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<br />000352 <br /> <br />DRAFT-Not for distribution <br /> <br />However dubious their effectiveness to date, however, some customary law principles <br />and rules have enough substance and potential relevancy to the issue of international ecological <br />flows to warrant examination in this context. For example, the Courses of Action document <br />developed by the Mexican delegation to the IBWC raises some factors implicating customary <br />law, specifically the international water apportionment rule, the watershed principle, and the <br />sustainability principle. 108 The document contains no allusions to the transboundary harm rule or <br />the precautionary principle, but the latter has been mentioned at least by u.s. NGO's,109 and both <br />will be touched upon below. In the current instance, where a bilateral treaty is in effect, and is <br />clear, these customary international law principles should not be dispositive in any event. But <br />they are discussed in the alternative in order to explore potential claims which might exist if <br />there were no treaty. <br /> <br />a. Equitable and Reasonable Utilization <br /> <br />The customary international law with respect to international water apportionment is that <br />the allocation of the resource value of international rivers occurs through "equitable <br />apportionment," as expressed in the United Nations Convention on the Law of the Non- <br />Navigational Uses of International Watercourses} 10 an approach not unlike one used by the U.S. <br />Supreme Court in its equitable apportionment cases. III The existence of a treaty between two <br />nations regarding an international river presumes that the equitable apportionment is complete <br />I Il2 <br />and that the treaty contro s. <br /> <br />Mexico's initial claims to the waters of international rivers shared with the United States <br />were based on "equitable rights" I 13 and a principle similar to riparianism, namely that each such <br />river is a "commonwealth" in which the respective nations share equally (50 % to each). 1 14 This <br />position, advocated by the Mexican Minister of Foreign Affairs as early as 1877 and later in <br />negotiations leading to the 1906 Treaty on the Rio Grande, was advocated throughout the <br />bilateral Colorado River negotiations until 1944. Mexico also intermittently relied upon the <br />principle of "existing use," a principle not dissimilar to prior appropriation. The United States <br />ultimately conceded to the principle of existin~ usellS as a basis for establishing the allocations <br />in the 1944 Treaty. The "Harmon Doctrine,,,l 6 holding that the right of territorial sovereignty <br />over a portion of an international river (e.g., headwaters) entitled that sovereign to totally <br />consume the river's resources if necessary, was also relinquished by the U.S. by implication in <br />the final adoption of the U.S.-Mexican Water Treaty. <br /> <br />Mexico might invoke the apportionment principle of equitable and reasonable utilization, <br />as found in Article 6 of the U.N. Convention on the Law of Non-navigational Uses of <br />International Watercourses and argue that the 1944 Treaty (as construed by the United States) is <br />inconsistent with the U.N. Convention's provision that "[U]tilization of an international <br />watercourse in an equitable and reasonable manner. . . requires taking into account all relevant <br />factors and circumstances, including: Geographic, hydrographic, hydrological, climatic, <br />ecological and other factors of a natural character" (emphasis added). Contemporary arguments <br />have been made that requiring Mexico to address its ecological problems without U.S. assistance <br />is inequitable1l7 and that water treaties ought to provide expressly for environmental protection <br />in the form of minimum flows on the basis that such a principle has become an implicit feature <br />of customary law.lls These arguments miss the mark, however, because the equities whose <br /> <br />11 <br />