Fieldwork without clear overwash evidences

On January 19th, there was a red alert for waves on the Portuguese coast. In the Algarve, Hs reached 4.5 m with maximum wave height exceeding 8 m. We went to Albufeira groin to undertake a fieldwork campaign within another national project (SPACE). An electromagnetic current meter and 5 pressure transducers were deployed, and cool videos were recorded during the overtopping of the coastal structure.
On January 21st, we made a post-storm survey on Barreta Island, expecting serious overwash all over the island.

Top of the barrier, looking westwards.

 However, we found almost no evidences of overwash. What we did find was significant aeolian rework of the barrier surface.

Aeolian ripples on the bare sand surface.

Now the questions are: Did overwash occur? Did sand transport by wind cover overwash evidences afterwards? We think it is difficult to assume that this area was not overwashed under such energetic waves, but we have no way to prove it. The lesson is to try our best to do fieldwork within the next 24 hours after overwash is supposed to occur.

Meanwhile there was a fishing contest in Barreta Island.

December fieldwork

Because we've been busy with the project dissemination, during December we've only made one topographic survey. On December 28th we've repeated the 24 topographic profiles to have a reference situation in case storm waves occur.

No overwash occurred during the last high-tides, but probably during December there were overwash events in some parts of Barreta Island.

Shell debris alignments consistent with overwash.

Aeolian rework of the barrier surface is visible in many areas, either by ripples, lag surfaces or depositions behind obstacles on the surface. Some vegetation is covered by this process.

Aeolian ripples and aeolian sand accumulation.

The lagoon margin is varied along Barreta Island. In places, a tidal flat exists, while in others there is a sandy beach adjacent to the tidal channel.

Tidal flat at the backbarrier.

During this survey, barrier erosion was noticed on the lagoon beach, which is likely related to changes in the inner channel currents.

Erosion bluff on top of the lagoon beach.

Dissemination of the project

First results of RUSH project were presented on the 7th Symposium on the Atlantic Iberian Margin (MIA 2012), in Lisbon.

For more information about the conference click here.

The communication details are:
Matias, A., Carrasco, A.R., Pacheco, A., Loureiro, C., Nunes, M., Ferreira, Ó., Armaroli, C., Masselink, G. (2012). Do espraio ao galgamento: uma perspetiva integrada. 7th Simposium on the Atlantic Iberian Margin, Lisbon, Portugal, pp. 30.

Another abstract was accepted for the 8th IAG International Conference on Geomorphology, August 27th to 31st, 2013, in Paris. 

For more information about the conference click here.

The communication detais are:

Matias, A., Carrasco, A.R., Pacheco, A., Loureiro, C., Nunes, M., Ferreira, Ó., Armaroli, C., Masselink, G. (accepted). Longshore variation of overwash occurrence in a barrier Island (Portugal). 8^th IAG International Conference on Geomorphology. Paris, France.

pre- and post-overwash in November 2012

In November we were able to do what we've been trying for the 3D fieldwork: a good timing on pre- and post-overwash surveys.

We've made a survey on November 14th and 19th, and the waves increased between November 15th and 17th. During this period, the significant wave heigth was more than 3.0 m (threshold for storm occurrence) and the tidal level reached 1.6 m above Mean Sea Level.

Average  wave period (blue) and maximum period (red) between 11 and 18 November, 2012.

Overwash occured in many sites of Barreta Island, and in places the water intrusion reached the lagoon water, on the backbarrier side of the island.
We noticed that some features are crucial for the occurrence (or not) of overwash. The swash bars of Ancão Inlet seam to play a role.

Ancão Inlet ebb delta.

Aahhhh, and during the bathymetric survey we were visited by a group of dolphis. Here's a photo to prove it. They're really hard to photograph!!!

Glimpse of a dolphin's fin.

Team:
14/11/2012: Ana, Rita, Carlos, Sílvia.
19/11/2012: Ana, André, Mara

skipper: Zapa

3D Fieldwork - October 31st - post post-overwash

Again on October 25 and 26, waves reached almost 3 m height, therefore we made another post post-overwash survey. During fieldwork, the waves were still about 1.5 to 2 m height.

Waves during fieldwork.

Surprisingly, overwash intrusion was smaller than the one reached during previous survey. Is it a result of the beach morphology adjustment to winter oceanographic conditions?

Evidences of overwash intrusion.

Some profiles developed an erosion bluff at the barrier crest.

Erosional bluff.

Team: Ana, Rita, Mara, Carlos.

3D Fieldwork - bathymetry

On October 3, a bathymetric survey was made in front of the topographic survey. The survey was made between the shore limit reachable by boat, and the 6 m water depth.

GPS mounted on top of the pole that connects to the eco-sounder . 

The sea was calm, so we were able to reach further onshore, and data-quality was good.

The skipper following profiles on Hypack software.

Team: Ana and Carlos.
Skipper: Daniel and Zapa.

3D Fireldwork - post-overwash topographic survey

On October 2nd we repeated the 3D fieldwork to measure a post-overwash situation. Overwash occurred probably between 23 and 25 September, when Hs reached about 1.5 m.
Fortunately, overwash intrusion was variable alongshore. Closer to Ancão Inlet no overwash occurred, whilst on other areas overwash reached more than 20 m.

Profile close to Ancão Inlet where no overwash occurred.

On some profiles, overwash intrusion reached the lagoon (during high tide), and therefore the entire barrier island was affected.

Profile with overwash.

Overwash occurred even in areas with more dune vegetation.

Overwash on the barrier front and vegetation on the backbarrier.

Team: Ana, Rita, Mara, Isabel.