Finding the Direction of the Groundwater Flow
In groundwater that is open to atmospheric pressure (unconfined aquifers), hydraulic gradient is the degree of inclination of the water table in the direction of the flow, usually described as the number of feet the water table drops per mile.
To determine the gradient under a certain area, we assume that the face of the groundwater represents a plane in space. In an area with no faults or fractures, it is a safe assumption, on the order of the assumption that the face of water in a calm pond is flat.
A point in space cannot be assigned a location but only in relation to a viewpoint. To establish orientation, we arbitrarily “fix” points in space from where we view the point in question and derive relative distances and orientations. For example, in enjoying a beautiful sunset at the beach, we take Earth as a fixed object, while in actuality it is rotating in at least five different planes as far as itself, the solar system and Milk Way galaxy are concerned.
To determine the location of a point in space we fixate a system of three lines that intersect each other perpendicularly in one point (Cartesian coordinates, see below) and we measure the shortest distance to the point from each of these lines.
René Descartes (IPA: , March 31, 1596 – February 11, 1650), also known as Cartesius, worked as a philosopher and mathematician. He is equally notable for both his groundbreaking work in philosophy and mathematics. As the inventor of the Cartesian coordinate system, he formulated the basis of modern geometry (analytic geometry), which in turn influenced the development of modern calculus. en.wikipedia.org/wiki/René_Descartes
A line in space is determined by connecting two points.
To determine a plane in space you need to connect three points (or establish two intersection lines).
Thus, to determine the facial plane of the water table, we find three points on it: we install three wells and measure the elevations of the water in the wells (usually relative to sea level).
The diagram below shows three wells: MW-2, MW-3 and MW-4. The number next to each well marks the elevation of the water in the well above mean sea level. The outer red triangle represents the spatial plane of the groundwater and with a bit of geometry we fine the direction of the flow (the southwest turquoise arrow) and the slope of the water table, that is 47.56 feet per mile.
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