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.