The Tropical Trip

By Maarten and Jessica
On Friday 16th it was time for a special assignment. Everybody can adjust the field trip to their own preferences. So Vincent (professor) and Maarten K. had the brilliant idea to visit a little sand and grass island in the Ria Boco, close to the ocean. Maarten W. (professor) and Jessica were soon convinced to come along! The title of this log is "the tropical island", but actually, the island looks more like a very small version of Texel… But anyway, we were interested in the possibility of freshening of the groundwater by rainwater. At 8:30 we left from lovely Costa Nova to find a fisherman (or his friend) willing to take us to the island. We found Louis, our German speaking Mister Guide for the day! On the island we started doing some electrical magnetic soundings, which is basically a device to measure the salinity of the water (by the electrical conductance). The results of the measurements were really nice!

Doing the hoola hoop dance!

The next plan was digging a hole! Normally you have an auger to do that, but that would have been too easy for us; we had to do it the old school way. The sand was too loose and we had to use our hands. And that until a depth of 6 meters… Actually, soon we could use a bailer, which was not much better. It was hard work under the burning sun, but what the hack, we were on a lovely tropical island! When we finally managed to complete our hole, we started with the so-called borehole logging. This is almost the same as an electrical magnetic sounding, but with electricity instead of magnetism. In order to use the electricity we had to hammer some electrodes in the ground and lower others in the hole. By the time this was finished it was time for lunch. Unfortunately we expected to be done at lunch time so we didn’t bring any food at all. The earthquakes in our stomachs made the hole almost collapse! We tried to order a pizza but for some strange reason it didn’t work out… We were not done and we had to continue for a few hard hours.
After the borehole logging, we had to begin all over again… We dug out the hole again and installed a piezometer (pipe to measure groundwater levels). In the piezometer we put a diver that measures the salinity of the water. This enables us to monitor the tidal influences. Having done that, we were done for the day! Except Vincent, he had to put on some after sun cream for his lighthouse face… ;-) We called Louis and we got back to Costa Nova with all the equipment. It was just a perfect day!