Water Power and Dam Construction. Issue December 2010
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WWW.WATERPOWERMAGAZINE.COM DECEMBER 2010 21
PLANNING & PROJECTS
MARINE ENERGY DEVELOPMENTS
There have been major developments in the marine energy sector
recently, and it looks like these will continue over the coming years.
Early last month for example, the pioneering Wave Hub marine
energy project off the coast of Cornwall in South West England was
plugged in for the rst time since its installation over the summer
and is now ofcially open for business.
Wave Hub has created the world’s largest test site for wave energy
technology by building a grid-connected socket on the seabed 16km
off the coast, to which wave power devices can be connected and
their performance evaluated. The £42M project has been developed
by the South West RDA (Regional Development Agency) and is a
cornerstone of its strategy to develop a world class marine energy
industry in South West England and the UK.
Wave Hub consists of a 12-tonne steel chamber on the seabed
in 55m of water some 16km offshore connected to land via an
armoured subsea cable. The chamber splits the main subsea cable
into four 300m ‘tails’, each of which serves one of the four berths
available at Wave Hub.
The project holds a 25-year lease on an 8km
2
area of sea, and
each berth measures 1km by 2km. The Wave Hub site boasts one
of the best wave climates in Europe and the system has a capacity of
20MW, but is designed to be scaled up to 50MW in the future.
The project’s rst customer will be Ocean Power Technologies,
using its PowerBuoy wave energy converter.
Other major developments in the marine sector includes Atlantis
Resources Corporation recent successful deployment of its AK1000
tidal power turbine, believed to be the largest of its kind anywhere
in the world, on its subsea berth in 35m of water at the European
Marine Energy Centre (EMEC) in Orkney, Scotland where it will
undergo three years of testing.
EMEC recently completed a £5M expansion, taking the number
of test sites from nine to twelve. As well as Atlantis, Voith Hydro
Ocean Current Technologies contracted to begin installing turbine
prototypes on the new tidal berths this year, Finnish company Wello
Oy is preparing to trial a wave energy device next year, and Scottish
Power Renewables and E.On have just joined forces to trial two
Pelamis wave power machines at the centre.
There have been numerous other marine and tidal projects in
development recently, and details of these can be found on our
website: www.waterpowermagazine.com. Once these projects
begin commercial operation, they are likely to have a major effect
on renewable power development globally.
PUMPED STORAGE WORKING WITH OTHER
RENEWABLES
The issue often at the forefront of many hydro engineers discus-
sions is the use of pumped storage to control the power balance in
a network.
There is no doubt that the hydropower industry will grow as more
variable renewable energy come onto the grid. The US Department
of Energy (DOE) for example predicts that growth in wind power
alone will require an additional 50,000MW of energy storage on
the grid, creating a strong opportunity for new pumped storage
development.
The countries which already have a higher penetration of renewa-
ble energy into the grid/or are planning for a large renewable capac-
ity; are also planning to ramp up their pumped storage capacity at
the same pace. Even companies with higher wind installation are
looking to develop their own pumped storage plants for the opti-
misation of renewable energy sources. A recent report by business
information company GlobalData showed that an increasing trend
in pumped storage installation can be observed in countries with a
higher renewable penetration plan.
Pumped storage is the most established and efcient energy stor-
age technology – so far no other storage technology meets the cri-
teria to absorb the intermittent nature of renewable energy sources
on a larger scale in a cost effective manner.
As wind power continues to develop globally, so too will pumped
storage. This technology is likely to attract some major investments
from both the public and private sector, and we will no doubt see
new projects spring up throughout the world to join the many
projects currently under development, such as the Ingula project
in South Africa, Nant de Drance in Switzerland, and Limberg II in
Austria.
Below: Construction work underway on the Nant de Drance PS scheme
Top 5 developments in hydro
Above: Atlantis Resource Corporations AK100 tidal power turbine
22 DECEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING & PROJECTS
ADDING HYDROPOWER TO EXISTING DAMS
At the end of last year, the National Hydropower Association in the US
released details on a report that examined the hydropower industry’s job
creation and capacity growth potential. The Job Creation Opportunities
in Hydropower report, prepared by Navigant Consulting, said that the
US hydropower industry could install 60,000MW of new capacity by
2025, creating up to 700,000 new jobs. Much of this potential could
be found at existing facilities, as in the US only a small percentage (3%)
of dams are used to generate electricity.
