3. Northwest Division

The tropical northwest Australian coast grades from hot desert in the south to monsoonal in the north and the geology from the ancient Pilbara Craton to the Carnarvon and Canning sedimentary basins. Tide range increases northwards from meso to mega and waves are predominately low to moderate seas which are further reduced by the shallow shelf and nearshore and an island and reef studded inner shelf. Coastal sediments are a mix of shelf carbonate and terrigenous material, the latter delivered by usually dry rivers which flood following tropical cyclonic rains and which have aggraded the coastal plain and deposited deltas at the coast. The climate and carbonate-rich sediment have combined to lithify the low linear Pleistocene barriers and barrier islands which dominate parts of the coast. The predominately southerly waves and flooding tides drive a northerly sediment transport which is interrupted by numerous hard obstacles and tidal creeks and rivers. The beaches are predominately tide-dominated with extensive tidal flats and the barriers a mix of regressive beach-foredunes and limited dune transgression.