Vertical Gradient
Water levels in nested well clusters (wells located closely together) indicate upward or downward flow
in aquifers or flow between adjacent geologic units.
Flow is governed by Darcy's Law:
where q is the Darcy flux (volume of water per unit area per unit time) and K is the hydraulic conductivity.
The change of head (roughly water level) divided by the distance determines the direction of flow.
Calculator Inputs
Definition of inputs for each well:
- dw = depth to water
- d = depth to top of screen
- s = screen length
One choice is to use the mid-points of the well screens to calculate the gradients (as illustrated).
Because there are other options, an estimate of the range of possible gradients is given in the output.
These values are calculated from
varying assumptions about the influence of the well screen.
A separate version of the calculator gives these
values more explicitly.
Water Level Options
There are three possibilities for how the water levels relate to the well screen:
- Submerged. The water level is above the top of the well screen.
- Water-table. The well screen intersects the water-table.
The gradient is calculated from the mid-point of the water level and the bottom of the well screen.
- Dry. The well is dry and no calculation is performed.
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