Southampton:

Southampton Water has the benefit of a double high tide, with two high tide peaks, making the movement of large ships easier. This is not caused as popularly supposed by the presence of the Isle of Wight, but is a function of the shape and depth of the English Channel. In this area the general water flow is distorted by more local conditions reaching across to France.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". In addition to its shape, what property of the English Channel affects water flow in Southampton Water?
depth