A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but provide water for activities such as irrigation, human consumption, industrial use and navigability. Hydropower is used in conjunction with dams to generate electricity. A dam can be used to collect water or for storage of water which can be evenly distributed between locations. Dams 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; the earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC. The word dam can be traced back to Middle English, before that, from Middle Dutch, as seen in the names of many old cities; the first known appearance of dam occurs in 1165. However, there is one village, mentioned in 1120; the word seems to be related to the Greek word taphos, meaning "grave" or "grave hill". So the word should be understood as "dike from dug out earth".
The names of more than 40 places from the Middle Dutch era such as Amsterdam and Rotterdam bear testimony to the use of the word in Middle Dutch at that time. Early dam building took place in the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers; the earliest known dam is the Jawa Dam in Jordan, 100 kilometres northeast of the capital Amman. This gravity dam featured an 9-metre-high and 1 m-wide stone wall, supported by a 50 m-wide earth rampart; the structure is dated to 3000 BC. The Ancient Egyptian Sadd-el-Kafara Dam at Wadi Al-Garawi, located about 25 km south of Cairo, was 102 m long at its base and 87 m wide; the structure was built around 2800 or 2600 BC as a diversion dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards. During the Twelfth Dynasty in the 19th century BC, the Pharaohs Senosert III, Amenemhat III and Amenemhat IV dug a canal 16 km long linking the Fayum Depression to the Nile in Middle Egypt.
Two dams called Ha-Uar running east-west were built to retain water during the annual flood and release it to surrounding lands. The lake called "Mer-wer" or Lake Moeris is known today as Birket Qarun. By the mid-late third millennium BC, an intricate water-management system within Dholavira in modern-day India was built; the system included 16 reservoirs and various channels for collecting water and storing it. One of the engineering wonders of the ancient world was the Great Dam of Marib in Yemen. Initiated somewhere between 1750 and 1700 BC, it was made of packed earth – triangular in cross section, 580 m in length and 4 m high – running between two groups of rocks on either side, to which it was linked by substantial stonework. Repairs were carried out during various periods, most important around 750 BC, 250 years the dam height was increased to 7 m. After the end of the Kingdom of Saba, the dam fell under the control of the Ḥimyarites who undertook further improvements, creating a structure 14 m high, with five spillway channels, two masonry-reinforced sluices, a settling pond, a 1,000 m canal to a distribution tank.
These extensive works were not finalized until 325 AD and allowed the irrigation of 25,000 acres. Eflatun Pınar is a Hittite spring temple near Konya, Turkey, it is thought to be from the time of the Hittite empire between the 15th and 13th century BC. The Kallanai is constructed of unhewn stone, over 300 m long, 4.5 m high and 20 m wide, across the main stream of the Kaveri river in Tamil Nadu, South India. The basic structure dates to the 2nd century AD and is considered one of the oldest water-diversion or water-regulator structures in the world, still in use; the purpose of the dam was to divert the waters of the Kaveri across the fertile delta region for irrigation via canals. Du Jiang Yan is the oldest surviving irrigation system in China that included a dam that directed waterflow, it was finished in 251 BC. A large earthen dam, made by Sunshu Ao, the prime minister of Chu, flooded a valley in modern-day northern Anhui province that created an enormous irrigation reservoir, a reservoir, still present today.
