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26 <br />P and • <br />Tb 1/2 <br />B = leakance = (K a) <br />a <br />T = transmissivity.of coal seam <br />b~ thickness of overburden aquitar <br />Ka = vertical hydraulic conductivity of overburden aquitard <br />The parameter ba/Ka that occurs in the leakance factor is the hydraulic <br />resistance that characterizes the.ability of the aquitard to transmit water <br />vertically. <br />The above equation can be rearranged so that the distance x from the <br />t face to the point where the drawdown is s can be calculated. <br />xBin (S) <br />1 s° <br />This farm of the equation is useful for calculating distance to points where • <br />the drawdown is negligible and can be used to compute B if other factors <br />are known. <br />l The theory from which the above equations were developed (McWhorter <br />and 5unada, 1977) also yields <br />Ts <br />q • B <br />~~ where q is the steady discharge to the mine per unit length of perimeter. <br />The total iateral inflow through the face is computed by multiplying q by <br />the length of the perimeter. <br />The inflow from the roof must be added to that from the face to obtain <br />the total inflow. Elow from the roof is omputed by multiplying the area of <br />the exposed roof b~he vertical hydraulic conductivity_of the aquitard. <br />This formula is based on the fact that vertical drainage to a plane of at- <br />L mospheric pressure (the mine roof in this case) occurs under the influence • <br />of gravitational driving forces only. This in turn means that the hydraulic <br />