No. If the river bed is below sea level, dredging it deeper will make no difference to the flow, Raising the banks will, providing they are raised to a height above sea level, allow the level of the river to be higher and increase the river capacity and flow
I believe dredging could help in some areas and make things worse in other areas. It neets clever people indeed to work out what to do and where
The truth of this whole problem is the phenominal amount of rain, wind direction rising seasonal high tides (sea level) even higher, modern ideas on building drainage farming etc., and nobody realising what would happen when all this accumulated. Where was the "Visionary" we needed? Ah yes, I remember his plans now,. "Build a big Ark"