Many many moons ago when on a hire boat we moored further towards Brundall but could see these moorings (as we thought) in the distance. We sat there as the tide went down and were horrified to see all along the river bits of tree root etc appearing and realising that that could be under us , we moved. We were moored against a quay heading albeit a metal one but we still moved. As has been said up North it is ok to moor on informal moorings , making sure that you are not over tree roots etc, but darn Sarf it is a different ball game.