The Guri Dam
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The Guri Dam in Venezuela measuring 7,426m in length and 162m in height is the third largest hydroelectric plant in the world. With an installed capacity of 10,200 MW, it catered to about 73% of Venezuela’s electricity demand. This dependence started posing a major problem when Venezuela was hit by a prolonged drought attributed to El Niño in 2010. The government was forced to implement 2 hour black outs everyday throughout the country to make up for the low water levels behind the dam.
The water levels dropped to about 248.22m above sea level. The declining water levels meant the turbines had to work harder to generate electricity – thus giving rise to a water vortex which in turn would cause water bubbles to get sucked in and move up to the water blades. This process could eat away at the metal plates – a process called cavitation. The cavitation could cause massive vibrations that can be felt throughout the plant. If the turbine is shut down quickly enough there could be an explosion eventually leading to complete shutdown of the plant. The vibrations were beginning to affect Unit 8 of the Guri Dam; it had to be shut down, leading to an electric cut down of 400MW.
Though the mid-April rains in 2010 led Venezuelan officials to believe that they could survive the crisis, water level in the dam continued its descent. There was a drop of about 76cm in the water level in a span of two weeks. Venezuela expected to be blessed with rain at least in May (the start of the rainy season), but El Nino did not will so. The drought prolonged, leading to more complications.
(Juan Mabromata 2010)
The current project to try and restore water levels to the Guri Dam is named involves the technological modification of the dam so that it can last another thirty years without any major problems. This has come in the wake of a serious electric blackout and electrical rationing in Venezuela. While they cannot do anything but wait and watch the different colors of the El Nino, they can prepare themselves for the worst, or the best hopefully.RESEARCH AND INVESTIGATIONS TO RESOLVE THE ISSUE
Electrical rationing plans began to be implemented in order to keep the water level above 240m above sea level; consequently preventing a complete shutdown and the halt of operations. As a result of this, Venezuela has had to bear the brunt of widespread electrical shortages and blackouts; apart from being a discomfort to the citizens it also proved to be a hit to Venezuela’s economy. The water levels at the Guri Dam are a major determinant of Venezuela’s future. In the pages that follow we aim to look into a few more aspects of the crisis and its management.
(ICIS News 2010)
The future of the Guri Dam does depend on nature to a large extent. Here we attempt to look at what improvements can be made to the construction or design of the dam such that it functions without any glitches in conditions of compromised water levels as well.
The Guri dam is a gravity type dam. The spillways are three-chute concrete spillways and each chute consists of an overflow gated crest, a step chute and a terminal flip bucket. The spillway flow occurs through a bucket which projects a highly arched jet of water that falls into the tail water pool. The tail water pool is responsible for the final dissipation of energy.
In 1969 it was observed that the lips of the bucket and the ends of the side training walls were showing signs of scouring/erosion. An investigation on the same led to Harza Engineering suggesting the CVG to restore the damaged areas with epoxy concrete and epoxy protective coatings. The repairs were made in early 1970, but investigations in late 1970 showed greater damage in the form of renewed scouring. Further field inspections revealed that the damage was happening due to cavitation and was not self-arresting. This indeed could prove to be hazardous if not handled appropriately.
The St. Anthony Falls Hydraulic Laboratory of the University of Minnesota started an experimental study aimed at determining the mechanism of damage and proposed modifications to the existing design. It started with an analysis of the existing structure and went on to Model Investigation Tests.
The analysis of the existing structure took into consideration the discharge, lateral tail water flow, chute velocities, vortex cavity sources and the tail water stages.
It was observed that the maximum design capacity of the spillway was 40,000 cms at an 88m head drop and the energy contained in the flows of the Guri Dam at the point of exit from the flip bucket was 46,000,000 hp. This could cause enormous damage.
1.2 LATERAL TAIL WATER FLOW
High discharges of waste water from the spillway were generating a large clockwise vortex which substantially affected the lateral pool velocity across the ends of the flip bucket. This lateral flow was proving to be a significant factor in spillway damage.
1.3 VORTEX CAVITY SOURCES
A traveling vapor cavity of relatively small size was found to be a common cause of cavitation damage.
1.4 TAILWATER STAGES
The tail water stages were found to be unusually large. This required more attention because the stage level of the tail water pool substantially impacted the pressure values which in turn played a role in cavitation damage.
It was also observed that there existed Sill Damage and Wall Damage. The bucket lips which were the principal controllers of the location of the final dissipation of the flow of energy had lost quite a significant volume of concrete due to erosive removal of the same. The disintegration of bucket lips could threaten the existence of the entire structure. Though wall damage was seen to be occurring simultaneously, it did not require ‘emergency’ status because it did not threaten the structure of the dam. It was stated that a solution that addressed the more serious issue of sill damage would automatically remedy the wall damage issue.
Model investigation tests conducted in a Variable Pressure Test Facility which allowed the modeling of the cavitation process helped gather more insight into the issues and their impending threats to the dam, the ecosystem and the people in the area.
A combination of high velocity flows and pressure levels below one-half atmosphere will certainly lead to erosion. At the Guri dam erosion was mainly observed in areas with pulsating negative pressure values greater than one half atmospheres. The turbulence due to flow overtopping in the bucket side wall strongly contributed to the negative pressure pulsations. An increase in the height of the walls was suggested to reduce or rather eliminate the source of low pressure.
