Water Power and Dam Construction. Issue September 2010

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WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 41

UPRATING & REFURBISHMENT

pied by three privately-owned domestic properties. These homes are

built into the dam, which increases the difculties in establishing a

means to protect against internal erosion along the entire length of

the dam. The team has also had to work closely with the residents, to

ensure that major civil engineering operations can be completed on

the cherished gardens.

Chasewater Country Park is a high prole venue, popular with

residents and visitors. Because of this, the works will be complet-

ed under the closest public scrutiny. And, with a circumference of

approximately 6.4km and numerous entry points, it is impossible to

prevent public access to the park – and neither would we want to,

because people come to the park to relax in the natural peace and

quiet, to participate in water sports and to enjoy a ride on Chasewater

Railway, a growing heritage steam railway.

Since the ending of mining and heavy industrial activity in the area,

the park’s ecological and bio-diversity value has rejuvenated spec-

tacularly. Now large parts of the reservoir are designated as sites of

special scientic interest (SSSI). Of particular interest to ecologists is

the presence of the European protected species of great crested newts,

little ringed plovers and oating water plantain. Because of this, all

engineering plans have had to be designed and implemented in a way

which meets with the approval of Natural England, and which mini-

mises the impact on the area’s ecological value.

We also knew that to complete any works to the toe of the dam,

the water level of the reservoir would need to be lowered signicantly,

if not completely emptied. But the area’s industrial and coal mining

heritage has left a legacy of pollution, which could be mobilised as

the level drops, and the reservoir bed becomes increasingly exposed.

Initial tests suggested that the risk of discharging heavily polluted

water was minimal, but more condence was needed to conrm that

water of poor quality would not be pumped into the canal and hence

into a Special Area of Conservation further downstream.

Overshadowing all of these issues is that fact the Licheld District

Council is a small organisation with limited nance to meet the costs

of bringing the reservoir to an acceptable standard. Moreover, it

inherited the reservoir as a result of a local government boundary

change, and had no real desire to own it. The council also has limited

opportunity to exploit the water to their benet to cover the cost of

any works, as the rights to the water in the reservoir remain with

British Waterways.

Licheld District is home to just 40,000 council taxpayers. The

possible repair bill of £5M (US$7.9M) would cost each household

£125 (US$199) – which would represent a council tax rise of approx-

imately 80%. With the UK government forcibly preventing rises

greater than 5%, there is little opportunity for the council to meet

the costs of the improvement works without it signicantly impact-

ing upon the provision of core services offered by the council. In

consequence, any expenditure incurred and planned comes under the

closest political scrutiny.

THE TEAM

Licheld District Council takes its responsibility for maintaining

Chasewater extremely seriously, but as a small local authority, it

understandably has no in-house engineers and other specialists. Given

the complexity of the project, the council has appointed a highly

skilled and experienced team to ensure that action taken to reduce

the risk of failure are proportionate and practicable.

Below: View of the reservoir

Above: View of the eastern dam, before the reservoir was re-drained

42 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

The team is led by Ron Bridle of Dam Safety, who has appointed

Ian Carter of MWH, Alan Brown of Jacobs, and Dr Jean-Jacques

Fry, Head of Reservoir Safety at EDF, France to a specially formed

Chasewater review panel.

The panel provides technical insight and academic challenge, and is

supported by geo-technical, geological and water chemistry expertise

from Adrian Jones of MWH, plus Simon Hake and Rob Reuter of

Wardell Armstrong.

Bringing all this together and bridging the academic and technical

gap between engineers and the council has been Rob Travis of Travis

Baker Associates, the council’s consulting engineer. David Brown of

British Waterways acts as the reservoir’s supervising engineer.

Ryszard Kawak of Townsend and Renaudon has accepted the most

difcult task of estimating and controlling the construction costs of

the emerging designs.

To ensure that the council operates within conservation legislation

and to minimise the negative impact on the area, Penny Anderson

Associates has been appointed to advise and implement appropriate

mitigating actions.

THE ENGINEERING PROPOSALS

To meet contemporary standards, Chasewater needs to be able to

withstand the effects of a 1 in 10,000 storm. A report by Jacobs sug-

gested that in the event of a probable maximum ood, ows into

the reservoir would peak at around 77m

/sec, compared with an

existing discharge capacity of just 10m

/sec, causing the water to rise

uncontrollably, and overtop the reservoir’s western embankments

and eastern dam.

To improve the overow capacity, an extra culvert is to be installed

in the railway causeway that divides the two parts of the reservoir.

