Irrigation is the application of controlled amounts of water to plants at needed intervals. Irrigation helps to grow agricultural crops, maintain landscapes, revegetate disturbed soils in dry areas and during periods of less than average rainfall. Irrigation has other uses in crop production, including frost protection, suppressing weed growth in grain fields and preventing soil consolidation. In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dry land farming. Irrigation systems are used for cooling livestock, dust suppression, disposal of sewage, in mining. Irrigation is studied together with drainage, the removal of surface and sub-surface water from a given area. Irrigation has been a central feature of agriculture for over 5,000 years and is the product of many cultures, it was the basis for economies and societies across the globe, from Asia to the Southwestern United States. Archaeological investigation has found evidence of irrigation in areas lacking sufficient natural rainfall to support crops for rainfed agriculture.
The earliest known use of the technology dates to the 6th millennium BCE in Khuzistan in the south-west of present-day Iran. Irrigation was used as a means of manipulation of water in the alluvial plains of the Indus valley civilization, the application of it is estimated to have begun around 4500 BC and drastically increased the size and prosperity of their agricultural settlements; the Indus Valley Civilization developed sophisticated irrigation and water-storage systems, including artificial reservoirs at Girnar dated to 3000 BCE, an early canal irrigation system from c. 2600 BCE. Large-scale agriculture was practiced, with an extensive network of canals used for the purpose of irrigation. Farmers in the Mesopotamian plain used irrigation from at least the third millennium BCE, they developed perennial irrigation watering crops throughout the growing season by coaxing water through a matrix of small channels formed in the field. Ancient Egyptians practiced basin irrigation using the flooding of the Nile to inundate land plots, surrounded by dykes.
The flood water remained until the fertile sediment had settled before the engineers returned the surplus to the watercourse. There is evidence of the ancient Egyptian pharaoh Amenemhet III in the twelfth dynasty using the natural lake of the Faiyum Oasis as a reservoir to store surpluses of water for use during dry seasons; the lake swelled annually from the flooding of the Nile. The Ancient Nubians developed a form of irrigation by using a waterwheel-like device called a sakia. Irrigation began in Nubia some time between the third and second millennia BCE, it depended upon the flood waters that would flow through the Nile River and other rivers in what is now the Sudan. In sub-Saharan Africa irrigation reached the Niger River region cultures and civilizations by the first or second millennium BCE and was based on wet-season flooding and water harvesting. Evidence of terrace irrigation occurs in pre-Columbian America, early Syria and China. In the Zana Valley of the Andes Mountains in Peru, archaeologists have found remains of three irrigation canals radiocarbon-dated from the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE.
These canals provide the earliest record of irrigation in the New World. Traces of a canal dating from the 5th millennium BCE were found under the 4th-millennium canal. Ancient Persia used irrigation as far back as the 6th millennium BCE to grow barley in areas with insufficient natural rainfall; the Qanats, developed in ancient Persia about 800 BCE, are among the oldest known irrigation methods still in use today. They are now found in the Middle East and North Africa; the system comprises a network of vertical wells and sloping tunnels driven into the sides of cliffs and of steep hills to tap groundwater. The noria, a water wheel with clay pots around the rim powered by the flow of the stream, first came into use at about this time among Roman settlers in North Africa. By 150 BCE the pots were fitted with valves to allow smoother filling as they were forced into the water; the irrigation works of ancient Sri Lanka, the earliest dating from about 300 BCE in the reign of King Pandukabhaya, under continuous development for the next thousand years, were one of the most complex irrigation systems of the ancient world.
In addition to underground canals, the Sinhalese were the first to build artificial reservoirs to store water. These reservoirs and canal systems were used to irrigate paddy fields, which require a lot of water to cultivate. Most of these irrigation systems still exist undamaged up to now, in Anuradhapura and Polonnaruwa, because of the advanced and precise engineering; the system was further extended during the reign of King Parakrama Bahu. The oldest known hydraulic engineers of China were Sunshu Ao of the Spring and Autumn period and Ximen Bao of the Warring States period, both of whom worked on large irrigation projects. In the Sichuan region belonging to the state of Qin of ancient China, the Dujiangyan Irrigation System devised by the Qin Chinese hydrologist and irrigation engineer Li Bing was built in 256 BCE to irrigate a vast area of farmland that today still supplies water. By the 2nd century AD, during the Han Dynasty, the Chinese used chain pumps which lifted water from a lower elevation to a higher one.
These were powered by manual foot-pedal, hydraulic waterwheels, or rotating mechanical wheels pulled by oxen. The water was used for public works, providing water for urban residential quarters and palace gardens, bu
The Jukskei River is one of the largest rivers in Johannesburg, South Africa. It is the southernmost river in the Crocodile River basin; the Jukskei begins in Ellis Park in Johannesburg. Its original spring was on the former Doornfontein farm, which measured at 18,000 liters per hour, but has since disappeared under subsequent urban development. Now the first surface expression of the Jukskei is in Bertrams at the intersection of Queen Street and Sports Avenue where it emerges from a storm drain. From there the river is dammed in Bruma, it meanders in a northerly direction through Bedfordview and Edenvale before flowing through Alexandra Township. It turns northwest and flows through Modderfontein, Leeuwkop Prison, Lone Hill and Steyn City before joining the Crocodile River outside Lanseria; the Jukskei River is joined by numerous streams along its course with its major tributaries being the Modderfontein Spruit, Braamfontein Spruit and Klein Jukskei River. The Jukskei River provides the largest amount of water, by discharge, into the Crocodile River Basin.
