Box 3.1 provides a simple conceptual model of an unconfined aquifer with linked surface water systems to illustrate key aspects and dynamics of the coupled "natural-human system". This simplified model shows: a) that there are multiple flows in groundwater systems; b) that different wells can have different effects, depending on their relative location and depth; and c) that crop irrigation practices may also matter. A simple model of human-natural interactions in an aquifer Figure 3.1.