This should remove the threat to the western embankments.

Further downstream, the main overow structure is to be exten-

sively remodelled and extended into the SSSI to ensure that it will

be able to discharge the volume of ow expected during a period of

heavy rain.

These works ought to ensure that the reservoir will be able to with-

stand the worst weather imaginable in this part of the UK.

But the solution for internal erosion has been more difcult to deter-

mine, so a series of detailed tests were conducted. These have included

two erosion measurement tests on core samples taken from the dam.

The hole erosion test (HET) and the jet erosion test (JET) were car-

ried out by Geo-Consult in France, under the supervision of Dr Jean-

Jacques Fry. The results showed the dam is an unzoned heterogeneous

earthern embankment comprising mixed alluvial and glacial materials

(including sands, gravels clays and some peat) and colliery spoil. This

knowledge has helped the team to predict the behaviour of the dam,

and importantly provide an insight into how it might erode and fail.

The results also showed that pore pressures in the dam, and hydro-

logical gradients were not too high, which has given the team con-

dence that the dam is stable enough to have the improvements work

carried out.

The proposed solution is to install sand lters that will trap the

smallest particles expected to be present, supplemented by relief wells,

along the entire length and height of the eastern embankment. This

will involve scraping the top soil and vegetation from the surface, and

installing a 200mm layer of graded ne lter material, covered with

a second layer of coarser graded lter material to a depth of no less

than 200mm, and then surfaced with the replaced topsoil. This will

also see the gradient of the downstream face reduce from a typical 1

in 3 slope to 1 in 2.5.

Where lters cannot be installed, for instance around the properties,

sheet piled walls are to be driven into the dam to provide an imperme-

able barrier and to direct the water towards high volume lters.

All this work will potentially leave the pipe between the reservoir

and the canal as the remaining weak link. As part of the works, the

pipe will be relined, so it can operate satisfactorily.

The council has undertaken a tendering exercise to appoint a suit-

ably skilled and experienced contractor to carry out these works.

Appointment was expected during July 2010, and the works are

expected to take around six months to complete.

In preparation for the works, the valves to the reservoir were

opened in February 2010, and the water has now reached canal level

at 144m AOD. Before the works to the downstream face can begin,

the remaining water will be pumped out.

FACING UP TO RESPONSIBILITIES

Ensuring the safety of Chasewater remains a most difficult and

burdensome obligation for an organisation like Licheld District

Council. But despite the multitude of challenges and complexi-

ties, Lichfield District Council has faced up to its responsibili-

ties and is nearing a position to carry out the required works

that will safeguard the structure of the dam, the reservoir,

the local wildlife, and nearby communities in years to come.

The lack of historical records has presented our engineers with a

unique challenge both to appreciate the condition of the dams and to

design an improvement scheme which not only addresses the twin threats

of internal erosion and overtopping, but which is proportionate,

practical and affordable.

Through this work, Licheld District Council will also ensure

that Chasewater continues to supply the canal network that runs

through the West Midlands with water thereby supporting thou-

sands of businesses, jobs and communities for many decades

to come.

Neil Turner and Lizzie Thatcher, Licheld District Council,

Frog Lane, Staffordshire, WS13 6ZD England

Readers can keep up-to-date with progress at Chasewater

dam via the project blog –www.lichelddc.gov.uk/

chasewaterdamblog

IWP& DC

Below: Eastern dam, before Chasewater was re-drained

44 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

HELAN County PUD owns and operates the Rocky Reach

hydroelectric project located just outside of Wenatchee,

Washington, on the Columbia River in the US. The project

consists of 11 generating units, the first of which was

installed in the early 1960s. Units C1 to C7 generators were originally

commissioned beginning in 1961, and were designed and supplied

by Westinghouse. Except for rewinds performed in the 1980s, the

117MVA machines ran fairly reliably for nearly 40 years.

In the late 1990s they began showing numerous signs of ageing, when

three major failure events occurred in a two-year period including two wind-

ing failures and a rotating strike. Post event investigations found signs of

fatigue cracking of the rotor rim and spider, and evidence that the rotor rim

oated at rated speed. Machine condition monitoring equipment indicated

that the stator shape was not round, creating a wide variation in air gap.

Feasibility studies were launched in 2001 to dene the problems.