Roman dam construction was characterized by "the Romans' ability to plan and organize engineering construction on a grand scale." Roman planners introduced the then-novel concept of large reservoir dams which could secure a permanent water supply for urban settlements over the dry season. Their pioneering use of water-proof hydraulic mortar and Roman concrete allowed for much larger dam structures than built, such as the Lake Homs Dam the largest water barrier to that date, the Harbaqa Dam, both in Roman Syria; the highest Roman dam was the Subiaco Dam near Rome. Roman engineers made routine use of ancient standard designs like embankment dams and masonry gravity dams. Apart from that, they displayed a high degree of inventiveness, introducing most of the other basic dam designs, unknown until then; these include arch-gravity dams, arch dams, buttress dams and multiple arch buttress dams, all of which were known and employed by the 2nd century AD. Roman workforces were the first to build dam bridges, such as the Bridge of Valerian in Iran
A drop structure known as a grade control, sill, or weir, is a manmade structure small and built on minor streams, or as part of a dam's spillway, to pass water to a lower elevation while controlling the energy and velocity of the water as it passes over. Unlike most dams, drop structures are not built for water impoundment, diversion or raising the water level. Built on watercourses with steep gradients, they serve other purposes such as water oxygenation and erosion prevention. Drop structures can be classified into three different basic types: "vertical hard basin", "grouted sloping boulder", "baffle chute"; each type is built depending on water flow, steepness of the site, location. The vertical hard basin drop structure called a dissipation wall, is the basic type of drop structure; the vertical hard basin drop consists of a vertical "cutoff wall" built of concrete, laid perpendicular to the stream flow. The purpose of the vertical hard basin drop is to force the water into a hydraulic jump.
Though the simplest type of drop structure, it is highest in maintenance needs and less safe, with most problems related to the impact basin. Sediment is deposited in the basin, requiring frequent removal, erosion downstream of the base of the structure. A grouted sloping boulder drop structure is the most versatile of drop structures. Able to accommodate both a broad floodplain or a narrow channel, they can handle many different drop heights. Heights of these structures range from 1 foot to 10 feet; these structures are built by creating a slope of riprap, which consists of large boulders or less blocks of concrete. These are cemented together to form the drop structure. Another less common type of drop structure, the sculpted sloping boulder drop, is derived from this; the sculpted sloping boulder drop is used to create a more natural appearance to the drop structure. Both of these structures tend to suffer from downstream erosion; the baffle chute drop is built of concrete and is effective with low maintenance needs.
They consist of a concrete chute lined with "baffle" teeth to slow velocity of water as it passes over the structure. Despite these appeals, they have "limited structural and aesthetic flexibility, which can cause them to be undesirable in most urban settings." Drop structures have been shown to either be detrimental to habitat in the stream. They create complexity of habitat by breaking up a stretch of stream into a series of pools. Surface turbulence and bubbles are generated by drop structures that provide hiding and cover for fish and other aquatic organisms. Water is aerated. Sediment is sorted in scour pools, which provide energy dissipation. On the other hand, drop structures may become barriers to fish; the downstream channel may erode and and unexpectedly increase the height of the structure, to a point where migratory fish, such as salmon, cannot pass over the structure. Other causes may be that the plunge pool is obstructed or the water flow is too shallow. However, many properly functioning drop structures themselves may impede the upstream and downstream migration of fish.
Unless the structure is designed to maintain them, existing fish spawning pools will be impacted or lost. Erosion is reduced by drop structures, natural river channel processes, such as channel migration and creation of stream pools and riffles, are reduced. Drop structures can be used for flow control and to stabilize waterways and prevent the formation of gullies, they have the potential to operate as inlets and outlets for other conservation structures, such as culverts. Check dam Knickpoint Weir
National Diet Library
The National Diet Library is the national library of Japan and among the largest libraries in the world. It was established in 1948 for the purpose of assisting members of the National Diet of Japan in researching matters of public policy; the library is similar in scope to the United States Library of Congress. The National Diet Library consists of two main facilities in Tōkyō and Kyōtō, several other branch libraries throughout Japan; the National Diet Library is the successor of three separate libraries: the library of the House of Peers, the library of the House of Representatives, both of which were established at the creation of Japan's Imperial Diet in 1890. The Diet's power in prewar Japan was limited, its need for information was "correspondingly small"; the original Diet libraries "never developed either the collections or the services which might have made them vital adjuncts of genuinely responsible legislative activity". Until Japan's defeat, the executive had controlled all political documents, depriving the people and the Diet of access to vital information.
