Doctoral Dissertation Research: Streamwood Flux from Forested Mountain Watersheds Into Reservoirs in the Sierra Nevada, California

University Of California-Davis, Davis CA

Investigators

Abstract

Forested mountain watersheds account for a large percentage of streamwood movements into and through river channels, with streamwood defined as live or dead wood greater than 1 m in length and greater than 10 cm in diameter. Streamwood "budgets" recently have been proposed to trace the movement of streamwood and in out of river channels, but few have been completed because of the complexity of field work in all but the smallest watersheds. One budget component that rarely has been measured is the export variable. Dams impede streamwood movement from upper watersheds, however, resulting in depositional zones where characterization can occur. This doctoral dissertation research project will use remotely sensed imagery analysis, video monitoring, and field studies to identify underlying linkages between streamwood and hydrologic, geomorphic, and terrestrial mechanisms at multiple spatial-temporal scales. The doctoral student will analyze streamwood aggregations associated with two California reservoirs in the Sierra Nevada: Bullard's Bar on the North Fork Yuba River and Don Pedro on the Tuolumne River. Remote sensing software methods will be used to analyze multispectral 30-m resolution Landsat images from 1982 to the present. Validations will be performed with archival 1-m resolution digital orthophoto quadrangle (DOQ) and National Agriculture Imagery Program (NAIP) images, and via field observations for current years. Digital video monitoring will be installed at the top of the study reservoirs to document streamwood transport volume and velocity across seasonal hydrographs, including baseflow, winter precipitation, and snow melt as well as rain-on-snow floods if they occur. Fieldwork will be used to characterize reservoir streamwood and upper watershed storage and decomposition processes, which will broadly explain the input (recruitment) component of a simplified streamwood budget (Inputs = Exports + Storage + Decomposition). GIS analyses will be used to understand the relationship between streamwood yield and physical processes, with expected results to include average streamwood export at daily, seasonal, yearly, and decadal scales; discharge-streamwood yield rating curves; streamwood recruitment and storage potentials; and regression relationships between streamwood discharge-dam outflow, transport distance-streamwood genera and decay classification-streamwood density. This project will fill spatial and temporal gaps in basic understanding regional variation of an important particulate organic component of the forest carbon cycle, streamwood export. Understanding streamwood export will provide insight into physical mechanisms that drive streamwood production and transport through a watershed. New methods may prompt quantification of streamwood export into reservoirs in other locales, which would lead to a deeper understanding of this important ecological and geomorphic river component. Reservoir mangers will have increased ability to predict streamwood export based on discharge and known watershed characteristics. Scientifically based recommendations of streamwood volume to be added to ecosystem rehabilitation projects below-dam could fundamentally alter reservoir and river management practices. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.