Development plans for the Garden Route Dam Capacity Increase project are gaining momentum as the George Municipality issued a call for tenders late last week.
The tender for the newly designed project was advertised on 7 September and will close on 9th October 2017. The project, which was initiated in 2009, had to be redesigned in favour of a more viable solution.
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.
At the time it was determined, with the hydrology data available then, that this would be the most favourable solution for increasing the dam storage capacity and the authorisation for this activity was granted in March 2012.
However, by the time the Water Affairs permit was issued in December 2014 the authorised fuse gate alternative was no longer considered to be the most viable option, following a comprehensive review of the catchment hydrology.
The newly designed plan
According to the George Municipality the alternative of constructing a side-channel was investigated to extend the flood overflow length and it was found to be the most effective option for raising the dam capacity, while minimising 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 department said.
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 also required the Environmental Authorisation being reviewed accordingly while inputs received during the EA process had to be dealt with.
The municipality has set aside R12.8 million for the project.