19-7. Sediment yield from watersheds on the U.S. West Coast: Projecting effects of future climate and river management

Terrestrial sediment supply from coastal watersheds is an important factor in nearshore morphodynamic evolution, and represents both a resource and a potential hazard in coastal zones (Barnard and Warrick, 2010). Understanding how watershed sediment supply responds to human activities and hydroclimatic variations is an urgent need at the forefront of earth-surface-process research. Landscapes of the western U.S. produce and export large sediment fluxes owing to steep terrain, tectonic activity, and the regional potential for wildfire and extreme rainfall. Recent studies suggest that the 21st century will see still greater sediment production in the western U.S. owing to shifting magnitude-frequency relationships for extreme rainfall, as well as increased wildfire frequency, area, and intensity (Sankey et al., 2017; East et al., 2018a; Swain et al., 2018). In addition, human activity is affecting sediment routing in new ways, through changes in watershed development and river management, including sediment augmentation and removal of aging dams (Foley et al., 2017; East et al., 2018b). However, much uncertainty remains regarding landscape responses to changing hydroclimate and river-management actions. Similarly, the ways in which these responses affect coastal morphodynamic evolution and nearshore sediment budgets are poorly understood, but will be closely linked to the evolution of beaches as sea level rises (Vitousek et al., 2017).

To better understand terrestrial sediment-supply changes in the 21st century, and to improve understanding of links between watershed and coastal change, the USGS Pacific Coastal and Marine Science Center (PCMSC) seeks a USGS Mendenhall Postdoctoral Fellow to develop geospatially-based models of future watershed sediment supply to the coast. Research at the USGS PCMSC through the Landscape Response to Disturbance project characterizes and quantifies landscape response to disturbance to provide new information on sediment-related hazards and resources along the West Coast, with implications for ecosystems and infrastructure. Related work through the USGS Coastal Change Hazards Program examines how coastal sediment supply and transport affects morphodynamic evolution of shorelines, quantifying ongoing change and anticipating potential future change in the context of sea-level rise and other climate and anthropogenic influences.

This Mendenhall opportunity is intended to improve fundamental understanding of hydroclimatic and human impacts on terrestrial geomorphic processes and the sediment supply that reaches the shoreline. The primary goal of the research opportunity is to apply techniques of quantitative geomorphology and/or applied sedimentology to develop new models of watershed sediment supply to the coast, employing various scenarios of hydroclimate and river management over multi-decadal time scales. Geospatial modeling will consider future sediment yield under conditions of greater magnitude and frequency of extreme rainfall, greater wildfire frequency and burn area, and (on local scales) the enhanced use of intentional sediment augmentation, dam removal, or dam breaching to reconnect upstream sediment supply to the coast. Relevant prior experience includes some or all of the following: numerical modeling; use of geospatial (GIS-based) models of sediment production (e.g., Soil & Water Assessment Tool, SWAT; geospatial interface for the Watershed Erosion Prediction Project, GeoWEPP; kinematic runoff and erosion model, KINEROS); digital terrain analysis and topographic change detection; remote-sensing image analysis and change detection; field examination of landscape responses to extreme rain, wildfire, or fluvial sediment pulses; data-driven scenario-based modeling in earth-surface-process research. The Mendenhall Fellow will focus their modeling efforts on the West Coast, with potential extension to other regions with different climatic and topographic regimes (Pacific and Caribbean islands; lower-gradient U.S. Gulf and East coasts). Results of this modeling effort, and the sediment-supply factors to be constrained through this research opportunity, ultimately will be incorporated into other models that simulate shoreline evolution, such as CoSMoS-COAST (Coastal One-line Assimilated Simulation Tool; Vitousek et al., 2017), to project coastal morphodynamic response to future storm and sea-level forcing.

This research should be developed to meet USGS science priorities, particularly those aligned with the USGS Coastal and Marine Hazards and Resources Program. The proposed work should complement existing research efforts at PCMSC and specifically the Landscape Response to Disturbance (LRD) project (https://www.usgs.gov/centers/pcmsc/science/landscape-response-disturban…). Results of the research also will be relevant to the Coastal Change Hazards program, USGS Landslide Hazards Program, and to wildfire-focused research at several USGS science centers and Mission Areas (Natural Hazards, Ecosystems, Water).

The research advisor team will work with prospective applicants to develop a research plan to address the scientific needs and goals of this opportunity in a logistically and financially feasible manner. Applicants may propose an approach that couples modeling and field efforts if targeted, feasible field data collection is identified that could substantially enhance the predictive value of the modeling exercises. Proposed work should be tractable for the two-year interval of research funding and should result in scientific publications in the peer-reviewed literature. Applicants are encouraged to evaluate detailed budget needs of the proposed work, taking into account expenses needed over a two-year period. The research advisors anticipate providing support and mentorship to the Mendenhall fellow throughout planning and conducting the work, and developing interpretations into peer-reviewed publications. Our team values the opportunity to work with a Mendenhall fellow as a means to develop long-term collaborations.

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

References:

Barnard, P.L., and Warrick, J.A., 2010, Dramatic beach and nearshore morphological changes due to extreme flooding at a wave-dominated river mouth. Marine Geology 271, 131–148.

East, A.E., Stevens, A.W., Ritchie, A.C., Barnard, P.L., et al., 2018a, A regime shift in sediment export from a coastal watershed during a record wet winter, California—implications for landscape response to hydroclimatic extremes: Earth Surface Processes and Landforms 43, 2562–2577.

East, A.E., Logan, J.B., Mastin, M.C., Ritchie, A.C., Bountry, J.A., Magirl, C.S., and Sankey, J.B., 2018b, Geomorphic evolution of a gravel-bed river under sediment-starved vs. sediment-rich conditions: river response to the world’s largest dam removal: Journal of Geophysical Research–Earth Surface 123, 3338–3369.

Foley, M.M., et al., 2017, Dam removal: listening in. Water Resources Research 53, 5229–5246.

Sankey, J.B., et al., 2017, Climate, wildfire, and erosion ensemble foretells more sediment in western USA watersheds. Geophysical Research Letters 44, 8884–8892.

Swain D.L., et al., 2018. Increasing precipitation volatility in twenty-first-century California. Nature Climate Change 8, 427–433.

Vitousek, S., Barnard, P.L., Limber, P., Erikson, L., and Cole, B., 2017, A model integrating longshore and cross-shore processes for predicting long-term shoreline response to climate change. Journal of Geophysical Research–Earth Surface 122, 782–806.

Proposed Duty Station: Santa Cruz, CA

Areas of Ph.D.: Earth science, geology, geophysics, geography, hydrological sciences or related fields (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for: Research Geologist.

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Beverly Ledbetter, 916-278-9396, bledbetter@usgs.gov

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