WATER YIELD of the rocks (EN: yield of water of rock; DE: Wasserabgabefahigkeit der Gesteine; FR: rendement deau des roches; ES: produccion de agua de las rocas; RU: водоотдача) is the ability of the water-saturated rocks to yield the water through the free flowing under the influence of the force of gravity, or as the result of the impact (pumping-out, vacuuming, and so on).
The mechanism of the water yield is determined by the ratio of the capillary forces and the forces, which are overcoming their action (the gravity, or the pressure of the substances, which are immiscible with the water, and which are pumped into the water-saturated rocks). The water yield is evaluated using the percentage of the volume of the water, which is freely flowing out of the sample of the rock to the volume of this sample; as the quantity of the water (in terms of litres), which is flowing out from 1 cubic metre of the rock (the specific water yield), and also the coefficient, which is defined as the difference between the complete and maximal molecular moisture capacities. Within the massifs of the rocks, they determine the coefficient of the gravitational moisture yield, which represents the reserves of the water, which are yielded through the free flow of this water down under the influence of the force of gravity, and they determine the coefficient of the elastic mois ture yield, which corresponds to the elastic reserves of the underground waters, and is determined according to the data of the experimental pumpings from the massif. The moisture yield increases with the increasing of the particle size of the particles of the rocks, with the increasing of the open porosity, and of the crackedness, and with the decreasing of the wettability. The thinly dispersed rocks, because of the large magnitude of the capillary and surface forces, which are retaining the water, possess very low water yield (for example, 0.01-0.1 for the loams; 0.05-0.1 for the sandy loams).
The water yield is the major characteristic for the selection of the methods for the water control of the mine workings, for the calculation of the network of the drainage boreholes, of the intensity of the lowering of the level of the water during the lowering of the level of the water, and also for the calculation of the operational reserves of the underground waters.
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