This map shows the appoximate outline of the catchment area which feeds into the measuring station at Rickmansworth. All the rain which falls onto the blue area, that is not absorbed into the soil or evaporated, will eventually flow to the sea via Rickmansworth.
This local monitoring station catchment area is contained within the Colne management catchment area.
Acknowledgement: Data from the UK National River Flow Archive. Used under the terms of the NRFA Data Licence.