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<br />(2) Ilow do we account for the magnitude of the impact during con- <br />ditions more extreme than those encountered during the <br />calibration period? <br />(3) How do we overcome the statistical problems associated with <br />the strong seasonal effects and serial correlation in the <br />variance of the relationship between paired watersheds? <br /> <br />All of these questions can be satisfactorily addressed through the use <br />of advanced statistical anaylsis procedures. Intervention analysis is <br />considered to be the most satisfactory procedure and the one recom- <br />mended for this problem. Intervention analysis wds developed by Box <br />and Tiao (1975) and has been employed by Hipel, et al (1978) to deter- <br />mine the effects of reservoirs on streamflow regime and the effects of <br />forest fire on the flow regime of a river. 'The procedure is attrac- <br />tive for analyzing potential impacts of subsidence on streamflo~+~ <br />because several intervention hypotheses can be examined, such as an <br />immediate long-term change occurring once mining has progressed into a <br />basin, a slowly developing change that might result from the gradual <br />development of subsidence cracks, or short-term changes that might <br />result from subsidence cracks developing and then sealing. <br />Additional studies of channel flow through the Dry Fork of i4innesota <br />Creek are planned in order to characterize the seasonal and dynamic <br />patterns of channel loss or channel inflow through the possible <br />affected areas. The proposed gauge relocation on the Upper Dry Fork <br />of tlinnesota (reek will facilitate these studies. <br />Conclusions and Reporting Procedures <br /> <br />The monitoring and analysis proposed in this plan is an integrated <br />approach that provides an accurate and sensitive procedure from which <br />any change in streamflow resulting from mine subsidence can be dis- <br />tinguished from the natural variability in streamflow. Atlantic <br />(17) <br />