The production of drinking water by mechanical methods alone also leads to unpleasant surprises in many areas lying close to the sea. The conditions for equilibrium between layers of fresh groundwater and underground seawater were exhaustively studied by Badon Ghijbens and later by Herzberg. In this case we are concerned with the problem of the hydrostatic equilibrium between two mixable fluids of different specific weight.
In his 1911 paper entitled Contribution to the Hydrology of Northern Holland, Wintgens writes about this as follows:
The specific weight of fluids 1 and 2 are G1 and G2 respectively, and the difference in height between the surfaces of the two fluids after the establishment of a state of equilibrium is H metres; in this case the interface between both fluids will lie at a depth h1 where:
h1 = (G2 / (G1 - G2)) × H m
below the overall surface of the fluids. Deriving from this equation, the calculated maximum depth of ground-water h1 = 42 × H m, on the assumption that the specific weight of freshwater G2 = 1 and saltwater G1 = 1.024.
In Norderny’s example, as quoted by Keilhack, the surface of the fresh-water lies between 1 and 1.5 metres above sea-level. By calculation this value of H of 1.5 metres would correspond to a ground-water depth of 42 × 1.5 = 63 metres. The actual depth of the ground-water was determined as lying between 50 and 60 metres.
If the freshwater-table is now lowered through the excessive extraction of water with large pumps, which also reduces the value of H, then the boundary-layer between fresh and salt water will be displaced upwards until it finally reaches the level of the suction-head of the pump, with the result that the salinity or the chlorine content of the drinking water increases until it becomes undrinkable.
These physico-mechanical processes are also augmented by the metabolic processes taking place between freshwater and seawater. Every new bore-hole driven into the Earth facilitates the penetration of oxygen into the boundary-layer between these two types of water. The condition of the temperature-gradient between the surface of the freshwater and the underlying boundary layer will also be altered. The combined effect of these two components is such that the water’s inner buoyant energies, which would normally maintain it at a certain level, are likewise reduced.
In this connection attention should be drawn to the salination of many mountain lakes, which is ultimately attributable to the activities of hydraulic and hydro-electric engineers. First of all, through the wanton clearing of forest the rivers were robbed of protection from Sun and heat afforded by the leafy canopy of the trees. In addition water-courses were subsequently subjected to regulation by mechanical means alone. Both events produced higher concentrations of oxygen in the water, which then sought out the coarse and fine carbones in the channel body, dislodging them from both bed and banks. Once this water reaches deeper and cooler lakes where the now-aggressive oxygen is concentrated and if the water is no longer able to retain the quantities of the now dispersing carbones in suspension, the precipitation of salts then follows and freshwater is transformed into seawater. The reverse process happens at great depths in the sea, where strong concentrations of high-grade, complex carbones can eventuate. There the water is not only fresh, but also develops a highly potent negative charge, which under certain circumstances can trigger off violent electrical disturbances in the depths of the ocean.