The Waimakariri River, pictured here flowing over the Canterbury Plains, is a classic example of a braided river. These rivers divide into channels, like the twisting strands in a braided rope. In the South Island they are common, but worldwide they are rare. They carry a lot of sediment, which falls to the river bed as the water flow slows down. As this sediment builds up, other parts of the dry river bed become lower, so water naturally follows the lowest point and the bed shifts. In this way braided rivers are constantly moving across a wide river bed.