THE DEFINITION OF DAM

a. A barrier constructed across a waterway to control the flow or raise the level of water.b. A body of water controlled by such a barrier.

Why dams are built?• were originally build so that farmers could have water to irrigate their crops, or to provide a source of water for a village or town.• to serve quite a number of services such as generating electricity and supplying water for day to day activities.• to control flooding of water and enhancing river navigation.

Merimbun Lake & Benutan Dam Sungai Kargu Dam

ADVANTAGES OF DAM.

•FLOOD AND DROUGHT CONTROL.•IRRIGATION.•HYDRO ELECTRIC POWER.•IMPROVED NAVIGATION.•RECREATION AND TOURISM.

FLOOD AND DROUGHT CONTROL.

IRRIGATION.

HYDRO ELECTRIC POWER.

IMPROVED NAVIGATION.

RECREATION AND TOURISM

The disadvantages of dams :

- Dam detract from natural settings , ruin nature’s work- Dams have inundated the spawning grounds of fish- Dams have inhibited the seasonal migration of fish- May have inundated the potential for archaeological findings- Dams have endangered some species of fish- Reservoirs can foster diseases if not properly maintained- Reservoir water can eveporate significantly- Some researcher believe that reservoirs can cause earthquakes

- The reservoir created by dam may inundate land , crops , cities and vilagers.- People may be displaced by reservoir and have to find new homes- The reservoir may cause instability of hillsides

Expensive and difficulties in becoming profitableThe larger dams are incredibly expensive to build , such as , they can take many years to pay for themselves and become profitable. Most dams are estimated to operate for at least two to three decades, if not more,to become profitable and this cost that is usually taken on by the government and the taxpayers. This debt can be a large burden on the governmant for a long time and can influence fiscal polices for the life of debt

Danger of dam breachesDams being built today are much more stable than dams built in the past but many older dams have problems with breaches or even collapse. Because of the large volumes of water behind this dams can cause catastrophes for nearby people and wildlife

DisadvantagesSiesmic stressThe pressure or stress built up when plates slide past each other .

• How does earthquakes caused by dams?It is related to the extra water pressure created in the micro-

cracks and fissures in the ground under and near a reservoir. When the pressure of the water in the rocks increases, it acts to lubricate faults which are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces.

• The earthquake of November 1981 is believed to have been caused by the Aswan Dam; as water levels in the Dam increases, so does seismic activity.

Channel erosion beneath the channel• Erosion lowers the channel by 25mm over 18 years

Considerations in decreasing the erosion are as follows:

•Not only must the system be resistant to erosion, but stable under the slope geometry and hydrostatic uplift forces.

 • The channel walls must also be somewhat flexible in order to ensure integrity in the face of localized deformations from seasonal factors and sub-base void formation.

• System permeability is desirable in some situations to allow natural drainage.  A pervious channel wall can relieve hydrostatic uplift forces, thus stabilizing the system.

STUDY CASE: EGYPT’S ASWAN DAM

• Where is the Aswan Dam located? In the Nile River around Aswan, Egypt.

Egypt encountered problems such as no direct control on its main water resource.

• Suggestions to making a dam.A dam was then proposed to be built at Aswan as they

planned for different seasonal storage, over-year storage and channelization schemes that involved more than one country in the basin.

This dam, which is also known as The High Dam, was constructed between 1960 and 1970.

Advantages

• Optimizing and rationalizing the Nile flow at Aswan.• Regulating and controlling the daily, monthly and yearly discharge downstream of the dam to match the actual water needs.• Protecting the Nile Valley and Delta from Hazards of high floods and peril of droughts.• Generating cheap and clean hydroelectric power.

•Inundation of populated areas Nubia is the name of area that was subject to inundation due to the construction of the Aswan’s High Dam. More than 100 000 Nubians occupied this inundated area before the construction of the dam. In 1963 the entire Nubian population that was subjected to resettlement represented about 0.4% of the Egyptian population.

Disadvantages

• The resettlement costs six million Egyptian pounds. Nearly 50% of indemnities were paid in advance to help the Nubians move to their new settlements. The other 50% were used to pay part of the land, infrastructure and houses. The new settlement area is in Khashm el Girba.• Nubians, as a distinctive community, being deeply attached to their lands, lost something they cannot be compensated for and suffered psychologically.

•Sedimentation problems There are a couple of aspects regarding

sedimentation that a population of people believed to be a benefit.

