The first constructed dams were gravity dams, which are straight dam made of masonry (stone brick) or concrete that resists the water load by means of weight. ." Around 2950-2750 B.C, the ancient Egyptians built the first known dam to exist. The dam was called the Sadd el-Kafara, which in Arabic means "Dam of the Pagans. The dam was 37 ft tall, 348 ft wide at the crest and 265 ft at the bottom. The dam was made of rubble masonry walls on the outsides and filled with 100,000 tons of gravel and stone. A limestone cover was applied to resist erosion and wave action. The structure had no need for cement because the shear weight of the structure was sufficient to ensure stability. Using the expected hydrology for ancient times, the capacity was estimated to be 20 million cubic ft or 460 acre-ft. The dam failed after a few years and it was concluded that overflow was the cause of failure. The poor workmanship from a hasty construction lead to the failure. The dam was not watertight and water flowed through the structure quickly eroding it away. Once the water overflowed the crest, it quickly eroded away the dam. The dam was a failure and the Egyptians never attempted to build another dam until modern times.
The second type of dam known to have been built was an earth dam called Nimrod's Dam in Mesopotamia around 2000 BC. Earth dams are massive dams similar to gravity dams except they are made of soil. The dam is made watertight, with a core wall and filled with an impervious center usually made of clays. Nimrod's dam was built north of Baghdad across the Tigris and was used to prevent erosion and reduce the threat of flooding. The intention was to divert the flow in the river and help irrigate the crops. The dam was built of earth and wood, so it is difficult to be certain of the exact characteristics of the dam.
Around 100 AD the Romans were the first civilization to use concrete and mortar in their gravity dams. The dam at Ponte di San Mauro has a great block of concrete among its remains. The evidence indicates that a large slab of concrete was used as the core and the outer layer finished with masonry.
Due to the large size and amount of building material need to construct these dams, the arch dam was invented. An arch dam is dependent on its shape for strength, requires less material to build, and is relatively thin. The first known arch dam is Kebar, which was built around 1280 AD in the Mongol period. The limestone dam is located near the ancient town of Quam and stands 85 ft high, 180 ft long at the crest, 16 ft thick at the crest and has a constant radius of curvature of 125 ft. An arch dam needs to be supported by the surrounding geology, the rock formations on either side support the arch.
In the seventeenth century Spanish dam building was superior to all other civilizations. A Spaniard named Don Pedro Bernardo Villarreal de Berriz wrote the first book on designing dams in 1736. In Don Pedro's time only two types of dams were built, arch dams for narrow gaps where the foundations had good solid rocks or gravity dams where the site was wide and shallow. Don Pedro's book suggested how to design dams properly and introduced new ideas such as a multiple arch dam. Don Pedro suggested that multiple arch dams would need artificial supports or buttresses to support the arches. This theory indirectly led to the invention of the buttress dam.
The buttress dam uses a series of cantilevers, slabs, arches or domes to support the face of the dam from the force of the water. Almendralejo dam is one of the earliest examples of a large buttress dam and is able to store water hydropower. Meer Allum dam is the earliest know examples of a true buttress dam of the multiple arch type.
The Spanish brought the art of dam building from Spain to the Americas. The idea of buttress dams was current in Spain, so many small buttress dams were used for irrigation purposes. In California, the Jesuit fathers established missions along the coastal regions. The Old Mission Dam built across the San Diego river in 1770 was one of the first dams in California. The dam was only 5ft tall and made of masonry and mortar. Soon modern multiple arch dams were built with concrete and rock filled dams was formed from dumped rock. A rock filled dam uses the large stone for stability and is filled with an impervious water face membrane and core wall. In 1884 the arch Bear Valley dam was built of masonry and morter but replaced with a concrete multiple arch dam in 1910. The large increase in dam building did not come until 1849 when the gold rush lead to a large increase in water demand.
Dam Construction in California: Trends Since 1850
California's diverse landscape and weather patterns, from wet in the northern half of the state to very dry in the southern part, has led to a vast reshaping of its waterscape. Much of the development and changing of watersheds to meet the needs of an ever-increasing population has been through the use of dams. California currently contains more than 1400 dams within its jurisdiction that provide water, electricity, flood control as well as recreational areas for nearly 35 million residents.
The following presents a brief summary
of trends, including typical reasons for the construction of dams.
During the second half of the 19th century, California experienced a large and sudden increase in population. The gold rush and California's mystique as a place of abundance and opportunity drew thousands of people to the state. Residents of the state, seeking to capitalize on the opportunities the state offered, began to market water. Dams during this time were primarily private ventures. Small dams were often used to divert water for mining operations and the irrigation of personal properties. The water diverted to mines was used for hydraulic mining, a practice that caused severe erosion, environmental degradation and silting of central California's rivers.
Most dams constructed in the earlier part of this period, were small by nature of the needs they served, and mainly constructed of earth and rock. As the turn of the century neared, and technology improved, larger concrete dams emerged. The Lower Crystal Springs Dam provided a significant example of a concrete gravity dam that set a precedence for future dam design. Built in 1888 near the San Andreas Fault, the Lower Crystal springs Dam withstood the 1906 San Francisco earthquake with little damage.
The constant arch
dam design also emerged in California at the end of the 19th century,
due to continued engineering and technological improvements, which reduced
costs and materials needed for construction. The arch dam was an
innovative design that used its shape to withstand forces induced by water
pressure, as opposed to the dam's weight (i.e. gravity dam). Despite
improved technology, stresses on arch dams were not adequately understood,
and most of the early arch dams resembled gravity dams with broad cross
sections. The lack of understanding delayed greater use of the arch dam
until the middle of the 20th century.
Agriculture became the dominant focus
of the state after the Gold Rush, and California's continued growth into
the 20th Century brought with it an increased demand for water, electricity,
and flood control. In order to meet these needs, private, local,
state and federal agencies began work on projects throughout the state.
Unpredictable weather, with frequent droughts and floods, served as fuel
for Progressive Era Politics and encouraged development of watersheds throughout
California, along with the rest of the United States, experienced major population growth with the "Baby Boomer" era following World War II. Agencies seeking to meet water demands constructed most of the major dams in California including Oroville, Don Pedro, San Luis, and Trinity Dams, all of which are over 2 million acre-feet. Following the major development of the 50's and 60's, the 1970's brought forth an era of environmental awareness.
The environmental movement, combined with the development of most of most major watersheds led to little change in California's water supply system during the following two decades. According to the California Water Plan, though, three major dams have currently been completed or are now under construction. The largest of these projects, the Eastside Dam in Riverside County, will hold an estimated capacity of 800,000 acre-ft when completed. With a lack of undeveloped watersheds, California faces the significant and difficult task of supplying water for modern urban, agricultural and environmental demands.