Water Power and Dam Construction. Issue May 2010
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WWW.WATERPOWERMAGAZINE.COM MAY 2010 11
SPILLWAYS
tigation had determined the extent of slurry wall required, due to
the limited information available, work proceeded with caution.
A geomembrane was also installed to protect the clay core. These
measures aim to reduce the leakage ow through and over the core,
consequently reducing the erosion of ne material that is causing
localised settlement of the crest and downstream slope.
r Repairs and refurbishment to the existing low level outlet. Further
underwater surveys were required to conrm exact dimensions of
the draw off culvert. Due to uncertainty of the existing structural
integrity of the culvert, and potential health and safety issues, the
latest micron scanning sonar mounted on a remote operated sub-
mersible was used. Divers then inserted an HDPE pipe with a
ange plate into the section of culvert upstream of the penstock and
grouted it into position while underwater, allowing inspection and
remedial work of the penstock and culvert in the dry. Some of the
culvert was in very poor condition and repairs required consider-
able expertise and planning to ensure its future structural integrity.
Future inspection will be much easier thanks to an old stop log
facility brought back into commission, as well as the option to t
the ange plate on to the HDPE pipe.
r Strengthening the sides of the cascade with a reinforced concrete
structure that supports, and is concealed behind, a series of lime-
stone boulders. Limited drawdown of the reservoir was possible,
so work needed to be planned and co-ordinated to allow continual
use of the spillway. These works enhanced the existing cascade and
allow for additional water levels and ow velocities associated with
the provision of increased overow capacity of the dam.
r Construction of an auxiliary 80m wide spillway on the dam crest
also provides an increased spillway capacity to accommodate a 1
in 10,000-year ood. This involved the removal of all planting,
stripping off the topsoil, and laying a bed of interlocking concrete
blocks (Armorloc), before replacing the topsoil and reseeding. The
auxiliary spillway will operate for events in excess of 25-50 year
return periods. The removal and containment of isolated areas of
Japanese Knotweed needed to be done in line with guidance from,
and in close liaison with, the Environment Agency.
REMEDIATION
Unfortunately, during restoration, three large plane trees and a
number of deciduous and evergreen trees that were planted on the
downstream face of the dam had to be felled. But once the works
were complete the team worked with Andrew Nichols of landscape
architect rm, Nichols Brown Webber, to restore the aesthetics of
this historic landscape.
Almost 1200 tonnes of topsoil were brought in and the whole area
re-seeded and planted with a selected grass and wild ower mix; the
Blenheim Dam
Catchment area: 127km
2
Reservoir surface area: 47.34ha
Reservoir volume: 570,000m
3
Primary spillway (Cascade): 17m wide at 76.7, AOD
(New) Auxiliary Armorloc spillway: 80m wide at 77.4m AOD
Top of dam: 78.3m AOD
Dam height (top of dam to downstream river bed): 8.1m
Total dam length: 200m
Crest width (typical): 8m
Downstream slope: 1:5
10,000 year peak inflow: 83m
3
/sec
1,000 year peak inflow: 48m
3
/sec
Top left: View of Blenheim Palace reservoir;
Top right: Geomembrane and topsoil going in on the new auxiliary spillway;
Above left: Spillway (cascade) crest and lake;
Above right: Crane preparing for work on the spillway
12 MAY 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
SPILLWAYS
major focus being to re-establish the dense, mainly evergreen, wood-
land on either side of the cascade. Over 30,000 wild daffodils were
also planted in the grassed areas.
Before the works, the only access to the bottom of the cascade was
by a set of steep steps, but these were also replaced with new graded
footpaths along the crest and up the downstream face. The new foot-
paths wind their way up to the top of the dam, with a new viewing
point overlooking the cascade and down the River Glyme in a view
made famous by photographer, Henry Taunt in 1900.
The construction contract was completed in November 2009
and celebrated with a ceremony led by His Grace the Duke of
Marlborough, attracting media coverage.
