I believe one of the issues with discharging flood water is the silt carried, our local reservoir (grafham water) has a pumping station from the local river but can't run in flood conditions due to the fact that it's running thick brown.
I am mean't to be taking my boat from gt.ouse in st.neots to the norfolk broads but not a chance at the moment, a week ago I was trying to work out the best time to do the tidal section at earith as they had too little water, now I'll be lucky to get under the town bridge.
Been to scotland over the weekend on the train and there was lots of standing water through notts and yorks.