Research Interests

My research program examines various aspects of erosion and sedimentation primarily in fluvial systems through the use of experimentation, theory, field studies, and numerical modeling. The overall goals of the research are to quantify flow and sediment transport processes using an interdisciplinary approach and to determine the impact of these processes on river form and function, water quality and ecology, landscape evolution, and watershed infrastructure and integrity. This work is fundamentally important because sediment is one of the leading causes of water quality impairment nationwide, and soil erosion is the leading cause of soil degradation worldwide. Excessive sedimentation also reduces the performance of flood-control reservoirs and increases risks to flooding within river corridors. Below is a brief description of these activities, divided into four categories.

Sediment Transport Processes in Streams and Rivers
For uniform and steady flows in rivers, the entrainment and transport of sediment of various sizes, shapes, and densities depend on the gravitational and frictional forces keeping the grains in place, the time- and space-varying fluid forces acting to move and suspend the particles, and the development of bedforms that further modulate boundary layer characteristics. Work to date, utilizing state-of-the-art instrumentation, has focused on the following topics.

• The entrainment, transport, and deposition of sediments with varying size, shape, and density
• The discrimination of fluid and sediment phases within sediment-laden, open channel flows
• The modulation of turbulence by bedload and suspended load transport in rivers
• Bedform development, stability, and transition in rivers, their interaction with turbulent flow, their growth from initially flat-bed boundaries, and the effect of sediment gradation on bedform characteristics and mass flux

Phase Doppler anemometer described in Bennett et al. (1998; flow is right to left)	RIpple bedforms described in Venditti et al. (2005; flow is left to right)
Low-relief bedwave (bedload sheet) described in Kuhnle et al. (2006; flow is left to right)	PIV laser being used to illuminate fluorescent tracer particles in a mixing box (Sean Bennett in 155 Wilkeson)

Some representative papers recently published include:

• Venditti, J.G., M.A. Church, and S.J. Bennett, 2006, On interfacial instability as a cause of transverse sedimentary bedforms, Water Resources Research, 42(7), W07423, 10.1029/2005WR004346.
• Kuhnle, R.A., J. Horton, S.J. Bennett, and J.L. Best, 2006, Bed forms in bimodal sand-gravel sediments: Laboratory and field analysis, Sedimentology, 53, 631-654.
• Venditti, J.G., M.A. Church, S.J. Bennett, 2005, On the transition between 2D and 3D bedforms, Sedimentology, 52, 1343-1359.
• Venditti, J.G., M. Church, and S.J. Bennett, 2005, Morphodynamics of small-scale superimposed sand waves over migrating dune bed forms, Water Resources Research, 41, W10423, doi:10.1029/2004WR003461.
• Wren, D.G., S.J. Bennett, B.D. Barkdoll, and R.A. Kuhnle, 2005, Variability in suspended-sediment concentration over mobile sand beds, Journal of Hydraulic Engineering, 131(8), 733-736.

Erosion Processes on Hillslopes and Upland Areas
Rill and gully development in upland concentrated flows occur as a discrete soil erosion process intimately related to the occurrence and upstream migration of headcuts. These areas of intense, localized erosion often are the primary cause of soil loss and the dominant source of sediment yield from agricultural landscapes. The formation, growth, and migration of headcuts has been linked to the concentration of overland flow, rill and gully erosion and development, erosion of bedrock channels, the initiation of drainage systems and landscape evolution, and the response of landscapes to land use change and extreme hydrologic events. Work to date, utilizing specially-designed experimental facilities and state-of-the-art instrumentation, has focused on the following topics.

