Shoal - Harbour and River Bars

Harbour and River Bars

A harbour or river bar is a sedimentary deposit formed at a harbour entrance or river mouth by the deposition of sediment or the action of waves on the sea floor or adjacent beaches. A bar can form a dangerous obstacle to shipping, preventing access to the river or harbour in unfavourable weather conditions or at some states of the tide. Where beaches are suitably mobile, or the river’s suspended and/or bed loads are large enough, wave action can build up a bar to completely block a river mouth, damming the river, preventing access for boats or shipping, and causing flooding in the lower reaches of the river. This situation will persist until the bar is eroded by the sea, or the dammed river develops sufficient head to break through the bar.