Initial feedback and monitoring of the project has been very posi-
tive. Maintenance employees from Blenheim Park report that they are
now able to operate the penstock easily and with more condence.
As yet, the auxiliary spillway is untested, but the v-notch chamber
measuring leakage through one section of the dam, which had been
running copiously before the clay core remedial works, is now dry,
indicating the remediation of the clay core has been successful.
THE FUTURE
New legislation is currently going through the Parliamentary proc-
ess which will mean reservoirs as small as 10,000m
3
will have simi-
lar safety requirements to those currently in place for reservoirs of
25,000m
3
or more.
Inevitably, this will mean that many more ornamental lakes will be
subject to such inspection requirements in future. But for now, this
particular Brown masterpiece and the nest view in England have
been preserved for future generations.
Kate Crawford, Communications Ofcer at JN Bentley.
Email: kate.crawford@jnbentley.co.uk.
The author would like to thank the following for their
help in producing this article:
Historical information kindly provided by: Jeri Bapasola
– Archival Researcher at Blenheim Palace and author of
‘The Finest View in England - The Landscape & Gardens
at Blenheim Palace’.
Technical information kindly provided by: Richard
Dawson – Supervising Engineer, Peter Brett Associates;
Martyn Higham – Associate, Peter Brett Associates; Rob
Culledge – Contracts Manager, JN Bentley Ltd; Andrew
Nichols – Landscape Architect, Nichols Brown Webber;
Martin Airey – Inspecting Engineer, Mott MacDonald
Limited.
Permission kindly granted by Roger File – Estates
Director, Blenheim Palace.
IWP& DC
Reduction of lake water level
Reconstruction
of wave wall
Construction of
crest footpath
Raising and
remediation
of clay core
Raising of ground
level with Armorloc
protection
Replacement of
topsoil/subsoil
Excavation of topsoil/subsoil
Benching of existing
downstream slope
Clay core Earth fill
Existing lake edgeLake water level
Initial condition
Preparation of dam
Construction of raised dam
80.00
76.00
72.00
68.00
Existing, partially collapsed,
head wall and north wing
wall to be rebuilt with
concrete bagwork
Raise walls and provide new cover to finish
flush with proposed ground level
Stop Log Slot
Provide new galvanised steel plate approx 850 wide
by 1500 high to suit opening size with neoprene
seals on downstream side and stem to allow
installation and removal
Upstream section of culvert to be cleared of debris and slip lined with
1.0m I/D PE liner and gap between culvert and liner grouted for a
length of 16.85m (to be confirmed) with cement based grout.
Upstream end of liner to be flanged and provided
with a bolted flange plate. All by specialist sub-contractor.
75mm topsoil
Top of Armorloc
78.10mOD
78.10mOD
77.15mOD
Proposed footpath
type 2
Gravel anchor trench
90mm Armorloc 150
Concrete anchor trench
600
600
Penstoc
k
C
h
am
b
er
Remove existing concrete cover to chamber, raise chamber and install new 225mm thick reinforced
concrete cover with 600 x 600 access cover and 150ø hole for penstock spindle with hinged access
cover (note: existing lifting points in concrete cover are not to be used and contractor is to provide
alternative lifting arrangement)
Repoint brickwork to internal face of chamber
Refurbish existing penstock gate, frame and spindle including extending
top of spindle to suit new chamber top level and removing blockage at
base, to allow full closing of gate
Raise chamber in engineering brick and install new 750 x 750
access cover to finish flush with proposed ground level
Remove existing step irons and repoint brickwork to internal face of
chamber (permitted future access down the chamber is by winch
only, due to restricted plan dimension of the chamber)
Inspection Chamber No1:
Gravel anchor trench
Existing ground level
Proposed ground level
16.85m
Reduction of lake water level
Reconstruction
of wave wall
Construction of
crest footpath
Raising and
remediation
of clay core
Raising of ground
level with Armorloc
protection
Replacement of
topsoil/subsoil
Excavation of topsoil/subsoil
Benching of existing
downstream slope
Clay core Earth fill
Existing lake edgeLake water level
Initial condition
Preparation of dam
Construction of raised dam
80.00
76.00
72.00
68.00
Existing, partially collapsed,
head wall and north wing
wall to be rebuilt with
concrete bagwork
Raise walls and provide new cover to finish
flush with proposed ground level
Stop Log Slot
Provide new galvanised steel plate approx 850 wide
by 1500 high to suit opening size with neoprene
seals on downstream side and stem to allow
installation and removal
Upstream section of culvert to be cleared of debris and slip lined with
1.0m I/D PE liner and gap between culvert and liner grouted for a
length of 16.85m (to be confirmed) with cement based grout.
