Dams' common problems

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DAMS' COMMON PROBLEMS

INTRODUCTION

A Dam (shown in Fig 1) is a physical barrier constructed across a river or a waterway to control the flow of or raise the level of water. The purpose of such a construction may be flood control, irrigation needs and generation of hydroelectricity. A dam is obstructs the water to prevent its' unused flow in the sea. It controls the flow of water via outlet pipes and gates. It creates a reservoir to store the water and its huge potential. Most dams have a section called a spillway or weir over which, or through which, water flows, either intermittently or continuously, and many have hydroelectric power generation systems installed. The dams are advantageous in more than a single way. Advantages of a dam are listed below:

  • They are helpful in preventing floods.
  • They serve as a solution to energy crises by generating hydroelectricity.
  • They prove to be helpful in irrigation
  • They better the water transport.
  • And last but not the least they attract tourists.

Dams are too beneficial for mankind but at the same time they are harmful too in several ways. Disadvantages of a dam are listed below:

  • Building a dam is an expensive affair.
  • For building a dam a huge population of nearby area is moved.
  • The living environment of aquatic and semi aquatic flora and fauna gets disturbed in lower case.
  • Collapse of the dam causes great damage.

Now in this paper we will be viewing and observing the main causes of Dam Failure along with case study for every cause. Main causes of Dam Failure are:

  • Spillway designing error.
  • Sliding of mountain into the dam lake.
  • Poor maintenance especially of outlet pipes.

We will be discussing all of the above mentioned causes one by one. Besides all the above causes there is one more reason due to which dams are collapsed. In technical terms it is called Deliberate Dam Failure. This happens during the course of War. When force of one country destroys the dam of other country deliberately then this is known as Deliberate Dam Failure. As this cause is nat a common cause so we would not consider this in our study.

SPILLWAY DESIGN ERROR

Spillway (shown in Fig 2) is a characteristic structure of a dam which is used to provide controlled release of flows of water from the dam into the downstream. Spillways release floods so that the water does not overtop and damage or even destroy the dam. There are two ways of spillways: Controlled and Uncontrolled.

  • Controlled Spillway: It has gates which regulate the water. This design gives us an opportunity to exploit the full height of the dam and flood waters can be released as required by opening one or more gates.
  • Uncontrolled Spillway: It does not have gates, when the water rises above the lip of the spillway it begins to be released from the reservoir. The rate of discharge of water is controlled only by the depth of water within the reservoir. All of the storage volume in the reservoir above the spillway lip can be used only for the temporary storage of floodwater, and cannot be used as water supply storage because it is normally empty.

CASE STUDY: The South Fork Dam

As a case study under this cause of Dam Failure we will study the demolition of South Fork Dam which was located on Lake Conemaugh, an artificial water body located near South Park, Pennsylvania, USA. On May 31, 1889, the South Fork Dam failed and 20 million tons of water from Lake Conemaugh burst through and raced 14 miles (23 km) downstream, causing the Johnstown Flood.

History of South Fork Dam

The South Fork Dam was built by the Commonwealth of Pennsylvania between 1838 and 1852. It was built as reservoir for the canal basin in Johnstown. The location of dam is at 14 miles upstream from Johnstown. The Comenaugh River heads through the heart of Johnstown which has been made narrower so as to build more and more structures on it banks. The river was prone to flooding as it was located on a flood plain. The Commonwealth of Pennsylvania sold the dam to the Pennsylvania Railroad in 1857. As soon as the rail services arrived in 1852, the use of the canal for transportation of goods took a downturn. The South Fork Dam was abandoned and forced to go into a state of disrepair. In 1862, part of the culvert gave way but was never repaired. In 1879, some of the businessmen formed a private company and called it the South Fork Hunting and Fishing Club. They purchased the dam for the purpose of building a summer resort on Lake Comenaugh for wealthy Pittsburg families. Plans included lowering the dam so as to build a road on top and to raise the level of the lake. [www.suit101.com]

From the above abstract we can easily make out that the ill maintenance of the spillway and rising of the level of river made the condition worse and finally the continuous rain made the Dam collapsed. After the Dam gave up nearly about 20 million tons of water spilled over the dam and Jhonstown was hit without any prior warning. The water headed towards the town with a speed of nearly 40 miles per hour. The flood played havoc and made over 2,200 people lose their lives and all over damage was estimated to cost $17 million. This was the first major disaster faced by the newly-formed American Red Cross. 18 countries across the globe offered their help. The Dam Break is shown Below [Fig 3]

Beside the Spillway failure there are other causes which are responsible for the Disaster and they are:

  • Heavy and continuous Rainfall.
  • Rising water caused erosion of new embankment which was made up of mud and straw.

Precautions which could have saved South Fork Dam:

  • The main cause of the break was Spillway design error. There were insufficient spillways which made the enormous amount of water to spill. If there had been more spillways then the disaster would have been avoided.
  • The damaged parts of the dam should have been repaired.
  • The new parts should have been made up of concrete instead of stone, mud and straw.

SLIDING OF MOUNTAIN INTO THE DAM LAKE

A dam is made at the base of a river and in between a valley which means that the lake or water body which is dammed has mountains on both side of it. Now as a dam is made the natural geological balance is disturbed and these mountains get loosen up and develops cracks which causes landslides to occur. These landslides pose a great threat when they fall in the lake. If a landslide of great volume falls in the lake then it raises the water level to a great extent and that too suddenly. This sudden rise makes a huge amount of water to spill over the dam causing tsunami (seiche wave). This wave brings a massive flood and destruction to the valley below which wipes a great area.

