Complex sentence: A second embankment, 3.5 km upstream was completed in 1923 to form the Upper Reservoir which has a capacity of 5.6 billion litres and a maximum depth of 13.4 metres.
Split into simpler sentences: A second embankment, 3.5 km upstream, was completed in 1923 to form the upper reservoir. This has a capacity of 5.6 billion litres and a maximum depth of 13.4 metres.