Based on the earlier investigations, it was concluded that the rotors were

at the end of their useful life, and the stator windings were at, or near,

theirs. Different implementation plans were identied and analysed for

the total benets and impact on future operations. Each plan had dif-

ferent capital costs, outage duration and long term benets, including

impact on O&M cost. Based on the analysis of the different options,

a nal decision was reached to replace the generators completely. This

solution provided for the best balance of addressing the expected root

causes, minimising the outage duration, and providing the maximum

life extension (anticipated 30-50 years). In order to combine the rst

unit outage with another planned outage, a fast-tracked implementa-

tion was desired, and the project specications were quickly prepared

and the project was awarded to Alstom Power in 2001.

NEW GENERATOR DESIGN AND INSTALLATION

As a result of the previous rotor-stator contact and subsequent inves-

tigations, maintaining a generator air gap that was circular and uni-

form was important to the PUD. Therefore, the project specications

included technical requirements meant to achieve this goal. In par-

ticular, the stator frame movement was to be controlled such that at

no time would the air gap have a difference of more than 20%, from

the smallest to the largest reading. The total eccentricity of the air

gap at any time also could not exceed 10%. These criteria would be

difcult to achieve with a large stator (diameter 10.6m, core height

1.8m), but due to the previous rotor/stator contact event and lessons

learned from it, the PUD wanted to prevent this type of event from

occurring again.

Based on these requirements, along with contractually required

studies, and Alstom’s design standards, the new generators were

designed to obtain an overall mechanical stiffness higher than the

magnetic stiffness. The resulting design has a rotor rim that remains

shrunk t to the rotor spider at speeds up 150% of nominal. The

stator frame is designed to be sufciently stiff, but still without risk

of buckling the core. As a result, thermal expansion capabilities of the

frame are not hampered. The interface between the stator frame sole-

plate and its foundation is designed to utilise the existing embedded

plates, which helped to keep the installation outage duration short.

The soleplates allow only radial expansion while also controlling the

eccentricity of the frame. With these design elements, it was believed

that a very stable air gap could be obtained.

Alstom erected the new stators and rotors entirely in the erection

bay of the powerhouse prior to the outage. When the scheduled

outage time arrived, the old generator components were removed,

and the new ones were installed in their place. This reduced outage

time to between 29 and 38 days (later units were quicker). During

installation, particular attention was paid to the alignment of the

stator and rotor in order to achieve the air gap variation tolerances

required by the specications.

To provide a means to verify that the specication requirements

were met and provide ongoing machine condition assessment, air gap

Refurbishment at Rocky Reach hydropower plant in the US brought to light interactions

between the civil works and generators that had not been documented prior to rehabilitation

Concrete facts for

air gap variation

WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 45

UPRATING & REFURBISHMENT

monitoring equipment manufactured by VibroSystM was installed

on each generator. The monitoring equipment consisted of sensors

mounted to the face of the stator core that were capable of moni-

toring the air gap between the rotor and stator during operation.

Additional sensors to monitor stator frame movement relative to the

stator foundation were also installed. The primary items of concern

to the PUD were the overall maximum to minimum variation of the

air gap, and free movement of the stator frame during thermal cycling

of the generator.

Overall, the project was implemented very effectively and was n-

ished on schedule and under budget. However, after installation of

the third unit, it was conrmed that the new generators were experi-

encing air gap variations that were well outside of the specied and

expected value. The ndings caused the project team to re-evaluate

what was thought to be the root cause of previous problems, and

brought to light interactions between the civil works and the genera-

tors that had not been documented prior to the rehabilitation.

AIR GA P VARIATION ISSUES

The rst unit of the replacement project (at the south end of pow-

erhouse) was installed in March 2003. Operation of this is rarely

stopped as it is a sh attraction unit and supply for several critical sta-

tion service loads. The air gap variation experienced here was slightly

larger than specied but not excessive and was primarily chalked up

to it being the rst unit.

However a fairly dramatic air gap variation increase was noted

immediately after commissioning of the second unit in November

2003. With the rst unit performing just outside of specied toler-

ances and the second well outside of them, it was unclear if either

unit was an anomaly.

When the third unit returned to service in November 2004 it quick-

ly erased any notion that the air gap variation issue was not real. This

unit experienced a variation in stator air gap that approached 35% by

mid March 2005 but then decreased to a minimum of about 16% by

mid September (almost back at installed condition). However it then

began to climb again, following a predictable, repeatable pattern.

Data gathered for the rst two units conrmed a similar pattern of

variation, but to a lesser extent.

When trended, it was apparent that the air gap variation was cycli-

cal in nature and appeared to be tied to the seasonal variation of the

temperature of the Columbia River. The water temperature varies

between about 3-20ºC, with the minimum and maximum being

reached, on average, around 20 February and 20 August respectively.