There are many more opportunities globally. Dams that have cur-
rently being used for water supply and recreation could be utilised for
the multiple purpose of power generation. As the facilities already exist,
it is a case of adding the extra equipment at, often, minimal costs.
There is a variety of equipment in the marketplace that can be
utilised at existing projects. Last month, for example, we carried an
article looking at Norwegian rm CleanPower AS’ latest offering – a
combined axial turbine and generator called the Turbinator. The unit,
which is a compact fully sealed generator, can be installed at a site
without the need for a powerhouse. A pilot installation, in coopera-
tion with Statkraft, was recently completed, with the unit operational
more than 98% of the time.
In the US, Texas-based renewable energy systems developer and
integrator Hydro Green Energy has developed patented hydroki-
netic technology which is deployable downstream, in the tailrace,
from existing hydropower projects. This system, which is known
as Hydro+, bolsters the overall clean energy output of the existing
project in an environmentally-sound manner. This type of project is
an innovative approach to conducting an incremental hydropower
upgrade, which is eligible for a variety of green energy incentives.
In late 2008, Hydro Green Energy, in partnership with the City
of Hastings, MN, installed the US’ rst-ever commercial, federally-
licensed hydrokinetic power station. Power operations began in early
2009 at this Hydro+ facility, which is a 4.4MW run-of-river hydro
plant on the US Army Corps of Engineers’ Lock & Dam No. 2.
The company has also developed a patented technology that allows
for power generation at existing non-powered lock and dam infra-
structure. Known as Lock+, this patented technology is a power-
generating lock gate that is deployed in the downstream portion of
an auxiliary or active navigational lock, thus converting the facility
into a renewable waterpower facility. Hydro Green’s technology is
also deployable in the cooling water discharge systems at thermal
power plants for energy recovery or energy efciency purposes and
is called Efciency+.
SMALL HYDRO
Small hydro is big business. As governments strive to meet grow-
ing renewable energy targets, small scale hydropower projects look
an increasing attractive option. According to a new report, Global
Small Hydro Power Market Analysis to 2020: Installed Capacity,
Generation, Investment Trends and Regional Analysis, produced by
industry analysis specialist company GlobalData, small hydro power
generation is gaining importance due to its social and nancial ben-
ets over large hydro power, with global small hydro cumulative
installations growing at a CAGR of 6%.
China currently has the largest market in small hydro, with the
use of government incentives one of the reasons behind the success-
ful development of such resources, including obtaining grant subsi-
dies and low-interest, long-term loans from the central government;
keeping prot from existing plants instead of handing it over to the
government for further expansion of the electricity sector; and the
introduction of public-private participation in the small hydro eld.
Internationally, the classication of small hydro projects typical-
ly ranges from 5MW-20MW but in China the scale encompasses
projects up to 50MW. By the end of 2007, rural small hydro stations
accounted for over 53GW of total installed capacity, with much more
under development.
In China, over a quarter of the population is supplied by small
hydro but such gures are not replicated across the globe. In numer-
ous developing countries a large proportion of small hydro potential
is yet to be harnessed. For example, in Africa there is huge potential
but less than 20% of possible resources have been exploited and the
majority of the population there has no access to electricity.
Only 4% of the population has access to electricity in Rwanda, and
the comparable gures for neighbouring countries include 7% in the
Democratic Republic of Congo, 8% in Kenya and 13% in Ethiopia.
Furthermore, in other countries a large number of small hydro sta-
tions have been built but many are not operational or are operating
inefciently. The majority in Malaysia – 35 out of 42 stations – need
to be refurbished.