The U. S. occupation forces under General Douglas MacArthur deemed reform of the Diet library system to be an important part of the democratization of Japan after its defeat in World War II. In 1946, each house of the Diet formed its own National Diet Library Standing Committee. Hani Gorō, a Marxist historian, imprisoned during the war for thought crimes and had been elected to the House of Councillors after the war, spearheaded the reform efforts. Hani envisioned the new body as "both a'citadel of popular sovereignty'", the means of realizing a "peaceful revolution"; the Occupation officers responsible for overseeing library reforms reported that, although the Occupation was a catalyst for change, local initiative pre-existed the Occupation, the successful reforms were due to dedicated Japanese like Hani. The National Diet Library opened in June 1948 in the present-day State Guest-House with an initial collection of 100,000 volumes; the first Librarian of the Diet Library was the politician Tokujirō Kanamori.
The philosopher Masakazu Nakai served as the first Vice Librarian. In 1949, the NDL became the only national library in Japan. At this time the collection gained an additional million volumes housed in the former National Library in Ueno. In 1961, the NDL opened at its present location in Nagatachō, adjacent to the National Diet. In 1986, the NDL's Annex was completed to accommodate a combined total of 12 million books and periodicals; the Kansai-kan, which opened in October 2002 in the Kansai Science City, has a collection of 6 million items. In May 2002, the NDL opened a new branch, the International Library of Children's Literature, in the former building of the Imperial Library in Ueno; this branch contains some 400,000 items of children's literature from around the world. Though the NDL's original mandate was to be a research library for the National Diet, the general public is the largest consumer of the library's services. In the fiscal year ending March 2004, for example, the library reported more than 250,000 reference inquiries.
As Japan's national library, the NDL collects copies of all publications published in Japan. Moreover, because the NDL serves as a research library for Diet members, their staffs, the general public, it maintains an extensive collection of materials published in foreign languages on a wide range of topics; the NDL has eight major specialized collections: Modern Political and Constitutional History. The Modern Political and Constitutional History Collection comprises some 300,000 items related to Japan's political and legal modernization in the 19th century, including the original document archives of important Japanese statesmen from the latter half of the 19th century and the early 20th century like Itō Hirobumi, Iwakura Tomomi, Sanjō Sanetomi, Mutsu Munemitsu, Terauchi Masatake, other influential figures from the Meiji and Taishō periods; the NDL has an extensive microform collection of some 30 million pages of documents relating to the Occupation of Japan after World War II. This collection include the documents prepared by General Headquarters and the Supreme Commander of the Allied Powers, the Far Eastern Commission, the United States Strategic Bombing Survey Team.
The Laws and Preliminary Records Collection consists of some 170,000 Japanese and 200,000 foreign-language documents concerning proceedings of the National Diet and the legislatures of some 70 foreign countries, the official gazettes, judicial opinions, international treaties pertaining to some 150 foreign countries. The NDL maintains a collection of some 530,000 books and booklets and 2 million microform titles relating to the sciences; these materials include, among other things, foreign doctoral dissertations in the sciences, the proceedings and reports of academic societies, catalogues of technical standards, etc. The NDL has a collection of 440,000 maps of Japan and other countries, including the topographica
Bioswales are landscape elements designed to concentrate or remove debris and pollution out of surface runoff water. They consist of a swaled drainage course with sloped sides and filled with vegetation, compost and/or riprap; the water's flow path, along with the wide and shallow ditch, is designed to maximize the time water spends in the swale, which aids the collection and removal of pollutants and debris. Bioswales are beneficial in groundwater recharge and are effective stormwater mitigation tools. Depending upon the topography of the land, a bioswale may have a meandering or straight channel alignment. A bioswale's make-up can be influenced by many different variables, including climate, rainfall patterns, size of the site and available vegetation that can be planted, it is important to maintain bioswales to ensure best possible efficiency and effectiveness in removal of pollutants in the stormwater runoff. Planning for these things is an important step, which can include the introduction of filters or large rocks to prevent clogging.
