Well pumping. Draining trench. Infiltration. Groundwater flow (x,y) or (x,y,z) Flows between tanks (x,y) Leakage rate in a tunnel Q(t) Infiltration - ground water evaporation (z) Unsteady infiltration due to run-off (z,t) Interaction between groundwater and river Q(t) Salt wedge in coastal aquifer : interface Z(x,y)