Water Level Gradient A Necessary Condition for Determining Flow Direction but Not a Sufficient

Water flows from high points to low points, and hence a water level gradient is an essential condition for underground flow. A common practice among hydrologists is to reconstruct groundwater flow directions based on water level gradients (section 4.3). However, a glance at Figs. 6.12-6.14 reveals that a gradient is a necessary but insufficient condition. Figure 6.12 portrays three wells tapping the same aquifer, and the water flows from the region of well I to well II and on to well III, down-gradient. In Fig. 6.13 three wells manifest a relatively high water table at well I, a medium water table at well II, and a relatively low water table at well III. However, the three wells are not interconnected; they are separated by aquicludes. The three wells shown in Fig. 6.14 are separated by a buried anticline disconnecting well I from wells II and III, in spite of the apparent water table gradient. Wells II and III are hydraulically interconnected.

As already mentioned in section 4.4, one can never deduce flow directions from water levels alone.

Fig. 6.13 Three wells with water tables similar to those seen in Fig. 6.12 but separated by aquicludes. They have no hydrological connections in spite of the apparent water table gradient.
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