Complex sentence: Once the barges have travelled 30 miles downstream from Tower Bridge, mechanical cranes at Mucking Wharf unload the distinctive yellow containers onto trucks that make their way up the mound that has been created artificially by decades of garbage that towers over the surrounding flat landscape.
Split into simpler sentences: Once the barges have travelled 30 miles downstream from Tower Bridge, mechanical cranes at Mucking Wharf unload the distinctive yellow containers onto trucks. The trucks make their way up the artificial mound created by decades of garbage compaction that towers over the surrounding flat landscape.