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<br />26 <br />I <br />and <br />Tb 1/2 <br />B = leakance (K a) <br />a <br />r, <br />T = transmissivity of coal seam <br />ba = thickness of overburden aquitard <br />Ka = vertical hydraulic conductivity of overburden aquitard <br />I 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 />i The above equation can be rearranged so that the distance x from the <br />face to the point where the drawdown is s can be calculated. <br />5 <br />x=6Tn (°) <br />s <br />C1 This form 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 />The theory from which the above equations were developed (Mc:Jhorter <br />and Sunada, 1977) also yields <br />Ts <br />q = Bo <br />~ where q is the steady discharge to the mine per unit length of perimeter. <br />The total lateral 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. Flow from the roof is computed by multiplying the area of <br />the exposed roof by the vertical hydraulic conductivity of the aquitard. <br />This formula is based on the fact that vertical drainage to~a plane of at- <br />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 />