The ground
River gravel · Upper Greensand · Gault clay
Benson is mapped on river sand and gravel — the Summertown-Radley terrace — over Upper Greensand. Ground like this typically drains freely.
On the river side, to the west, Gault clay and river alluvium are mapped within half a kilometre; expect heavier, slower-draining soil there. Soil can change markedly over a short distance, so two gardens in the same village can behave quite differently.
Planning
Benson Conservation Area · Chilterns (part of the parish)
The village centre is in the Benson Conservation Area, and the Preston Crowmarsh Conservation Area is about half a kilometre away. Inside a conservation area, you need to give the council six weeks’ notice before tree work (unless the trunk is under 75 mm across, 1.5 m above the ground), and demolishing a boundary fence, wall or gate may need permission first. It also counts as designated land, so an outbuilding at the side of a house needs planning permission.
Benson itself is outside any National Landscape, but about 29% of the parish is in the Chilterns National Landscape. At addresses there, anything built more than 20 metres from the house — sheds, enclosures, even a pool — is capped at 10 square metres in total without planning permission.