There is massive potential in small hydro and lately it seems that
the world’s governments are beginning to recognise this. For exam-
ple, a number of countries are now providing cash incentives for
home owners to implement small hydro projects on their land. In
the UK for example, Climate Change Minister Greg Barker recently
announced that former mills and water turbines which are brought
back to life in the UK will now be eligible for nancial support under
the UK Government’s feed-in tariff scheme. To help drive forward the
ambitious new plan, the Department of Energy and Climate Change
(DECC) is also launching the new hydropower help guide, prepared
by the Environment Agency, which offers advice to groups looking
to use the power of local streams, weirs or rivers to cut emissions and
generate new income for their areas.
Currently hydropower in the UK is generating the equivalent of
1.4% of electricity demand with a potential to contribute up to a
further 1%– enough to power the equivalent of one million homes.
In the last two years alone the EA have seen a 12-fold increase in
applications for hydropower permits.
Such developments offer many opportunities for the industry – in par-
ticular the equipment manufacturers who will be needed to kit out new
projects or work on the refurbishment of existing schemes.
IWP& DC
Above: View of the Hastings site in the US
Above: View of the dam at the Canedo small hydro project, Portugal
instrumentation, data acquisition and
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The latest issue of
Dam Engineering
is on its way to subscribers.
This issue contains the following papers:
%
Design procedure for a spiral casing for hydraulic turbines with a numerical flow study by Ahmed
Alnaga & Jean-Louis Kueny.
A smart design procedure for a spiral casing for hydraulic
turbines has been developed and described.
%
Dynamic analysis of anchored concrete linings of plunge pools loaded by high velocity jet
impacts issuing from dam spillways by Maziar Mahzari & Anton J Schleiss.
A theoretical stochastic
approach for the structural analysis of plunge pool liners dynamically loaded by the impact of free-falling jets.
%
Investigation of compaction methods of embankment cores in high rainfall regions by J Jalili & M Jahanandish.
In this paper a
literature review of trends applied in the construction of embankment dam cores in wet regions is presented, followed by an
experimental procedure, as a rule for choosing the best compaction method for such soils.
%
Performance evaluation of a vortex-type sediment extractor with diaphragm by Nayan Sharma, D Das & Gopal Das Singhal.
The
study reported in this paper investigates the effect of the variation of key components of a vortex extractor.
%
Shape optimisation of the new section in raising existing concrete gravity dams using genetic algorithm by Mahmoud R Maheri & M
Ranjbarzadeh.
A simple genetic algorithm (GA) is adopted to optimise the shape of the new section in a raised gravity dam.
Dam Engineering is an academic journal, published quarterly. It contains refereed papers on subjects related to all areas of
dams and hydro power. At present there is no restriction on the length of submitted papers.
For information on submitting papers, or for more details about subscribing to
Dam Engineering
, contact: Tracey Honney,
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New Issue of
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DamEngineeringAD_May2010 26/5/10 15:48 Page 1
24 DECEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING AND PROJECTS
A
NUMBER of Piano Key Weir (PK Weir) spillways are
under construction in Vietnam to function in conjunc-
tion with other structures, such as gates. A range of col-
laborative research is also underway in the country to
explore further applications, for example working in combination
with stepped faced on RCC dams to increase energy dissipation.
PK Weirs spillways have recently developed out of the eld of
short, labyrinth-type hydraulic structures. The concept was pre-
sented almost a decade ago by Lemperiere and Ouamane, and, fol-
lowing some years of concept development, the rst PK Weir was
installed four years ago, at Goulours dam in France, by Electricite
de France (EdF).
Interest in PK Weir spillways is increasing internationally, reected
in increased research and applications. Next February, an interna-
tional workshop on labyrinth and PK Weirs will be held in Liege,
Belgium, and will include a visit to a hydraulics laboratory and a
technical tour of works at some EdF dams.
However, it will be clear that while the conference has a European
platform, Vietnam is also growing in importance with regards to both
projects and research. Two new dams are under construction in the
country with PK Weirs – Van Phong and Dakmi 2 – and there are
two more in design – Ngan Truoi and Vinh Son 3. A PK Weir is also
involved in Lower Sesan 2 hydro project. In terms of research, there
has been work that goes beyond the challenge of combined use of PK
Weirs with gated spillways on gravity dams to examine their utilisa-
tion with stepped spillways in RCC dams.
