Population growth along with possible future droughts in the Red River of the North (Red River) Basin will create an increasing need for reliable water supplies. Therefore, as a result of the Dakota Water Resources Act of 2000, the Bureau of Reclamation identified eight water-supply alternatives (including a no-action alternative) to meet future water needs in the basin. Because of concerns about the possible effects of the alternatives on water quality in the Red River and the Sheyenne River and in Lake Winnipeg, Manitoba, the Bureau of Reclamation needs to prepare an environmental impact statement that describes the specific environmental effects of each alternative. To provide information for the environmental impact statement, the U.S. Geological Survey, in cooperation with the Bureau of Reclamation, conducted a study to develop and apply a water-quality model, hereinafter referred to as the Red River water-quality model, to part of the Red River and the Sheyenne River to simulate conservative-constituent transport in the Red River Basin. The Red River water-quality model is a one-dimensional, steady-state flow and transport model for selected constituents in the Red River and the Sheyenne River. The model simulates the flow and transport of total dissolved solids, sulfate, and chloride during steady-state conditions. The physical model domain includes the Red River from the confluence of the Bois de Sioux and Otter Tail Rivers to the Red River at Emerson, Manitoba, and the Sheyenne River from above Harvey, N. Dak., to the confluence with the Red River.

 The Red River water-quality model was calibrated and tested using data collected at 34 sites from September 15 through 16, 2003, and from May 10 through 13, 2004. Water-quality samples were collected during low, steady-flow conditions from September 15 through 16, 2003, and during medium, unsteady-flow conditions from May 10 through 13, 2004. The simulated total dissolved-solids, sulfate, and chloride concentrations generally were within 5 percent of the measured concentrations.

 The Red River water-quality model was used to simulate conservative-constituent transport in the Red River and the Sheyenne River for the eight water-supply alternatives identified by the Bureau of Reclamation. For the first set of eight simulations, September 2003 streamflows were used with projected 2050 return flows and withdrawals. For the second set of eight simulations, the September 2003 streamflows were reduced by 25 percent. The simulated concentrations for three of the alternatives generally were lower than for the no-action alternative. Of those alternatives, one would result in a decrease in concentrations for two constituents, one would result in a decrease in concentrations for all three constituents, and one would result in a decrease in concentrations for one constituent and an increase in concentrations for another constituent. For four of the alternatives, the differences between the mean simulated concentrations were less than calibration errors, indicating the effects of those alternatives on water quality in the rivers is uncertain. The effects of reduced streamflow on simulated total dissolved-solids, sulfate, and chloride concentrations were greatest for alternative 2. Reduced streamflow probably has an effect on simulated total dissolved-solids concentrations for alternatives 2, 3, 5, and 7 and on simulated sulfate concentrations for alternatives 2 and 5. Except for alternative 2, reduced streamflow had little effect on simulated chloride concentrations.