With the chemistry done, nitrate pollution found and dirty smelling wells (indication of anoxic conditions in the clay) visited, this group is now focussed on determining the palaeo-topography of the clay surface. Between the Cretecous and the dune deposits, there is a time hiatus of some 60 million years! So there was ample time for erosion creating valleys in the clay deposits that are now covered by dune sand. You cannot see these valleys obviously, but they can influence the flow of water in the area. With our geophysics, you can find the depth of the clay below the sand, and if you do enough measurements, you can see a 3D pattern, or the old landscape that existed before the sand was deposited on it.
|Seife, Jelmer and Laurus working on the terrameter in a Eucalypt plantation in search for clay|
|Bart looking on while Seife and Laurus calculate apparent resistivities, also discovered that Laurus name sounds better in French...|
|Artesian (free flowing) piezometer in the São Romão catchment|
This place has a pumping piezometer, a monitoring piezometer in the confined (artesian) aquifer, and a piezometer in the phreatic zone. If the clay layer causing the artesian conditions is closed, we should see no change in the phreatic level while pumping below the clay layer.
|Pumping test in the São Romão aquifer|
Pump was brought out, water level data logger installed and programmed to do a pumping test, pump started and pump discharge measured. And indeed, while the water level in the confined piezometer went down like a pelican going for fish, the one in the phreatic zone did not care to respond at all to the pumping. Textbook case! Now they have a good indication of the hydraulic conductivity of their sandy area. We are nearing the end of our field course, next week the final measurements...