Upstream end of liner to be flanged and provided
with a bolted flange plate. All by specialist sub-contractor.
75mm topsoil
Top of Armorloc
78.10mOD
78.10mOD
77.15mOD
Proposed footpath
type 2
Gravel anchor trench
90mm Armorloc 150
Concrete anchor trench
600
600
Penstoc
k
C
h
am
b
er
Remove existing concrete cover to chamber, raise chamber and install new 225mm thick reinforced
concrete cover with 600 x 600 access cover and 150ø hole for penstock spindle with hinged access
cover (note: existing lifting points in concrete cover are not to be used and contractor is to provide
alternative lifting arrangement)
Repoint brickwork to internal face of chamber
Refurbish existing penstock gate, frame and spindle including extending
top of spindle to suit new chamber top level and removing blockage at
base, to allow full closing of gate
Raise chamber in engineering brick and install new 750 x 750
access cover to finish flush with proposed ground level
Remove existing step irons and repoint brickwork to internal face of
chamber (permitted future access down the chamber is by winch
only, due to restricted plan dimension of the chamber)
Inspection Chamber No1:
Gravel anchor trench
Existing ground level
Proposed ground level
16.85m
Company information
Peter Brett Associates provides services including modelling, design,
procurement of river and canal engineering, lake design, reservoirs, ood risk
assessments, hydrology and ood risk analysis as well as coastal engineering.
www.peterbrett.com
JN Bentley Ltd is a privately owned building and civil engineering contractor.
The company has a successful heritage within water sector markets and is now
rapidly making its mark in the eld of hydropower. www.jnbentley.co.uk
Nichols Brown Webber offers a full range of architectural and landscape
services. www.nbwarchitects.co.uk
Right: Embankment raising schematics
Above: Cross section of the dam
14 MAY 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
SPILLWAYS
R
ECENTLY completed studies of rainfall data gathered
over the past 100 years have prompted dam safety revi-
sions in Australia. Following Bureau of Meteorology
revisions to methods for estimating extreme rainfall
events, new dam safety regulations were established in 2007.
“While the possibility of an extreme rainfall event occurring is very
low, it is possible,” says Phil Webber from Queensland-based water
company SunWater. “As a responsible dam owner and operator it
would be remiss of us not to take action.”
SunWater owns 19 major dams, 63 weirs and barrages and supplies
over 40% of the water used commercially in Queensland. Following
the Bureau of Meteorology’s announcements, SunWater embarked
on a major dam spillway upgrade programme to proactively respond
to the new projections.
A detailed assessment of all the company’s dams was carried out to
determine a prioritised list of spillways requiring action. The criteria
used to assess the structures included:
r C urrent rainfall event capability.
r Risk to affected populations should an extreme rainfall event occur.
r Integrity of the dam structure under increased water loads.
r Impact to provision of ongoing water supply during an extreme
rainfall event.
r E conomic impact of the dam’s failure during an extreme
rainfall event.
Based on this, higher priority was given to dams with the lowest
capacity to release excess water in a controlled manner, as well as
those dams presenting an unacceptable level of risk to the commu-
nity surrounding the dam. As a result the upgrade programme got
underway in 2005 when four dams were selected as having spillways
requiring prioritised action.