A key contributing agency to the early, and ongoing, research is
Hydrocoop, a non-prot association of experts in spillways, oods
and sedimentation.
THE PK WEIR DIFFERENCE
In terms of spillway design, a PK Weir is a variation on a labyrinth
spillway. Both are simple structures but hydraulically complex, the
PK Weir even more so.
Measured along a dam axis, both types of weir are relatively short.
However, with their ‘folded’, or zig-zag, geometries (as viewed on
plan), they offer longer crest lengths to pass a ood. Consequently,
they offer hydraulic solutions to achieving signicantly more ood
discharge capacity without the need to widen a dam or the top chute
at existing structures. At new structures they can also offer relatively
compact solutions with high discharge and low overow depth.
What is different between general labyrinth and PK Weir is that the
former consists of interlocking vertical walls that require a wide foot-
ing area, and which needs either a bigger bite out of an existing dam
or a larger new dam for that section, whereas the latter does not – a
smaller footprint solves the need. It also is more efcient.
A PK Weir is a major evolution in weirs as it is a self-balanced
structure, with no mechanical components, that sits on a small foun-
dation and can be either built from precast concrete or prefabricated
steel. It is able to achieve the high crest length to low foundation area
ratio by employing an alternating sequence of overhanging channels
- either upstream and downstream, or upstream only but by a much
longer distance – and chutes to receive the spilled water.
The channels then act as alternating ponds and chutes. In these
In addition to their application on some
dam upgrades in France, Piano Key Weirs
are being increasingly researched as well
as employed on new projects in Vietnam.
Report by Patrick Reynolds
Above, main: Construction underway at Van Phong dam, which will have two
sets of PK Weirs; Above: Physical model of Van Phong barrage, including very
long PK Weirs spillways at sides to limit upstream water level
PK Weirs in Vietnam
WWW.WATERPOWERMAGAZINE.COM DECEMBER 2010 25
PLANNING AND PROJECTS
serrated, free-ow structures, the majority of water spills over the long
sides of the pond channels and falls onto chutes to be discharged down
the main, or a supplementary, spillway. It is this run of chutes and
channels that has won this type of weir the moniker of ‘piano key’.
Lemperiere and Ouamane initiated the development of PK Weirs
by discussing the footprint restriction of labyrinth weirs despite the
benet they could bring of providing greater crest length and conse-
quently higher specic ows, and the possibility of also allowing for
greater live reservoir storage compared with gated spillways. Research
moved forward in the late 1990s through Hydrocoop, and hydraulic
laboratory tests were performed in France, India and Algeria.
The PK Weir can pass at least four times the specic discharge of
a classic (Creager) weir for a relatively low overow depth. Specic
ows range from 3m
3
per m to 100m
3
per m, say designers.
VIETNAM PROJECTS
The projects under construction or in design in Vietnam that feature
PK Weirs include:
Van Phong
The Van Phong barrage is a 475m long, 18m high reregulating struc-
ture under construction on Song Con River in Binh Dinh province in
the centre of Vietnam. It will also have a 6MW powerhouse in the right
abutment. In addition to its central, 172m long spillway with 10 radial
gates, the barrage will also have PK Weirs of 121m and 181m lengths,
respectively. The design ood event is 15,350m
3
/sec and the maximum
combined design discharge of the PK Weirs is 8700m
3
/sec.
The PK Weirs were selected as part of the project design as they
can spill a signicant discharge for a low nappe depth, which ts the
site constraint of there being low allowable upstream water level,
says researcher Michel Ho Ta Khanh, adding that the combination is
better than solutions with either all gates or aps gates.
Dakmi 2
Dakmi 2 is a multipurpose scheme with irrigation and hydro fea-
tures (98MW) under construction on the Dakmi River in Quang
Nam province. The dam is a 38m high, 145m wide concrete gravity
structure in a narrow valley with a high ood discharge.
