Coast KZN


Estuary Mouth Status

Estuary mouth state is an important component of estuary monitoring, providing information about other estuary attributes such as estuary water levels and interaction with the marine environment.

Eighty percent of our KZN estuaries close for various periods every year and are classified as Small or Large Temporarily Closed systems. Even small connections with the ocean can facilitate important processes such as larval exchange into the estuary, where animals such as estuary-dependent fishes and invertebrates can grow in these sheltered environments. This can happen even when an estuary is closed.

The four main conditions that are recorded for mouth state are 1) 'Open' : the estuary is fully open and subject to daily tidal movements 2) 'Overwashing' : the estuary is closed and the sea washes into the system 3) 'Closed' : the estuary is closed and no exchange of water occurs over the mouth sandbar 4) 'Overtopping' : the estuary is closed and full, and estuary water is periodically washing over the mouth sandbar.

Capturing changes through ground or air-based monitoring allows us to identify unusual mouth dynamics that assist with estuarine management. Every estuary has a unique natural breaching cycle, occuring seasonally or after large events such as heavy rains or sea storms. Each estuary is adapted to this cycle and artificial manipulation of the mouth state, by opening or closing a system, will critically change the ecology and influence the resources and services offered by that estuary. Artificially opening a system without permission is an illegal offence and must be reported to the authorities.

The following images show different mouth states.

The following Story Map is a geo-spatial tool providing historical and current mouth status data for KZN estuaries from a variety of sources, through various time scales.

KZN Estuary Mouth Status Story Map



Research Funders



Fiona MacKay •Bronwyn Goble • Clare Pillay • Tshegofatso Ramohlale