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26 <br /> and <br /> B = leakance = (K Tba)1/2 <br /> a <br /> T = transmissivity of coal seam <br /> ba = thickness of overburden aquitard <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 /> face to the point where the drawdown is s can be calculated. <br /> s <br /> x = BTn (s) <br /> 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 (McWhorter <br /> and Sunada, 1977) also yields <br /> Tso <br /> q 6 <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 />