Annual maintenance through soil testing, visual inspection, mechanical testing is crucial to the health of a bioswale. A common application is around parking lots, where substantial automotive pollution is settled on the paving and flushed by the first instance of rain, known as the first flush; the bioswales, or other type of biofilter, can be created around the edges of parking lots to capture and treat the stormwater runoff before releasing it to the watershed or storm sewer. Bioswales work to remove pollutants through the soil; as the storm water runoff flows through the bioswale, the pollutants are captured and settled by the leaves and stems of the plants. The pollutants enter the soil where they decompose or can be broken down by bacteria in healthy soil. There are several classes of water pollutants that may be arrested with bioswales; these fall into the categories of inorganic contaminants, organic chemicals and pathogens. Silt – How bioswales and plants are constructed slow the conveyance of silt and reduce the turbidity of receiving waters.
Filters can be established to capture silt during the process. Organics – Many organic contaminants including Polycyclic aromatic hydrocarbons will volatilize or degrade over time and Bioswales slow the conveyance of these materials into waterways, before they can affect aquatic life. Although not all organic material will be captured, the concentration of organic material is reduced by bioswales. Pathogens – are deprived of a host or from a nutrient supply long enough for them to become the target of a heterotroph. Common inorganic compounds are macronutrients such as nitrates. Principal sources of these nutrients comes from agricultural runoff attributed to excess fertilization. Excess phosphates and nitrates can cause eutrophication in disposal zones and receiving waters. Specific bioswale plants absorb these excess nutrients. Metallic compounds such as mercury, chromium and other heavy metals are concentrated in the structures; these metals poison the surrounding soil. Regular soil removal is required in order to prevent metals from dissolving and releasing back into the environment.
Some bioswales are designed to include hyperaccumulator plant species. These plants do not transform the metals. Cuttings from these plants decompose back into the pond or are pruned by gardening services that do not know the compost they are collecting is poisonous. Bioswales can be implemented in areas that require stormwater management to regulate the runoff velocity and decontaminate the runoff. Bioswales are created to handle the first flush of pollutants during the event of rain, locations that have high areas of impervious surface such as roads, parking lots, or rooftops can benefit from additions of bioswales, they can be integrated into road medians, curb cutouts, sidewalks, or any public space. Bioswales are useful low-impact development work to decrease the velocity of stormwater runoff while removing pollutants from the discharge, they are beneficial in protecting surface water and local waterways from excessive pollution from stormwater runoff. The longer the runoff stays within the bioswale, the better the pollutant removal outcome.
It is beneficial in removing standing ponds that could attract mosquitos. Bioswales can be designed to be aesthetically pleasing and attract animals and create habitats. Bioswales can be beneficial for groundwater recharge. Improper maintenance can lead to high restoration costs to address inefficient bioswales. An accumulation of large sediments and improper growth of vegetation can all affect the quality and performance of bioswales, it is beneficial at the planning stages to set apart easements to allow for easier maintenance of biowales, whether it be adequate space to locate machinery or safety to those working. Different types of filters can be used to catch sediments. Grass filter strips or rock inlets can be used to filter particulates. Structural inlets have become more common due to the ease of maintenance and its effectiveness. Avoiding the use of floating mulch and selecting the best fit low-maintenance plants ensure better efficiency in the bioswales. Depending on a community's needs for a bioswale, a four step assessment program can be developed.
Visual inspection, capacity testing, synthetic runoff, monitoring are the four steps that can be used to evaluate performance and maintenance of bioswales. Routine inspection is required to ensure that the performance and aesthetics of bios
Liman irrigation system
A Liman in Israel is the name for an artificial earthen construction used to collect floodwater by damming a desert wadi. The runoff water is slowed down by the dam, thus flooding a small area and allowing the water to infiltrate into the soil; this way, a small groves of trees can be sustained in the desert. The JNF-KKL has been funding the construction of limans in the Negev Desert. Limans were built in order to fight desertification without depleting groundwater resources, which are becoming rare in arid ecosystems. Remaining soil humidity can be found in dry river beds after rains occur, but these wadis are prone to flash floods; the result is the destruction of infrastructure. The infiltration is insufficient because of the water's velocity though the runoff would be able to allow for the growth of trees in appropriate places; the aim of building limans is to stop flash floods and to increase water infiltration, thus sustaining the growth of drought-hardy tree species and vegetation underneath them.
