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39 <br />varies from point-to-point, of course, but it was necessary to use a <br />uniform average value in the computations. The use of a uniform initial <br />saturated thickness does not severely limit the validity of the results, <br />however. <br />Inflow to the pit from all directions will occur when the trench <br />is initiated, and the trench will be extended into overburden that has <br />experienced some drainage, therefore. The difficulties of a rigorous <br />mathematical treatment of this phenomena are considerable. An estimate <br />of the maximum inflow that can be reasonably expected is made by assuming <br />one-dimensional inflow through the lateral surfaces of the trench. During <br />the initial .stages of overburden removal, the length of the trench will <br />increase with time. This was handled by calculating the inflow to the <br />i trench in segments, taking into account that inflow into each segment <br />begins at different times. Once the pit reaches maximum length, each <br />new segment of the pit will be advanced into previously drained overburden, <br />and it was assumed that no additional new inflow was induced. Therefore, <br />inflow estimates after the trench has reached maximum length were made <br />as if the position of the trench no longer changed with time. <br />The cumulative volume of inflow from both sides of a trench segment <br />of length L is estimated from <br />Vi = 4L( l2 2 )-l/Z (t-ti)1/2 + goL(t-ti) <br />SyaTho <br />where Vi = cumulative volume for segment i, (L3) <br />L =length of trench segment i, (L) <br />Sya = apparent specific yield (dimensionless), <br />T = transmissivlty (L2/T), <br />ho = initial saturated thickness (L), <br />(1) <br />0 <br /> <br />