Hydrology
Hughs Dale Waterfall
Most rain percolates through the soil and limestone and surface runoff only occurs after heavy rain. A few perennial streams flow at the Dales, Ross Hill Gardens, The Ravine, Jones Spring, Freshwater Spring, Dolly Beach, Hosnie's Springs and Waterfall. Underground water accumulates at the interface of limestone and the underlying volcanic rock strata. Here it either flows along the interface, as in the case of the flow system from Grant's Well through Jedda Cave and Jane-up beyond, or flows down fractures in the volcanic rock. The flows along the limestone-volcanic rock interface emerge in some places as springs. There is evidence of a freshwater lens floating on top of underlying seawater and flows just above sea level from some of the cave systems on the Island which are thought to be the outflows from the edges of such a lens.