Background and Overview
- Porters Creek Dam was constructed in 1968 and comprised of a 17 metre high by 139 metre long post-tensioned concrete gravity section with an overflow spillway integral with the crest.
- The dam is located on Porters Creek, about 11 km west of Lake Conjola and is situated within Morton National Park.
- The dam has a reservoir capacity of 1,900 mega litres and provides about 30 per cent of Southern Shoalhaven’s drinking water supply.
Over a number of years various assessments have been undertaken on the dam, its hazard rating and its compliance with contemporary standards. The most recent dam safety inspection report (2011) by the NSW Office of Water indicated that the dam was performing well with an overall satisfactory standard of operation and maintenance.
However, that report also provided a number of recommendations to carry out further investigations into the operation of the post-tensioned cables, to assess the longer term integrity and stability rating of the dam.
Council Awarded the Porters Creek Dam Remediation Works to Leed Engineering and Construction Pty Ltd in November 2015. Project planning and preparation Works commenced immediately. Considerable consultation and development was required to ensure that the Project addressed obligations identified in the Review of Environmental Factors (REF); particularly the Construction Environmental Management Plan (CEMP). Leed started with Roadworks in February to maintain the over 14km of access road from the Princes Highway to the Dam; this includes a 3.6km section of road which was primersealed to suppress dust in the vicinity of local houses.
The project site is located in the Morton National Park, consequently OEH along with Council were the determining authorities; both NPWS and Council provided approval of the Project on the 14 March 2016 which enabled Works to commence at the Dam site.
The construction work primarily involved the batching and pouring of 4,500m3 of concrete on site to form the new buttress type dam wall.
A stilling basin was constructed to control the velocity and turbulence of water entering the downstream water way.
A sophisticated survey network was established to monitor any movement in the dam wall during construction.
Porters Creek road was closed west of Graydons Pointer road from 23 August 2016 to reduce the safety risk to visitors and construction workers. The road was reopened on 2 December 2016.
Restoration and revegetation work will proceed through November and December with all work expected to be complete by the end of this year.
Council would like to thank all local residents and other stakeholders for their patience through the construction of this signification project.
The upgrade works are now complete, with the exception of some minor rectification works which are normal at the end of such a large project.
The dam water level was lowered to facilitate the construction so rain is now needed to increase the level to the normal operating range. The Water level is currently sitting around 2.75m below top water level.
Council would like to acknowledge the support and cooperation of key stakeholders which contributed to a successful project outcome.
These stakeholders included:
- NSW Office of Environment and Heritage
- NSW National Parks and Wildlife Service
- NSW Environment Protection Authority
- Leed Engineering
- The local Shoalhaven community
Enquiries regarding this Project can be directed Shoalhaven Water on (02) 4429 3214.