Cite as: 514 U. S. 673 (1995)
Opinion of the Court
that it does not materially deplete stateline flows "in usable quantity or availability." App. to Report 5 (Article IV-D) (emphasis added). In order to establish a violation of Article IV-D, Kansas was required to establish that development in Colorado resulted in material depletions of "usable" river flow. The Compact does not define the term "usable." Cf. Colorado v. Kansas, 320 U. S., at 396-397 ("The critical matter is the amount of divertible flow at times when water is most needed for irrigation. Calculations of average annual flow, which include flood flows, are, therefore, not helpful in ascertaining the dependable supply of water usable for irrigation"). At trial, Kansas presented three methods for determining depletions of "usable" flow.
Kansas' first expert, Timothy J. Durbin, analyzed flow data for the period between 1951 and 1985 by plotting actual river diversions in Kansas against actual stateline flows. Report 293-294. Using these data, Durbin developed criteria to determine what river flows were usable. Durbin concluded that during the summer months, April through October, (1) 78% of the stateline flows were diverted; (2) flows greater than 40,000 acre-feet per month were not usable; and (3) flows greater than 140,000 acre-feet for the whole period were not usable. Id., at 293. With respect to the winter months, November through March, Durbin concluded that (1) 24% of the winter flow was diverted; (2) flows greater than 7,500 acre-feet per month were not usable; and (3) flows greater than 40,000 acre-feet for the whole period were not usable. Id., at 293-294.
After Colorado isolated errors in Durbin's analysis, Kansas presented a replacement case. Kansas' second group of experts, led by Stephen P. Larson, adopted the same methodology but revised certain exhibits and made minor corrections in data. As a result, Larson modified Durbin's coefficients, using 72% for the summer months and 25% for the winter months. Id., at 295.
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