I was Project Geologist for the following major dam engineering projects
in New South Wales, Australia:
Lostock Dam (38 metres high, earth and rock fill dam) on the Paterson
River, near Newcastle.
Lostock Dam is an earth and rock fill embankment visible in the
background. In the foreground is the concrete lined flip bucket spillway.
The dam was constructed with sandstone rock fill obtained from a
separate quarry.
Glennies Creek Dam (67 metres high, concrete faced rock fill dam) on
Glennies Creek near Singleton. Geotechnical problems included
weathered, non-welded tuff in dam foundation and toppling slope failures
in welded tuff in unlined spillway cutting.
Glennies Creek Dam concrete faced rock fill embankment. The intake
tower for the dam outlet works is located at the diversion tunnel inlet
portal and is visible to the right of the photo.
Glennies Creek Dam spillway. The spillway is an unlined cutting in
welded ash flow tuff which supplied the entire rock fill requirement for the
construction of the dam embankment. The spillway excavation was
designed to be located entirely in welded tuff and not to encroach on
either the underlying non-welded tuff or the overlying sandstone, both of
these rock types being much inferior to the welded tuff as a rock fill
construction material.
Windamere Dam (69 metres high, earth and rock fill dam) on the
Cudgegong River near Mudgee. Geotechnical problems included
excessive grout takes in highly fractured rock in dam foundation. The
spillway was an unlined cutting in andesite about 1 km from the dam site
and supplied the entire rock fill requirement for the construction of the
dam embankment. If a spillway had been built in the weathered
sedimentary rocks at the dam site full concrete lining would have been
required.
Windamere Dam earth and rock fill embankment. The dam
foundations are weathered Devonian conglomerates, sandstones and
shales. The spillway is located about 1km away from the dam in mostly
unweathered Ordovician andesite. The spillway is an unlined rock
cutting that provided all the rock fill required for the construction of the
dam embankment. The access road bridge over the spillway cutting is
just visible in the upper left of the photo.
The Windamere Dam spillway is an unlined cutting in unweathered
andesite that proved an excellent rock fill construction material. A
spillway adjacent to the dam embankment would have been located in
weathered sedimentary rocks and would have required concrete lining,
resulting in a much more expensive project than the chosen
spillway-cum-quarry design.
Burrinjuck Dam (92 metres high, concrete gravity dam) on the
Murrumbidgee River near Yass. This project involved raising the existing
dam wall by 12 metres to its present height of 92 metres and installing
post-tensioned ground anchor cables to improve the security of the dam
during major floods. At the time, the Burrinjuck Dam Flood Security
Upgrading project was unprecedented in two respects;
(1) the post-tensioning force required per metre length of dam crest and,
(2) the intensity of the flood discharge over the unlined sections of the
side channel spillways during the Probable Maximum Flood (PMF).
A major flood in 1974 eroded unweathered granite from an unlined
spillway discharge channel which then resulted in the destruction of a
penstock to a downstream hydroelectric power station. The outlet valves
of the dam were also destroyed during the same flood. These events
prompted a review of the safety of the dam which recommended the
remedial works program described above.
Burrinjuck Dam before the 1974 flood. The downstream hydro power
station and the penstock connecting the power station to the dam can
be seen at the bottom of the photo. This penstock passed through the
discharge area of the northern spillway (on the left hand side of the
photo). Erosion of unweathered granite from the unlined section of the
northern spillway discharge channel during the 1974 flood destroyed this
penstock, which, in turn, resulted in the destruction of the outlet valves
located at the downstream toe of the dam.
Burrinjuck Dam after the 1974 flood showing the power station penstock
destroyed by erosion of granite in the discharge area of the northern
spillway (spillway visible on right hand side of photo). Downstream power
station which the penstock served is visible in upper, left hand corner of
photo.
Downstream end of Burrinjuck Dam northern spillway. Downstream end
of the concrete spillway training wall can be seen in the upper right hand
corner of the photo. The break in the concrete encased power station
penstock caused by rock erosion during the 1974 flood is clearly visible
in the centre left of the photo.
The total outflow from Burrinjuck Dam during the August, 1974 flood was
4,525 cubic metres per second. During this flood the northern spillway
experienced a unit discharge of 102 cubic metres per section per metre
width of discharge channel. This was 49% of the design flood outflow.
