Model for a dune field with an exposed water table

Aeolian transport in coastal areas can be significantly affected by the presence of an exposed water table. In some dune fields, such as in Lençَis Maranhenses, northeastern Brazil, the water table oscillates in response to seasonal changes of rainfall and rates of evapotranspiration, rising above the ground during the wet season and sinking below in the dry period. Understanding dune mobility in an environment with a varying groundwater level is essential for the study of long-term evolution of many dune fields. Here we apply a model for aeolian dunes to study the genesis of coastal dune fields in the presence of an oscillating water table. We find that the morphology of the field depends on the time cycle, Tw, of the water table and the maximum height, Hw, of its oscillation. Our calculations show that long chains of barchanoids alternating with interdune ponds, such as those found at Lençَis Maranhenses, arise when Tw is of the order of the dune turnover time, whereas Hw dictates the growth rate of dune height with distance downwind.