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.