Earth, branches, small trees thrown down the river bank

Where GCC just did work on the footpath alongside the Berkeley Pill and installed a fence, to the rear of 41B Lynch Rd. The riverbank is overgrown with brambles. The contractors have put earth, branches, whole trees on top of the brambles. When the river is high this will all be under water. We already have a problem with this river bursting it's banks and flooding property, we're struggling to get this main river riverbank maintained, GCC contractors shouldn't be adding the problem like this by essentially flytipping on the riverbank.