Googong Dam was completed in 1978 and forms one of the main
water supply storage reservoirs for the Australian Capital
Territory (ACT) and surrounding region. It is a 66m high zoned
earth and rockfill embankment on the Queanbeyan River and has been
classified as an extreme consequence category dam in accordance
with the guidelines in DSC (2002). Successive flood events in 1978
and through the 1980s resulted in extensive erosion in the unlined
section of the spillway chute, including a large erosion hole, up
to 19 m deep and 25 m wide, in the upper part of the
unlined spillway chute. Staged remedial works were undertaken in
the 1980s to protect the eroded structure.
GHD was engaged in 2006 to undertake a review
of the historical performance and prediction of future performance
of the structure. This engagement included a review and
assessment of previous work, the development and comparison of
options and ultimately the detailed design of the preferred
arrangement. A scale physical model was constructed as a validation
tool during the detailed design phase. The project also included an
increase in the capacity of the spillway to discharge the required
spillway design flood which had significantly increased due to
changes in hydrological methods in recent years.
The scope of the upgrade works included:
- Filling of the erosion hole
with backfill concrete
- Construction of an extension
to the existing concrete-lined chute with an anchored reinforced
- Placement of anchored
reinforced concrete protection over the downstream cut slope
- Construction of walls in the
spillway chute extension up to 17m high
- Excavation of a plunge pool
below the end of the spillway
- Anchorage of the existing
concrete chute slab to resist uplift pressures
- Retrofitting of drains in
the existing concrete chute slab
- Raising of the walls in
existing chute to contain the PMF
The construction of the remedial works was
undertaken as a construction-only package by the Bulk Water
Alliance involving ACTEW Corporation (the Owner Partners), GHD
(the Design Partner) and Abigroup and John Holland (the
Construction Partners). Construction of the remedial works was
completed in late 2010. Other packages included in the Alliance
were the design and construction of the Enlarged Cotter Dam, an
inter-basin transfer pipeline from the Murrumbidgee River to
Googong Dam and other bulk water assets.
The project was awarded a high commendation in
the 2011 Engineers Australia Excellence Awards.
Photos: Completed spillway discharging the
flood of record in December 2010 (left) and aerial view of project
towards the end of construction in October 2010 (right).
Courtesy of Bulk Water Alliance.
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