It is a very good point Rob, we keep on draining upland moorland and marshes, I might be wrong and this is just my opinion, but these areas of land act as sponges for rainfall, holding the water from flowing as speedily into the rivers. As we drain these tracts of land, generally to build houses on, then the water is not slowed down at all..
I'm afraid this suddenly trendy idea of blocking up streams to pre-waterlog land is a complete red herring so far as preventing flooding is concerned.
How anyone can think waterlogged land is going to hold more water defies logic.
If you lower the water table by draining an area, it can soak up water until it is waterlogged - then it just runs off.
Putting logs in streams seems like an excellent way to ensure masses of debris go downstream and block up any bridges along teh way.
The small area which might conceivably retain a bit more water alongside an upland stream is ridiculously small compared to the amount flowing down anyway.
In some locations a large balancing reservoir might help especially in summer flash flood events.
When it rains day after day like now they will just fill up and stay full, almost no help at all but very costly.
The correct way to minimise flooding problems is:
a) Don't build on areas which flood!
b) Maintain watercourses properly to maximise flow rates, and keep the water table lower so land can soak up water rather than almost immediately reach capacity.
c) Consider bold new drainage projects such as storm channels, to take peak flows away more directly.