The variation in air gap values peak and bottom out about three

weeks after these dates.

It is worth noting that the air gap variation was occurring only to

the stator; the rotor maintained its original shape very well through-

out the variations. The eccentricity also does not vary much for the

stator frame. This is testament to the good performance of the rotor

and overall centering of the unit. Polar plots indicated that the shape

of the stator frames tended towards an elliptical shape, with the major

axis aligned north/south, which is the axis of the powerhouse.

POTENTIAL CAUSES

With excessive air gap variation conrmed on the third unit, project

team members from the PUD, the PUD’s consultant MWH, and

Alstom met to discuss possible causes. Among the items brought up

for discussion were:

r Stator frame stiffness.

r Alkali aggregate reaction (AAR) of the concrete.

r Free expansion/contraction of the stator frame.

r Non-uniform stator cooling.

r Stator soleplate design.

r Powerhouse design.

The rst three items were deemed to be unlikely, as the stiffness was

more rigid than the majority of units designed by Alstom; the power-

house structure had not experienced any symptoms related to AAR;

and inspections did not reveal any external components restricting

free expansion/contraction of the frame. The remaining items were

thought to be likely contributors to the excessive air gap variation.

During installation of the next two units, attempts were made to

reduce the air gap variation to within specied limits by balancing

the stator cooling and making modications to the stator soleplate

design. While marginal improvement was achieved, the air gap varia-

tion remained outside of specied tolerances. It was also learned that

the time of year of stator installation (centering) dictated when the

maximum air gap variation would occur. A unit installed in the fall

experienced its maximum air gap variation the next March; a unit

installed in the spring experienced its maximum in September, which

was in phase with the river temperature variation curve. This would

lead to an important revelation later.

Concrete facts for

air gap variation

40.00

35.00

30.00

25.00

20.00

15.00

10.00

5.00

0.00

Unit 1 avg

Unit 3 avg

Unit 2 avg

River temp

River temperature (ªC)

Air gap variation (% of nominal air gap)

45.00

40.00

35.00

30.00

25.00

20.00

15.00

10.00

5.00

0.00

Air gap variation (% o

nominal air gap)

12/10/02 6/28/03 1/14/04 8/1/04 2/17/05 9/5/05 3/24/06

11/.9/04 5/28/05 12/14/05 7/2/06 1/18/07 8/6/07 2/22/08

/ // // // // // //

Unit 3 (37) avg

Water ºC

Opposite page: Rocky Reach hydroelectric project located near Wenatchee,

Washington on the Columbia River; Left: Air gap sensor installed on the

stator core

Below: Average air gap variations for the ﬁrst three units installed

46 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

Faced with only two units remaining to install, the theory of pow-

erhouse concrete expansion and contraction returned to the forefront.

Although in great physical condition, the concrete does expand and

contract seasonally, with a coefcient of expansion that is similar to

steel. The Rocky Reach units are low head units, and utilize large

Kaplan runners. With the low head, the water passages are very

large, and the affect of the water temperature variations may be more

pronounced than on other types of units with smaller passages. There

is a very large surface area for the concrete to “soak up” the tempera-

ture from the water. These large water passages also tend to make the

concrete monolith less rigid and prone to distortion.

Rocky Reach consists of multiple concrete monoliths that make

up the powerhouse structure. The expansion of each unit monolith is

restricted on the sides by another unit monolith that is similarly trying

to expand (except the end units, which are unrestricted on one side).

Expansion is less restricted on the upstream and downstream sides.

The shape of the concrete where the stator soleplates are attached

tends to expand more in the upstream-downstream axis of the unit.

This difference in expansion leads to the greatest elliptical shape of

the stator soleplates along this axis three weeks after the water tem-

perature reaches its maximum (approx 20 August); it then returns

to its most circular shape in mid-March, three weeks after the water

temperature reaches a minimum (approx 20 February).

The stator frame is xed to the concrete via its soleplates at the

time of centering the stator during installation. The soleplates consist

of a sliding surface and radial dowels to allow for thermal expansion

and contraction of the stator frame. Since the concrete is expanding

and contracting in this location, and taking a non-circular shape, the

radial dowels can become misaligned in the radial direction, caus-

ing the sliding feature to be reduced or eliminated altogether. The

stator frame will continue to expand with any temperature rise; it just

expands where the resistance is least (or least misaligned), resulting in

non-uniform movement. In the case of Rocky Reach, this is along the

upstream/downstream and north/south axes.

