Small sand particles play havoc at uShaka

SIZE does matter, and it’s costing uShaka Sea World R1.6 million to get it right to keep its sea life alive.

It’s all down to the nittygritty of the sand being pumped on to Durban’s beaches.

The composition of the sand – which acts as a filter for feeder pipes that suck in much-needed seawater to flow through the tanks – has changed, with smaller granules allowing less water into pipes sunk 6m under the sand.

“In the past six months, we increased the number of times we backwashed and air lanced (pumping compressed air into the pipes),” said Sea World director Tony McEwan, explaining how the organisation realised the composition of the sand had changed.

Sand dumping is a municipal function.

“Our water supply is essential,” McEwan said, likening the open water aquarium to a “fish sewage farm”.

“Like any feedlot or chicken farm, an important thing to do is to get rid of the waste. Fish release ammonia, which is toxic and highly soluble.

In the ocean, a fish would be able to swim away from it, but in a tank it bumps back into it.

“It’s important that we keep the water clean for the fish, and clear for the public to be able to see the fish.”

The pipes under the uShaka Pier bring 350 000 litres of water an hour into the aquariums and, when the flow dropped to only 160000 litres, it prompted the need for remedial action.

From Monday, a team will pull up their sleeves to replace this unsuitable sand with presized river gravel made up of granules of 2mm to 6mm.

They will have to access their work from manholes in the pier through the floor of uShaka’s Moyo restaurant (on the pier), which has had to dismantle its ground floor and will be temporarily closed for 16 weeks.

The main restaurant at uShaka will remain open, though.

“They are going to be waving big pipes around this area,” said McEwan.

A reduced water supply will, meanwhile, keep marine life going in the exhibits.

“We could kill the place very quickly if the system had to stop and there was no back-up,” said McEwan.

“It has to run 24/7 and every day of the year.”

McEwan said the pier was designed to need periodic sand replacing, “something we haven’t done since about 2008”.

Maintaining the size of the sand granules around the pipes was a balancing act, he said.

“The finer the sand granules, the more waterborne particles it takes out, but the more difficult it is to take in water.”

For every 350000 litres that enter uShaka Sea World every hour, the same amount leaves via canals in the Durban Point Development Company area.

“We have an understanding with them to keep the canal fresh.”

In fact, it’s cleaner than the water that comes in, having been through further filtering in the system.

At the time of going to press, eThekwini Municipality had not commented on what was behind the regime change in sand dumping.