MODELING HYDROLOGIC IMPACTS OF TRIBAL WATER RIGHTS QUANTIFICATION AND SETTLEMENT ON THE FLATHEAD INDIAN IRRIGATION PROJECT

The Confederated Salish and Kootenai Tribes (CSKT) of the Flathead Reservation are a federally-recognized group of tribes (Kootenai, Salish, and Pend d’Oreille) located in western Montana. On the reservation lies the expansive Flathead Indian Irrigation Project (FIIP), which supplies irrigation water to approximately 127,000 acres of tribal and non-tribal agricultural land. The 1904 Flathead Allotment Act opened “surplus” land to non-native homesteaders without tribal consent, initiating the land ownership fragmentation observed on the reservation today. This legacy, combined with historically unquantified tribal reserved water rights and the antiquated state of the FIIP infrastructure, including water losses from unlined earthen canals, decaying dams, and inefficient diversion points, make the FIIP extremely difficult to manage. In 2015, the CSKT, State of Montana (MT), and U.S. federal government completed decades of negotiations that ultimately quantified CSKT reserved water rights in a state-tribal water Compact; these quantifications are now codified in MT state law and are awaiting further approvals from the U.S. Congress and the CSKT membership. Compact provisions also attempt to provide adequate water to protect the aquatic habit of culturally-significant fish species, such as endangered bull trout (Salvelinus confluentus), on and around the reservation through newly quantified instream flow water rights. The parties also negotiated terms of the CSKT Water Rights Settlement that seeks to resolve any future tribal water claims, and allocate federal funding aimed at rehabilitating and modernizing FIIP infrastructure. The Settlement awaits U.S. Congressional and CSKT membership approval to become law and be eligible for federal appropriation. The goal of this thesis research is to determine potential spatial variability in flow regimes under enforced Compact allocations before or in the absence of Settlement and FIIP rehabilitation. I approach these questions by employing the Soil and Water Assessment Tool (SWAT) to demonstrate how the Compact provisions will impact hydrology in the Lower Flathead River Basin, specifically in tributaries of the Flathead River where irrigated agriculture and CSKT instream flow rights coexist. Through modeling various scenarios, I found that future hydrologic variability (i.e., dry, normal, and wet years) will likely influence changing surface water hydrologic processes in the FIIP more so than irrigation efficiency and crop water demand, and thus climatic scenarios will likely determine whether tribal instream flow rights are adequate to protect aquatic habitat and species. Quantifying reserved water rights of federally-recognized tribal nations is vital for the enhancement of tribal sovereignty over water resources, economic development, natural resource management, and cultural and traditional practices. As with many tribes located in prior appropriation states, the CSKT has not had legally-enforceable water rights to allocate to other uses such as environmental flows for endangered species habitat until the recent Compact. However, in the absence of an approved federal Settlement, modeling and understanding contemporary FIIP flow conveyance regimes is critical for managing the watershed, tribal and non-tribal irrigated agriculture, and culturally-significant fish species habitat, especially in the absence FIIP improvements