Construction World December 2021

CPUT RETENTION POND D uring the drought in 2017, the Cape Peninsula Univers i ty of Technology (CPUT) Bel lvi l le Campus announced that al l thei r exi st ing green spaces were being i rrigated wi th recycled water that i s col lected and pumped into an on-s i te lake. In August 2020 – to comply wi th Ci ty of Cape Town’s by- laws and regulat ions for storm-water management - thi s lake was extended and upgraded to increase the capaci ty of the exi st ing retent ion pond as wel l as refurbi sh the exi st ing out let and inlet structures . The capaci ty of thi s pond i s now greater than ever and has been improved in terms of aesthet ics and funct ional i ty, so that the campus can deal wi th flooding and drought al ike. Says Douglas Curran, CPUT’s Chief Hort icul turi st : “I t ’s been nearly 30 years s ince the treated ef fluent water i s used to i rrigate the sport fields and thei r drainage system col lects the water and sends i t to the campus’ lake which pumps i t back to the dam. The i rrigat ion system ends up us ing the same water five t imes .” A retent ion pond (or wet pond) i s a man-made reser voi r – bui l t in lower land areas that tend to accumulate excess water - that i s des igned to catch storm-water f rom higher elevat ion areas , to give that water a place to go, where i t can be concentrated and contained. Thi s prevents eros ion and foundat ional i ssues in the immediate surroundings , as wel l as reduce the ri sk of flooding. Retent ion ponds also aid in the removal of pol lutants , such a fert i l i sers , oi ls , petroleum, and animal droppings f rom the stormwater runof f : the algae, bacteria, and other biological organi sms in the water consume the pol lutants , eventual ly puri fying the water to a large extent . Westcoast Retaining Systems , Terraforce Recommended Contractor, was contracted by Ruwacon, a leading construct ion company in Southern Af rica (51% black ownership and a 9GBPE rat ing f rom cidb) , to instal l the Terraforce L12 interlocking retaining blocks along the edges of the pond. Says Hannes Mostert , Westcoast Retaining Systems :

PROJECT INFORMATION

• Company entering: Terraforce • Project start date: August 2020 • Project end date: February 2021 • Client: Cape Peninsula University of Technology • Main Contractor: Ruwacon • Subcontractor: Westcoast Retaining Systems • Consultants: KFD Wilkinson Consulting Engineers • Terraforce Block Supplier: Klapmuts Concrete

“The exi st ing pond was los ing a lot of water, and that i s why CPUT decided to bui ld a 420 m long retaining wal l around i ts ci rcumference. The blocks were instal led on a 750 x 300 mm, 25 Mpa concrete foundat ion, wi th drainpipes running behind the ent i re length of the wal l . Al l blocks were concrete fi l led for extra stabi l i ty. In some places the wal l had to be bui l t higher to accommodate some big trees growing along the pond boundar y, to protect thei r roots f rom too much water ingress .” Albert Botha, Contracts Manager, Ruwacon, says that i t was di f ficul t wi th rain, sludge, and ground water seepage to get the pond to the new des ign levels for instal lat ion: “The sludge wi thin the pond and wi th the reducing of levels during construct ion made i t di f ficul t to instal l the concrete foundat ion upon which the Terraforce blocks were instal led. We had to instal l a concrete stone pioneer layer before the concrete could be cast . The cast could also only be for short lengths . A pump had to be run a lot of the t ime during instal lat ion to keep the water at bay”. Once these chal lenges were overcome, the verges of the pond were grassed, and a fami ly of ducks introduced to the area. Vi sual ly the pond now showcases a lush, green, and peaceful sett ing that students and animals can enjoy al ike. On a funct ional level , leakage i s curbed, and more water wi l l be avai lable for future water shortages . 

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20 th Best Project Awards 2021