Experimental
Tidal Channel Geometries in Space and Time
Vlaswinkel, Brigitte M.1,
Eugene C. Rankey2 (1) Rosenstiel School of
Marine and Atmospheric Science, University of Miami, Miami, FL (2) Rosenstiel School of Marine and Atmospheric Science,
University of Miami, Miami, FL
Channel networks are ubiquitous in
nature. Tidal channel networks are one of the least studied tributary systems
with respect to their network characteristics and three-dimensional geometric
patterns. Many topological similarities exist between tidal and fluvial
networks, even though tidal systems are characterized by different processes,
most notably bi-directional flow, daily bankfull
discharge and lower gradient. We present results of an experimental study from
St. Anthony Falls Laboratory (UMinn), investigating
the spatio-temporal dynamics of tidal channel network
systems, focusing on high-resolution topographic analysis of channel geometry
and associated changes both downstream and through time.
Morphometric data show that networks
include exponential length-width-depth frequency distributions. Empirical
relationships are established between width and respectively depth and length
of channel segments. Cross-sectional geometry downstream illustrates distinct
trends between channel order and width, depth, W/D ratio, sinuosity and skewness. These channel geometry attributes are fairly
constant through time for small tributary channels but vary for the larger,
more ‘seaward' channels.
Despite constant flow and
sediment variables, network growth is non-linear, with short pulses of headward channel extension followed by long periods of
stasis. Autogenic effects in the nearshore distributary system are thought to be responsible for the
burst-like behavior in the upstream tributaries. Distinct scaling relations and
self-similar characteristics imply that the network and channel patterns are
stochastically predictable. These patterns offer unique snapshots of evolution
of channel geometries, akin to those that form the stratigraphic
record, and may provide stratigraphers with new
insights into channel evolution.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California