Question: Why do rivers rise

Alistair Young answered on 6 Feb 2021:

hi … two main reasons affect river levels. For rivers near the sea tides will change the river levels twice each day as far as the tidal range upstream.
Above that, the river level will change as water runs into it from the catchment area which feeds it. Rain – even in the distant hills – will mean the accumulation of water in the river will raise the levels as it moves downstream. In the recent heavy rains, the towns and cities downstream of the rains were able to prepare additional flood defences to cope with the rise as it took some time for that to run downstream.