• Systematic behavior of headcut growth, development, and upstream migration in concentrated flows with varying boundary conditions
• Turbulent flow structure and bed pressure distributions within the plunge pool region downstream of a migrating headcut
• Application of impinging jet theory to soil erosion processes due to headcut migration
• Integral time- and length-scales for headcut development and migration
• Modeling of soil erosion processes due to headcut migration and plunge-pool scour
• Modeling gully development, migration, and widening on agricultural fields in spatially-varied, unsteady flows and its integration into AGNPS

Actively migrating headcut described in Bennett et al. (2000; flow is from left to right)	Velocity magnitude within a headcut plunge pool described in Bennett and Alonso (2006; flow is from left to right)
Variation of flow velocity orthogonal to free jet axis as a function of distance along the axis within the established flow region described in Bennett and Alonso (2005)	A migrating heacut arrested in place by raising the tailwater control described in Wells et al. (2009b; flow is from left to right)

Some representative papers recently published include:

• Wells, R.R., S.J. Bennett, and C.V. Alonso, 2009b, Effect of soil texture, tailwater height, and pore-water pressure on the morphodynamics of migrating headcuts in upland concentrated flows, Earth Surface Processes and Landforms, 34, 1867-1877.
• Wells, R.R., C.V. Alonso, and S.J. Bennett, 2009a, Morphodynamics of headcut development and soil erosion in upland concentrated flows, Soil Science Society of America Journal, 73, 521-530, doi: 10.2136/sssaj2008.0007.
• Gordon, L.M., S.J. Bennett, C.V. Alonso, and R.L. Bingner, 2008, Modeling long-term soil losses on agricultural fields due to ephemeral gully erosion, Journal of Soil and Water Conservation, 63(4), 173-181.
• Gordon, L.M., S.J. Bennett, R.R. Wells, and C.V. Alonso, 2007, Effect of soil stratification on the development and migration of headcuts in upland concentrated flows, Water Resources Research, 43, W07412, doi: 10.1029/2006WR005659.
• Gordon, L.M., S.J. Bennett, R.L. Bingner, F.D. Theurer, and C.V. Alonso, 2007, Simulating ephemeral gully erosion in AnnAGNPS, Transactions of the American Society of Agricultural and Biological Engineers, 50(3), 857-866.

Sedimentation Issues in Flood-control Reservoirs
There are more than 75,000 dams in the continental U.S., and these structures provide opportunities for navigation, hydroelectric power, irrigation, flood reduction, and hazard protection. Yet these dams divide or segment watersheds with respect to water, sediment, nutrient transfer, and ecosystem dynamics. Because reservoirs effectively trap sediment, these impoundments have proven to be important environmental “archives” of changes in water quality parameters, land use, and sediment yield. The overall goals of the current research program are to assess the sediment impounded by these dams in terms of the structure’s ability to regulate floodwaters and the potential hazard these sediments may pose to the environment. Work to date, utilizing various techniques, has focused on the following topics.

• Discriminating post-impoundment sediment accumulations using stratigraphic, geochronologic, and geophysical techniques
• Determining the textures, spatial distributions, and rates of reservoir sedimentation at local and regional scales
• Use of reservoir sediments as environmental, geomorphic, and hydrologic archives
• Quantifying the geochemical characteristics of the sediment impounded within reservoirs and their effect on the environment
• Use of acoustic, sub-bottom profiling to map impounded sediment and its comparison to vibracoring and stratigraphic analysis

Stratigraphic intrepretation of impounded sediment described in Bennett and Dunbar (2003)	Vibracore system on Grenada Lake, MS described in Bennett et al. (2005)
Variations in arsenic, mercury, lead, and zinc concentrations within the sediment below the bottom of Grenada Lake, MS, showing the time of reservoir construction (1954) as described in Bennett and Rhoton (2007)	Spatial variation in depth-averaged agrichemical concentrations within the impounded sediment of Grenada Lake, MS along the Yalobusha RIver arm as described in Bennett and Rhoton (2009)

Some representative papers recently published include:

