ABSTRACT
The prior appropriation doctrine ideally protects water-right holders from encroachment by other water-right holders taking water out-of-priority or enlarging their rights in a manner not prescribed by statute. This protection depends on the security of complicated interrelationships or ‘‘use-dependencies’’ created among water users due to the fugitive nature of water resources. Actual consumption of water (‘‘consumptive use’’) in irrigation is often less than the full amount diverted from the stream (‘‘diversion’’). Unconsumed water may return to the stream (‘‘return flow’’). Return flows, along with natural stream flows, supply water available for appropriation by other irrigators, and thus constitute a portion of their water rights. Appropriators who modify water use from that prevailing when their water rights were granted may shift the timing, location, quantity, or quality of return/escape flows, and consequently may impair other use-dependent water rights.
