River Mole River Mole The River Mole is a tributary of the River Thames in southern England. It rises in West Sussex near Horsham and flows northwest through Surrey for to the Thames at East Molesey, opposite Hampton Court Palace. The river gives its name to the Surrey district of Mole Valley. The Mole crosses the North Downs between Dorking and Leatherhead, where it cuts a steep-sided valley, known as the Mole Gap, through the chalk. Much of the catchment area lies on impermeable rock (including Wealden Clay and London Clay), meaning that the river level responds rapidly to heavy rainfall. During
River Mole the Pipp Brook, a tributary draining the northeastern slopes of Leith Hill. Between Dorking and Leatherhead the Mole cuts a steep-sided valley (the Mole Gap) though the North Downs, carving a river cliff on the western flank of Box Hill and a smaller cliff at Ham Bank in Norbury Park. The sudden change from impermeable Wealden Clay to permeable chalk and the increased gradient of the river (which drops in the stretch between Brockham and Leatherhead, compared to in between Horley and Brockham) allow the water table to drop below the bed of the river. Water is able to flow