As part of the Hanford Environmental Dose Reconstruction Project, an unsteady flow hydraulic model, modified to include radionuclide decay, was used to simulate the transport of radionuclides released to the Columbia River from Hanford. The model was applied to the river from Priest Rapids Dam to the vicinity of Portland, Oregon, for the period from January 1950 through January 1971. Model output consisted of monthly-average water concentrations for 24Na, 32P, 65Zn, 76As, and 239Np. Model validation was accomplished by comparing computed water depths and 51Cr concentrations to measured field data. This paper discusses the modeling approach and compares the results to historical river monitoring data collected during the peak years of operation.