The River Severn (UK)
Its source is in the mountains of Mid Wales. The mountain is called Plynlimon (where it rains every two days out of three) and can be seen in the image below.
The Forestry Commission manage much of the upper catchment with coniferous plantation. Interception rates will be significant throughout the year as the pine needles remain on the trees during the winter months.
The River Severn is the longest river in Great Britain. From its source in the mountains of Mid Wales, to its estuary in the Bristol Channel it is 354 km long.