• Electrical India
  • Aug 5, 2015

Challenges In Setting Up The Three Gorges Dam In China

Since the Chinese were looking for a mega project, which needed a location that could give maximum storable head of water (H) as well as maximum water flow rate (Q), they selected a gorge area along the Yangtze river for construction of the dam, where, besides minimum length of the dam, storage of water would provide the increased levels of both Q and H to deliver optimum power output...

- C V Govinda Raju


 Hydro Electric power provides a major part of the renewable energy in the world. Other renewable resources include geothermal, wave power, tidal power, wind power, and solar power. Hydroelectric power plants neither use up resources to create electricity nor do they pollute the air, land or water, as other power plants may do. Hydroelectric power has played an important part in the development of a country from ancient times. Both small and large hydroelectric power developments were instrumental in the early expansion of the electric power industry. Hydropower is an essential contributor in the national power grid because of its ability to respond quickly to rapidly varying loads or system disturbances, which, base load plants with steam systems powered by combustion of coal, gas, oil or nuclear power plants cannot accommodate.

  Demands for power vary greatly during the day and night. These demands vary considerably from season to season, as well. For example, the highest peaks are usually found during summer daylight hours when air conditioners are running. Nuclear and fossil fuel plants are not efficient for producing increased demand for short peak periods. Their operational requirements and their long startup times make them more efficient for meeting base load applications. Since hydroelectric generators can be started or stopped almost instantly, hydropower is more responsive than most other energy sources for meeting peak demands. Water can be stored overnight in a reservoir until needed during the day, and then released through turbines to generate power to supply the peak load demand. This mixing of power sources offers a utility company the flexibility to operate steam plants most efficiently as base plants while meeting peak needs with the help of hydropower. This technique can help ensure reliable supplies – and may help eliminate blackouts caused by partial or total power failures. With this important load-following capability, peaking capacity and voltage stability attributes, hydropower plays a significant part in ensuring reliable electricity service and in meeting customer needs in a market driven industry. Beyond all, it is the cheapest form of electrical energy.

Three Gorges Dam in China

  Yangtze river, which is over 6,300 km long, flowing from West to East of China, is the biggest river virtually dividing China into North &South. (See Fig. 1) 
 



  For comparison, the entire length of Great Britain between two extreme points in the south west & north east by road, is only 1407 Km.

Reasons for implementing the Three Gorges Dam project:

  • The Chinese Govt. for quite many decades had planned to utilise the potential of the Yangtze river. Periodic flooding of Yangtze river had caused great havocs & destruction of lives, farm lands and damages to millions of houses resulting in relocation of people from affected areas. Flood in the year 1998 was considered the worst in the history of China with a loss of over 4000 people, lives of 180 million people were affected, 13.3 million houses were damaged/ destroyed causing $26 billion in damages. In order to have an effective flood control and prevent such losses, the Chinese wanted to build a dam across this river.
  • Yangtze river is one of the busiest shipping traffic river in Asia. The Chinese Govt. wanted to further increase the shipping capacity of this river six fold, thus reducing the carbon emission by 630,000 tons as well as reduce the transportation cost by 25%, when compared to transport by road or rail. 
  • Another most important reason for the Chinese Govt. was to use the full potential of this river to generate cheap, renewable, pollution free, environment-friendly hydro electrical power to meet the country’s ever growing power demand – by building the biggest hydro electric power plant in the world. This hydel plant is producing 22,500MW (32 units of 700MW each plus 2 units of 50 MW each), which is the largest capacity hydro electric power plant presently operating in the world. The Chinese Govt. consider this mega project as an historic engineering, social & economic success with state-of-the-art large turbines. The requirement of coal for generating 1 MW of power is about 366 kg per hour. At this rate, to run a thermal power plant of 22,500 MW capacity, operating on coal would need a supply of about 8,000 tons of coal every hour (70 Million tons per year). Imagine cost of mining, transportation of such large quantity either by road / rail / or by barges and the amount of resulting environmental pollution etc. It is totally avoided by simply switching over to this hydel power.
  • To improve the tourism industry: After the completion of thedam project, visitors  would  be  delighted to  see a wonder in  the  Yangtze river where a calm lake sits among the steep gorges, thereby many scenic spots, which were originally inaccessible, are now reachable. The tour of the main dam itself presents a magnificent  piece of engineering talent.  

Technical details of the Three Gorges dam (See. Fig. 2 & 3):
 




Fig. 3: View inside the power house...