CASE STUDY: The Vajont Dam

As a case study under this cause of Dam Failure we will study the demolition of Vajont Dam [shown in Fig 4] which was located on Vajont River under Monte Toc, 100 km north to the Venice, Italy. It suffered with the human casualties of approximately 2,000 people in a 1963 landslide. One of the highest dams in the world, it was 262 meters (860 ft) high, 27 meters (89 ft) thick at the base and 3.4 meters (11 ft) at the top. The dam was built by SADE (Society of Adriatic Energy Corporation), the electricity supply and distribution monopolist in North-Eastern Italy.

History of Vajont Dam:

The construction work of the dam started in 1950. In 1959 some slides were noticed and new studies were made and the experts told SADE that the side of Mount Toc is unstable and is likely to collapse if the filling is continued. The study and experts were ignored completely. In October 1959 the construction was complete and in February 1960 SADE was authorized to start filling the basin. As soon as the filling started and reached to certain level till summers of 1960 minor land slides started taking place. But even these slides were ignored and the few journalists who raised their voice were sued. Finally on 4 of November 1960 a landslide of about 800,000 cubic meters collapsed in the lake. This made SADE to halt filling but it was started again after lowering the level by 50 meters and start building an artificial gallery. The minor slides kept on taking place and officials of SADE kept on predicting the disaster but they were ignored.

On 9 October 1963 at approximately 10:35pm, the combination of 'drawing-down the reservoir' and heavy rains triggered a landslide of about 260 million cubic meters of uprooted forest, loose earth, and rock fell into the reservoir. The resulting displacement of water caused 50 million cubic meters of water to over-top the dam in a 250-metre high wave. Despite this, the dam's structure was largely undamaged. Approximately 1900 to 2500 people were dead and 350 families were completely wiped off.

The major causes of this disaster are:

  • The heavy 50 million cubic meter landslide into the lake which made the tsunami wave rose.
  • The other minor land slides in the lake and in the artificial gallery.
  • Heavy rainfall which paved the path for the disaster.

Major causes for the land slides are:

  • Disturbance in the geological balance of Mount Toc.
  • Continuous filling of the basin.
  • Time to time rainfall.

Precautions which could have saved South Fork Dam: If anyhow the land slide could be prevented then the disaster might have been avoided. The landslide can be prevented by following two methods:

  • Plantation: More and more plants on the seaward side of the mountain. The roots of the plants help in binding the rocks and soil together and prevent erosion thus land sliding. Terrace plantation is a good option.
  • By artificial mountain binding: In this process the mountain is bound with the help steel net which prevent slides and even if land slide, the net prevent it from falling.

POOR MAINTENANCE ESPECIALLY OF OUTLET PIPES

Outlets came in range of designs, sizes, materials and type of control. Most of the controlling mechanisms and conduits are usually submerged and are pretty tedious to access for maintenance as well as inspection. This is the reason of negligence and some serious problems start developing. The problem can range from the control works becoming inoperable to the conduit deteriorating to the point of embankment failure. Proper inspection of the outlet usually requires advanced planning to allow outflows to be shut off and inundated areas to be pumped out.

CASE STUDY: Lawn Lake Dam

Now as a case study under this section we will make a thorough study of Lawn Lake Dam [Fig 5]. This dam failure occurred due to the disrepair of the outlet pipe which was located at the remote and tedious location. The continuous negligence of remotely situated leaky pipes caused the disaster when on July 15, 1982 at 6 a.m. 830,000 m3 of water exploded out of the faulty pipes. This enormous amount of water caused a flash flood and priced $31 million.

History of Lawn Lake Dam:

Originally the Lawn Lake was a natural lake covering a surface area of over 66,000 m3. It was situated at a height of 3,400 m in the rocky mountain. In 1903 some farmers seeking irrigation facilities out of this lake, built a dam and the covering land of the lake increased to 190,000m3. It was started in 1902 and the dam was completed in 1903. The dam increased the storage capacity of this natural water body. This dam was built in the eastern part. The water from this dam was released through the steep channel into the Big Thompson River. As the dam was built in the rocky mountain, its design was such that it made the location of outlet pipe quit remote. Bearing the negligence of officials the dam survived 80 long years.

On the morning of 15 July 1982 the dam collapsed releasing 228 million gallons of water all of a sudden. This huge amount of water poured through the steep and narrow mountainside. It is said that there was tremendous sound and the earth shook. The release rate of water was 510 m3/s. Though this great aquatic rampage killed only one person camping alongside but economically the cost of this disaster was estimated to be $31 million. The water got poured in the river and hit the cascade dam resulting in downfall of the same adding more amount of water to the flood. This flood destroyed the Aspenglen campground. Then after the flood water entered the town of Estes Park and caused great damage to the downtown shops after which the flood joined Thompson River. This flood deposited an alluvial fan of debris in Horseshoe Park.

Precautions that could have saved the Lake Lawn Dam: Only two precautions would have saved the disastrous end of Lake Lawn Dam and they are

  • If the dam would have been design in such a way that the outlet pipes could have been easily accessed then the repair work won't have been delayed and the leakage could have been avoided.
  • Timely repairing work of the dam would have saved this great damage.

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