Author: Monique Eggenhuizen. The Victorian division of the ANCOLD YP Group organised a site visit on the 27 February 2015 at St Georges Dam in Creswick Victoria. Parks Victoria are currently undertaking upgrade works at St Georges Dam and were kind enough to host the YP Group at the site with the assistance of the contractor, Entracon.
The reservoir is located within the Creswick Regional Park and was originally constructed to supply water for the Creswick quartz crushing plant in the 1890s, however has since been established as a popular recreational storage for the township. The dam is approximately 16m high and located across a relatively steep gully. The embankment consists of earthfill with an upstream face of rock beaching and a grass covered downstream face. No filters within the embankment have been identified however the investigations have revealed that the embankment includes a clay core of high plasticity.
At the completion of the detailed design reviews of the six high priority dams, St Georges Dam was assessed to be within the top three of Parks Victoria’s dams portfolio in regards to Public Safety Risks. The detailed design review assessed that the risk position for the dam plotted within the unacceptable region of the ANCOLD Guidelines for the static, earthquake and flood failure modes. As such, upgrade measures were considered to be required. In 2010 and 2011, a number of significant flood events emphasised the importance of upgrade works at this dam, particularly in regards to upgrading the spillway capacity, and consequently Parks Victoria assigned these works a high priority.
The upgrade works, which are about 90% complete, include the following key aspects:
- lowering the FSL by 1m by reducing the invert level of the primary spillway (located on the right abutment);
- decommissioning the secondary spillway (located on the left abutment) which had been subjected to significant erosion damage during the 2010 and 2011 flood events;
- retrofitting the dam embankment with chimney and blanket filter zones and protecting this zone with a downstream rockfill stabilising berm;
- decommissioning the outlet works which are no longer in use;
- constructing a new secondary spillway over the dam embankment by
- lowering the dam crest level by approximately 2m
- flattening the slope of the downstream shoulder to 6H: 1V
- protecting the downstream shoulder with layers of filters, bedding material and rock armouring
A few photos from the site visit are provided below.
The Victorian YP Group would like to express our gratitude to Parks Victoria and Entracon for providing a very interactive and informative tour of the site.