Civil Engineering June 2022 | Vol 30 No 5

Q Q Until the Highbury WTW comes online in 2025, the Thornhill WTW remains the sole source of potable water for the entire Mthatha area. The lack of backup sources of potable water, together with Eskom loadshedding, puts severe limita- tions on planned shutdowns for tie-ins and equipment change-overs. Q Q For the last three years the Thornhill WTW has been dependant on emergency river pumps drawing from the Mthatha River, flowing past the waterworks site due to a ruptured pipeline under the dam spillway dis- charge channel. These had to be kept going at all costs as Mthatha’s water demand could not be fully met with the constrained raw water inflow. Q Q The site was upgraded from its original 20 Mℓ/day output to 60 Mℓ/day in 2005 and to 80 Mℓ/day in 2016. A further 35 Mℓ/day treatment module still has to be constructed to achieve the required KSD PI masterplan capacity of 115 Mℓ/day. Space limitations meant that the original Clear Water pump hall could not be expanded in size. The pumpstation upgrade just completed (designed for the full masterplan capacity) involved refurbishing four 400 kW pumpsets (and replacing rusty delivery pipework) and replacing five 250 kW pumpsets with five 630 kW pumpsets (including major excavations for constructing larger pump plinths in a tight configuration). Being an opera- tional pumpstation with three separate areas to supply, it was necessary for the upgrade to be carried out in several carefully managed stages. A new elec- trical building had to be constructed and equipped before the first two of five new pumps could be installed and commissioned. Only then could the remaining three old pumps be removed, new plinths constructed, and the new pumps installed and commissioned. To Figure 4 Before, during and after photos of the Thornhill WTW Clear Water pump hall 16 June 2022 Civil Engineering Figure 5 Cross connection between rising mains with flow and pressure regulation