tion, mining and industrial applications, stock watering, and domestic and municipal use, for example, are commonly recognized beneficial uses. Exercising the water rights permit and using the water for a beneficial purpose formally creates a legal right to the water.

The underlying principle under prior appropriation doctrine is that water and its rights are allocated on a “first in time, first in right” basis. The earliest water users have priority over later water users (“appropriators”) during times of water shortage, and water diversions and beneficial uses are fully allowed, in order of seniority of the water right, until the available water supply is exhausted. The concept of establishing a “priority date”—the date when the first water user obtains priority over other users—is thus very significant. Interstate water rights agreements, such as the Colorado River Compact, the Upper Colorado River Basin Compact (see Appendix E), and the Yellowstone River Compact of 1951 are illustrative in this connection. The Yellowstone River Compact (Pub. L. No. 82-231, 65 Stat. 663) forms the basis of ongoing claims related to the impacts CBM development on the water rights of Montana and the Northern Cheyenne Tribe under the Compact (see also Appendix F) (SCOTUS, 2010).

Beneficial use of water is a fundamentally important consideration in western water law under which public waters are obligated to be used for a useful or beneficial purpose. The appropriator can use only the amount of water presently needed, allowing excess water to remain in the stream. Generally, once the water has served its beneficial use, any waste or return flow is required to be returned to the stream. To change either the point of diversion or the point of use of the water, a modification to an existing permit is often required. In this context the concept of “instream flow” also becomes important. Instream flow is defined as the amount of water flowing through a natural stream course required to sustain the instream values at an acceptable level. Instream “values” and/or beneficial uses may include protection of fish and wildlife habitat, migration, and propagation; recreation activities; navigation; hydropower; waste assimilation (water quality); and ecosystem maintenance. Water requirements adequate to maintain all of these uses at an acceptable level are the “instream flow requirements.”4 Each state considered in this study addresses the issue of instream flow in a slightly different manner: Wyoming, Colorado, and Utah recognize beneficial uses for some instream flows and have specific provisions and state agencies responsible for addressing instream flow issues; in Montana and North Dakota, beneficial uses for instream flows are not explicitly defined, although cases may be decided at the discretion of state agencies overseeing this water resource; and New Mexico does not recognize instream flow as a beneficial use at this time (Table 3.1).5 The relevance of instream flow for CBM produced water relates to managed discharge of some CBM produced water into perennial and ephemeral streams.

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