Nooitgedacht Low Level Water Supply Scheme achieves ‘first water’

Nooitgedacht Low Level Water Supply Scheme achieves ‘first water’

Aerial view of the Nooitgedagt WTW

Nooitgedacht Low Level Water Supply Scheme achieves ‘first water’

The Nooitgedagt/ Coega Low Level Supply Scheme (NCLLS) increases the supply of treated water (sourced from the Gariep Dam) from 70 Mℓ/day to 210 Mℓ/day for Nelson Mandela Bay Municipality (NMBM). The first water flowed through the new Phase 3 module on 31 March.

By Kevin McRae

At first, the NCLLS was to be implemented as a single project under multiple contracts; however, due to funding constraints, the scheme had to be implemented in phases. Phase 1: On completion (1993), Nooitgedagt Water Treatment Works (WTW) had a capacity of 70 Mℓ/day and a hydraulic peak capacity of 84 Mℓ/day. A fourth pump was added to the pump station, boosting pumping output to 92 Mℓ/day with three pumps operating and one pump on standby. In 2008, two additional pulsator clarifiers were built, increasing the capacity of Nooitgedagt WTW to 100 Mℓ/day. Additional sludge lagoons and a 10 Mℓ balancing reservoir at Olifantskop Farm were constructed. There was also the implementation of bulk electrical supply to the WTW, and the rising (1 200 mm) and gravity (1 400 mm) mains from the WTW to Motherwell and the Coega Industrial Development Zone (IDZ). Phase 2: This included the low-lift pump station building, as well as the construction of the western bank with six additional filters, and pumping equipment, electric and control systems for the low-lift scheme. Phase 3: This comprised a complete stand-alone 70 Mℓ/day treatment module at Nooitgedagt WTW, a 45 Mℓ balancing reservoir at Olifantskop Farm, installation of cathodic protection systems on both the original Nooitgedagt to Motherwell highlevel pipeline and the low-level pipeline built under Phase 1. The building of various bulk pipelines and rehabilitation of structures, as well as the replacement of certain valves and fittings on the Motherwell to Chelsea pipeline were also included.

This is the last significant milestone for the Nooitgedagt/Coega Low Level Supply Scheme project that commenced with construction in 2010.

Interestingly, the original scheme was also built under emergency drought conditions. Back then, while Nooitgedagt WTW was under construction, the Grassridge Reservoir was used as an emergency treatment works where settling and chlorination took place. In order to maximise the water supply to NMBM while Phase 3 was under construction, the Grassridge emergency treatment works was again put into use and upgraded with improved treatment and chlorination systems.

NCLLS PROJECT PARTICIPANTS

Client: Nelson Mandela Bay Municipality Funder: DWS and NMBM

Implementing Agent (Phase 3):

Amatola Water Lead Consultant: AfriCoast Consulting Engineers WTW and Reservoirs: AfriCoast Consulting Engineers

Rising Main and Pump Station M&E:

iX engineers Gravity Main: Manong & Associates

Geotech and Environmental:

SRK Consulting WTW Electrical and Electronic: CA du Toit Eastern Cape Cathodic Protection: Pipe & Tank Africa Quality Assurance: QPI

Once excavations were completed for the new filter block and clear well, groundwater appeared

Pile caps and ground beams below filters Kevin McRae, COO, AfriCoast Consulting Engineers

Nooitgedacht WTW – design

Sited on the right bank of the Sundays River, Nooitgedagt WTW is supplied with raw water from the Scheepersvlakte Balancing Dam on the left bank via 9.1 km of 1 470 mm diameter gravity pipeline. It is now the largest water treatment works serving NMBM.

The water treatment process at Nooitgedagt is conventional, comprising chemical dosing, flocculation, settling, filtration and disinfection, followed by distribution. Ultraviolet treatment is added between the settling tanks and filters to guard against Cryptosporidium and Giardia.

Designed as a zero-effluent works where dirty backwash water and settled sludge supernatant is collected and recycled, Nooitgedacht WTW can achieve water savings of up to 10.5 Mℓ/day.

In Phase 3, conventional gravity tanks replaced the pulsator-type settling tanks used for the first two phases, allowing Phase 3 works to operate during off-peak electrical usage times, providing additional cost savings.

