A Groundwater Management Toolbox—Anticipating Coordinated Management of Indian and Non-Indian Water Rights

A Groundwater Management Toolbox was developed to support water resource management on the Flathead Indian Reservation in Montana, one component of unitary management of Indian and Non-Indian water rights envisioned during negotiations towards quantification agreements. The proposed water rights settlement agreement was not ratified, sending parties into an alternate adjudication path.  Nevertheless, some form of coordinated groundwater management may ultimately develop, and management can benefit from information easily accessed through the Toolbox.

The Toolbox provides a graphical user interface through which groundwater declines and stream depletion from existing and proposed wells can be evaluated. Water managers can specify information on well location and pumping rates, then implement simulations of impacts using an underlying groundwater model developed with MODFLOW. Results including maps, tables, and graphs are provided as on-screen graphical displays for rapid evaluation and can be exported as GIS shape files or to Excel files. Simulations of permitted wells, proposed wells, and custom simulations can be executed without the need to locate, open, and manipulate the actual MODFLOW files.

The Toolbox is illustrated for the Jocko Basin, located in the southernmost part of the Flathead Reservation. The underlying Jocko Basin Model simulates groundwater flow within the alluvial aquifers and exchanges with surface streams. Modeled recharge includes mountain-front recharge, stream and canal seepage, and infiltration of excess applied irrigation water. Groundwater discharge occurs through pumping wells, evapotranspiration, springs, and to streams. The Toolbox initiates with a historical base case condition. From user input, the Toolbox runs the groundwater model and provides summaries of existing conditions, incremental drawdown from proposed pumping, cumulative drawdown from existing and proposed wells, and stream depletion impacts. Coordinated groundwater management can be achieved if administrative criteria for acceptable levels of decline and depletion are developed, and used as a basis for permitting changes or new water uses.