Durban's Sand Pumping Scheme
The Sand Pumping Scheme is operated to provide about 280 000 cubic metres of sand to the beaches every year (equivalent to the amount of sand eroded from the beach annually). Any sand over and above that quantity which is pumped onto the beaches will aid in regaining beach width lost in previous years.
The sand used for the scheme comes from the Dredging Services (Portnet) dredger, whose prime function is to maintain the harbour entrance. The dredger removes sand from the sand-trap area mentioned earlier and discharges about two in three of the 2 500 cubic metre loads into a Council owned concrete storage hopper near the North pier. The sand is subsequently re-dredged from this hopper by means of equipment housed on a mobile bridge which injects water from a nearby jet water station into the sand to loosen it, sucking it up and pumping it to the first booster station.
From there the sand/water mixture can be boosted to four other stations along a pipeline which runs northwards as far as the Somtseu Road stormwater outfall. Along the route, the four booster stations maintain pressure, and the sand can be discharged onto the beaches from any one of a number of outlets situated along the beachfront from Addington to Bay of Plenty beaches.
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The booster stations are approximately 700 m apart and the pumping main is a HDPE pipe of 400 mm OD Class 6. The system has been designed to deliver a maximum concentration of 30% by volume. The total length of the pumping main is about 3,5 km and the entire scheme is automated and controlled from the hopper site. The power and signal cables run along the beach along the same route as the pumping main. The Dredging Services dredger delivers about 2 500 cubic metres of sand into the hopper, which has a total capacity of 5 000 cubic metres at a time.
The quantity of sand received into the pumping scheme depends on the weather, so in extremely rough conditions no dredging can take place at all, and on the availability of sand in the sand-trap. In addition to the sand received from the maintenance dredging of the sand-trap area, the dredger is also chartered by the Council to provide additional sand by dredging from off-shore and placing into the hopper.
The sand-pumping scheme was completed in 1982 and up to the end of December 1993, has already delivered 2,500,000 cubic metres of sand to the worst affected areas. This quantity is in addition to an initial fill of 650,000 cubic metres of sand pumped directly to the beaches in 1982 as a one-off contract with an international dredging company.
For further information contact the Coastal Stormawater and Catchment Management Department on telephone +27-31-311 7332. |
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