Stand with your back to the river, and look around. What you see will have a huge impact on the river.
The catchment — especially the geology, topography and land use — is fundamental to the river.
For example, the River Itchen in Hampshire is a chalk stream. The underlying rock is chalk and it is fed by spring water. The gradient is low and the river flows gently through water meadows, arable fields and urban areas. The Itchen is a low energy river, with moderate flows and the water level doesn’t vary much through the year, nor does it change course very much over time. Plants can thrive in the river and on the banks.
It is very different to the River Usk in Wales which is rain fed, with it’s headwaters in the Brecon Beacons. Here there are steep gradients and sandstone rock, sheep pasture and coniferous woodland. The upper River Usk is fast flowing and ‘spatey’ — when it rains, the river rises rapidly to become a brown torrent and in summer it can have very low flows. It is a high energy river, changing it’s course by eroding banks and depositing sediment. It has few plants in the river and bankside trees can be removed by floods and deposited in the channel.