The Vagos area in Portugal is perfect for our field course hydrology. It has plenty of wells (groundwater access), a simple but sometimes hidden geology, many different land uses, several rivers that have water at this time of the year, many days with sunshine and always a few days of rainfall. In addition, the Portuguese people are very hospitable.
After a week of sunny weather, we now have a depression passing over Portugal that brings us rain. Rainfall causes changes in the river flow and this means that any schedule that the students have devised for measurements now has to be changed as they have to concentrate in getting the discharge rating curves to capture these changes in runoff caused by the storms and taking river water samples.
It rained last night about 26 mm. All students woke up this morning knowing what to do. Salt dilution discharge measurement method, propeller method, Nautilus method and the float method could all be practiced to get results. We joined the BARF group (Barry, Alexander, Rick and Frans) today. They went to Rua Sambal to measure discharge in the Presa Velha river. They started out with the salt dilution method, but as there was too much flow for their 10 l of salt water.
So they switched to the propeller method to check if this would give different results. As they did not have a rod, some improvisation was needed using a bamboo stick thtat was fortunately present at the site.
Then time to install a new piezometer at the meteorological tower to measure groundwater level changes! Again, the sucking soil did not make life easy.
Tired from all these exciting student activities, Vincent and I decided to visit the island for some fresh-salt water research. We took a rainfall sample and, amazing discovery, we found the spot where the brackish water returns to the surface after passing through the island, just as Vincent's groundwater model predicted!
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