An examination of the shape differences for units installed at dif-

ferent times of the year also bears this out. The fourth unit was

installed in the spring, and its shape variation is directly opposite

to that of units installed in the fall. In all cases, the best shape, ie

smallest air gap variation, occurs near the time when each unit was

centered and the soleplates were radially aligned. When installed in

the spring, a unit develops its maximum elliptical shape in the fall

and vice versa for a unit installed in the fall (also with a 90º axes

shift). This reversal of the phenomenon ts a seasonal distortion of

the generator foundation.

Based on the foregoing, it was apparent that a different approach

was required. It was thought that if the radial dowels in the soleplates

could simply be removed from all but the primary axes (US/DS, N/S),

the stator frames would likely remain round and experience very little

air gap variation. However, due to the particular design of the genera-

tors, an electrical fault could result in serious damage, including possi-

ble damage to the concrete structure. Instead, increasing the clearance

of the radial dowels by 0.5mm was proposed, in the hope that this

would prevent the dowels from becoming misaligned or locked.

This was carried out on the sixth unit. The results were similar to

previous attempts (some improvement), but the air gap variation still

exceeded the specied maximum. With six of the seven units now

Above: Stator frame shape versus generator foundation shape depending on

installation date

Below, left: Stator frame shape for spring installed unit in the fall.

Note elliptical shape with US/DS major axis (Worst case);

Below, right: Stator frame shape for fall installed unit in the spring. Note

elliptical shape with N/S major axis (Worst case).

WWW.WATERPOWERMAGAZINE.COM SEPTEMBER 2010 47

UPRATING & REFURBISHMENT

installed and none of them meeting the specication requirements,

another idea that was previously set aside had to be considered.

PRESETTING THE STATOR FRAME SHAPE

The notion of presetting the stator frame in such a way as to take

advantage of the predictable nature of the air gap variation had ini-

tially been rejected, since doing so would not x the main cause of the

variation. However, since a complete redesign of the stator soleplate

system was not feasible without major cost and outage time, reducing

the overall magnitude of variation became a viable option.

To test the presetting method, the seventh unit was installed in a

preset elliptical shape to compensate for the expected movement of

the concrete. The goal was to set the stator so it would equally dis-

tribute the resulting deformation plus and minus of the perfect round

shape. If the presetting is precisely correct, then it should reduce the

air gap variation by 50%. The risk of this exercise appeared to be

low; if the shape was incorrect and the deformation moved the wrong

way, then the unit could be shut down for a short outage to correct

the shape with adjustable keys.

A review of the air gap data from the earlier units provided the

basis for deciding how elliptical to preset the seventh unit. The air gap

sensors located on the primary axes of the generators (the 90s) were

seeing approximately 1.5mm of air gap variation, while the ones on

the secondary axes (the 45s) were seeing very little variation. In this

way, the secondary axes act as inection points on the ellipse, and

are nearly stationary.

In mid October 2006 work on the seventh unit was carried out.

Slightly less than half of 1.5mm was used as the value for presetting

the frame. Initially, the stator was centered and rounded out to be near

perfect (<5% roundness). Then jacks were used at the north and south

locations of the stator frame to push the stator in about 0.75mm. An

outward deection of 0.75mm was obtained at the upstream and

downstream locations, with very little movement noted at the 45s (as

predicted). Rotational air gap measurements conrmed the desired

preset shape had been obtained, which was slightly elliptical, with the

US/DS axis as the major axis. The stator frame was then xed to the

embedded soleplates per the procedure used for the other units.

When the unit returned to service in late October 2006, it was obvi-

ous that a change had been achieved. Instead of the air gap variation

immediately beginning to increase dramatically, it decreased. It con-

tinued to decrease into December and then the variation started to

increase. The maximum variation occurred in mid March 2007 as pre-

dicted, but at a value that averaged approximately 27%, which was

well below maximums experienced on the other units. Another mini-

mum occurred in late June that matched the December value. The vari-

ation then increased into September and then started the cycle again.

After the seventh unit was returned to service, the third unit, which

had conrmed the existence of an excessive air gap variation issue, also

had its stator frame preset. After it was returned to service, the unit

experienced a very similar variation pattern to the seventh unit. The air

gap variation was reduced from over 35% to approximately 27%.

