I've been talking with my neighbour whose lived in his cottage for almost 50 years and says he doesn't recall ever seeing the dykes as low as they are at the moment. He reckons it's because "they" have opened sluices a little way down river in order to flood the fields. I'm not sure if that means the Broads Authority or Environment Agency.
I have always said that the dyke water level goes up and down at a surprising rate while the lake is much slower to adjust. I hadn't realised that the reason the dyke level changes so dramatically is less to do with the weather and is almost entirely to do with human intervention.