The other solutions suggested to improve the engineering of the Guri Dam included routing the flow via a reduced number of chutes, increasing flow depth, lowering the tail water to reduce back-up in the bucket and reforming the lip shape and fabricating it with highly ‘cavitation’ resistant metal that could also bear the resistance of the water – to reduce cavitation damage. Stainless Steel in its most preferable form was suggested. If these solutions could be implemented, the biggest problem that the Guri Dam is facing can be reduced to a great extent.
The study also suggested operating with a deeper flow in the bucket and depressing the tail water stage to eliminate the turbulent water jump in the downstream end of the bucket. Rebuilding the bucket to raise the lip above all normal tail water stages, though an expensive option could be carefully considered to reduce tail water back up effects.
Reviewing and reducing the number of gates and gate openings could minimize the generation of discrete waves and turbulence centers that contribute to the damage of the lip. Minimizing boundary areas possessing low mean static pressure as a result of high velocity will also help reduce damage to the lip of the bucket.
Elevation of the sill to a position above the tail water will nullify the influence of lateral flow that contributes to cavitation damage. (Ripken & Warren 1972)
ROLE OF POLITICS
President Hugo Chavez maintained that the current electricity crisis that Venezuela is battling is the result of the El Nino, but critics do not agree. Chavez and his government are being blamed for sheer lack of planning, corruption and swindling of the resources allocated for the construction of the Guri Dam. The money was not invested in the infrastructure of the dam.
Even in the wake of a crisis and technological modification the government does not seem to have realized its mistake. The corruption in the electricity sector has impacted engineers’ ability to repair the electricity issue in time to avoid a crisis. It is too late now. The receipts for the electricity equipment were highly inflated so that government officials could keep a good amount of the money, there were mismatch between the requirement specifications and the equipment ordered – the officials placing the orders did not consult with the engineers. Much of the purchased material is said to be unusable till date.
Research shows that only 25-30% of the funds approved for infrastructure upgrades were put to intended use. However Rodriguez stated that the government had invested about $16.5 billion to help the electrical sector keep up with the rising consumer demand – most of them were long term projects with no immediate solutions. (Fox News 2010) (Fabiola Sanchez 2010)
Brazilian contract workers who are threatening to abandon the technical modification unless they receive their paychecks claim that they have not been paid (by EDELCA). Venezuela would be in a serious spot if the Brazilians left, taking their technical expertise with them. Even though the issue seems to have come up in one of Chavez’s meeting with the Brazilian President, there seems to be no change in the situation and the payment dispute remains unresolved.
(Juan Mabroamata 2010)
Whether the Guri Dam turns out to be as successful as predicted or no, whether Chavez has minimized the impacts of the crisis or no and whether the Venezuelans can trust Chavez and his government with their lives and land or no is a matter of whether it will rain or no. If yes, would that be enough to reverse the environmental impact of the Guri Dam, to refill the dam and restore normality to the lives of the Venezuelans?
RELATED CONCERNS –
For millions of years the warm waters of the Caribbean caused huge quantities of moisture to rise up into the air and drift southwest to Venezuela’s plains. When the wet air hit the Andes mountain range, it resulted in a lot of rain. It was this kind of rain that formed rivers like the Ornica that fed all their water back to the oceans. This cycle gave rise to the rain-soaked tropical jungle, that later became the venue for the Guri Dam – because of its ideal conditions. The dam was constructed with the aim of harnessing hydroelectric power and making Venezuela independent from the use of fossil fuels. However, the construction of the dam and the dam itself altered the rainfall pattern in the area – leading to the present drought. This will turn into a vicious cycle if alternative measures are not taken.
(Alex Lu 2011)
4.2 ECONOMIC CONDITION/ GLOBALIZATION
The decreased water levels behind the Guri Dam have led to electricity rationing. Industries are short of power, manufacturing and other markets are strongly hit as a result of electric shortages and black outs. People are asked to work for shorter durations so that power can be saved. Rollout electric shortages are being implemented to keep the water level at at least 240m above sea level so that the hydroelectric plant continues to function in hopes of recovering one day. Shopping Malls and most other business are allowed to start business only after 11 AM and function for lesser durations. If the scenario persists, it is only a matter time before Venezuela is severely crippled.
President Chavez promulgated the construction of the Guri Dam with a view to moving towards a more “Green Policy” and reducing his country’s dependence on fossil fuels. It catered to about 73% of the electricity demand in Venezuela. However it failed to take into consideration the disastrous environmental impact that it was to have. The very basis of the dam – the rain forest and the rivers were affected, there were no rains and there was no water in the river, then where was the water for the dam to come from?
In an attempt to maximize the use of hydroelectric power Venezuela ended up in a crisis that crippled it economically, environmentally and most of personally. Life in Venezuela is not what it was before Guri Dam, not what they expected it to be after Guri Dam and can never be expected to be either of them, again. The activities of the Venezuelan government should be directed towards technically modifying the dam, minimizing its effects on the environment, developing alternative sources of energy so that they are not dependent on just one source, eliminating corruption and keeping in mind the larger picture of the project, because what Venezuela has lost from nature she cannot reclaim.
The proposed modifications of the dam if carried out in time and appropriately can prevent any further disasters.
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