  • Type of the dam: Gravity dam.
  • Height: 181 meters. 
  • Length: 2335 meters.
  • Top width (Crest)): 40 meters.
  • Base width: 115 Meters.
  • Spillway capacity: 116,000 M3/Sec (116,000 Tons/Sec).
  • Power generation: 32 nos. of 700MW each plus 2 nos. of 50 MW each, totaling 22,500 MW of cheap, environment friendly & renewable energy.
  • This single project caters 10% of the entire China’s power requirement.
  • Difference in upstream & downstream water height: 110 meters.
  • Construction of the dam used 16 million cubic meters of concrete in the dam structure, which is a world record.
  • It took 17 years, for completion of the project with 40,000 workers working.

Challenges encountered:-

  • Selection of the site:

  In view of the above advantages Chinese Govt. decided to build the Three Gorges Dam (TGD) across the river Yangtze. Amount of electrical power generated in a hydro electric system is directly proportional to the head of water in the dam – as well as the flow rate of water as per the following formula.

THP = (Q X H) / 8.8,
where THP = Theoretical Horse Power (One HP = 746 Watts),
Q = Flow rate in cubic feet per second, H = Water Head in the dam in feet
& 8.8 = a constant. (Note: More refined formula has to take into account losses in the head due to friction in the penstock pipe, and other variations like efficiency of mechanical devices etc., used to harness this power).

  Since the Chinese were looking for a mega project, which needed a location that could give maximum storable head of water (H) as well as maximum water flow rate (Q), they selected a gorge area along the Yangtze river (Gorge is a valley between two mountains/ like a Canyon) for construction of the dam, where, besides minimum length of the dam, storage of water would provide the increased levels of both Q and H to deliver optimum power output.

  • Soil study & consolidation:

  The theoretically calculated weight of the stored water in the upstream of the dam is around 42 billion tons, which is quite considerable – and this could exert hydrostatic pressure on the upstream face of the dam and topple the dam, if proper soil study as well as soil consolidation work were not carried out, prior to start of the dam construction. Even though the location of the dam was between two mountains, despite the soil underneath the river was rocky, yet it had lot of voids & porosity. 'Compaction grouting', which is a ground treatment technique that involves injection of a thick-consistency soil-cement grout under pressure into the soil mass, was adopted, thus consolidating, and increasing the density of surrounding soils in-situ. The injected grout mass created by pressure-densification filled up the void space. 

  • Planning for the increased up & down ship movement along the river during the period of dam construction, as well as, thereafter:

  After the construction of the dam, height difference between upstream and downstream water levels was 110 meters (370 feet) and ships of max. 14,000 tons needed to be lifted up or lifted down across the dam, depending on the direction of their travel (See fig. 2). Since the height difference between upstream and downstream was too much, special five tier ‘SHIP LOCK’ systems were designed, one for the upstream movement and another for the down stream movement of the ships. When lowering a ship, ship is moved into a watertight compartment called a lock. The gate is closed behind it, and the water in the compartment is released into the next watertight compartment, which is lower than the first.

  As the water is released, the ship is lowered. When the water level in the ship's lock is the same as the next lock's, a gate opens between the two locks and the ship is moved forward into the next lock. The door is closed behind it and the process repeats itself until the ship has been lowered to the downstream level. Raising a ship is essentially the same, but instead of releasing water to lower the ship, water is pumped into the lock to raise the ship. The Ship Locks, near the Three Gorges Dam, is the world's largest ship lock. For vessels weighing less than 1000 tons, a special ‘Ship Lift Crane’ facility has also been provided. All these facilities created for handling of ships have resulted in increasing the Yangtze river’s shipping capability by SIX fold.

  • Sequence of construction of the dam:

  The planning of the construction of the dam was in three phases. Phase-1 of construction involved construction of part of the dam housing Power Station-1 & part of the Ship locking facility.

  Phase-2 of the construction involved part of the dam housing the Sluice Gates and the balance portion of the Ship locking facility.

  For taking up the construction of Phase-1 & Phase-2 of the dam in the river basin, a special Stone Cofferdam was constructed (See Fig. 4 ). A cofferdam is an enclosure around the construction site to exclude water so that the construction works can be done in dry. It is thus a temporary dam constructed for facilitating construction in water. Construction activities of Phase-1 and Phase-2 were done within this cofferdam. During this period, the river water as well as the shipping traffic were diverted as shown in Fig. 4.
 

Fig. 4: For taking up the construction of Phase - 1 & Phase - 2 of the dam in the river basin, a special Stone Cofferdam was constructed...
 

