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.

Waves during 2D fieldwork

Below are data from the offshore rider buoy for the period between September 14 and 21, 2012. Graphs taken from Instituto Hidrográfico.

Significant wave height (blue) and maximum wave height (red).

Average  wave period (blue) and maximum period (red).

Less than 1 m significant wave height, with 5 s average wave period is not enough, even during equinoctial tides that reach 1.5 m above MSL (mean sea level).
Nevertheless, for those of us who stayed at the beach during those long hours, the parameter below was very important!

Water temperature.

Yes, yes, the ADP, PTs and our bodies confirm: 23 degrees water temperature during the afternoon. GREAT!

2D fieldwork on Ancão

The meeting was at 5:30 AM (ouch!!!) to load the boat and transport the team to the study site.

Station 1 was already on site (PT moored offshore, click here for more information).

Station 2 included the ADP (Acoustic Doppler Profiler) and a PT, on an aluminium frame, located lower on the profile.

ADP (on top) and PT (on the leg) on station 2.

Station 3 included an EMC (Electro-Magnetic Current meter) and a PT.

EMC (middle of the frame) and PT (rigth pole of the frame) on station 3.

Station 4 included an ADV (Acoustic Doppler Velocimeter) and a PT.

ADV being deployed on the metal frame by Óscar, Maria and Bruno.

On station 5, 6, and 7 the equipment was not fixed since we didn't know if overwash was going to occur or not.

Poles to fix PTs on stations 5, 6, and 7.

Some people got excited about fixing the frames.

Erwan hammering the pole.

Then we had a lot of waiting for the tide to rise... From 8:00 until 15:00 nothing to do............

For 7 long hours we rested, read, dip, chat, slept, took a walk. Thanks guys for keeping the good  mood!

And at the end of the day, this was the highest water level we got.

Our last action was to retrieve the PT that was moored offshore.On September, 19, the divers were Zapa and Nuno and RUSH team was Ana and Carlos.

Nuno, Ana and Zapa.

The location of equipment was precise and we recovered the PT smoothly.

Here it is. Safe and sound.

Mooring the PT

The first action of the 2D fieldwork was mooring a PT (Pressure Transducer) offshore the study site at about -14 m, below the closing depth of the beach profile (around -12 m in this area).

The mooring structure is a car tire filled with concrete and metal  bars,  with a stainless steel structure on top to attach the PT.

The PT was deployed by two divers (Zapa and Inês), on September 13, at a depth during diving of 16 m.

Daniel is passing the PT to Zapa. Inês is behind the boat in this photo.

The skipper was Daniel and the RUSH team was Ana and André, who did the location of the equipment with the GPS.