Streamflow and Quality in the Columbia River Basin

Streamflow and quality in the Columbia River Basin are predictably related maximum concentrations accompany minimum flows. Each reach of river has a unique signature which defines the local dependence of mineral quality upon flow. The basic form of flow quality relationships is a continuous annual cycle reflecting variations in rates at which minerals are weathered or leached from rocks or soils and in streamflow rates. These cyclic variations are most pronounced in tipper reaches of streams where they may be described by elliptical doughnuts on logarithmic plots of concentration versus flow. The pattern becomes more complex as tributaries from different elevations and snowmelt periods combine. Annual cycles of irrigation and drainage appear indistinguishable from purely natural processes. In either case, rising (spring) flows flush accumulated salts from the basin while falling (summer) flows remove only newly leached salts. Where annual cyclic variations in quality occur, their sequences are such that reservoirs, which are filled by early season rains up to limits required for flood control, will be filled with the most highly mineralized water.