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So with the ground being previously subsided the maximum possible :subside;nce • for asuper-critical width panel, S,,,a„V(H), is 9.5 feet (1.0 X 9.5). They go further to estimate the maximum subsidence for a panel at sub-critical width, s,,,,,, with the expression; s,,,~ = S/m(S,,,a„) Where; S/m is obtained from Figure 15-2 Figure 15-2 produces a subsidence reduction factor for the fact that the panel is sub-critical of 0.52 fora 1,500 feet deep panel, so s,,,a„ is 4.9 feet. Under the current mine plan the maximum amount of subsidence anticipated will be experienced in the center of longwall panels D-2, D-3, and D-7 where the overburden depth reaches approximately 800 feet. Figure 15-2 produces a panel correction factor of 0.85 at this depth, so s,,,,,, is 8.1 feet. Gentry and Abel (1978) report values of subsidence reduction factor ranging between 0.51 and 0.71, with the higher values corresponding to subsidence on the ridge line. Their data were measured at the York Canyon Mine, a longwall operation, in New Mexico, where the Raton Formation, which overlies the mined seam is of a somewhat similar character to the Mesaverde Formation in the North Fork of the Gunnison River Valley. Maximum Subsidence Over Mined Areas The maximum subsidence over mined areas (S) would equal the maximum possible subsidence (S,,,ax = 9.5 feet) if the total width of the extracted zone exceeded the critical width, the width of the extracted zone exceeded 1.4 times the overburden height. Such a case may not arise at the proposed mine. Subsidence Profile The accuracy with which the subsidence profile can be predicted is limited in mining regions where there has been no previous measurement of subsidence profiles. The SEH method can be used to obtain the general form of the curve, but the profile obtained will be in error by an unknown amount. In the North Fork Valley extensive subsidence - 6 - 10/00 P~e-4 y