2019 AAPG Annual Convention and Exhibition:

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Predictions for the Width of River Channel Belts From Physical Experiments and the Rock Record


River channels and their remnants can imprint broad corridors across low-relief landscapes. These corridors, or channel belts, are preserved in stratigraphy as packages of coarse sediment (i.e., channel bodies) and are key targets for development of energy and water resources. Sustainable management of these resources depends on predictions for channel body geometry in the subsurface, which determines aquifer capacity and accessibility. Empirical data sets have established scaling relationships between the dimensions of channels and active channel belts and preserved channel bodies. Key uncertainties remain, however, regarding the evolution and downstream variation of channel belt width. Sedimentary geoscience can address these challenges through controlled experiments. To this end, we conducted a set of physical experiments at St. Anthony Falls Laboratory (Univ. of Minnesota) to quantify the temporal and spatial evolution of an initially straight channel in a non-cohesive, sediment bed. The experiments built on established methods for evolving braided rivers: constant fluxes of water and sediment were fed to an initially straight channel with a fixed base level. Guided by previous studies, we designed four runs that separately varied water discharge and initial bed slope as independent variables. To further quantify channel belt evolution, we collected time-resolved topographic measurements and ran the experiments in a flume with sufficient width (2.7 m) and length (37 m) to allow unconstrained channel movement and to capture downstream variation in channel belt width over a distance > 200 times greater than the initial channel width. We observed that all four experiments followed a classic evolution in which the initially straight channel developed alternate bars, meanders, and eventually braided channels that widened the channel belt and abandoned previously worked areas. The initial meandering instability created a persistent, quasi-periodic variation in the width of the channel belt. This presentation will use statistical analyses of the laboratory channel belts and targeted comparisons to modern landscapes and ancient deposits to test a new, quantitative model for channel belt width. The discussion will highlight opportunities for using physical experiments and targeted geologic observations to inform sustainable management of subsurface resources.