A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding, for example land use changes such as deforestation and removal of wetlands, changes in waterway course or flood controls such as with levees, and larger environmental issues such as climate change and sea level rise. In particular climate change's increased rainfall and extreme weather events increases the severity of other causes for flooding, resulting in more intense floods and increased flood risk.
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such 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 or store 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 are used to manage or prevent water flow into specific land regions.
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower. Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and also more than nuclear power. Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel-powered energy plants. However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.
A diversion dam is a dam that diverts all or a portion of the flow of a river from its natural course. Diversion dams do not generally impound water in a reservoir; instead, the water is diverted into an artificial water course or canal, which may be used for irrigation or return to the river after passing through hydroelectric generators, flow into a different river or be itself dammed forming an onground or groundwater reservoir or a storm drain.
A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure that water does not damage parts of the structure not designed to convey water.
Dworshak Dam is a concrete gravity dam in the western United States, on the North Fork of the Clearwater River in north central Idaho. In Clearwater County, the dam is located approximately four miles (6 km) northwest of Orofino and impounds the Dworshak Reservoir for flood control and hydroelectricity generation.
A reservoir is an enlarged lake behind a dam. Such a dam may be either artificial, usually built to store fresh water, or it may be a natural formation.
Gavins Point Dam is a 1.9 mi (3 km) long embankment rolled-earth and chalk-fill dam which spans the Missouri River and impounds Lewis and Clark Lake. The dam joins Cedar County, Nebraska with Yankton County, South Dakota a distance of 811.1 river miles (1,305 km) upstream of St. Louis, Missouri, where the river joins the Mississippi River. The dam and hydroelectric power plant were constructed as the Gavins Point Project from 1952 to 1957 by the United States Army Corps of Engineers as part of the Pick-Sloan Plan. The dam is located approximately 4 miles (6.4 km) west or upstream of Yankton, South Dakota.
The environmental impact of reservoirs comes under ever-increasing scrutiny as the global demand for water and energy increases and the number and size of reservoirs increases.
Clifton Court Forebay is a reservoir in the San Joaquin River Delta region of eastern Contra Costa County, California, 17 mi (27 km) southwest of Stockton. The estuary region the forebay is located in is only 1m to 3m above mean sea level.
Flood control methods are used to reduce or prevent the detrimental effects of flood waters. Flood relief methods are used to reduce the effects of flood waters or high water levels. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and runoff. A distinction is made between structural and non-structural flood control measures. Structural methods physically restrain the flood waters, whereas non-structural methods do not. Building hard infrastructure to prevent flooding, such as flood walls, is effective at managing flooding. However, increased best practice within landscape engineering is to rely more on soft infrastructure and natural systems, such as marshes and flood plains, for handling the increase in water. To prevent or manage coastal flooding, coastal management practices have to handle natural processes like tides but also the human cased sea level rise.
A check dam is a small, sometimes temporary, dam constructed across a swale, drainage ditch, or waterway to counteract erosion by reducing water flow velocity. Check dams themselves are not a type of new technology; rather, they are an ancient technique dating from the second century AD. Check dams are typically, though not always, implemented in a system of several dams situated at regular intervals across the area of interest.
Feicui Dam is a double curvature concrete arch dam on the Beishi River in Shiding District, New Taipei, Taiwan, forming Feicui Reservoir (翡翠水庫). The dam is located in Shiding District, New Taipei City, and is usually misunderstood as the principal water source for the Greater Taipei area. The name of the dam and reservoir translates as "emerald lake", in reference to the pure quality of the water. The area is managed by the Taipei Feicui Reservoir Administration. Public access is heavily restricted in order to protect water quality, which is among the highest of Taiwan's reservoirs.
San Gabriel Dam is a rock-fill dam on the San Gabriel River in Los Angeles County, California, within the Angeles National Forest. Completed in 1939, the dam impounds the main stem of the San Gabriel River about 2.5 miles (4.0 km) downstream from the confluence of the river's East and West Forks, which drain a large portion of the San Gabriel Mountains. It is located directly upstream from the Morris Dam. The dam provides flood control, groundwater recharge flows and hydroelectricity for the heavily populated San Gabriel Valley in the Greater Los Angeles metropolitan area.
The Sanmenxia Dam is a concrete gravity dam on the middle-reaches of the Yellow River near Sanmenxia Gorge on the border between Shanxi province and Henan Province, China. The dam is multi-purpose and was constructed for flood and ice control along with irrigation, hydroelectric power generation and navigation. Construction began in 1957 and was completed in 1960. It is the first major water control project on the Yellow River and was viewed as a major achievement of the new People's Republic of China. Subsequently, its image was printed on the country's bank notes. However, due to sediment accumulation in the reservoir, the dam later had to be re-engineered and renovated. The effects from sediment, which include flooding upstream, have placed the dam at the center of controversy and criticism-related arrests by the Chinese government.
Morris Dam is a concrete gravity dam across the San Gabriel River in the U.S. state of California. It impounds Morris Reservoir, directly downstream of San Gabriel Dam.
Keswick Dam is a concrete gravity dam on the Sacramento River about 2 miles (3.2 km) northwest of Redding, California. Part of the U.S. Bureau of Reclamation's Central Valley Project, the dam is 157 feet (48 m) high and impounds the Keswick Reservoir, which has a capacity of 23,800 acre⋅ft (29,400,000 m3). The dam's power plant has three turbines with a generating capacity of 117 megawatts (MW), which, in 1992, was uprated from its original 75 MW. The dam and reservoir serve as an afterbay to regulate peaking power releases from the Shasta Dam upstream.
Gibraltar Dam is located on the Santa Ynez River, in southeastern Santa Barbara County, California, in the United States. Forming Gibraltar Reservoir, the dam is owned by the city of Santa Barbara. Originally constructed in 1920 and expanded in 1948, the dam and reservoir are located in a remote part of the Los Padres National Forest.
A detention dam is a dam built to catch surface runoff and stream water flow to regulate the water flow in areas below the dam. Detention dams are commonly used to reduce the damage caused by flooding or to manage the flow rate through a channel. Detention dams can also be constructed to replenish groundwater and trap sediment. Detention dams are one of three classifications of dams: storage dams, diversion dams, and detention dams. Storage dams store water for extended times for irrigation, livestock, municipal water supply, recreation, and hydroelectric power generation. Diversion dams raise the water level to redirect the water to a designated location. The diverted water typically supplies irrigation systems or reservoirs.
Matilija Dam is a concrete arch dam in Ventura County, California, completed in 1947. Designed for water storage and flood control, it impounds Matilija Creek to create the Matilija Reservoir in the Los Padres National Forest, south of the Matilija Wilderness and north of Ojai.
