Andrew Wilcox Research

Research

Dam Removal Dam removal and downstream transport of reservoir sediments create exciting experiments and research opportunities in sediment transport, channel evolution, and habitat response. I am interested in several related questions pertaining to dam removal: How do downstream channels respond to increases in sediment supply, including both short-term increases from downstream transport of reservoir sediments and long-term restoration of supplies from upstream drainage basins? How do pulses of sediment travel through river systems? What are the effective discharges for redistributing reservoir sediments? How do aquatic habitats respond to dam removal?
Milltown Dam, Clark Fork River, MT Milltown Dam, located on the Clark Fork River just east of Missoula, was removed in stages between 2007 and 2009. Contaminated sediments originating from mines near Butte, MT are being removed from Milltown Reservoir, but the dam removal exposed several million cubic meters of less contaminated reservoir sediments to river erosion and downstream transport into the Clark Fork River. My students and I are taking advantage of the fantastic natural experiment created by this dam removal to (1) investigate the upstream channel responses to dam removal in both the Blackfoot and Clark Fork arms of the former Milltown reservoir; (2) construct a sediment budget for the Milltown reservoir area, including measurements of bedload transport into and out of the reservoir, to document volumetric erosion of reservoir sediments; and (3) analysis of downstream geomorphic changes related to sediment deposition in side channels, on point bars, and on the channel bed. Initial results have been presented at the Fall 2008 AGU meeting (talk pdf, poster pdf) and the 2009 GSA meeting (pdf). To learn more about issues associated with Milltown Dam: Clark Fork River Technical Assistance Committee
Restoration science and geomorphology-geochemistry linkages in mining-impaired streams
Restoration of mining-impaired streams in the Northern Rockies presents opportunities for developing new insights into relationships between channel form, geomorphic processes, and water and sediment quality. My research group is engaged in contributing to two restoration projects in Montana that confront these issues. On Mattie V Creek, we have collaborated with consultants to provide channel alignment and design recommendations to Trout Unlimited as part of broader efforts to restore habitat for native bull trout and westslope cutthroat trout. In the Mike Horse Mine area, located in the upper Blackfoot River basin, we are conducting EPA-funded research to investigate metals in water, sediment, invertebrates, and fish and their relationship to sediment transport and channel morphology. Collaborators include Heiko Langner and Lisa Eby (U. Montana).
Ecogeomorphic feedbacks and river morphodynamics
Interactions among flow, sediment, and riparian vegetation The interacting effects of changes in flow, sediment, and riparian vegetation on channel form and aquatic habitat are a primary research interest of mine. I began this research as part of my postdoc with the U.S. Geological Survey Geomorphology and Sediment Transport Laboratory in Colorado. This research entails both field studies and modeling; my collaborators are Patrick Shafroth (USGS Fort Collins Science Center), Rich McDonald, and Jonathan Nelson (both USGS Geomorphology and Sediment Transport Laboratory). Hydrogeomorphic effects of controlled floods on native versus non-native seedlings On the Bill Williams River (BWR), AZ, we have documented the geomorphic and vegetation responses to a series of controlled flood releases from a U.S. Army Corps dam. These floods, although small compared to historic floods on the BWR, were designed with input from scientists in order to investigate the hydrograph characteristics needed to promote establishment of native riparian vegetation (primarily cottonwood and willow), to cause mortality of non-native tamarisk seedlings, and to affect geomorphic changes associated with vegetation responses. The BWR is serving as a unique natural laboratory for investigating ecosystem responses to flow regimes and thereby for improving the quantitative basis of environmental flows. Environmental flow releases on the BWR are motivated by the presence of a high-quality native riparian ecosystem and associated bird communities, and are part of a broader partnership between The Nature Conservancy and Army Corps of Engineers, the Sustainable Rivers Project. We are also using flow and sediment transport modeling with the USGS Multidimensional Surface Water Modeling System (MDSWMS) to assess relationships between hydrograph characteristics, channel morphology, hydraulics, and vegetation response.
Fossil Creek, AZ In collaboration with Leonard Sklar (SFSU), his students, and researchers at Northern Arizona University, I have contributed to investigation of ecogeomorphic feedbacks in the evolution of travertine step-pool morphology in Fossil Creek, AZ following dam decommissioning. Fossil Creek is a remarkable stream in which calcium carbonate precipitates out of carbonate-rich water to form travertine dams. Following a decommissioning agreement with Arizona Public Service, full flows were returned to Fossil Creek in 2005 and the Fossil Creek Diversion Dam was removed in 2008. We have taken advantage of the restoration of Fossil Creek and the rapid regrowth of travertine step-pool units to study geomorphic-ecosystem interactions and effective discharges. Learn more about the restoration of Fossil Creek and associated research: Fossil Creek Watershed and Riparian Restoration Project
Steep channel processes I also study flow hydraulics and morphology of step-pool stream channels, which are high-gradient channels in which channel-spanning steps formed by boulders, woody debris, or bedrock alternate with pools. My work seeks to increase understanding of basic physical processes in these channels and to elucidate how these channels differ from low-gradient stream channels. Such knowledge is critical for analyses of sediment transport, aquatic habitat, stream restoration, and other resource management issues in low-order mountain watersheds.
Flow resistance dynamics in step-pool channels My doctoral research examined flow resistance dynamics in step-pool channels. Using a laboratory flume configured to resemble a step-pool channel, I investigated several questions: (1) What are the dominant controls on flow resistance in step-pool channels, (2) How does large woody debris (LWD) influence hydraulics in step-pool channels, and (3) How is flow resistance partitioned among LWD, steps, and grains? Approximately 400 flume runs were completed using a factorial experimental design in which variables contributing to flow resistance in step-pool channels were manipulated, including LWD configurations (density, orientation, piece length, arrangement), step geometry, discharge, bed slope, and presence versus absence of steps and grains. The experiments employed a 10-m long, 0.6-m wide recirculating flume at Colorado State University's Engineering Research Center. (pdf1, pdf2)
Velocity and turbulence characteristics in step-pool channels My research also investigates spatial and temporal variations in velocity and turbulence characteristics in step-pool channels in order to provide insight into patterns of energy dissipation and flow structure in these channels. This has entailed detailed field measurements of three-dimensional time-averaged and turbulent velocity components using a SonTek FlowTracker Acoustic Doppler Velocimeter (ADV). Primary field sites have included East St. Louis Creek, Colorado, and the Rio Cordon, Italy, which differ in terms of climate, sediment supply, and land use. Collaborators on this work include Ellen Wohl (Colorado State) and Francesco Comiti (University of Padua, Italy). (pdf) Other previous work on steep channels: —Linkages between hydraulics, morphology, and benthic communities in high-gradient streams —Downstream hydraulic geometry of mountain streams (pdf)