Complex sentence: It rises at Thames Head in Gloucestershire, and flows into the North Sea at the Thames Estuary via London, the country's capital, where it is particularly deep and navigable to ships; the Thames drains the whole of Greater London.
Split into simpler sentences: It rises at Thames Head in Gloucestershire, and flows into the North Sea via the Thames Estuary. On its way, it passes through London, the country's capital, where the river is deep and navigable to ships; the Thames drains the whole of Greater London.