The total vertical fall from the storage full supply level to the river bed
below the spillway was about 64 metres. The area where granite was
eroded during the 1974 flood was the narrowest part of the unlined
discharge channel (26 metres wide as against 29 metres wide further
upstream).
Burrinjuck Dam wall viewed from upstream. In the foreground is the old
foot access bridge supported by piers resting on the crest of the side
channel spillway. This foot bridge was at the level of the dam crest as it
was prior to the 12m raising of the dam wall during the Flood Security
Upgrading project. The only other original access to the dam crest was a
cableway.
In the background the new road bridge which gives access to the raised
dam wall can be seen. The curved, blue coloured object visible on the
crest of the dam is a steel frame which was used in the installation of the
ground anchor cables. The cables were transported to the dam in a
horizontal position and had to be passed over the steel frame before
they could be lowered down the vertical holes in the dam wall.
These cables had an average length of 110m and each cable was
inserted into a vertical hole drilled through the dam wall and into the
granite foundation. After placement in the hole the lower end of each
cable was grouted to the foundation rock and stressed to provide an
additional downward "clamping" force holding the dam onto the
foundation. The purpose of the Upgrading project was to increase the
stability and security of the dam wall during extreme flood events.
Burrinjuck Dam northern side channel spillway. The original foot access
bridge in the foreground shows the level of the dam crest before the 12m
raising. The dam also has a similar side channel spillway on southern
side of the dam wall. The erosion of unweathered granite which took
place during the 1974 flood and destroyed a power station penstock was
in the downstream, unlined section of the northern spillway.
Construction in progress on the northern side of Burrinjuck Dam. In the
foreground are the two sector gates which form part of the northern
spillway of the dam. The temporary low level access bridges across the
top of the sector gates are at the original level of the dam crest prior to
the 12m raising carried out during the Upgrading project. The new, high
level road access bridge is being used to transport the ground anchor
cables onto the raised dam crest before they are installed in the dam wall.
A ground anchor cable being transported across the new road access
bridge onto the raised dam crest prior to installation in the dam wall.
Copeton Dam (113 metres high, earth and rock fill dam) on the Gwydir
River near Inverell. Unexpected erosion of hard, sound, unweathered
granite in the unlined spillway discharge channel was caused by rock
failure under high in-situ compressive stress.
Remedial works involved
building a training wall to separate the original single spillway into a
service spillway and a secondary (emergency) spillway. A concrete slab,
anchored to the underlying rock was constructed in the floor of the main
scour channel to provide some additional protection on those rare
occasions when the secondary spillway will discharge water over this
area. The smaller, more frequent flood events will be discharged through
the service spillway onto more scour resistant rock which has performed
satisfactorily to date. The secondary spillway will operate very
infrequently and will only discharge when the capacity of the service
spillway is exceeded.
Geological investigations for the design of these remedial works included
surface stress measurements in the unlined spillway discharge channel
as well as geological mapping and diamond core drilling. To view a presentation on the history and geological investigations of the spillway see Copeton Dam Spillway.
Copeton Dam and spillway before 1976 floods. The earth and rock fill
dam embankment is in the background. The spillway in the foreground is
controlled by radial gates which discharge into a short concrete lined
chute. On leaving the concrete chute the flood waters flow over an
unlined discharge channel excavated in granite for a short distance
before flowing over the steep natural surface to return to the river
downstream of the dam. The spillway has no energy dissipation
structures.
Copeton Dam and spillway after the 1976 floods. Note the large amount
of scour debris deposited in the river bed downstream of the spillway.
Scour channel eroded in unweathered granite downstream of the
Copeton spillway. Two figures in the upper centre of the photo give the
scale. The exceptional depth of erosion of unweathered granite was due
to rock failure under high, in-situ compressive stress in the granite forming
the floor of the scour channel. This photo is looking upstream from near
the downstream end of the spillway discharge area.
Failure of unweathered granite in the floor of the main scour channel
downstream of the Copeton Dam spillway. Failure caused by high in-situ
compressive stress in the rock forming the floor of the scour channel.
Intense stress relief fracturing in the wall of the main scour channel
downstream of the Copeton Dam spillway. The rock is unweathered
granite and the staff is 1m long.