FRED HAIGH DAM
Fred Haigh dam was built in 1975. A 52m high rockll dam with a
crest length of 646m it has a reservoir capacity of 586m
3
x10
6
. This
A$4M (US$3.7M) upgrade was identied as being of the highest
priority. The seven month project involved raising the top of the
dam by 2m and providing a watertight gate to allow operational
access to SunWater’s Monduran pump station. The rst stage of
the upgrade was completed in 2006 and the second stage will be
undertaken in the near future.
Spillways step up
for assessment
Australian dam owners are responding to revised rainfall data
and spillway safety guidelines. SunWater is one such company
to undertake a major assessment of its spillways, resulting in an
upgrade programme which is currently in full swing
Spillway upgrades
The following ten dams will undergo spillway upgrades over the next 5-20
years, again based on a priority assessment. These dams are:
Dam Date
built
Type (m) Height
(m)
Crest
length
Reservoir capacity
(m
3
x10
6
)
Boondooma 1983 Rockll 64 565 212
Burdekin Falls 1987 Gravity 55 830 1860
Callide 1965 Earthll 46 2118 127
Eungella 1969 Rockll 49 276 131
Fairbairn 1972 Earthll 49 823 1440
Julius 1976 Multi-arch 38 400 127
Kroombit 1992 Earthll 31 900 13.3
Leslie 1965 Gravity 33 384 108
Teemburra 1997 Rockll 56 350 148
Wuruma 1969 Gravity 46 343 194
Above, left to right: Bridge constructed on the Tinaroo Falls spillway for the
drilling rig; concrete skirting below the wall. Photographs by G Price
WWW.WATERPOWERMAGAZINE.COM MAY 2010 15
SPILLWAYS
BJELKE-PETERSEN DAM
The 43m high Bjelke-Petersen rockll dam was the second spill-
way to be upgraded, at a cost of A$5.7M (US$5M). Work on
this 560m long dam with a reservoir capacity of 125m
3
x10
6
was
started in February 2007 and completed by October 2007. The
main dam and saddle dam wall were both raised by 1.2m and the
saddle dam wall was extended. Again the second stage of upgrad-
ing this dam, which was originally built in 1988, will be under-
taken in the near future.
BORUMBA DAM
The rst stage of upgrading the 53mhigh Borumba rockll dam start-
ed in March 2008 and was completed by January 2009. The height
of the dam wall was increased by 1.6m. The cost of the work at this
36-year-old dam was estimated at A$5.1M (US$4.7M).
TINAROO FALLS DAM
Tinaroo Falls dam was built in 1959 and is a 53m high rockll dam,
343m in length with a reservoir capacity of 42.6m
3
x10
6
. Work start-
ed on the A$21M (US$19.5M) spillway upgrade in April 2009 and is
due for completion by late 2010 – all of the work is to be completed
in one stage.
Here the main dam wall will be reinforced with 32x10” wide
steel cable anchors which will be inserted up to 80m through the
dam wall and the foundation rock below. The cables will be tested
to 2000 tonnes to ensure that in an extreme rainfall event the dam
will not suffer from any undermining, erosion or lifting and will
be able to pass ows safely through the spillway as designed. In
addition, a 250m long, concrete protection slab will be placed
along the downstream base of the dam wall. The height of the
saddle dam will be increased by 30cm and lter zones will be put
on the downstream face.
“We are very pleased with the progress we have made to date,”
says Col Bendall, SunWater’s area operations manager. The project
looks set to be nished on time and within budget.
Five of SunWater’s dams can already safely manage an extreme
rainfall event, as identied by the Bureau of Meteorology’s new
assessments, and do not require upgrading. These are: Beardmore;
Cania; Coolmunda; Kinchant; and Peter Faust.