The WTW operates at full capacity during offpeak times with both the high level and low-level pumps running, while the new eastern Phase 3 module can be stopped and only the low-level pumps run with the original western modules during off-peak electrical demand.

The new setting tanks were designed to accommodate the new Phase 3 module that can be switched on and off without compromising treatment capacity or efficiency. The raw water has a fairly high suspended solids load that is easily settled and, therefore, bottom-entry, horizontal-upflow settling tanks fitted with lamella packs were provided. Hoppers below the lamellas collect settled sludge, which is drawn off via timer-actuated valves controlled by means of a PLC.

During the design stage for Phase 2, the decision was taken to fit the filters with dual

A D V A N C E D W A T E R P R O D U C T S

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First water passing through the Phase 3 filters

lateral underdrain systems. This decision was carried through to Phase 3 with the original six filters also refurbished with dual lateral underdrain systems under the Phase 3 contract. This filter system has proven to be up to 30% more efficient than the older false floor and nozzle systems previously used on NMBM water treatment plants.

Integration with the NMBM bulk water supply system

The NMBM bulk water supply system is a complex system of interlinking supply sources.

The Chelsea Reservoir to the west of Port Elizabeth, which supplies large parts of the metro, has historically always been supplied from Loerie WTW, which receives raw water from Kouga Dam.

The Churchill/Elandsjagdt system supplied from the Churchill and Mpofu dams, respectively, supplies water to the southern and central parts of Port Elizabeth via the Seaview, Emerald Hill, Driftsands, St George’s Park and Glendinning reservoirs, among others.

Recent completion of the Gamtoos Booster Pump Station allows water from the Churchill pipeline to be lifted into the Summit Reservoir close to Loerie, from where it gravitates to the Chelsea Reservoir. There is also a connection between the Seaview Reservoir, fed from the Churchill pipeline via the Seaview pump station, and the Chelsea Reservoir.

The Nooitgedagt High and Low Level schemes deliver potable water to the Motherwell Reservoir. An offtake on the High Level Scheme just before this reservoir connects to the Chelsea Reservoir to the west of Port Elizabeth, which has the same top water level as the Grassridge Reservoir. Booster pump stations

CONTRACTORS

Phase 1

- WK Construction (WTW civils, 10 Mℓ reservoir and booster pump stations) - Cycad/Stefanutti Stocks JV (rising main) - Scribante Construction (gravity main)

Phase 2

- Ruwacon (WTW civils and building) - PCI Africa (WTW M&E) - Hidro-Tech Systems (pump station M&E)

Phase 3

- Stefanutti Stocks (all works)

at Motherwell and Stanford Road boost the pressure in the link pipeline, allowing water from Nooitgedagt to be delivered into the Chelsea Reservoir, from where it is distributed to large areas of the metro.

A number of offtakes between the Motherwell and Chelsea reservoirs feed smaller supply reservoirs serving areas such as Bloemendal, Bethelsdorp, Linton Grange, Despatch and Uitenhage.

The Motherwell Reservoir supplies the Markman industrial area as well as the

Settling tanks under construction, with floc channels in foreground

Clearwater pipeline to pump stations

Coega IDZ and Sundays River/Colchester via the Coegakop Reservoir.

The pipeline between the Olifantskop and Motherwell reservoirs has an offtake to the Coega IDZ boundary that is not yet connected to the Coega supply zone.

Conclusion

Since first water was achieved, Nooitgedagt WTW has been supplying on average approximately 190 Mℓ/day of purified water to Nelson Mandela Bay. Final completion of all outstanding work is scheduled for July 2022. Items remaining include roofing over the filters, backfilling and shaping, and finalisation of the Scada system for the entire WTW, including incorporation of the previous phases. Without the Nooitgedagt supply scheme, NMBM would have run out of water some years ago, with disastrous consequences for all. Nooitgedagt will ensure that NMBM will not run out of water entirely should the western supply fail completely due to the persistent drought and will be able to provide a large portion of the metro with a continued supply of quality potable water, albeit at lesser quantities than current demand.

AfriCoast is very proud to have led the team that successfully delivered this major, once-in-alifetime project. Despite numerous challenges encountered, a high-quality project has been delivered that will provide NMBM with an assured supply of purified water for many years to come.

Refurbished original filter control gallery

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Phase 3 settling tanks in operation