Complex sentence: For reasons of engineering and safety, Mulwray opposes the dam that Cross and the city want, arguing he will not make the same mistake as when his previous dam broke, resulting in the deaths of hundreds.
Split into simpler sentences: For reasons of engineering and safety, Mulwray opposes the dam that Cross and the city want to build. Mulwray says he will not make the same mistake as when he built a previous dam, which broke, resulting in the deaths of hundreds.