More photographs and information is available in the
book ‘More than just the dam - the story of Tinaroo Falls’
which is available from Atherton Library in Australia
Email - athertonl@trc.qld.gov.au
IWP& DC
Australia’s largest spillways - in
order of decreasing capacity
All spillways 10,000m
3
per second or more
discharge capacity
NAME Discharge
capacity
(m
3
/sec)
Spillway type Year
completed
State
1 Burdekin falls 64600 Uncontrolled 1987 QLD
2 Burrinjuck 29100 Uncontrolled 1928 NSW
3 Kununurra
diversion
28300 Controlled 1963 WA
4 Fitzroy river
barrage
23800 Controlled 1970 QLD
5 Harding 21500 Uncontrolled 1985 WA
6 Pindari 20650 Uncontrolled 1969 NSW
7 Warragamba 20300 Controlled 1960 NSW
8 Tallowa 20200 Uncontrolled 1976 NSW
9 Fairbairn 15580 Uncontrolled 1972 QLD
10 Copeton 14800 Controlled 1976 NSW
11 Wyangla 14700 Controlled 1971 NSW
12 Julius 14500 Uncontrolled 1976 QLD
13 Burrendong 13720 Controlled 1967 NSW
14 Boondooma 13420 Uncontrolled 1983 QLD
15 Opthalmia 13000 Uncontrolled 1982 WA
16 Wivenhoe 12000 Controlled 1985 QLD
17 Glenbawn 11115 Uncontrolled 1958 NSW
18 Keepit 10480 Controlled 1960 NSW
Source: Register of Large Dams in Australia, 2002
Drilling rig for the cable holes at Tinaroo Falls. Photo by G Price
22
nd
- 23
rd
September 2010 Innsbruck, Austria
DAM SAFETY
Sustainability in a Changing Environment
ATCOLD
Organized by
http://www.IECS2010.TUGraz.at
TOPICS
'XULQJ WKH ODVW GHFDGHV VLJQL¿FDQW FKDQJHV LQ
personnel resources for design, construction, and
operation of dams occurred in many European
countries, leading to a decrease of skilled practiti-
oners. In contrast to that, the construction of new
dams undergoes a renaissance now, due to the de-
mands of sustainable water and energy management,
whereas the existing dams require increasing efforts
for their maintenance and upgrading in order to sustain
adequate safety and operability.
Therefore, strategic resource management beco-
mes more and more important for the dam industry.
One main aspect thereby is the transfer of valuable
experience and knowledge from senior practitio-
ners to their successors – an issue crucial for all
parties involved: dam owners, designers, and contrac-
tors, as well as authorities. Accordingly, sustainable
management of knowledge transfer between the ge-
nerations and between science and “day-to-day-busi-
ness” will be one main scope of the symposium.
Day 1
21
st
September 2010
Technical Excursion: Finstertal, Zillergruendl
Evening: Meeting European Working Groups
SYMPOSIUM
Day 2
22
nd
September 2010
Sypmposium
Evening Event
Day 3
23
rd
September 2010
Symposium
Evening: Meeting European Club Board
Day 4
24
th
September 2010
Technical Excursion: Finstertal, Zillergruendl
PROGRAMM
Sustainability of Know How
Public Awareness of Dams and Dam Safety
Maintenance and Rehabilitation
Regulations and Guidelines
Small Dams
Surveillance Practice
WWW.WATERPOWERMAGAZINE.COM MAY 2010 17
SPILLWAYS
A
VARIATION of traditional labyrinth weirs, the rela-
tively recent development of Piano Key Weir (PK Weir)
spillways has resulted in the rst of a new generation of
the new, serrated free-ow structures being installed on
both existing dams and in new hydraulic structures. The develop-
ment potential of the hydraulically complex, but simple, structures
continues to grow for project applications and research. The main
areas where they are being used so far are France and Vietnam.
Seen less as a revolutionary breakthrough in weirs and more as
an evolution – albeit a major one – the PK Weir is physically a self-
balanced structure that can be either built from precast concrete or
prefabricated steel and has no mechanical components.
