MODELING THE LARGE-SCALE STRUCTURE OF A BARCHAN DUNE FIELD

Barchans are mobile, crescent-shaped dunes that form atop hard, flat surfaces in regions where sediment supply is limited and fluid flow is approximately unidirectional. To explore the large- scale (kms) and long-term (10^4 yrs) evolution of a barchan field, we use insights and parameterizations derived from empirical and theoretical work to build a partly rule-based numerical model that treats dunes as discrete entities that interact with one another according to all currently known processes: Sand-flux exchange, collisions, and calving. A rich array of patterns, similar to those observed in nature, emerge from these relatively simple interactions, offering a potential explanation of field-scale phenomena. This is the first model to integrate calving and results support the hypothesis that it exerts a first order control on the system: It appears to facilitate individual dune stability as well as control communally selected sizes. Yielding a cohesive picture of large-scale and long-term barchan dynamics, this model helps elucidate and disentangle the relative roles that external forcing and internal dynamic play in these complex systems. We characterize model dune fields using basic statistical metrics and provide testable predictions for future empirical work.