CROSS-CHANNEL MIXING AND ITS EFFECT ON SEDIMENTATION IN THE ORINOCO RIVER

At high discharge, cross-channel mixing of water in the Orinoco River main stem requires several days and up to 500 km of downriver transit for completion. During mixing, substantial amounts of less than 0. 063 mm sediment are lost from suspension. The water closest to the left bank appears to lose the most, probably by deposition onto the floodplain. This occurs in two ways. First, sediment-laden left-bank tributaries draining the Andes, such as the Apure, deposit sediment in distributary systems following impoundment by the Orinoco backwater. Second, when sediment-laden waters from the Andes actually join the Orinoco, the slow nature of cross-channel mixing causes the water and sediment to be confined more to the left side of the channel.