Complex sentence: The Rivers Aire and Calder are more southerly contributors to the River Ouse and the most southerly Yorkshire tributary is the River Don, which flows northwards to join the main river at Goole.
Split into simpler sentences: The Rivers Aire and Calder are more southerly contributors to the River Ouse. The most southerly Yorkshire tributary is the River Don, which flows northwards to join the main river at Goole.