Geometrically, a PK Weir is congured as overhanging spilling
channels alternating with receiving chutes. Each has its own leading
and trailing weir edges. But the majority of the water spills over the
sides of the channels onto the counter-sloping slabs of the chutes to
be discharged down the spillway.
In plan view, this high-low conguration is seen by some as being
like an arrangement of black and white piano keys running atop the
crest of a spillway chute on a dam.
PK Weir spillways are often used alone on a dam or barrage but
can also be designed to work in conjunction with existing spillway
provision, such as stepped structures. They can also be installed on
top of existing concrete dams after some modication works.
The first PK Weir was installed at Electricite de France’s (EdF)
Goulours dam in 2006. The utility has since installed a further PK Weir
at its Saint-Marc dam and further projects include installations at the
L’Etroit, Malarce, Gloriettes, La Raviege and Campauliel dams.
Separately, PK Weir developments are underway in Vietnam.
LABYRINTH WEIRS
A labyrinth weir is a non-linear, or folded, structure used at the top
of a spillway as an effective way to increase the crest length without
having to increase the top width of the chute or dam. It allows for
relatively higher discharges for a unit width of spillway, and does so
by using various ‘folding’ geometries – triangles, trapeziums or rec-
tangles – to stretch-out the weir’s contact length with water.
Such weirs, therefore, can be suited to new sites that pose restric-
tions on the size of the impounding structure or spillway but the
hydrology requires a sizeable discharge capacity. They also can be
helpful at some existing dams that need upgraded to meet larger
design oods, especially as their folded form provides for an increase
in specic ow rate at constant head. The higher design oods may
result from combinations of improved hydrological data, calculation
methods and calls for improved margins of safety.
In addition, the weirs can also usually provide additional storage
more economically than employing gates.
In plan view, a labyrinth weir appears like a jagged or square wave
across the top of a spillway chute. But while the conguration has a
longer length to spill more water per unit head, it generates compli-
cated ow patterns that partly offset the improved efciency. The
degree of impact is dependent on geometry between chutes, the depth
of water over the weir and also, in the direction of ow, any down-
stream slope there may be across the top of the structure.
Additionally, as head increases the relative performance in ef-
ciency falls off due to geometrical restrictions for the approaching
ow and, eventually, it nears what can be expected of a conventional
straight crest weir.
However, despite the benets afforded by labyrinth weirs a major
restriction for their use is that their vertical reinforced concrete walls,
interlocking in the trapezoidal plan shape, need to be built on a at
base. Therefore, in addition to construction economics limiting
their use, as specic ow increases above approximately 20m
3
/sec
per metre, their application is limited because more foundation area
is needed than is usually available at the narrow spillway crests of
standard concrete gravity dams.
With ood design calculations giving higher estimates of capacities
needed, these restrictions were a problem for existing concrete dams.
To help overcome these limitations, a new concept emerged that was
both simple and requires little maintenance but, of particular value, it
can be used on existing concrete dams. It was tested in Europe, Asia
and north Africa, and has become known as the PK Weir.
EMERGENCE OF PK WEIRS
The concept for the PK Weir was presented almost a decade ago
by Lemperiere and Ouamane, discussing two points: the problem of
free-ow spillways having low specic ows and the resulting loss of
live reservoir storage compared with gated spillways; and, the specic
ow benet of labyrinth weirs but their restrictive need for extensive
at areas, meaning they cannot be used for most upgrades of concrete
gravity dams.
PK Weirs emerged from research – started in the late 1990s by
non-prot international association Hydrocoop. The hydraulic labo-
ratory tests were done at EdF’s LNH Laboratory as well as Roorke
University, India, and Biskra University, Algeria.
The new design offers, like a labyrinth weir, a system of improved
specic ows compared to a standard weir. However, it beats a laby-
rinth weir by offering a smaller footprint and greater efciency.
