My research program has examined 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 floodcontrol reservoirs and increases risks to flooding within river corridors. Below is a brief
description of these activities, divided into four categories.
1. Flow and sediment transport in 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. My Ph.D. work
focused on the processes that cause the entrainment, transport, and deposition of sediment
mixtures as well as the characteristics of low-relief bedwaves termed bedload sheets.
The presence of sediment in geophysical flows, either as bedload or suspended load, has a
measurable effect on the turbulence characteristics of such boundary layers. State-of-the-art
instrumentation enables the discrimination of fluid and sediment phases in sediment-laden openchannel flows, and these work can now define, verify, and challenge many of the concepts,
theories, and equations used for describing clear-water and sediment-laden geophysical flows
including velocity distributions, turbulence modulation, and suspended sediment load.
Bedform development, stability, and transition are intimately coupled to the turbulent flow field
present over these topographic features. The turbulent flow fields over fixed ripple and dune
bedforms have been quantified, providing new quantitative evidence for the fluid dynamical
differences of flow over such bedforms, new conceptualizations for the turbulent entrainment
and suspension of bed sediment, and a new hydrodynamic basis for bedform transition. Recent
work as examined the spectral signatures of flow and sediment transport over dune bedforms and
the development and evolution of bedforms from an initially flat bed.
2.
Soil erosion by upland concentrated flows
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. This research, which
utilized a specially-designed flume, demonstrated systematic behavior in headcut erosion
including self-similar steady-state erosion, varying erosion mechanics as a function of boundary
conditions, and integral time- and length-scales for headcut development. Recent work has
focused on the analytic modeling of soil erosion due to plunge-pool scour and the
hydrodynamics and erosivity of jet flow within headcut scour holes.
3.
Reservoir sedimentation and assessment
At the direct request of the NRCS, I was asked to develop technologies and procedures for the
cost-effective assessment of flood-control reservoirs laden with sediment of questionable quality
(with NRCS funding).
Since the 1940s, the NRCS has constructed nearly 11,000 flood-control structures nationwide,
and these aging reservoirs are nearing the end of their service life, and these aging flood-control
structures are assessed using vibracoring and geophysical techniques combined with
geochemical and geochronologic analyses of the sediments. This enables the quantitative and
unambiguous identification of post-impoundment sedimentation, sediment sorting processes
within the reservoir, and the environmental techniques for sample procurement and analysis.
These results have been transferred to the NRCS and the U.S. Environmental Protection
Agencies through reports, workshops, and invited lectures, and the NRCS has adopted these
procedures in their current reservoir assessment program. Work initiated in Oklahoma was
expanded to Wisconsin, Texas, and Mississippi, and it further included senior and student
researchers from the University of Mississippi (#3) and Baylor University. Moreover, these
results enabled the securing of competitive funds (USDA-Cooperative State Research,
Education, and Extension Service; CSREES) for the continued development of acoustic-based
surveying techniques for sediment impoundment assessment (on-going).
As a direct result of these studies, I attracted significant interest and funding from the COE for
multidisciplinary work in a relatively large flood-control reservoir in Mississippi. Here,
stratigraphic, geophysical, geochronologic, and geochemical techniques were (and continue to
be) used to determine rates and patterns of recent sedimentation and sediment quality (heavy
metal and agrichemical concentrations) within one of the most erosive regions within the U.S.
(#4, and on-going). The COE currently is using these data to assess the impact of upstream
channelization projects on water quality and ecology within the lake. From this work,
collaborations with Ohio State University and Louisiana State University are examining porewater geochemical processes occurring in the subsurface sediment, which show high
concentrations of arsenic at depth (on-going), and work with the U.S. Geological Survey is
examining nutrient loadings and residence times within this ecoregion (#7).
4.
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 and riparian
vegetation. I designed an experimental stream-restoration program to use managed vegetation
plantings analogous to the willow-post technique (emergent, rigid vegetation) to transform
straight, degraded stream corridors typical of the loess region of the U.S. into biologically
functional, meandering streams (T. Pirim, student; #11). The sinuosity of the meandering
thalweg, as deduced using particle image velocimetry, and the magnitude of the lateral mixing
and flow resistance were shown to depend on the position and density of vegetation zones.
Competitive funds (USDA-CSREES) were secured to continue this work to address (a) alluvial
adjustment to rigid, emergent vegetation using a movable-bed Froude-scale model (on-going)
and (b) flow resistance within vegetated stream corridors (S. Vittalam, student; recently
completed). Additional collaborative studies have examined the geomorphic and hydraulic
response of alluvial channels to large woody debris (#12, #13), and the modeling of flow and
sediment transport processes within vegetated stream corridors (#1).