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• Surface curvatures and strains approximately four times larger than those typically experienced in Britain have been measured in the U.S. (O'Rourke and Turner, 1981). This may be due to rock mass characteristics which result in steeper limit angles under U.S, conditions than those observed in Britain. As a consequence, the subsidence profile under U. S. conditions should generally be sharper and narrower than that predicted using the SEH methods. However, using profile functions would not necessarily provide a better estimate of the subsidence profile unless site-specific experience in selection of input parameters is available. Using the SEH method to give an estimate of the form of the subsidence profile indicates that, even under British conditions, the subsidence trough would be relatively steep- sided at the limit of an extraction area. For an overburden depth of 1,000 feet, two thirds of the subsidence would occur over a horizontal distance of approximately 300 feet, ~ohile 80 0 of the subsidence would occur within some 500 feet. The subsidence trough is steeper where the overburden is thinner and flatter where the overburden is thicker. In the hiesaverde Formation, the subsidence trough can be expected to be somewhat steeper than that predicted for British conditions. • British experience indicates that about 25 ~ of maximum subsidence occurs above ribside for super-critical panel widths. With steeper draw angles typical in the U. S., somewhat less subsidence will probably occur over ribside. In order to develop a contour map of subsidence, it has been assumed that the general characteristics of the subsidence profile developed using the SEH will be valid. This is considered reasonable for a general evaluation of subsidence where site-specific subsidence data are lacking, particularly in view of the expected accuracy of the subsidence predictions and the scale at which the subsidence is plotted. The .assumption will not influence the maximum subsidence calculated, but will affect the locations of the subsidence contours around the perimeter of the extraction zones. A map showing the contours of predicted subsidence is presented as Plate 19. While this prediction is considered to be a realistic generalization, the limitations involved in its development should be understood. Subsidence contours have been developed based on what are considered to be generally upper bound estimates of subsidence magni=udes. These estimates are most realistic in • - 35-