Heritage Cases

Alternative 1 (preferred) Alternative 1 includes excavating (with an unmanned tunnel-boring machine) two underground 1.5 meter (m) diameter tunnels into the Mthatha Dam. One is proposed to be located approximately 6m below dam full supply level (FSL), and the other about 13m below FSL. The length of the tunnels is proposed to be about 80m. The two tunnels will connect to an underground New Abstraction Tower Pump Station which will accommodate water of the same level as the dam FSL (693m). Thus, the New Abstraction Tower Pump Station will have the same base as the Mthatha Dam. A 60Mℓ Thornhill Raw Water Storage Basin with a Tail Water Level of 700.5m and Full Level of 693m excavated into the rock alongside the dam is also proposed by the Applicant. A 220 megalitre per day (Mℓ/d) Rising Main will convey water from the New Abstraction Tower to the 60Mℓ Thornhill Raw Water Storage Basin. A 100Mℓ/d Suction Main will convey water from the Raw Water Storage Basin to the Highbury Highlift Pump Station. Associated with the New Abstraction Tower Pump Station, 60Mℓ Thornhill Raw Water Storage and Highbury Highlift Pump Station is: • An access road of about 280m in length and 7m in width; • A mass concrete gravity wall of maximum 4.5m height, constructed along the one side of the 60Mℓ Thornhill Raw Water Storage Basin, in order to reduce the volume of rock that has to be excavated; • A platform for finished ground level, at approximately 697.6 metres above sea level (masl); • A guardhouse of approximately 5m x 6m in extent; and • A security gate within the access road. The New Abstraction Tower Pump Station, 60Mℓ Thornhill Raw Water Storage, Highbury Highlift Pump Station and associated infrastructure will be completely ring-fenced with a razor-mesh fence of approximately 2m high. All other infrastructure (access road) will be fenced with a 1m high fence. Additionally, the Applicant proposes to install a 1 200 millimetre (mm) diameter, 100 Mℓ/d Rising Main from the Highbury Highlift Pump Station to the existing Highbury Raw Water Storage within the Highbury WTW instead of the two 600mm diameter Rising Mains authorized by the DEDEAT. The 1 200mm diameter, 100Mℓ/d Rising Main will deliver raw water from the dam to the Highbury WTW, and another 1200mm diameter pipeline will convey treated water from the Highbury WTW up to the existing Rosedale Command Reservoir. The latter will follow the already-authorized route; albeit in one pipeline rather than two. The combined length of the Raw Water and Clear Water Rising Mains will be approximately 2 800m. Furthermore, the proposal includes a 550m long, 1 200mm diameter Gravity Main from the 60Mℓ Thornhill Raw Water Storage Basin to the existing Thornhill WTW Raw Water Pipelines (seeing that Thornhill can no longer be supplied from the existing failed dam outlet pipework which is authorized as per the existing EA). As a large volume of hard rock spoil will be produced during the construction works associated with the preferred alternative, rather than transport the spoil to an approved dump site far away, the Applicant proposes to create four level platforms (max fill height of 10m and fill slope of approximately 1:1.5) in the immediate vicinity of the storage basin. The four platforms will cover an extent of about (1) 120m x 100m, (2) 170m x 90m, (3) 100m x 135m, and (4) 85m x 85m. The platforms will be capped with soft material to promote vegetation growth and lessen the visual issues associated with bare hard rocks. Alternative 2 This alternative comprises the construction of: • A large (120Mℓ/d) booster pump station (replacing an existing booster pump station below the Mthatha Dam wall to the Thornhill WTW); • A large new high-lift pump station for transferring up to 100Mℓ/d to the Highbury WTW; • A 140m long, 1200mm diameter link pipeline from the proposed Thornhill Booster Pump Station to tie into the existing 1200mm Thornhill Raw Water Main; and • A 1 500m long, 1 200mm diameter pipeline from the proposed high-lift pump station to the Highbury WTW Raw Water Reservoirs. The raw water supply to the pump stations will be the responsibility of the Department of Water and Sanitation (DWS) and the subject of a separate authorization process to upgrade the existing dam outlet tower (which would need major upgrading).