[wind_erosion] Mendenhall Fellowship in aeolian-fluvial interactions and lidar

Please see our Mendenhall Fellowship post-doc opportunity in aeolian-fluvial interactions and ground-based lidar: http://ift.tt/1HsHovm

Deadline for application is February 17, 2015.

Please forward to anyone who might be interested.

Best

Joel Sankey,

— 

Joel B. Sankey

Research Geologist

Southwest Biological Science Center

Grand Canyon Monitoring and Research Center

US Geological Survey

2255 N. Gemini Dr.

Flagstaff, AZ 86001

928-556-7289

http://ift.tt/1HsHnHY

Here is the the full text of the description:

15-26. The fluvial-aeolian-hillslope continuum: measurement and modeling of topography and vegetation to inform landscape-scale connectivity for sediment in river valley ecosystems

River valley ecosystems comprise fluvial and upland environments. Each environment is dominated by a different but overlapping suite of sediment transport processes. Landscape-scale transport, erosion and deposition of sediments in river valley ecosystems cannot be understood by studying fluvial, aeolian and hillslope processes in isolation, because considerable exchanges of sediment between these systems occur. The details of how river valley sediments become recycled into and out of isolated systems (i.e. exchanged across boundaries) where the transporting agent is water, wind, or gravity is poorly understood (Belnap et al. , 2011; Draut, 2012; Sankey and Draut, 2014).

The degree to which a landscape facilitates or impedes exchanges of sediment between different systems is termed connectivity. Connectivity governs where sediments are deposited or eroded in coupled fluvial-aeolian-hillslope systems, and is therefore important to ecosystem structure and function. Many studies have shown in upland environments that enhanced connectivity, and therefore increased sediment transport can cause increased soil erosion, land degradation, and desertification. In river valley ecosystems, however, where connected pathways are conduits for the movement of sediment between the fluvial and upland environments, the effects of changes and feedbacks for connectivity and sediment transport are less well understood.

The Colorado River, southwestern U.S.A. , is an example of a river valley in which changes in connectivity that increase transport among different sediment systems can have ecological value. In the portion of this ecosystem that is downstream of Glen Canyon Dam, connectivity has been strongly affected by changes in flow regime and by a reduction in the fine sediment supply. Lowered flood magnitude and frequency have greatly restricted the area where fluvial processes can transport sediment, effectively expanding the area dominated by upland processes. Reduced fine sediment supply has led to a reduction in sandbars within the active river channel, which in turn has decreased the amount of sediment available for aeolian (wind) transport outside of the active channel. This specific type of connectivity, which focuses on the potential for movement of sediment by wind from active channel sandbars to higher elevation landscapes, is very important in this, and potentially other, river ecosystems. Redistribution of sediment from the active river channel to higher elevations can provide important habitat for the upland ecosystem and can produce a protective surface cover on hillslopes that otherwise can erode rapidly by overland flow and gullying. In the Grand Canyon of the Colorado River such erosion can be particularly detrimental because hillslopes can be laden with archaeological materials.

Potentially important controls on connectivity include: the size of subaerially exposed sandbars that are upwind from upland landscapes; the grain size distribution of fluvial sediment; topographic barriers such as rock outcrops and debris fans positioned between sandbars and higher elevation areas; and vegetation (either barriers positioned between fluvial sand bars and higher elevation areas or cover of formerly open sediment areas). Many of these potentially important controls are directly affected by contemporary environmental issues and management actions. For example, controlled floods from Glen Canyon Dam are currently being used as a management tool to redistribute sand from the bed of the river to eddies along the channel margins thereby increasing sandbar size (Mueller et al. , 2014). The area of dry exposed sand that may be transported by wind is influenced by flow regime and operation of the dam. The invasive shrub Tamarisk (Tamarix spp. ) affects depositional and erosional processes on fluvial sandbars, forms a barrier affecting transport by wind from fluvial to upland environments, and affects aeolian processes within the upland environment. Each of these controls (and potentially many others) operates over different spatial and temporal scales to affect the amount and spatial distribution of sediment transported between the fluvial and upland environments.

Research is needed to express connectivity as a series of interconnected sediment budgets in order to better understand the source-and-sink dynamics of sediment between fluvial and upland environments. We seek a postdoctoral fellow who can address questions of whether, and how, the quantity and distribution of fluvial sediment within the active river channel can significantly influence the amount and distribution of sediment that occurs above the active river channel?

The development of tools to measure, model and predict connectivity for river-derived sediment among fluvial, aeolian and hillslope systems, necessitates linkages among fluvial and aeolian geomorphology, hydrology, hydraulics, and riparian ecology, in a “whole-system” science. It requires extrapolation of fine-scale topographic and vegetation measurements to understand processes operating across the entire landscape, using deterministic, statistical, and/or process-based modeling. An approach to this research might be to develop a quantitative sediment budget for sandbar(s) that would consider fluvial erosion and deposition, and transport by wind between the active channel and upland area, as a function of local hydraulic and atmospheric conditions. This might entail high resolution and high frequency topographic surveys with ground-based lidar at individual sandbars and upland sites to develop local sediment budget(s). It might also entail a conceptual framework to extrapolate observations to the greater riverine landscape. We expect the research to place greater emphasis on measurement-based observational science, though depending on the applicant’s strengths the research may focus more or less on modeling. The candidate’s background may be in the physical, hydrological, or ecological sciences.

REFERENCES

Belnap, J. , et al. , 2011. Aeolian and fluvial processes in dryland regions: the need for integrated studies. Ecohydrology 4(5), 615-622.

Draut, A. , 2012. Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA: Journal of Geophysical Research – Earth Surface, v. 117, F2

Mueller, Erich R. , et al. , 2014. The influence of controlled floods on fine sediment storage in debris fan-affected canyons of the Colorado River basin. Geomorphology 226, 65-75.

Sankey, JB, Draut, AE, 2014. Gully annealing by aeolian sediment: Field and remote-sensing investigation of aeolian-hillslope-fluvial interactions, Colorado River corridor, Arizona, USA. Geomorphology 220, 68-80.

Proposed Duty Station : Flagstaff, AZ

Areas of Ph.D. : Geology, geomorphology, hydrology, watershed science, earth science, environmental science or related discipline (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 one of the following qualifications: Research Geologist, Research Physical Scientist, Research Hydrologist, Research Geographer (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 USGS Human Resources specialist. )

Research Advisor(s) : Joel Sankey, (928) 556-7289, jsankey@usgs.gov ;  Paul Grams, (928) 556-7385, pgrams@usgs.gov ;  Amy East, (831) 460-7533, aeast@usgs.gov ;  Daniel Buscombe, (928) 556-7216, dbuscombe@usgs.gov ; Temuulen Sankey, (928) 523-7098,Temuulen.Sankey@nau.edu

Human Resources Office Contact: Aleecia Leyba, (303) 236-5973, aleyba@usgs.gov .

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