Marco Conceptual

An irregular grid was defined for the study area according to the morphologic and hydrodynamic characteristics at the time (Figure 4.4). It is important to note that the grid was defined to the east of the westernmost injection point because of the hydrodynamic conditions, waves and currents were eastward directed. This grid was used for topographic measurements and sample collection for all the experiments. Names were given to the profiles using the distance of their origins to a reference profile (Profile 0, P0). Distance between profiles was 50 m in the straight part of the area (P0 to P400), while radial profiles were defined for the inlet margin with a spacing of 10 m between profile origins (P410 to P500). The profiles P520 to P650 were located on the inner beach, spacing between these profiles was variable ranging from 10 to 50 m.

For the preparation of the fluorescent tracers (FT) the methodology given by Ciavola et al. (1998) was followed: sediment from the study area was collected

Figure 4.4: Aerial photo of the study area showing the profiling/sampling grid as well as the instrument and injection locations for each campaign. Sectors dividing the study area (A, B, C and D) are also shown.

before each experiment, it was washed with fresh water to eliminate the salt, dried, dyed with orange fluorescent ink (Atomlac Industrie Glycero Orange Fluo) and dried again. The sand was then sieved, eliminating grains with diameter larger than 2 mm in order to remove aggregates that could have formed during the dying process. A sample from the FT was taken to compare it with the natural sand from the study area. Before placing the FT in the field, they were washed with sea-water and a small amount of detergent to lubricate the grains, to avoid the transport of the tracers as a floating layer. As mentioned above, samples were collected along the established grid (Figure 4.4). The area where the samples were to be collected was determined, prior to each sampling, by

detecting the presence of FT using a portable UV light. Shore-normal spacing between the samples along a profile was between 10 and 60 m, depending on the total length of the profile, the spacing being larger on the longer radial profiles located on the sand spit. Sampling was undertaken during the first and second low tides after tracer deployment. Sample collection consisted of shallow cores (∼30 to 40 cm) that were then sectioned into 5 cm samples. Semi-surficial samples, using small containers of 10 cm depth, were taken in areas covered with water or when dispersion of the tracers was expected to be too high. When available, a boat was used for taking submarine samples in the adjacent areas using a Van Veen grab.

AMI.1

The objectives of this campaign were to determine the sedimentary transport patterns of the updrift beach and the inputs of sediment from the beach into the inlet area, quantifying the percentages of sediment either moving towards the backbarrier area or going towards the ebb-delta area.

The AMI.1 campaign was undertaken between the 20th and the 22nd January 1999. The FT, 300 kg, were placed on the lower beach face at P0 (Figure 4.4) on the first low tide of the 20th January. Topographic profiles were measured under low tide conditions on the 22nd using a total station. Deployment of both the EMCM’s was carried out at the same time as the placement of the FT. EMCMn was deployed on the lowest part of P0 (Figure 4.4) and EMCMo was deployed close to P500. In both cases, the axis orientation was chosen to measure longshore and cross-shore currents along the beach and at the inner areas. Due to technical problems EMCMo did not acquire any data during this campaign, therefore, its position is not marked in the figure. Elevations above the bed for EMCMn were 10 cm for the first recorded tide and 12.5 cm for the second tide. The first low tide sampling (LTS1) was carried out on the night of the 20th January (AMI.1-1), corer samples were collected along the sampling grid from P0 to P420. The second low tide sampling (LTS2) was undertaken on the morning of the 21st January (AMI.1-2), corer sample collection was performed between P150 and P520. After the sectioning of the cores a total of 930 samples were obtained, 418 of which correspond to AMI.1-1 and 512 to AMI.1-2.

AMI.2

The objectives of this campaign were to determine the sedimentary exchange at the western edge of the inlet and the interactions with both the oceanic and internal beaches, the channel and the ebb delta.

The AMI.2 campaign was undertaken between the 17th and the 19th February 1999. The FT, 100 kg, were placed on the lower part of P490 (Figure 4.4) on the second tide of the 17th February. Topographic measurements of beach profiles were carried out between profile P400 and P550 on the 18th February under low tide conditions. Both EMCM’s were deployed, at the same time as the FT, on the lowest part of the inlet margin, on P490 (Figure 4.4), close to the FT injection point. Orientation of the currentmeter axes was: longshore, vertical for EMCMo, and longshore, cross-shore for EMCMn. Elevations above the bed for EMCMo and EMCMn were respectively 31.5 and 34 cm for the first recorded tide and 47 and 48 cm for the second one. Both the EMCM’s were higher for the second tide in order to avoid burial due to sand wave movement. The LTS1 was carried out on the morning of the 18th February (AMI.2-1), corer samples were collected between P430 and P520, and a total of 527 samples were obtained after the sectioning of the cores. Additionally, 22 submarine samples were taken from the channel and from the area located in front of the swash platform. The LTS2 was undertaken on the night of the 18th February (AMI.2-2), large dispersion of the FT was expected, and thus 93 semi-surficial samples were collected between P400 and P550. In total, 620 samples were collected during AMI.2.

AMI.3

The objectives of this campaign were to determine the sedimentary exchanges between the swash platform, the western shore of the inlet, the inlet channel and the beach.

The AMI.3 campaign was carried out between the 18th and the 20th March 1999. During the second low tide of the 18th March, 290 kg of FT were placed between P450 and P460, on the swash platform that connects the inlet margin with the ebb delta (Figure 4.4). Due to the coarse nature of the sediments on the swash platform, FT were not sieved for AMI.3. Topographic measurements of the profiles was performed between P350 and P600 on the 18th March. Both the EMCM’s were deployed, at the same time as the FT, on the lowest parts of the inlet margin between P480 and P490. Axis orientation was: longshore,

vertical for EMCMn, and longshore, cross-shore for EMCMo. Elevations above the bed for EMCMn and EMCMo were respectively 40 and 18 cm for the first recorded tide and 37 and 44 cm for the second tide, the large variations being due to sand wave migration in the area of deployment. The RUNTI system was deployed on the swash platform close to the FT injection point (Figure 4.4). Axis orientation of EMCMr was to measure longshore and cross-shore currents. The LTS1 was undertaken with cores on the morning of the 19th March (AMI.3-1) between P440 and P500 giving a total number of samples after sectioning of 487. Additionally, 30 submarine samples were taken in the channel and in front of the swash platform using a boat. The LTS2 was carried out on the night of the 19th March between profiles P400 and P540 (AMI.3-2). Due to the expected high dispersion of FT semi-surficial samples were collected, giving 99 samples. In total, 586 samples were collected during AMI.3.