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Alan Kasprak - Current Research
1. Fluvial Audits - John Day River Watershed, Oregon
Rivers exhibit large
longitudinal variations, which may
range from continuous predictable gradients (e.g. discharge) to
small-scale
anomalies, such as bedrock outcrops, fault zones, and sediment point
sources. Understanding
the gradient and distribution of channel types and geomorphic
characteristics
such as substrate, pool density, and gradient, among many others, is
integral
to interpreting results from studies which sample point data along the
stream
channel (e.g. salmonid habitat surveys and fish counts).
Interpreting the results
of such surveys, which are conducted over short (~200 m) reaches may be
difficult, especially when determining the influence of local factors
influencing physical habitat (e.g. point source runoff, land use)
versus shifts
occurring naturally as a result of longitudinal stream variations (e.g.
increased discharge) and/or short-duration differences, such as a
tributary
junction).
A
fluvial audit is conducted in two phases, (A) a
desktop-based GIS exercise and (B) a rapid field assessment.
DESKTOP
GIS: Relevant
geospatial data are obtained for the study watershed. This spatial
information is then
synthesized and used to delineate physiographic provinces occurring in
the
study watershed. Ccombining these relevant sources of information is
used to produce a
first-order approximation of the geomorphic reach breaks that may be
encountered in the field.
RAPID
FIELD
ASSESMENT:
Crews visit the study streams with minimally the geospatial
data used in the desktop GIS exercise. Notes were taken at
GPS-collected data points
and described geomorphic characteristics about the channels being
surveyed.
Additionally, a comprehensive photo record along the course of the
channel was obtained using a digital camera with geotagging capability.
Field crews
walked the entire course of the study streams and recorded datapoints
which
described channel attributes
including gradient, substrate,
sinuosity, valley confinement, pool density, LWD density, and
Montgomery/Buffington channel type. With the downstream
progression of the survey, noticeable
shifts in a number of these attributes results in the delineation of a
new
geomorphic reach.
Fluvial audit with Justin Stout (Utah State University) on Bridge Creek, Oregon (a tributary of the John Day River).
2. Morphodynamic Modeling for Gravel-Bed Rivers
Frequent turnover in gravel bed river substrate produces essential physical habitat for aquatic species ranging from salmonids to insects to riparian vegetation. This variation in channel bed topography through time as a function of hydraulics and sediment transport is called morphodynamics, and is fundamental in creating new habitat niches, maintaining existing habitat, and promoting habitat heterogeneity and biodiversity. Despite the reliance of aquatic organisms on the morphodynamics of their physical habitat, we remain unable to predict gravel bed river behavior at ecologically-relevant spatial scales (individual channel bars) and timespans (individual floods to centuries).
This study involves the development of a new morphodynamic model for gravel-bed rivers, which is capable of driving channel bed evolution at bar scales over decades to centuries. This model will be coupled with existing ecohydraulic models to document the potential impact on aquatic habitat resulting from discharge and sediment supply shifts potentially stemming from climate change, land use variations, dam management.
The developed
morphodynamic model will be driven using a
two-dimensional hydraulic scheme (currently the CFD-driven Hydro2de model). Following
calculation of hydraulics, sediment
transport will be driven using a new step-length based component. In
contrast
to calculating whether sufficient shear stress exists for particle
entrainment
continuously downstream, volumes of eroded sediment will be distributed
according to a specified step-length distribution, which has been
demonstrated
in gravel-bed channels by previous studies (Habersack, 2001; Pyrce and
Ashmore,
2003). The major advantage in using a step-length based scheme is the
reduction
in computational overhead achieved by simplifying downstream sediment
transport, allowing for greater spatiotemporal modeling range and a
higher
resolution. Following sediment mobilization downstream, the channel bed
elevation is updated at each computational node (i.e. Exner equation),
hydraulics
are recomputed using the 2D CFD model and the process is repeated
through time.
akasprak@aggiemail.usu.edu | Phone: 435.797.9189 | Fax: 435.797.1871