The dam has been designed with a 31m wide, central gated spill-
way, and 37.5m wide PK weirs on each side of the structure. The
maximum discharge capacity of the gates spillway is 3000m
3
/sec and
combined capacities of PK Weirs is 3440m
3
/sec, and together they are
designed to pass a on 1000 year ood of almost 6500m
3
/sec.
Khanh notes that the PK Weirs were chosen for the same reasons
as on the Van Phong project, but adds that the Dakmi 2 dam also has
a stepped spillway for increased energy dissipation. In addition, the
design avoids the need for extensive excavation on the steep left bank
and also provides for good aeration of the overow, which minimises
the size of the stilling pond.
Ngan Truoi
A 96m long PK Weir with a discharge capacity of 1126m
3
/sec is to be
built on the right bank of the Ngan Truoi irrigation barrage, presently
under design for construction in Ha Tinh province. The design ood
for the project is almost 2500m
3
/sec, and the barrage will also feature
a 72.5m long spillway with ve radial gates on the left bank.
Vinh Son 3
Under design for construction in Binh Dinh province, the Vinh Son 3
hydro project may feature a PK Weir in its ood discharge capability.
The PK Weir is being explored as a non-gated and less expensive
alternative in capital and operating cost terms.
The design ood at the 51m high, 317m high dam is 4000m
3
/sec.
Lower Sesan 2
The Lower Sesan 2 hydro project is being developed as part of a
larger scheme with Sesan 5 on the Vietnamese-Cambodian border.
Construction is due to start in 2011.
RESEARCH
A combination of PK Weir and gated spillway is often the optimal
solution for passing oods at dams, as indicated by these studies in
Vietnam, says Khanh, who has been working for more than ve years
with Vietnamese engineers and with the support of Hydrocoop on
such work and research.
Earlier this year a paper he co-authored with Dr Truong Chi Hien,
on combining PK Weirs and stepped spillways, was given at the
ICOLD meeting in Hanoi. Khanh explains that tests with PK Weirs
have been carried out in the hydraulic laboratory of the HCM City
University of Technology. The tests have looked at: different charac-
teristics and performances of shapes and sizes of PK Weirs; energy
dissipation through analysing 2D and 3D stepped spillways; scour
at the dam toe; and comparing different types of weir and the down
stream face of the spillway.
Principal conclusions from the research are: that RCC dams in high
narrow valleys prone to high ood discharges could benet from the
combination of PK Weirs and stepped spillways, enabling shorter still-
ing basins to be built; and, that while PK Weirs can help reduce scour
the contribution may be signicant only for the lower spillway chutes.
To conrm these ndings, and examine how to optimise using
both PK Weirs and stepped spillway, more research is required,
says Khanh.
IWP& DC
Further information
The international workshop on labyrinth and PK Weirs to be held next year will
be at the University of Liege, Belgium, on 9-11 February.
For further information, please contact: Sebastien Erpicum, Université
de Liège, HACH, Chemin des Chevreuils, 1 B52/3, 4000 Liège, Belgium
Email: pk-weirs@ulg.ac.be Website: www.pk-weirs.ulg.ac.be
The website for Hydrocoop is www.hydrocoop.org
Below: Physical model of Dakmi 2 dam with PK Weirs and gates spillway for
hydraulic tests; Hydraulic test underway with model of Dakmi 2 dam
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WWW.WATERPOWERMAGAZINE.COM DECEMBER 2010 27
PLANNING AND PROJECTS
C
ONSTRUCTION is underway on a scheme to provide
the UK’s second largest airport with greater ood pro-
tection. Work on the multi-million pound Upper Mole
Flood Alleviation Scheme started in May 2010 thanks
to £11M (US$17M) of funding from the Environment Agency, a
£4M (US$6M) contribution from Gatwick Airport and £100,000
(US$158,000) from Crawley Borough Council. The work is sched-
uled for completion by 2013.
The upper reaches of the River Mole are at risk of ooding, and
more than 1300 homes and businesses across the nearby towns of
Crawley and Horley are set to benet from the project. Properties
in the towns have previously suffered from the devastating
effects of ooding, including serious incidents in 1968 and 2000
and smaller oods in other years. The areas of Furnace Green
and Three Bridges are particularly at risk. In addition Gatwick
Airport, which is the busiest single runway airport in the world,
is vulnerable to ooding from three watercourses. A major ood
could cause the whole airport to close for a period of weeks whilst
specialist equipment is replaced; causing major disruption to the
whole region.
