A deliberately simplified aquifer budget

A fictional class models an aquifer covering 500 square kilometers. Annual recharge is prescribed as 45 millimeters uniformly over that area, while annual pumping is prescribed as 40 cubic hectometers. For this calculation only, the model sets all other boundary inflows, natural discharge, evaporation and exchanges with rivers to zero. These are explicit exercise assumptions rather than a description of any real Spanish aquifer. Students are asked to compute recharge volume and the change in storage over one year. One report treats all rainfall as recharge, although the exercise has already supplied recharge separately. Another converts 45 millimeters to 0.45 meters. A final report correctly calculates a negative storage change but declares that every well must fall by exactly the same number of meters. No storage coefficient, saturated thickness or well geometry has been supplied, so that final inference requires separate examination.