A delta forms over time when a river carrying sediment meets slow moving or stagnant waters at its mouth and deposits the sediment to form landmass. Look at the topography of South Africa: (Source: Wikipedia). read more
River deltas are found on the lower reaches of rivers, where the flow of water spreads out and slows down, depositing sediments into expanses of wetlands and shallow water. There are tow types of deltas: coastal deltas where the river meets the sea and inland deltas where the river fills extensive floodplains and marshes. read more