Construction of the Dumaresq Dam Safety (DDSU) Upgrade Project was completed in mid-August 2022.
The 340ML Dumaresq Dam is situated approximately 10km North West of the City of Armidale in NSW and currently functions as a local reserve after serving the Armidale community from 1896 to 1968 when the Malpas Dam became the water source for the city.
The initial scope of works included installation of post tensioned bar anchors in the crest and toe of the wall, upgrade of the inlet and outlet systems, decommissioning of the scour outlet, the installation of a valve house, extension of the LH abutment, the upgrading of the RH abutment and the installation of an apron slab at the toe of the dam.
The construction contract was tendered in July 2020 and included and alternate design proposal. The construction contract was awarded to Leed Engineering and Construction Pty Ltd in December 2020 with the acceptance of their alternate design proposal. The alternate design proposal included a reduction of anchors from the original detailed design from 99 No. to 60 No. and the inclusion of an anchor monitoring system from Dywidag International Pty Ltd – a first for an Australian Dam.
After an initial additional foundation geotechnical investigation in December 2020 to confirm foundation properties, works commenced in February 2021 on site with the revised design. The result was 39 crest anchors and 21 toe anchors, with 14 monitored crest anchors and 2 monitored toe anchors. The inlet trunnion system was removed and replaced with a fixed submerged inlet pipe, and the outlet pipeline upgraded with dual outlet valves housed in a new valve house. The existing raw water supply line was reinstated via the new outlet pipeline.
During construction of the RH embankment, it was found that tree roots had infiltrated the clay foundation – this resulted in the complete rebuild of the RH earthen embankment to current standards. In addition, during construction of the LH abutment extension, several foundation areas of concern were discovered – this led to the installation of erosion control slabs along the LH wall from the lower valve house to the upper abutment sections.
Finalisation of the construction and completion documentation submission to DS NSW and DPIE is currently underway with envisaged completion in December 2022.