Ian Tomes, Area Flood Risk Manager for the Environment
Agency, said: “This is an exciting project and one that will poten-
tially benet hundreds of residents in the area. It also has the
added bonus of helping to safeguard the operation of Gatwick
Airport. As has already been seen, ooding is very destructive and
so it is vital we do everything we can to reduce the impacts where
and when we can.”
Stewart Wingate, Chief Executive of Gatwick Airport, said: “We
are delighted to be part of the Environment Agency’s scheme to bol-
ster the ood protection for the airport and surrounding areas. In
2000 the A23 road under the airport’s south terminal was closed
because of torrential rain, and this scheme will dramatically reduce
the risk of this happening again.”
The Upper Mole Flood Risk Management Scheme comprises four
separate elements which, when combined, will increase the storage
capacity of ood water to 1.8Mm
3
.
The rst phase of the scheme will raise the level of the existing dam
at Tilgate Lake in Crawley. The crest of the dam will be raised (with no
change to normal water level) and an orice plate added to attenuate
outows from the existing spillway, thus providing ood storage.
The Upper Mole Flood Alleviation Scheme
in the UK will reduce Gatwick Airport’s
vulnerability to ooding
Runway success for flood protection
Table 1: Key parameters
Parameter Units Value
Existing
(2009 survey)
After
raising
Catchment area km
2
2.57 No change
Reservoir volume
a) permanent impoundment
m
3
106,000 No change
b) controlled ood storage m
3
Nil 233,000
c) Total m
3
106,000 339,000
Surface area at
overow level
m
2
68,000 No change
Crest of non-overow
embankment
mOD 88.02 91.10
Maximum storage level mOD 87.02 89.72
River Bed level mOD 80.8 No change
Dam height above stream bed m 7.4 10.5
Diameter of orice to attenuate
ood ows
m N/A 0.35
Tilgate dam spillway form works: workmen level
concrete over the steel reinforced control structure
28 DECEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING AND PROJECTS
RAISING TILGATE
Improvements to Tilgate Dam include raising the existing earth
embankment dam to provide ood protection for a 1 in 1000-year
event. Key parameters, for both the existing and proposed dam, are
provided in Table 1
The proposed option is raising the dam crest on the downstream
face to effectively create a new dam. A downstream slope of 4H:1V
is adopted for ease of maintenance of the grass cover. Raising the
existing embankment by construction of a new portion of embank-
ment on the downstream side was selected to avoid disturbance to
the reservoir and existing upstream face and dam crest. ‘Raising’ only
commences on the downstream side of the existing crest path to mini-
mise the load imposed on the existing dam.
In order to provide added condence in the temporary stability of
the downstream face of the existing embankment it was determined
that the reservoir should be lowered by not less than 2m during the
construction period. Such a lowering could retain the existing factor
of safety against uplift at the downstream toe of the dam.
The design assumes that ll procured from within Tilgate Park
will be used as general ll for the majority of the embankment. The
ground investigation has indicated that the geology at the site is
interbedded mudstones, siltstones and ne sandstones which tend to
weather to silty clay and sandy silty clay with some gravel. These
materials are considered suitable for general ll and investigation into
their use as core material has been implemented as part of a value
engineering exercise.
The spillway to discharge extreme floods is an overtoppable
embankment spillway with grasscrete armour layer situated on the
right abutment and thence into the sherman’s car park. The spillway
should operate, in theory, only once every 1000 years and has been
designed to safely discharge the probable maximum ood.
A stilling basin has been provided to destroy the energy of high
velocity ow over the spillway to minimise the risk of damage for
oods in excess of 1 in 1000 years. This is a shallow depression at
the toe of the spillway, with a pipe to drain rainwater laterally into
the middle of the valley.
