the basin runs in a broadly south-west to north-east direction, with an extension to the north around the west glen and east glen rivers. the underlying geology consists of lias clays at the western end of the catchment, with lincolnshire limestone in the centre, including the valleys of the glen. the eastern third is mostly alluvial soils, and it is this part that relies on artificial pumping to prevent flooding. rainfall over the area varies between per year, which is quite light, and because the land is efficiently drained during the winter months, there are few reserves, making the area prone to drought in the summer months.