A pattern of alternating channels and chutes pointing upstream and
Piano Key Weir growth
The relatively recent development of Piano Key Weir spillways is taking sure steps forward
for dam upgrade and new projects. Report by Patrick Reynolds
PK Weir at EdF’s L’Etroit Dam
18 MAY 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
SPILLWAYS
downstream, respectively, became the established conguration from
the research. Specic ows that can be passed by a PK Weir can range
from 3m
3
per m to 100m
3
per m, say designers. The new weir design
can pass at least four times the specic discharge of a classic (Creager)
weir for a relatively low overow depth.
Two main types of PK Weir were identied, those with: 1) chutes
overhanging on both the upstream and downstream sides; 2) a chute
overhanging only on the upstream side, and by longer distance. The
former can be used for specic ows of up to 20m
3
/sec per metre, and
the latter is considered of particular interest for large dams.
In comparison to the labyrinth weirs, the PK Weir is able to have a
smaller footprint on a dam body as both the channels and interven-
ing chutes overhang the structure. They have counter-sloping slabs
that cantilever upstream and downstream of the crest, which results
in a generally self-balancing structure. However, anchors are usually
added. The slabs have 2:1 slopes.
To achieve a level base for a PK Weir on an existing concrete grav-
ity dam, however, requires some demolition at the tip of the rounded
weir crest. In section, the length of the new base across the modied
dam crest needs to be between 1.5-2.0 that of the maximum height of
a thin wall forming the boundary of a typical channel/chute.
A typical PK Weir can have the total length of the circuitous chan-
nel walls being about six times that of the spillway width that houses
the device. The relationship of total wall length-to-spillway width is
known as the N ratio. Also typically, the spilling channels are wider
than the receiving chutes. The maximum depth of the channels is
about a quarter of their length.
Tests show that oating debris can be a hindrance to discharge
rates as with any type of spillway. However, reduction in the specic
outow is about 15% but lessens as discharge rates rise further. As
with many hydraulic structures the use of a oating boom has helped
minimise the interference.
Other loading that may need to be considered includes ice pressure
on the myriad walls in their snaking alignment. The structure, if con-
structed of reinforced concrete and not a steel fabrication, may need
extra rebars in such instances.
A further benet is that the PK Weir should be able to be con-
structed of local resources and does not require to be an imported
hydraulic structure.
ACTIVITIES IN FR ANCE
Goulours Dam
In 2003, shortly after the PK Weir concept was generally made known,
EdF rapidly decided to test the concept at Goulours dam in the rst of
what was believed could become a series of upgrade projects.
The PK Weir concept was attractive for a variety of reasons,
explains EdF engineer Frederic Laugier, such as being able to increase
discharge capacity by providing high specic ow rates, the ability to
install them on existing concrete dams, and that relatively little main-
tenance would be needed. Further, the PK Weirs would also help to
raise the level, and therefore storage volume, in a reservoir.
Less than four years ago, EdF completed its rst PK Weir installa-
tion, at Goulours dam in south west France. The project started in
2003 and saw the basic concept tested for passing oating debris and
also adapted to the site needs in terms of geology, dam curvature and
constraints such as ice load, seismic load and concrete durability.
The Goulours dam was constructed in the early 1940s and is a
21m high concrete, single curvature arch gravity structure with a crest
length of 71m. Originally, the dam had only a central 4m by 4m gate
on a standard weir crest and a spillway down the face of the structure.
Laboratory tests with a 1/20 scale model showed the discharge capac-
ity to be 92m
3
/sec with a 1m nappe depth. However, the challenge
facing EdF was that the updated design ood is 162m
3
/sec.
Options considered included changes to the operating level of the
reservoir, construction of another spillway – either gated, standard or
labyrinth – or installation of fuse gates, an a PK Weir. The latter was
selected for its minimum impact and cost, and reliability. And, to ensure
the ongoing reliability of the existing gate, it is always to be operated to
spill rst and the PK Weir – installed on the right bank – would only be
required for major oods exceeding the 25-year return period.
