Some areas of Hull lie on reclaimed land at or below sea level. The Hull Tidal Surge Barrier is at the point where the River Hull joins the Humber Estuary and is lowered at times when unusually high tides are expected. It is used between 8 and 12 times per year and protects the homes of approximately 10,000 people from flooding. Due to its low level, Hull is expected to be at increasing levels of risk from flooding due to global warming.