Friday, March 09, 2007

St Lucia mouth wide open

THE Lake St Lucia mouth which breached last Friday has widened to about 110m.By Tuesday the Narrows water levels had risen by 10 cm at low tide to 70 cm at high tide above what it was prior to the breaching of the mouth.Salinity varies from just below that of sea water at 34 ppt (parts of salt per thousand) near the mouth to 30 ppt at Potters Channel (measured on the morning of 5 March).Much of this incoming seawater is moving up the Narrows and is flowing over the natural ‘spillway’ at Makakatana into Catalina Bay.There has not been a large increase in Lake water levels as the water is spreading out over a large surface area, according to a Wetland Park Authority press release.It is expected that the lake will continue to fill over the next six weeks, to an equilibrium level which will be a bit lower than mean lake level.This will be mainly seawater with a salinity concentration of over 30 ppt throughout.Quantities of sediments have also been brought into the estuary over the past four days.As a precaution against this sort of event, Park managers had dredged a sediment trap. While significant quantities of this sediment have been trapped during peak tides when the current is flowing strongly, sediment would have passed over the trap.The inflowing seawater is expected to bring more sediment over the next several weeks.The situation is dynamic and will continue to be monitored closely by Park ecologists and managers over the next few weeks.

Artical by Zululand Observer

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