The control structure to attenuate ood ows whilst retaining
the existing normal reservoir level will be in the area of the existing
structures on the right abutment, with control provided by an orice
plate with an open area of 0.10m
2
. A right abutment outlet will be
provided to replace the existing 0.6m diameter outlet on a like for like
basis in its existing alignment. This allows the reservoir to be lowered
by about 1m in a day, for the top 1.5m
The results of the 2006 and 2009 ground investigations show that
the embankment comprises soft sandy silty clay overlying alluvium
and terrace deposits which in turn overlie Upper Tunbridge Wells
Sands (UTWS). The UTWS comprises interbedded mudstones and
siltstones with occasional sandstone beds. Excavatability of UTWS,
both in terms of potential borrow area, and foundations for outlet
structures on right abutment could be a key issue.
In addition, near the dam there are long standing seepages emerg-
ing at the toe of the dam, and artesian groundwater was encountered
in a borehole at the toe of the existing dam. To the east groundwater
levels rise above reservoir level in the valley side
Construction work at Tilgate dam started on site in May 2010 and
has a programmed completion for the end of May 2011. The princi-
pal contractor for the works is Morrison Construction Ltd.
FLOOD STORAGE
There are three other ood storage areas and a river restoration site,
which together with the works at Tilgate Lake, make up the Upper
Mole Flood Alleviation Scheme. Two of the ood storage areas,
Worth Farm and Ield, are greeneld sites on the Gatwick Stream
and River Mole, respectively. The third site, Clay’s Lake, near Pease
Pottage, is on a tributary of the Gatwick Stream and like Tilgate
Lake, is an existing lake and involves raising the existing embank-
ment dam. Construction at these sites is currently expected to begin in
March 2012 and be completed by September 2013. The ood storage
capacity at each location is shown in table 2.
The capacity of each of the ood storage sites has been optimised
based on current guidance for climate change impacts given by
the Department of Environment, Food and Rural Affairs (Defra).
As a consequence, a precautionary approach has been adopted in
the designs for Tilgate Lake, Clays Lake and Ield and an adaptive
approach for Worth Farm. The designer for the ood storage sites
is Jacobs.
Inevitably in a large scale project such as this one there will be
some loss of woodland and vegetation. To offset this loss, new trees
will be replanted and new wildlife habitats will also be created. The
Environment Agency is taking the opportunity of carrying out these
major works to implement over ve hectares of Biodiversity Action
Plan habitat, including the regeneration of wet woodlands which are
extremely rich in invertebrate life and support a very large number of
native species.
By Graham Piper, Upper FAS Project Executive, National
Capital Programme Management Service, Environment
Agency. www.environment-agency.gov.uk
Tilgate Lake
Tilgate Lake is an existing reservoir in Tilgate Park in south Crawley, situated
on a tributary of Gatwick Stream, which itself is a tributary of the River Mole,
joining just downstream of Gatwick Airport.
Tilgate Lake is believed to have been built as an ornamental lake, probably
around 1861 when the site was purchased and the mansion built. Inspections
under the Reservoirs Acts commenced in 1958, and it was acquired by Crawley
Borough Council in 1964. The current spillway and outlet were built in 1965,
whilst the toe drains and V-notch were installed in 1970. Following overtopping
in the 1968 oods, the spillway capacity was increased by raising the dam by
0.6m in 1970. The sheet piling along the upstream face was added in 1992.
The existing reservoir comes under the Reservoirs Act 1975, as being
designed to retain more than 25,000m
3
above ‘lowest natural ground level’.
After a reservoir safety inspection in 2007 various requirements were identied
and included that:
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Left: Ian Tomes (Flood Risk Manager, Thames Region of the Environment
Agency), Councillor Keith Blake, Stewart Wingate (CEO Gatwick Airport) and
Graham piper (Project lead Environment Agency)
Table 2: Flood storage capacity
Flood storage location Max. height (m) of
dam above river bed
Flood storage
capacity m
3
Worth Farm 7.0 230,000
Clays Lake 10.8 350,000
Ield 2.7 520,000
IWP& DC
Shaver Lake dam, USA 2010/2011/2012 – Waterproofing of a con-
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Carpi_dec10.indd 1 15/12/10 09:59:57
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Untitled-1 1 13/7/10 09:00:27
1
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30 DECEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING AND PROJECTS
C
LIMATE study ndings indicate that it will be neces-
sary for industrial nations to reduce their greenhouse gas
emissions by 80-95% by 2050 (IPCC 2007) – a goal that
was ofcially endorsed by the Council of the European
Union in October 2009. The European Union has established the
target of achieving a 20% share of renewable energies in the over-
all energy mix by 2020. To reach this goal, 34% of Europe’s elec-
tricity needs must be met by renewable technologies, with wind
power taking much of the increase.
