynamic and morphodynamic modelling of lagoon systems work package:

1- Cabras Lagoon Field Campaign, Sardinia, Italy

A field campaign was carried out in association with ISMAR (Institute of Marine Science) and IAMC (Institute for Coastal Marine Environment) both of the National Research Council (CNR) of Italy, in Cabras Lagoon, Sardinia in September 2013.The University of Southampton team (Carl Amos and Hachem Kassem) carried out multiple deployments of the Benthic Roughness Acoustic Device (BRAD), a motorized frame-mounted Sediment Imaging Sonar (SIS) used to scan acoustically the water column and sea bed, providing a 3D image of varying seabed types and roughnesses across the main lagoon inlets/channels. Multiple oceanographic instruments were also deployed, including current metres and Langragian drifters, with ADCP transects also collected by the ISMAR/IAMC team. The data collected was used to validate the SHYFEM coastal numerical model developed at IAMC by Andrea Cucco, and support a Masters project on hydrodynamic and physical roughness (published: Chirol et al, 2015; The Influence of Bed Roughness on Turbulence: Cabras Lagoon, Sardinia, Italy; J. Mar. Sci. Eng. 2015, 3(3), 935-956; doi:10.3390/jmse3030935).

For more information visit: http://sotoncoastalprocesses.blogspot.co.uk/2013/10/fieldwork-in-cabras-lagoon-sardinia.html

Benthic Roughness Acoustic Device (BRAD v.2.0) deployed in the main channel of Cabras Lagoon, Sardinia
Figure 1
Setting up Valeport Current metres
Figure 2
Setting up BRAD
Figure 3
(a) Venice Lagoon and (b) CNR's LITUS coastal research vessel
Figure 4

 

 

 

 

 

 

 

 

 

 

 

 

 

2- Venice Lagoon Field campaign

A second field campaign was carried out in September 2014, working again in collaboration with ISMAR. The work comprised three different elements: (a) studying the hydrodynamics and scour processes at the triple-junction in Torcello; (b) studying the dynamics of sand megaripples in the Lido Inlet of Venice Lagoon; and (c) investigating the currents driving longshore sediment transport in Cavallino.

(a) Scour processes at Torcello triple-junction:

The aim of this element was to investigate the hydrodynamics and sediment dynamics that cause a 19 m deep scour hole at a triple-junction in Torcello, the confluence of three canals/channels. Two boats and 12 researchers were involved in the 12 hour (full tidal cycle) campaign, collecting two Multibeam echosounder swath bathymetry surveys, near-hourly measurements of near bed turbulence and sediment resuspension through a benthic lander, and of horizontal shear through a high resolution micro-structure and turbulence shear probe. A continuous stationary (temporal) transect of flow using an Acoustic Doppler Current Profiler (ADCP) at the junction, and hourly ADCP (spatial) transects in the three channels were collected, of Langragian current drifters were deployed to validate the hydrodynamic model SHYFEM, developed by Georg’s team.

Figure 5 (a) MBES swath bathymetry; (b) horizontal shear probe; (c) deployment of langragian drifters and ADCP transects onboard Boston whaler; and (d) bed biology GoPro

Figure 5
Figure 5

(b) Studying the dynamics of sand megaripples in the Lido Inlet of Venice Lagoon

The second element of the campaign was carried out on Friday 12th September 2014; to investigate the bed load migration rates of large scale megaripples in the Lido Inlet, which appeared in regular bathymetric surveys. Three boats carried out this work; which included hourly bathymetric surveys with a Multi-beam echo-sounder (MBES); following the deployment of 3 current metres measuring nearbed current magnitude and direction along the inlet. In addition, 14 sets of bedload (traction and saltation) measurements where collected using benthic and epi-benthic modified Helley-Smith sand traps (60 micron meshes) to evaluate sand transport and bedform migration rates in the inlet (just outside of the main navigation channel used by Cruise liners) over the course of 12 hour tidal cycle. This work has been presented at the ECSA conference (see: Madricardo et al, 2015, Sediment Transport in a tidal inlet: the case of the lido Inlet, Venice, Italy, ECSA 55 Unbounded boundaries and shifting baselines: Estuaries and coastal seas in a rapidly changing world, London.)

(c) Longshore transport in Cavallino, Treporti

The final element comprised the deployment of an integrated Valeport 808 unit, measuring the magnitude and direction of horizontal currents (2D); with a pressure transducer logging water elevation (waves and tides); and an optical backscatter sensor. This was essentially a brief prelude to future work that will investigate longshore and cross shore sediment transport to evaluate the rate of sediment bypassing across the Lido Inlet; which has consequences for the MOSE project, designed to protect the city of Venice from future flooding.

(a) Cavallino beach; and (b) the recovered Valeport & Tripod
Figure 6

Further information available at: http://sotoncoastalprocesses.blogspot.co.uk/2014/09/field-campaign-investigating.html

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