Durban - Authorities are scrambling to open the uMngeni River mouth at Blue Lagoon after erosion caused a sandbank to form, while high seas and a “king tide” battered the KwaZulu-Natal coastline on Wednesday.
The entire central Durban beachfront was lashed by heavy waves that damaged the promenade. Dairy Beach was hard hit, with concrete capping on the promenade barrier flipped on to the walkway, underground pipes exposed and the promenade’s foundation exposed by the force of the sea.
New Pier was closed for safety reasons.
More than a metre of sand was washed away from the shoreline embankment in places and sand art sculptures were swept away.
Contract sweepers, hired by the city council, battled to clear the sand from the promenade outside the Rachel Finlayson pool.
Officials used excavators to try to remove a sandbank that had formed at the uMngeni River mouth. Wildlife experts are concerned that the rising water could damage nearby mangrove swamps.
The river mouth became blocked last weekend, preventing water from entering or leaving except during high tide. Yesterday sand was pushed up on to the promenade at Blue Lagoon.
Municipal authorities had hoped the powerful tides would erode the sandbar overnight.
Another attempt to remove the sand was set to take place this morning.
eThekwini Municipality spokeswoman, Tozi Mthethwa, said the heavy seas had pushed an “abundant” amount of sand up the beach to form the sandbank.
“The sandbank is not beneficial to the river because pollutants are not flushed out to sea and dispersed. Ezemvelo KZN Wildlife is concerned about the health of the mangroves and associated fauna which will stress under periods of prolonged closure,” she said.
“They also believe the current rain combined with this week’s high tides may favour natural breaching. Ezemvelo wanted to be proactive and artificially breach the system should it not open naturally over the next few days.”
She said the mouth was recently breached with an excavator before low tide to save the model yacht pond and part of the Windsor Golf Club from flooding.
Durban North resident, Colin Naidoo, said he was at the river mouth at 11.30am on Wednesday when a city excavator arrived from the mangrove swamp area.
“The excavator attempted to dig out the sandbank, but failed because of the high seas and soft sand. A short while later, another excavator with a front and back scoop arrived to assist. It too began sinking. Both machines were taken away. The trench they dug kept washing away,” he said.
At the river mouth, litter, plastic bottles, branches, and a massive tree piled up along the rocky embankment. Upstream, a popular fishing and picnic spot, the river water flowed over the embankment into the Blue Lagoon pool.
The water covered a vast area, closing off part of the promenade.
Marine ecologist, Mahomed Desai, said he had received a report from the municipality of the build-up of sand.
According to a study by the eThekwini River Health Programme (RHP) in 2005, the river is a permanently opened estuary. The Beachwood mangrove, according to the RHP, represents the fifth largest in South Africa. The system supports some 24 species of invertebrates.
On Sunday, a Daily News team saw people walk from Blue Lagoon pier across the sandbank to the mangroves. This morning the river and ocean were separated by a bank about 50m wide.
Mthethwa said people could walk across the sandbank safely, if there was no chance of breaching.
University of KwaZulu-Natal marine expert, Dr Deborah Robertson-Andersson, said waves came under the “gravitational pull of the moon”.
During the new moon (or spring tide) when the sun, Earth and moon lined up, “higher high spring tide” occurred.
The new moon period began on January 20 just after 3pm, according to lunar charts.
This combination of the new moon (which is closest to the earth in its orbit) and the presence of a high tide and storm on Wednesday all led to the high waves and consequent destruction, she said.
The new moon, when it is closest to Earth, coupled with the advent of the spring tide, is referred to colloquially as a “king tide”.
“The power of the wave is its height cubed, meaning that if there is even a 2cm increase in height, the wave will be eight times as strong,” she explained.
eThekwini climate protection scientist, Lisa Smith, said the time between waves was important as it increased the wave height and energy as the swell moved into shallower water.
“The swell has lifted and we are on spring tides, with a high of 2.07m at 3.51pm (on Wednesday). The swell is easterly and predicted to be sustained over the next couple of days, although I suspect it may drop off as the cold front moves eastward,” Smith explained.
Smith warned that there would be a number of above-average tides this year.
Daily News