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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Institut für ComputerphysikStart date: 2004End date: 2009Author: search.filters.author.Durán, Orencio

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    Vegetated dunes and barchan dune fields
    (2007) Durán, Orencio; Herrmann, Hans J. (Prof. Dr.)
    Desertification is closely related to aeolian sediment transport, including sand dunes formation, evolution and migration. Sand dunes propagate in huge clusters of thousand of dunes with an internal complex dynamics that determines their size and spatial distribution. Furthermore, it is known that the vegetation growing on sand dunes is an active agent that modifies dune mobility and sand distribution in a desert area, ultimately leading to an inactive sand landscape. This work addresses three crucial problems related to aeolian sand transport, barchan dune fields and vegetated dunes. First, what are the phenomenological parameters behind our sand transport model, and how they are related with the physical properties of the system. Second, how are barchan dunes distributed over desert? Which factors determine the size and spatial distribution of dune fields? And, third, how can vegetation deactivate a barchan dune? Which conditions are behind this inactivation process? As a result, we were able to extend the phenomenological parameters of our sand transport model to different physical conditions, such as under water or in the Mars atmosphere. We found that the size distribution of barchan dune fields is log-normal and dunes are regularly spaced. Therefore, barchan dune fields are fully described by the mean dune size, the standard deviation and the inter-dune spacing. Furthermore, these properties are not independent but are related by a simple constitutive equation and are dynamically selected by the upwind boundary conditions in the dune field. Finally, we found that active barchan dunes are transformed into inactive parabolic dunes under the effect of vegetation growth. This inactivation process occurs if the fixation index, a parameter fully determined by initial conditions, is below a critical value. This is a simple condition that leads to the first quantitative solution of the crucial dune inactivation problem.