Dikes used to hold back water are usually made of earth. Sometimes, dikes occur naturally. More often, people construct dikes to prevent flooding. When constructed along river banks, dikes control the flow of water.

Xenoliths can be a piece of rock trapped in a piece of sedimentary rock, but this is rare. Xenoliths have also been found in meteorites, or rocks from outer space that have crashed into Earth.

A xenolith (“foreign rock”) is a rock fragment that becomes enveloped in a larger rock during the latter’s development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption.

A sill is a concordant intrusive sheet, meaning that a sill does not cut across preexisting rock beds. In contrast, a dike is a discordant intrusive sheet, which does cut across older rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source.

Spread a layer of earth or sand 1 inch deep and about 1 foot wide along the bottom of the dike on the water side. beyond the bottom edge of the dike over the loose dirt. The upper edge should extend over the top of the dike. This sheeting is available from construction supply firms, lumberyards and farm stores.

A dike normally runs along or parallel to a body of water such as a river or a sea, a dam runs across or through a body of water. Dikes and levees are embankments constructed to prevent flooding. Levees may be formed naturally or artificially. They prevent the water from overflowing and flooding surrounding areas.

Levees protect land that is normally dry but that may be flooded when rain or melting snow raises the water level in a body of water, such as a river. Dikes protect land that would naturally be underwater most of the time. Levees and dikes look alike, and sometimes the terms levee and dike are used interchangeably.

First, they dug tunnels from below the dam to above the dam. Then, they put the cofferdam in place, and opened the tunnels. The water flowed around the site where the permanent dam would be built until they were done, at which point the cofferdam was removed.

What is a dam built on? Ans. A dam is a structure built across a river or stream.

Dams change the way rivers function. They can trap sediment, burying rock riverbeds where fish spawn. Gravel, logs, and other important food and habitat features can also become trapped behind dams. This negatively affects the creation and maintenance of more complex habitat (e.g., riffles, pools) downstream.

Ans. The two alternatives to big dams are: Recycling/Reuse of water: One of the ways of doing so is reusing or recycling the water. By recycling or reusing, we mean the process of sewage treatment.

Disadvantages of Building a Dam

• Building a dam is very expensive, the government needs to ensure that strict guidelines are followed and a very high standard is maintained.
• They must operate for many years in order to become profitable enough to compensate for the high building cost.

There are multiple benefits by big dams. They provide water for irrigation, prevents of floods and generates electricity. Large dams have the potential to save the country from critical food shortages. Dams are the main source for water in dry areas.

Dams slow the passage of water through a river and can act as a natural filter. These pollutants can have costly consequences downstream, creating a need to filter out the sediment, nitrogen, and phosphorous to meet clean drinking water standards.

Dams can be associated with a number of effects, including changes to hydrology, water quality, habitat, and river morphology. Lakes and reservoirs integrate many processes that take place in their contributing watersheds, including processes that contribute energy (heat), sediment, nutrients, and toxic substances.

Dams alter water temperatures By slowing water flow, most dams increase water temperatures. Other dams decrease temperatures by Page 2 releasing cooled water from the reservoir bottom. Fish and other species are sensitive to these temperature irregularities, which often destroy native populations.

80 million people

The World Commission on Dams found that on average, large dams have been at best only marginally economically viable. Another issue is that large dams are often the largest energy development in many poor countries, which can lead to an unbalanced (and climate-risky) energy supply.

An estimated 80 million people have been displaced by dam projects worldwide. Displacement caused by dams often involves resettlement, in which people are moved to another location. This should be, but is by no means always accompanied by compensation for their losses and assistance to rebuild their lives.

Among water infrastructure options, dams especially have been ascribed an unparalleled importance in fostering long-term economic development, because they facilitate multiple uses of water, including for productive activities (e.g. irrigation, in- dustrial production, low-cost cooling of power plants).