Damming has been an important engineering practice for thousands of years, with the first dam being constructed by Ancient Egyptians around 2800 B.C. Dams are built to block the flow of water, creating a reservoir behind the dam that can be used for flood control, as well as irrigation, municipal water supply, and other human activities. Inspired by a recent news story of dam failure in California, this blog looks at how dams have historically been constructed in the last 100 years, and what improvements are necessary in dam construction moving forward.
How to Build a DamBuilding 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.
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.
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.
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.
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.
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.
How to build a dam: Dams of the FutureAs 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.
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