Limans are structures with small dams which catch runoff from a wadi to hold about 400-600mm of water, which suffices for the growth of drought-hardy tree species. Limans can be built wherever tributary wadis widen or come onto a large plain with potential arable land. A check-dam is built to retain runoff waters. A spillway regulates the level of the water to prevent the destruction of the check-dam.. The embankment height should be 3-4 times the designed water depth, the outlet should be to the side of the main flow to prevent direct through flow. Grazers should be excluded from the site to prevent soil compaction which would in turn decrease water infiltration; because of its fast growth, Eucalyptus occidentalis was used in the past. However, some scientific studies have had better results with Eucalyptus sargentii. Overall, any drought-hardy species are suitable, such as tamarind, prosopis, eucalyptus, date palm and carob. Before the invention of Limans, their creators as well as scientists expected several positive and/or negative impacts: They expected a negative soil salinisation due to salt deposition and/or high evaporation rates.
This was not the case Carbon sequestration: Because of the biomass increase, a CO2 uptake is expected. Scientists were hoping for a methane uptake. Instead, they found a shallow zone of methane production; because desert crusts prevent rainwater from infiltrating the ground, they generate surface run-off that can lead to flash floods and to top-soil erosion. Limans prevent both of topsoil, as well as plant nutrients. On top of that, they provide a controlled place to deposit these resources. So far, no ecological research has been conducted on biodiversity within limans
A ditch is a small to moderate depression created to channel water. A ditch can be used for drainage, to drain water from low-lying areas, alongside roadways or fields, or to channel water from a more distant source for plant irrigation. Ditches are seen around farmland in areas that have required drainage, such as The Fens in eastern England and much of the Netherlands. Roadside ditches may provide a hazard to motorists and cyclists, whose vehicles may crash into them and get damaged, flipped over or stuck in poor weather conditions, in rural areas. Ditch is known as for sneaking off like waking up and escaping from bed during bedtime at night, escaping from school or jail and playing Ding Dong Ditch. In Anglo-Saxon, the word dïc existed and was pronounced "deek" in northern England and "deetch" in the south; the origins of the word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name dïc was given to either the excavation or the bank, evolved to both the words "dike"/"dyke" and "ditch".
Thus Offa's Dyke is a combined structure and Car Dyke is a trench, though it once had raised banks as well. In the midlands and north of England, a dike is what a ditch is in the south, a property boundary marker or small drainage channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike, which leads water from the catchwater drain, Car Dyke, to the South Forty Foot Drain in Lincolnshire; the Weir Dike is a soak dike near Twenty and alongside the River Glen. Drainage ditches play major roles in agriculture throughout the world. Improper drainage systems accelerate water contamination, excessively desiccate soils during seasonal drought, become a financial burden to maintain. Industrial earth-moving equipment facilitates maintenance of straight drainage trenches, but entrenchment results in increasing environmental and profound economic costs over time. Sustainable channel design can result in ditches that are self-maintaining due to natural geomorphological equilibrium.
Slowed net siltation and erosion result in net reduction in sediment transport. Encouraging development of a natural stream sinuosity and a multi-terraced channel cross section appear to be key to maintain both peak ditch drainage capacity, minimum net pollution and nutrient transport. Flooding can be a major cause of recurring crop loss—particularly in heavy soils—and can disrupt urban economies as well. Subsurface drainage to ditches offers a way to remove excess water from agricultural fields, or vital urban spaces, without the erosion rates and pollution transport that results from direct surface runoff. However, excess drainage results in recurring drought induced crop yield losses and more severe urban heat or desiccation issues. Controlled subsurface drainage from sensitive areas to vegetated drainage ditches makes possible a better balance between water drainage and water retention needs; the initial investment allows a community to draw down local water tables when and where necessary without exacerbating drought problems at other times.
In Colorado, the term ditch is applied to open aqueducts that traverse hillsides as part of transbasin diversion projects. Examples include the Grand Ditch over La Poudre Pass, the Berthoud Pass Ditch, the Boreas Pass Ditch. Barbagallo, Tricia. "Black Beach: The Mucklands of Canastota, New York". Archived from the original on June 25, 2008. Retrieved 2008-06-04