We were broads moorers/boaters/dwellers for 17 years. It's mainly down to atmospheic and weather conditions. All of the navigable broads system is tidal, low pressure allows the sea level to rise so up come the rivers, northerly wind piles up the north sea against the netherlands, Belgium and Kent/Essex so the sea level comes up and the rivers respond. The recent rainfall is also a factor but usually the least of the three. Extremes of these factors caused those awful 1950s floods.
We've seen 50 litre drums loaded onto boats to fill with water for ballast, crowds of people on boats, anything to try and get them through. When Belaugh boats were in operation and couldn't gety their boats through Wroxham Bridge they would turn round their boats at Royall's in Hoveton (but then they were family.
I once took Grebe through Potter Bridge with 6 ft on the gauge - that was tight.