Bar

in hydrography, a bank of sand, silt, etc., opposite the mouth of a river, which obstructs or bars the entrance of ve els. The bar is formed where the rush of the stream is arrested by the water of the sea, as the mud and sand suspended in the river water are thus allowed to be deposited. It is in this way that deltas are formed at the mouths of rivers. The navigation of many streams is kept open only by constant dredging.