Suspended sediment yields for selected watersheds in western Montana

Abstract

Annual suspended sediment yields for 17 watersheds in western Montana in a mild drought are recalculated. Previous methodology used sporadic to weekly direct measurements taken only during the annual snowmelt during the drought to estimate drought period yields. Yield approximations for wet period flows relied on predicted increases in the means of flow and sediment concentration of the measured values. This study uses synthetic flow duration curves developed using regional data of a longer period of record for drought and wet period estimates. These are combined with log-transformed sediment rating curves which are bias corrected. Mean flows for the drought average of half previous calculations, sediment yields average 70 percent less. The bias correction averages + 33 percent. Estimates of sediment yield due to increases in flow are 60 percent less than previous approximations.