Last week, the United States Supreme Court heard arguments from the States of Montana and Wyoming regarding their interests in the Powder and Tongue rivers, which flow from Wyoming into Montana, and are tributaries to the Yellowstone River. The Court has original jurisdiction to hear interstate disputes.
Montana brought the case and alleges that Wyoming is using more water than it is entitled to under a 1951 Compact between Montana, Wyoming and North Dakota. One of the primary issues is whether Wyoming may use modern irrigation techniques, diverting the same quantity of water, but reducing the amount of return flows.
The Court appointed a special master in the case: Barton Thompson of Stanford Law School. Thompson issued a report in February 2010, available here. The United States is not a party to the suit, but filed an amicus brief supporting Wyoming.
The most novel claim for Western law, including Utah Water Law, is Montana’s claim that Wyoming, by switching to more efficient irrigation, is consuming more water than it would under flood irrigation to Montana’s detriment because less water is running back into the river after irrigation. Wyoming was engaged in the same uses on the same acreage, diverting the same amount of water; the only change at issue was the amount of water consumed because of more efficient sprinkler systems. After a lengthy discussion of consumption versus diversion of water, Thompson’s report concluded that the Compact itself “establishes only the amount of water that can be diverted, not consumed.” However, the Compact states that each party’s diversion must be “in accordance with the laws governing the acquisition and use of water under the doctrine of appropriation.” Therefore, Thompson also addressed the issue of whether prior appropriation law addresses whether “(1) an agricultural appropriator, (2) [may] increase his or her consumption of water, (3) on the same irrigated acreage to which the appropriative right attaches, (4) to the detriment of downstream appropriators, (5) in the same water system from which the water was originally withdrawn?” Though he states that no western court has addressed this issue squarely, he concluded that the Compact should not be read to prohibit increased consumption in Wyoming because of irrigation efficiency, even where it harms Montana water users.
Montana also claimed that Wyoming was violating the Compact through “(1) irrigation of new acreage, (2) storage of water in new or expanded reservoirs, and (3) groundwater withdrawals.” Thompson’s report concluded that the Compact protected pre-1950 water rights in Montana from new diversions in Wyoming after 1950 and from new acreages in Wyoming if it harms pre-1950 Montana uses. The report concluded that appropriations for storage, new acreage, or supplemental water supplies must come from “unused and unappropriated water” and must protect pre-1950 water rights in Montana. “Montana, however, cannot demand that Wyoming release water from its reservoirs to meet the needs of pre-1950 appropriators in Montana if the water was stored at a time when the needs of the pre-1950 appropriators were fully met.” Lastly, Thompson’s report determined that some groundwater extractions could violate the Compact if the pumping began after January 1, 1950 and is hydrologically connected to the Yellowstone River or its tributaries. However, he concluded that this issue need not be resolved in this case.
In the end, Thompson recommends that the U.S. Supreme Court deny Wyoming’s motion to dismiss.