Arch dam

An arch dam is a solid dam made of concrete that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments. An arch dam is most suitable for narrow gorges or canyons with steep walls of stable rock to support the structure and stresses. Since they are thinner than any other dam type, they require much less construction material, making them economical and practical in remote areas.

Classification

In general, arch dams are classified based on the ratio of the base thickness to the structural height (b/h) as:

Arch dams classified with respect to their structural height are:

History

The development of arch dams throughout history began with the Romans in the 1st century BC and after several designs and techniques were developed, relative uniformity was achieved in the 20th century. The first known arch dam, the Glanum Dam, also known as the Vallon de Baume Dam, was built by the Romans in France and it dates back to the 1st century BC. The dam was about 12m high and 18m in length. Its radius was about 14m and it consisted of two masonry walls. The Romans built it to supply nearby Glanum with water.

Dam

A dam is a barrier that impounds water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for such activities as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect water or for storage of water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions.

The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities.

History

Ancient dams

Early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite unpredictable.

The earliest known dam is the Jawa Dam in Jordan, 100 kilometres (62 mi) northeast of the capital Amman. This gravity dam featured an originally 9-metre-high (30 ft) and 1 m-wide (3.3 ft) stone wall, supported by a 50 m-wide (160 ft) earth rampart. The structure is dated to 3000 BC.

Arch

An arch is a curved structure that spans a space and may or may not support weight above it. Arch may be synonymous with vault, but a vault may be distinguished as a continuous arch forming a roof. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture, and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.

Basic concepts

An arch is a pure compression form. It can span a large area by resolving forces into compressive stresses and, in turn eliminating tensile stresses. This is sometimes referred to as arch action. As the forces in the arch are carried to the ground, the arch will push outward at the base, called thrust. As the rise, or height of the arch decreases, the outward thrust increases. In order to maintain arch action and prevent the arch from collapsing, the thrust needs to be restrained, either with internal ties or external bracing, such as abutments.

Fixed vs hinged arch

Glen Canyon

Glen Canyon is a canyon that is located in southeastern and south central Utah and northwestern Arizona within the Vermilion Cliffs area. An immense area located north of the Grand Canyon, it too was carved by the Colorado River.

A reservoir, Lake Powell, was created by the Glen Canyon Dam in 1963, flooding much of Glen Canyon. Lake Powell emerged from a struggle over damming Dinosaur National Monument. The Sierra Club and its leader, David Brower, were instrumental in blocking the dam in Dinosaur, ignoring Glen Canyon in the process. Before Glen Canyon was flooded, but after the struggle in Congress, Brower floated the canyon and realized what a tremendous resource it was. This experience transformed Brower's attitude towards environmental preservation, making him more radical and less likely to compromise. It was very similar to the experience of John Muir with the Hetch Hetchy Reservoir. For Brower, it steeled him for the battle over a dam in the Grand Canyon. Beginning in the late 1990s, the Sierra Club and other organizations renewed the call to drain Lake Powell in Lower Glen Canyon. Edward Abbey documented his experience exploring Glen Canyon from the Colorado River prior to the completion of Glen Canyon Dam in his memoir Desert Solitaire in the chapter titled Down the River.

Colorado River

The Colorado River is one of the principal rivers of the Southwestern United States and northern Mexico (the other being the Rio Grande). The 1,450-mile (2,330 km) Colorado River drains an expansive, arid watershed that encompasses parts of seven U.S. and two Mexican states. Rising in the central Rocky Mountains in the U.S., the river flows generally southwest across the Colorado Plateau and through the Grand Canyon before reaching Lake Mead on the Arizona–Nevada border, where it turns south toward the international border. After entering Mexico, the Colorado approaches the large Colorado River Delta at the tip of the Gulf of California between Baja California and Sonora.

Known for its dramatic canyons and whitewater rapids, the Colorado is a vital source of water for agricultural and urban areas in the southwestern desert lands of North America. The river and its tributaries are controlled by an extensive system of dams, reservoirs, and aqueducts, which divert 90% of its water in the U.S. alone to furnish irrigation and municipal water supply for almost 40 million people both inside and outside the watershed. The Colorado's large flow and steep gradient are used for generating hydroelectric power, and its major dams regulate peaking power demands in much of the Intermountain West. Intensive water consumption has dried the lower 100 miles (160 km) of the river such that it has not consistently reached the sea since the 1960s.