Complex sentence: By the early 80s work had been undertaken to deepen the Knock River channel and the problem was solved, however it then gradually silted up and after several weather events during which there was unusually heavy rainfall flooding has happened at least 6 times since the mid 2000s.
Split into simpler sentences: By the early 1980s, work had been undertaken to deepen the Knock River channel and the problem was solved. However, it gradually silted up and after several weather events during which there was unusually heavy rainfall, flooding has happened at least six times since the mid 2000s.