11 September 2017
Update on Garden Route Dam Capacity Increase
In 2009 the George Municipality applied for Environmental Authorization to raise the Garden Route Dam spillway by up to 3m in height and to install a Fuse Gate System (FGS) at the point of overflow after it had been determined that, with the hydrology data available then, this was the most favorable solution for increasing the dam storage capacity. The authorisation for this activity was granted in March 2012. However, the authorised fuse gate alternative was no longer considered to be the most viable option, following a comprehensive review of the catchment hydrology when the Water Affairs permit was issued in December 2014.
The alternative of constructing a side-channel was investigated to extend the flood overflow length and it was found to be the most effective in raising the dam capacity, while minimizing any future damages risks caused by higher order floods, including those with 1:200 year return periods. This option requires the construction of a concrete spillway wall up to 100 m in length, in a "duckbill" shape in plan, upstream of the existing spillway, and is connected to the existing retaining wall. This design requires the dam wall overflow to be raised by 2,5m and the crest to be raised by 1,8 m to provide sufficient freeboard, to prevent overtopping of the embankment by wave action that may coincide with the occurrence of extreme flood events. The material required to raise the dam wall be sourced from within the dam. The projected increase to the dam capacity is 25% while the yield increase to the George water supply system would be in the region of 11%.
The reconceptualization of the project involved a further tender process for consultants which concluded in January 2017. The redesign required the Environmental Authorization being reviewed accordingly. Inputs received during the EA process had to be dealt with. In the final design of the project, a dam safety plan had to be drawn up, which was approved by Water Affairs on 22 August 2017.
Following administrative and further legal processes as required by the Municipal Supply Chain policy, the tender for the newly designed project was advertised on 7 September and will close on 9th October 2017. The supply chain process still requires some prescribed activities which will require several additional weeks prior to the official start of the construction portion of the project, which time cannot be fixed just yet– however it must be noted that this is a long project and which must by special effort be completed by 30th June 2018. The amount budgeted for this project is R12,8 million.
Last published 11 September 2017