Over a 12 month period it became clear that a slightly more aggres-

sive presetting could have been used which would have lowered the

maximum variations further. However it was decided best to err on

the side of caution on the rst attempts until a positive result was

achieved. Based on the results, a larger displacement may be consid-

ered for presetting other stator frames as required over the life of the

new generators.

CONFRONTATIONAL REMEDIES

The C1-C7 generator rehabilitation project specications were writ-

ten based on addressing observations (assumptions) about the root

cause of recent problems with the units. Though a thorough analysis

and new design were provided by Alstom per the specications, the

problems with an excessive air gap variation persisted. It was only

after trying several remedies, and carefully monitoring the units for

three years, that a primary root cause became clear.

Above: Lifting a completed stator (~230 tons) with the powerhouse cranes for

installation into the generator pit; Left: Assembling the parts that make up

a generator rotor spider; Below, left: Installing a new generator rotor (~430

tons) into the new stator frame

48 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

UPRATING & REFURBISHMENT

As time progressed, and no modications solved the problem, there

were opportunities for both the PUD and Alstom to choose more

confrontational remedies. However, a good working relationship was

the key to keeping everyone focused on the problem, and ultimately

nding a solution. This relationship was developed early on in the

project, and it cannot be stressed enough how important this was to

arriving at a satisfactory conclusion to this issue.

Once the concrete movement theory was satisfactorily proven,

presetting the stator frame shape in order to achieve a reasonable

air gap variation was the logical choice. Redesigning and rebuilding

the stator frames and/or soleplates was not a feasible alternative. The

results achieved have been positive. One other stator frame has been

preset by the PUD (October 2008), and another is scheduled.

Previously, most generator suppliers considered the foundation to

which the stator frame is attached as a stationary point. The experi-

ence on this project highlights that normal seasonal concrete expan-

sion and contraction should be expected and assessed. Depending on

the design of the powerhouse; number and type of units; temperature

swings experienced locally; and the physical size and arrangement of

the units, seasonal concrete movement will likely have some impact

on stator shape and alignment. Being aware of this in the design stage

can lead to a generator design that accommodates this movement,

and eliminates the excessive variation altogether.

The authors are Carey Schenck, Douglas County PUD;

Steve Sembritzky, Chelan County PUD; Don Erpenbeck,

MWH Global; and Daniel Chenard, Alstom Hydro Canada

Above: Lowering a new rotor (~430 tons) into the stator; Right: Erection of a

new stator and rotor in the powerhouse erection bay

IWP& DC

Filler metal: BÖHLER Ti 52-FD

Base metal: S235J0

Client: ANDRITZ HYDRO GmbH

Electrical power: 25,8 MVA

Rotation speed: 93,6 1/min

Cover-Ø: 5900 mm

Weight Carlotte: ~ 17 to

KAPLAN BULB NOSE

Hydro Power Plant Kongsvinger (NOR)

www.boehler-welding.com

50 SEPTEMBER 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

RESEARCH

ANAGING the risk of owning and operating dams

requires the best available knowledge on both the

potential failure modes and associated consequences.

Furthermore, CEATI believes that most dam failures

are not the result of extreme loading conditions. Dams typically

fail due to unforeseen or unrecognised conditions that result in

piping failures, overtopping, and errors in operation or founda-

tion failures.

In order to minimise the risk to those who live downstream of

dams or who otherwise benet from them, it is vital that the com-

bined knowledge of the dam safety community is shared. Case studies

of dam failures and incidents must be exchanged. The lessons of the

past must not be forgotten.

LEARNING FROM INCIDENTS AND FAILURES

According to CEATI, sharing of incidents is one of the most effec-

tive tools in driving down the risks in dam safety. And this appears

to be the motivating force behind the Dam Safety Interest Group’s

workshop which was held in Los Angeles, California, US in March

2009. Called Learning from International Dam Incidents and

Failures, the event was planned in co-ordination with the US Federal

Energy Regulatory Commission and the Division of Dam Safety

and Inspections.

The goal of the workshop was to:

The combination of ageing dams, retirement of experienced dam engineers and increased

consequences of dam failure due to downstream development underscore the need to

better ensure the future safety of dams worldwide. Past experience must not be forgotten

and lessons learned must be captured for future generations. The Centre for Energy

Advancement through Technological Innovation (CEATI International) is paving the way

forward in global communication, coordination and collaboration through their Dam

Safety Interest Group (DSIG). A selection of case studies from the organisation’s recent

workshop on international dam incidents and failures is presented below

Lest we forget: learning from

international dam incidients

Below: Placing RCC near the top of Saluda Dam