To what level (elevation) will water rise in the inclined wells?
Figure 2 – Illustration of the effect of dissolved solids on evaporation. The more solutes present (lower thermodynamic activity) the lower the evaporation rate.
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Figure 23 - shows the vertical head profile measured in nested wells. These data could also be measured in multilevel (multiport) wells, for example. Importantly, the figure shows that although vertical gradients are present, flow also has a horizontal component. That is, the presence of a vertical gradient does not necessarily indicate that flow is completely vertical, only that a component of flow is vertical.
Figure 23 – Example of vertical head profiles in an idealized unconfined aquifer (Cohen and Cherry, 2020).
The potentiometric contours and flow geometry in the unconfined aquifer scenario shown in Figure 23 are representative of a case in which a vertical no-flow boundary is present near the upgradient end of the system (left side). This boundary has the effect of causing significant vertical flow in that region. In many instances, a no-flow boundary may not be nearby, and flow in the area of interest is mainly horizontal as shown in Figure 24.
Figure 24 – Mainly horizontal flow in an unconfined aquifer. The potentiometric contours are orthogonal to the aquitard, which has a very low hydraulic conductivity (K) such that it behaves as a no-flow boundary (Cohen and Cherry, 2020).
In practice, horizontal flow in unconfined aquifers is often approximated as purely horizontal, especially when assessed on a sub-regional scale and away from boundary conditions, as shown in Figure 25.
Figure 25 – Water table represented as a planar surface with predominantly horizontal flow throughout the cross section (Cohen and Cherry, 2020).