Wilpattu National Park natural sand basins (Villus): rainwater drainage and salinity balance?
What unique hydrological processes sustain the freshwater cores of circular geological sand basins (Villus) across the Wilpattu limestone plateau?
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3 Answers from travellers
Wilpattu’s landscape is characterized by circular, shallow natural depressions called Villus, formed through karst sinkhole collapse in underlying Miocene limestone. These basins have no surface river inlets or outlets, functioning on localized rainwater catchment. Coarse red-brown latosol sands filter rainwater into a buoyant freshwater lens resting atop deeper brackish groundwater. While central water remains potable for wildlife, peripheral muddy margins accumulate evaporative salts, creating varied salinity zones that attract different bird and mammal species.
Safari jeeps must remain on the high sand perimeter track; driving onto the moist salt-grass margins causes severe ruts and sinks vehicles in sub-sand mud.
Villu margins feature specialized halophytic sedges and aquatic grasses that provide high-protein grazing for large herds of spotted deer and sambar.
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