Poole Harbour catchment
Four main rivers feed into Poole Harbour: the Dorset Frome and the Piddle, and the smaller Sherford and Corfe rivers. The catchment drains 820km2 of picturesque, mostly rural land, and is home to a number of internationally recognised chalk streams.
The catchment has mixed geology with older clays and greensand in the North West underlying less permeable soils, producing streams which rise and fall quickly in response to rainfall. A broad chalk belt crosses under much of the catchment which holds a large groundwater aquifer that provides drinking water to the population.
Younger clays, gravels and sands lower in the catchment sit beneath well-drained soils across Purbeck. The southern catchment boundary is dominated by a steep ridge, which separates the rivers that feed to Poole Harbour from the coastal streams that drain directly out to the sea.