How To Build A Dam

How to Build a Dam Building a dam is a complex, multi-step process that requires huge amounts of manpower, raw materials

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How to Build a Dam Building a dam is a complex, multi-step process that requires huge amounts of manpower, raw materials, and investment. Here are the basic steps to building a gravity dam – the most common type of dam that we build. Gravity dams are so named because they are held to the ground by gravity – they weigh a lot, and are typically made from concrete or stone. 1.

Engineers must de-water the river where the dam is meant to

be built. This is done by diverting the river through a tunnel that

runs around the intended construction zone. Tunnels like this may

be lined with concrete and are usually dug out using a combination

of drilling and explosives.

2.

Dam construction must be started when river levels are low. A

small dam called a cofferdam is built upstream of the construction

zone to help funnel water into the diversion tunnel. A cofferdam

may be built downstream as well, but the overall goal is to keep the

construction zone dry so that the main dam can be built. Pumps

may be used to remove water that penetrates the cofferdam.

3.

Loose rock is removed from the riverbed, and a plinth must be

constructed. A plinth is a concrete foundation for the dam that

embeds it in the walls and floor of the riverbed/valley. This prevents

water from leaking at the edges of the dam.

4.

Now, it’s time to build the dam to its desired height. A

concave-curved downstream surface for a dam helps it absorb the

constant pressure of water that it must endure. Reinforced steel is

used for the surfaces of the dam itself, and an enclosure is built. The

enclosure is filled with concrete to make it extremely strong and

resilient against water flow.

What’s Wrong with Dams Today? Our designs and methods for building dams have been reliable for decades – what’s gone so wrong in the last few years to make us want to reconsider? The simple answer is climate change. Dams that were built 50 or 60 years ago were designed with the assumption that the climate would always be stable. From today’s standpoint, however, we can see that this simply is not the case.

Hydrological cycles are sensitive to even minor changes in climate. Dams are typically designed by accounting for historical data but without an understanding of how water cycles might change in the future.

As an example, the Muela Hydropower Station was recently completed in Lesotho, a country thought to have considerable potential for hydropower resources. Following completion of the dam, Lesotho has had no issues meeting its domestic energy needs. However, the country is prone to natural disasters and desertification, and is highly vulnerable to climate change. Scientists

predict that increased temperatures and lower precipitation in coming years will create a period of water stress by 2019 that will worsen by 2060, making Lesotho’s dam considerably less effective, and threatening its energy security.

Conversely, in California, alternating cycles of extreme drought and excessive rainfall have highlighted the inflexible design of dams in that region. Record amounts of rainfall have led to record flooding, threatening the lives of those living around dams with inadequate spillways. While some dams are under improvement, such as the 340-foot Folsom Dam, where Army engineers are adding 40% capacity to the main spillway, other similar structures are being neglected. This could result in catastrophic flooding that would negatively affect residents and the environment.

Dams of the Future As we design dams in the future, it is crucial that we understand and account for our changing climate. We now know that we cannot predict water levels and required reservoir capacity based on

historical data. We know that climate change is the reality that we are living in, and that while some locations may become more prone to flooding than previously thought, other regions are facing water stress and may not be able to realize the benefits of damming over any reasonable period.

It is not enough to use historical data when planning a project like a dam. Engineers should consider not just one future, but several possible futures when working on a project that is so critical to local infrastructure. A hydroelectric developer in Iceland recently commissioned a study that investigates how it should develop a glacier-fed power generation facility. This study was deemed necessary because glacial melt appears to be increasing and increased water flow is anticipated in the coming decades. The study concluded that the dam should be “over-installed” – built with the capacity to handle more flow than currently exists. This type of thinking should be applied across the world to build dams that will safely and productively serve us in the uncertain times ahead.

Rock-fill dams[edit]

The Gathright Dam in Virginia is a rock-fill embankment dam.

Rock-fill dams are embankments of compacted free-draining granular earth with an impervious zone. The earth utilized often contains a high percentage of large particles, hence the term "rock-fill". The impervious zone may be on the upstream face and made of masonry, concrete, plastic membrane, steel sheet piles, timber or other material. The impervious zone may also be within the embankment in which case it is referred to as a core. In the instances where clay is utilized as the impervious material the dam is referred to as a composite dam. To prevent internal erosion of clay into the rock fill due to seepage forces, the core is separated using a filter. Filters are specifically graded soil designed to prevent the migration of fine grain soil particles. When suitable material is at hand, transportation is minimized leading to cost savings during construction. Rock-fill dams are resistant to damage from earthquakes. However, inadequate quality control during construction can lead to poor compaction and sand in the embankment which can lead to liquefaction of the rock-fill during an earthquake. Liquefaction potential can be reduced by keeping susceptible material from being saturated, and by providing adequate compaction during construction. An example of a rock-fill dam is New Melones Dam in California or the Fierza Dam in Albania. A core that is growing in popularity is asphalt concrete. The majority of such dams are built with rock and/or gravel as the main fill material. Almost 100 dams of this design have now been built worldwide since the first such dam was completed in 1962. All asphaltconcrete core dams built so far have an excellent performance record. The type of asphalt used is a viscoelastic-plastic material that can adjust to the movements and deformations imposed on the embankment as a whole, and to settlements in the foundation. The flexible properties of the asphalt make such dams especially suited in earthquake regions.[42]

For the Moglicë Hydro Power Plant in Albania the Norwegian power company Statkraft is currently building an asphalt-core rock-fill dam. Upon completion in 2018 the 320 m long, 150 m high and 460 m wide dam is anticipated to be the world's highest of its kind. [43][44][45]

Rockfill Dams: A rockfill dam is built of rock fragments and boulders of large size. An impervious membrane is placed on the rockfill on the upstream side to reduce the seepage through the dam. The membrane is usually made of cement concrete or asphaltic concrete. In early rockfill dams, steel and timber membrane were also used, but now they are obsolete. A dry rubble cushion is placed between the rockfill and the membrane for the distribution of water load and for providing a support to the membrane. Sometimes, the rockfill dams have an impervious earth core in the middle to check the seepage instead of an impervious upstream membrane. The earth core is placed against a dumped rockfill. It is necessary to provide adequate filters between the earth core and the rockfill on the upstream and downstream sides of the core so that the soil particles are not carried by water and piping does not occur. The side slopes of rockfill are usually kept equal to the angle of repose of rock, which is usually taken as 1.4:1 (or 1.3:1). Rockfill dams require foundation stronger than those for earth dams. Examples of rockfill dam: Mica Dam (Canada) and Chicoasen Dam (Mexico).