Complex sentence: High-tide in the River Mersey had been about 11:15 pm and the East Float was full of water, at around 12:25 am the foundation of the coffer dam gave way without warning, the fifteen workers were overwhelmed by water and debris.
Split into simpler sentences: High-tide in the River Mersey had been about 11:15 pm and the East Float was full of water. At around 12:25 am the foundation of the coffer dam gave way without warning; the fifteen workers were overwhelmed by water and debris.