My first thoughts. It looks to me as though the capping stones have gone. A panel, of ply, or something similar, would have been held by pressure against the piling and stopped most of the flow before the flow washed away more of the bank leading to a more serious breach. Then a slightly better fix, e.g. Tracy’s sandbag or Tony’s wheelbarrow, while they lowered the level of the pound.
Would that have stopped a major breach? As I intimidated at the start of this thread, a lengthsman would have prevented it, someone in an office scratching their head and wondering who to ask to get the risk assessment done shows the lack of basic understanding we are lumbered with now.