Measuring suspended sediment in small mountain streams

The Author: ROBERT B. THOMAS is a mathematical statistician assigned to the Station's research unit studying the management of Pacific Coastal forests on unstable lands, and is stationed in Arcata, California. He earned a bachelor's degree in mathematics at California State University, Hayward (1967) and a master's degree in statistics at the University of California, Berkeley (1971). He joined the Station's staff in 1977. Measuring suspended sediment concentration in streams provides a way of monitoring the effects of forest management activities on water quality. Collecting data on suspended sediment is an act of sampling. The nature of the delivery process and the circumstances under which data are collected combine to produce highly variable results that are difficult to analyze and interpret. Data-collection stations are set up to compare one set of measurements to another. They should be located with regard to channel morphology. Deciding when to measure suspended sediment is a major problem in carrying out most studies. Concentration depends heavily on streamflow discharge, which can be used to allocate sampling resources to appropriate flow levels. Restrictions in budgets and technical concerns have fostered the increased use of automatic pumping samplers in measuring suspended sediment.