1. It is the contributor to Egyptian land fertility2. Source of building material3. A carrier of nourishment for sardine fish in the

Mediterranean near the Nile estuaries

• How does a dam affect sedimentation? The dam prevented sediments to travel forward and continue its usual route of daily sedimentation system. It gets stuck inside the dam and will accumulate there. This became an issue, besides downstream morphological instability and coastal erosion.• The aftermath of the dam construction There have been plenty of problems ever since the dam was constructed. Some are as followed:

1. It is predicted that it takes 408 years for the sediments to fill up the dam’s dead storage.

2. Argricultural land was deprived with sedimentation and therefore received insignificant amount of feddans.

3. Stops the manufacturing of bricks.4. Sudden disappearance of sardine in the

Maditerranean estuaries

• ConclusionOverall, this Aswan High Dam has more positive

feedbacks more than negativity. It is proven to be a very economically efficient project. The national income has increased after 10 years of the construction of the dam.

Three Gorges Dams in ChinaCASE STUDY #2

• A hydroelectric dam that spans the Yangtze River• Located in Yilling District, Hubei China

• The world’s largest power station in terms of installed capacity (22,500 Megawatts/one million watts)

• In the year of 2012, the amount of electricity the dam generated is neck to neck with the Italipu dam – located between brazil and Paraguay

Each main turbine has a capacity of 700 MW. The dam body was completed in 2006. Coupling

the dam's 32 main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of

the dam is 22,500 MW.

• The dam project was completely and fully functional as of July 4, 2012

• As well as producing electricity, the dam is intended to increase the Yangtze River's shipping capacity

and reduce the potential for floods downstream by providing flood storage space.

Composition and Dimension• Made of concrete and steel

the dam is 2,335 m long and the top of the dam is 185 metres above sea level. The project used 27.2 million cubic metres (35.6×106 cu yd) of concrete (mainly for the dam wall)

463,000 tonnes (1 tonnes = 1000 kg) of steel (enough to build 63 Eiffel Towers) and moved about 102.6 million cubic metres (134.2×106 cu yd) of earth. The concrete dam wall is 181 metres high above the rock basis.

the water level is at its maximum of 175 metres above sea level, which is 110 metres higher than the river level downstream, the dam reservoir is on

average about 660 kilometres in length and 1.12 kilometres in width

. It contains 39.3 km3 of water and has a total surface area of 1,045 square kilometres. On

completion, the reservoir flooded a total area of 632 square

kilometre of land, compared to the 1,350 square kilometres of reservoir created by the Itaipu

Dam.

$$$• The government estimated that the Three Gorges Dam project would cost 180 billion yuan (US$22.5 billion)• By the end of 2008, spending had reached 148.365 billion yuan, among which 64.613 billion yuan was spent on construction, 68.557 billion yuan on relocating affected residents, and 15.195 billion yuan on financing

It is estimated that the construction cost will be recovered

when the dam has generated 1,000 terawatt-hours (3,600 PJ) of electricity, yielding 250 billion yuan. Full cost

recovery is expected to occur ten years after the dam starts full operation.

Effects

The dam flooded archaeological and cultural sites and displaced some 1.3 million people,

and is causing significant ecological changes, including an increased risk of landslides. The

dam has been a controversial topic both domestically and abroad.

Effects

Erosion and sedimentati

on

Earthquakes and landslides

WasteManagement

Wildlife

Erosion and sedimentation• At current levels, 80% of the land in the area is experiencing erosion, depositing about 40 million tons of sediment into the Yangtze annually

Because the flow is slower above the dam, much of this sediment will now settle there instead of flowing

downstream, and there will be less sediment downstream.

Earthquakes and landslides• Erosion in the reservoir, induced by rising water, causes frequent major landslides that have led to noticeable disturbance in the reservoir surface,

including two incidents in May 2009 when somewhere between 20,000 and 50,000 cubic

metres of material plunged into the flooded Wuxia Gorge of the Wu River. Also, in the first four months

of 2010, there were 97 significant landslides.

Waste Management•Over one billion tons of wastewater are

released annually into the river, which was more likely to be swept away before the

reservoir was created. This has left the water looking stagnant, polluted and murky.

Wildlife• The location of the Three Gorges Dam is the home to 6,388 species of plants, which belong to 238 families and 1508 genera. • Of these plant species, 57 percent are endangered. These rare species are also used as ingredients in traditional Chinese medicines. • Already, the percentage of forested area in the region surrounding the Three Gorges Dam has dropped from twenty percent in 1950 to less than ten percent as of 2002, negatively affecting all plant species in this locality. • The region also provides habitats to hundreds of freshwater and terrestrial animal species. • Freshwater fish are especially affected by dams due to changes in the water temperature and flow regime. Many other fish are hurt in the turbine blades of the hydroelectric plants as well. Other aquatic species are being endangered by the dam, particularly the Baiji, or the Chinese River Dolphin.[