The PK Weir was inserted in a 12m long section of the dam though,
due to typography, it is not strictly on the crest. It has two chan-
nels and three chutes – the ve conduits (alveoli) were the optimum
arrangement to minimise construction costs associated with achieving
the same total length of walls as seven and nine conduits. The built
walls are 3m high and 200mm thick, and the sloping slab thicknesses
are 200mm-350mm. The weir follows the dam curvature.
The construction schedule was achieved for the weir to be suc-
cessfully tested at the end of 2006. The total project costs was Euro
350,000.
Saint-Marc Dam
The development and operational success at Goulours gave the green-
light to further PK Weir installations in EdF’s portfolio where reha-
bilitation is needed due to insufcient discharge capacity.
EdF’s second PK Weir project was Saint-Marc dam, a late 1920s
structure near Limoges. The dam is a 40m-high concrete gravity
structure with two gates spillways, which have a combined capacity
ranging from 566m
3
/sec-623m
3
/sec, according to EdF estimates. The
new design ood (1000 year) is 750m
3
/sec.
The PK Weir is located between the existing gates and was com-
pleted in mid-2008 at a cost of Euro1.7M. It has been designed to
become operational after ows from the gates reach a total of 380m
3
/
sec, which equates to the 50-year return period event. The PK Weir
discharges – via its own unconventional “gutter ski-jump” half-length
spillway – into the main dissipation basin.
L’Etroit Dam
Another of EdF’s PK Weir projects is the L’Etroit dam, a 25m high
concrete gravity dam located upstream of Saint-Marc on the Taurion
river. It was built in the early 1930s with two gated spillways on the
right bank with a total discharge capacity of 456m
3
/sec.
The latest hydrological studies have estimated the design ood
to be approximately 570m
3
/sec. However, only an additional ood
discharge capacity of 75m
3
/sec is needed because of the attenuation
benet of another dam upstream – the Roche-Talamie.
Among the already recognised benets EdF saw in the PK Weir
solution, the utility also placed great emphasis on reliability and
operational safety of the system due to the remoteness of the site and
potential access difculties.
However, this project took PK Weir design in a further development
step with the introduction of a raised wall. The resulting capacity of
the PK Weir at maximum operation level is 100m
3
/sec – which is a
third more than would otherwise be available, though that would meet
the required additional discharge capacity at the dam.
IWP& DC
Upper view of a tested PK-Weir, trapezoidal shape, at the Laboratory of
Hydraulic Constructions
In the wake of a global financial crisis, with the additional concerns of environmental protection
and anticipated effects of climate change, and power shortages hampering socio-economicde-
velopment in some parts of the world, hydropower development has many solutions to offer.
The hydro profession is responding to the needs of a changing world,with innovations in plan-
ning methods, environmental assessments, technological innovation, approaches to financing
strategies, and optimized use of existing assets.
HYDRO 2010 will review progress and achievements, as well as needs and future challenges.
As usual, the Conference will focus strongly on the needs, priorities and plans of the developing
countries of Africa, Asia and Latin America, and discussions will cover technical, economic,
commercial and environmental/social aspects.
A major Technical Exhibition will run alongside the Conference and a full social programme will
offer extra networking opportunities.
Meeting Demands for
a Changing World
International Conference and Exhibition
Lisbon, Portugal ~ 27-29 September 2010
Organized by:
with
HYDRO 2010 CONTACT DETAILS:
Mrs Margaret Bourke,
Hydropower & Dams
, PO Box 285, Wallington, Surrey SM6 6AN, UK.
Tel: + 44 (0)20 8773 7244 • Fax: + 44 (0)20 8773 7255
Email: mb@hydropower-dams.com • Website: www.hydropower-dams.com
SUPPORTING ORGANIZATIONS INCLUDE: