The Jamieson and Milner dams are located on the upper reaches of the New Year’s River in the Eastern Cape and have a combined capacity of 830 000m³. Together they form the Slaaikraal scheme to supply additional water to the city of Makhanda (formerly Grahamstown). The water from these historic dams, both built at the turn of the 20th century, is gravity-fed to the Old Town Filters from where it is pumped to Waainek Water Treatment Works for treatment and distribution.
In our April 2020 newsletter (https://www.mbb.co.za/2020/04/15/rehabilitation-of-historic-dams/), we noted that the Department of Water and Sanitation (DWS) had approved funding under the Water Services Infrastructure Grant (WSIG) to undertake the repairs identified during the Dam Safety Evaluation, and that work had commenced in January 2020. Despite Covid-19 and national lockdown measures, we are thrilled to report that the planned repairs were completed in January 2021, thereby returning both dams to an operational state.
The most immediate issues identified and attended to as part of the planned repairs to the dams were the following :
- Removal of vegetation growth on the embankments. Once vegetation was removed, damage to the riprap was repaired and tree growth was eliminated.
- Repairs to spillways and the return channels were undertaken by constructing a concrete overflow structure to prevent further erosion to the spillway.
- Securing the rusted and unsafe access bridge. The decision was made to remove the first half of the bridge at both dams to prevent easy access to the tower head.
- Replacement of the stolen supply lines. Cast iron had been used as the original water main linking the two dams and a substantial section of the cast iron had been exposed, smashed, and carried off to scrap metal dealers.
- Replacement of the downstream valve gear, scour valves, and meters.
- Installation of gauge plates and the fitment of telemetry linking to the existing municipal SCADA system.
- Construction of service roads on top of embankments.
- Finding and repairing leaks. This was investigated and the following repairs made:
- Water leaks along the gravity main: several kilometres of leaking pipes downstream from the Milner dam were reported and repaired. One break on a low-lying farm drained the Milner dam of its last 5% of water storage overnight.
- A section of cast iron water main, installed at a shallow depth, was cracked when traversed by a bulldozer and required immediate repair.
- An additional ± 230m of exposed and unretained water main piping was replaced with uPVC in an area that was solid bedrock. The uPVC pipe was retained by concrete anchor blocks dowelled into the existing bedrock.