• Bennett, S.J., and F.E. Rhoton, 2009, Linking upstream channel instability to downstream degradation: Grenada Lake and the Skuna and Yalobusha River Basins, Mississippi, Ecohydrology, 2, 235-247.
• Rhoton, F.E., and S.J. Bennett, 2009, Soil and sediment properties affecting the transport and accumulation of mercury in a flood control reservoir, Catena, 79, 39-48.
• Bennett, S.J., and F.E. Rhoton, 2007, Reservoir sedimentation and environmental degradation: Assessing trends in sediment-associated trace elements in Grenada Lake, MS, Journal of Environmental Quality, 36, 815-826.
• Davidson, G.R., S.J. Bennett, W.C. Beard, II, and P. Waldo, 2005, Trace elements in sediments of an aging reservoir in rural Mississippi: Potential for mobilization following dredging, Water, Air, & Soil Pollution, 163(1-4), 281-292.
• Bennett, S.J., F.E. Rhoton, and J.A. Dunbar, 2005, Texture, spatial distribution, and rate of reservoir sedimentation within a highly erosive, cultivated watershed: Grenada Lake, MS, Water Resources Research, 41(1), W01005, doi:10.1029/2004WR003645.

Riparian Vegetation and Fluvial Geomorphology
Because of increased popularity of vegetation in stream restoration and streambank stabilization programs, there is renewed interest in examining the interactions between river flow, riparian vegetation, and large woody debris. There are instances, however, when bank instability causes excessive recruitment of large woody debris, which can effectively choke downstream river corridors as witnessed along the Yalobusha River, MS. The overall goals of the current research program are to assess the interactions between open channel flow and rigid vegetation and to determine how river flow processes and forms are modulated such vegetation. Work to date, utilizing various techniques and facilities, has focused on the following topics.

• Using managed vegetation plantings to transform a straight, degraded stream corridor into a meandering planform
• Examining the turbulent-flow structures created by riparian vegetation and their effects on mixing processes
• Determining the morphologic and hydraulic adjustment of rivers to vegetation using physical and numerical models
• Assessing the impact of large woody debris on river form and function
• Quantifying the drag on individual vegetal elements as a function of vegetation density and relative submergence

Turbulent flow around emergent, rigid vegetation using particle image velocimetry described in Bennett (2004; flow is from bottom to top)	Large woody debris accumulation along the Yalobusha River, MS described in Bennett and Rhoton (2009; looking upstream)
Alluvial response to managed plantings of rigid, emergent vegetation (staggered pattern placed in a semi-circular arrangment) within an experimental channel as desribed by Bennett et al. (2008; flow is from left to right)	Spatially-averaged surface flow vectors for a fixed-bed experimental channel with alternate zones of emergent, rigid vegetation (staggered pattern placed in a semicircular arrangment (only a portion of the flow field is shown; Bennett et al., 2002)

Some representative papers recently published include:

• Bennett, S.J., W. Wu, C.V. Alonso, and S.S.Y. Wang, 2008, Modeling fluvial response to in-stream woody vegetation: Implications for stream corridor restoration, Earth Surface Processes and Landforms, 33, 890-909.
• Jimenez-Hornero, F.J., J.V. Giraldez, A.M. Laguna, S.J. Bennett, and C.V. Alonso, 2007, Modeling the effects of emergent vegetation on an open channel flow using a lattice model, International Journal for Numerical Methods in Fluids, 55, 655-672.
• Wu, W., F.D. Shields, Jr., S.J. Bennett, and S.S.Y. Wang, 2005, A depth-averaged, two-dimensional model for flow, sediment transport, and bed topography in curved channels with riparian vegetation, Water Resources Research, 41(3), W03015, doi:10.1029/2004WR003730.
• Bennett, S.J., 2004, Effects of emergent riparian vegetation on spatially-averaged and turbulent flow within an experimental channel, in Riparian Vegetation and Fluvial Geomorphology, edited by S.J. Bennett and A. Simon, Water Science and Application Series Volume 8, p. 29-41, American Geophysical Union, Washington, D.C.
• Bennett, S.J., T. Pirim, and B.D. Barkdoll, 2002, Using simulated emergent vegetation to alter stream flow direction within a straight experimental channel, Geomorphology, 44(1-2), 115-126.

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