  After  completion  of  phase-1 & Phase-2  activities, part of  the  main dam  consisting of Power Station-1 & Sluice Gates were ready – and the  cofferdam was removed allowing  the river  water  to  flow  through  the turbines / Sluice gate & the  shipping  traffic  through  the  newly  constructed Ship Lock  system. (See Fig. 5).
 

Fig. 5: Phase - 1 of construction involved construction of part of the dam...Phase - 2 involved part of the dam housing the sluice gates...
 

  In order to undertake phase-3 construction, consisting of Power Station-2, a concrete cofferdam of width 480 meters & depth of 30 meters was constructed (See Fig. 6).
 

Fig. 6: Cofferdam is an enclosure around the construction site to exclude water so that the construction works can be done in dry...
 

  After completion of the Power Station-2, this concrete cofferdam had to be demolished using explosives under water. As this cofferdam was built very close to the main dam (86 meters) lot of care was needed to prevent damages to the main dam itself. Total demolition of concrete volume was 186,000 cubic meters and the total explosives consumed during  this  blasting was 191.5 Tons. A reputed Chinese company was entrusted with this demolition work who had to carry out lot of computer simulation studies and experimental blasting etc., prior to taking up the actual blasting works. This company had to develop high powered  environment-friendly water mixed emulsion explosives for this purpose, to avoid chemical pollution of the river water, which was used for drinking purposes. It is no wonder that this company has been awarded top prize by the Chinese Engg. Explosives Association for the precise and successful  blasting operation.

  • Prevention of soil erosion near the exit side of the dam:

  Initially when the Sluice gates were opened for release of flood water, the water with its large volume & energy used to fall very close to the dam thereby resulting in the erosion of downstream soil near the dam. This called for two things. 1) The energy of the discharged water after the Sluice, need to be reduced and 2) The fall of the discharged water to occur far away from the dam site. The Chinese engineers developed special tapered concrete shoes, and inserted them at the exit of the sluice, which resulted in forcing the exit water in to air, thereby most of the water energy was getting lost in the air before it hit the ground. This also helped, the delivered water to hit the ground far away from the dam site (See Fig. 7).
 

Fig 7: Flood water jetting out of the dam shows the effect of the tapered shoes installed...
 

Consequences of implementation of this mega project

  • 1.3 million people were displaced. The main concerns are population resettlement and human rights, the irreversible environmental and economic impact, the loss of cultural antiquities and historical & archeological sites, military considerations for the physical safety of the dam against terrorism & man made disasters, and hidden dam disasters from the past history. Initially, lot of opposition were there to kill the project or at least reduce the size of the mega dam, which was planned to be the biggest, most expensive and, incidentally, the most hazardous of all hydro-electric projects on this planet.
  • Three Gorges Dam (TGD), the largest in history, recently completed in China, brings with it many social and environmental concerns.
  • Construction of this dam led to extinction of many rare plant and animal species.
  • Thousands of factories, mines, hospitals, garbage dumping sites and grave yards have been wiped out. These facilities can release certain toxins into the water system.
  • 13 cities, 140 town & 1600 villages have been submerged.
  • The dam submerged as many as 1300 archaeological, cultural and heritage sites.
  • The Three Gorges Dam, according to some, has the potential to be one of China's largest environmental nightmares – increase in landslide activity, primarily from erosion caused by the drastic increases and decreases in reservoir water levels. Yangtze contains some of the densest clusters of human life in the world & and the dam’s construction had immense impact of flushing out this area of its inhabitants. It would be un-imaginable if 39 billion cubic metres of water in the Three Gorges reservoir ever escapes by natural or man-made catastrophes. 
  • Those forced to relocate were promised compensation for the value of their homes and land. In what is likely the over whelming majority of cases, relocated citizens have either been given far too little in compensation or their dues have been slimmed through corruption and embezzlement. This has meant problems for many as the cities and towns they have had to move to, are more expensive, driving many people deeper into poverty. Indeed, there is a major concern that the displaced will be made even poorer due to landlessness, joblessness, and food insecurity. The displaced are more often than not farmers with little formal education, causing their social mobility within the major cities, are now stuck in tents, their homes destroyed either during construction or in the wake of a landslide, without enough money to rebuild. Three Gorges Dam brings many controversial topics to the international forefront.
  • It is the question of what is more important: A country moving forward or protecting the rights of its people? Perhaps in the eyes of the Chinese Govt. the benefit achieved by 1.4 billion people of the country outweighed the sacrifices and sufferings of relocation experienced by its 1.3 million people. The latter are portrayed as 'Selfless Patriots' (See Fig. 8).
     


Author is Ex President of ISPAT Group of Companies.

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