In a recent study published by the European Commission (Caprose
& al 2009) it is estimated that renewable electricity production in the
27 countries in EU will increase from 467TWh/yr in 2005 to 1343 Wh/
yr in 2030. At the same time, the percentage of energy created from
wind power will increase from 15% in 2005 to nearly 50% in 2030.
Hydropower is expected to grow slowly in the EU since most of the
available sources have already been developed, with an increase from
307TWh in 2005 to 355TWh in 2030 (not including Norway which is
not member of EU). In 2005 hydro contribution is 66% of all renewa-
bles, this percentage will gradually decrease to 26% in 2030, according
to the Baseline 2009 Scenario. In total, this will bring renewable up to
supply nearly one third of electricity demand in Europe in 2030.
In another study, the German Advisory Council on the Environment
(SRU) investigated options for a reliable electricity supply in Germany,
completely based on renewable energy sources by 2050. This report
(SRU, 2010) shows that such a transition is possible, and that the main
contribution of new renewable electricity production would have to
come from wind power, mostly from offshore wind. But the report also
points to the fact that a system with mainly wind power will be vulner-
able due to large variability in wind power generation, and that some
sort of backup is needed to supply balancing power during calm peri-
ods. Hydropower, and in particular Norwegian hydropower, is seen
as the main contribution to load balancing, due to many large storage
reservoirs and the possibility to develop new pumped storage capacity,
utilising existing reservoirs. The energy storage capacity of Norwegian
reservoirs amounts to ca 50% of the total in Europe.
Other, similar studies have been published and the trend seems
clear. The expected increase in renewable electricity production in
Northern Europe will mainly come from wind power, and in particu-
lar from offshore wind parks in the North Sea. The variability in wind
will, however, also make it necessary to build a system of balanc-
ing power in order to maintain system stability. Today, hydropower
seems to be the best option for producing such balancing power, in
particular as pumped storage plants where water can be pumped into
upper reservoirs during periods of surplus wind and returned during
calm periods. The Norwegian hydropower system can give a very
important contribution to the development of renewable energy in
Europe, if new capacity is built and the grid is strengthened in and
around the North Sea.
In the German study (SRU, 2010) up to 60,000 MW of new hydro-
power capacity was included in the scenarios. In other, ongoing stud-
ies in Norway 20-25,000MW of new capacity is seen as realistic. The
new capacity will only be built in areas with existing hydropower
projects and will not require the construction of new reservoirs.
THE NORWEGIAN HYDROPOWER SYSTEM
Hydropower has been developed in Norway since 1885 when the
rst plant was commissioned. Today the total capacity is nearly
30,000MW and the average annual energy production is 120TWh,
supplying almost 99% of all electricity consumption in Norway. The
reservoirs can store 84TWh of energy, or nearly 70% of the average
annual inow. The total hydropower potential has been estimated to
The HydroPEAK project in Norway is researching the interaction between wind and water
power. As well as evaluating the current role of renewable energy in the European system
today, it is also looking towards the future
Hydro reaches the PEAK
2005 2010 2015 2020 2025 2030
TW
h/
year
1600
1400
1200
1000
800
600
400
200
0
Solar
Biomass/waste
Geothermal
Tidal
Wind offshore
Wind onshore
Hydro
Below: Figure 1 – Europe will probably build much wind power during the next
20 years in order to meet the 20/20/20 goals. A large part of the new
renewable capacity will be offshore wind power in the North Sea.
Renewable Energy Development in EU Baseline Scenario (Caprose & al, 2009)