The Jukskei is shallow and not deep enough for transportation. It is heavily polluted by urban runoff. Lack of infrastructure maintenance has let raw waste flow into the river on a daily basis. Cholera-causing bacteria have been found in the river; the river receives a large inflow from the Northern Waste Water Treatment Plant in northern Johannesburg. The Jukskei River is one of the largest contributing factors of the eutrophication problems facing Hartbeespoort Dam further down stream. Tons of waste such as plastic and rubber flow down the river annually; the banks are prone to bursting in summer when rainfalls are the heaviest for the year regionally. This spells disaster for the impoverished residents of the Alexandra Township who build makeshift shacks along the river banks owing to overcrowding and the need for access to water for washing and cooking; the Jukskei traditionally demarcated the boundary between the Northern Transvaal and Transvaal for sporting purposes, teams like the Titans cricket team and Blue Bulls continue to be headquartered in Pretoria, north of the Jukskei.
List of rivers of South Africa List of reservoirs and dams in South Africa Revamping the Jukskei River Alex Riverbank Face-lift
Eutrophication, or hypertrophication, is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body. One example is an "algal bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system. Eutrophication most arises from the oversupply of nutrients, most as nitrogen or phosphorus, which leads to overgrowth of plants and algae in aquatic ecosystems. After such organisms die, bacterial degradation of their biomass results in oxygen consumption, thereby creating the state of hypoxia. According to Ullmann's Encyclopedia, "the primary limiting factor for eutrophication is phosphate." The availability of phosphorus promotes excessive plant growth and decay, favouring simple algae and plankton over other more complicated plants, causes a severe reduction in water quality.
Phosphorus is a necessary nutrient for plants to live, is the limiting factor for plant growth in many freshwater ecosystems. Phosphate adheres to soil, so it is transported by erosion. Once translocated to lakes, the extraction of phosphate into water is slow, hence the difficulty of reversing the effects of eutrophication. However, numerous literature report that nitrogen is the primary limiting nutrient for the accumulation of algal biomass; the sources of these excess phosphates are phosphates in detergent, industrial/domestic run-offs, fertilizers. With the phasing out of phosphate-containing detergents in the 1970s, industrial/domestic run-off and agriculture have emerged as the dominant contributors to eutrophication. Cultural eutrophication is the process that speeds up natural eutrophication because of human activity. Due to clearing of land and building of towns and cities, land runoff is accelerated and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, to coastal estuaries and bays.
Extra nutrients are supplied by treatment plants, golf courses, farms, as well as untreated sewage in many countries. When algae die, they decompose and the nutrients contained in that organic matter are converted into inorganic form by microorganisms; this decomposition process consumes oxygen. The depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity. Nutrients may become concentrated in an anoxic zone and may only be made available again during autumn turn-over or in conditions of turbulent flow; the dead algae and the organic load carried by the water inflows in to the lake settle at its bottom and undergoes anaerobic digestion releasing greenhouse gases like methane and CO2. Some part of methane gas is consumed by the anaerobic methane oxidation bacteria which in turn works as food source to the zooplankton. In case the lake is not deficit of dissolved oxygen at all depths the aerobic methane oxidation bacteria like Methylococcus capsulatus can consume most of the methane by releasing CO2 which in turn aid the production of algae.
Thus a self-sustaining biological process can take place to generate primary food source for the phytoplankton and zooplankton depending on availability of adequate dissolved oxygen in the water bodies which are subjected to higher organic pollution loads. Adequate dissolved oxygen in water bodies is crucial for fisheries production and elimination of green house gas emissions. Enhanced growth of aquatic vegetation or phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen needed for fish and shellfish to survive; the water becomes cloudy coloured a shade of green, brown, or red. Eutrophication decreases the value of rivers and aesthetic enjoyment. Health problems can occur. Human activities can accelerate the rate. Runoff from agriculture and development, pollution from septic systems and sewers, sewage sludge spreading, other human-related activities increase the flow of both inorganic nutrients and organic substances into ecosystems.
Elevated levels of atmospheric compounds of nitrogen can increase nitrogen availability. Phosphorus is regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes; the concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Humankind has increased the rate of phosphorus cycling on Earth by four times due to agricultural fertilizer production and application. Between 1950 and 1995, an estimated 600,000,000 tonnes of phosphorus was applied to Earth's surface on croplands. Although eutrophication is caused by human activities, it can be a natural process in lakes. Eutrophy occurs for instance. Paleolimnologists now recognise that climate change and other external influences are critical in regulating the natural productivity of lakes; some lakes demonstrate the reverse process, becoming less nutrient rich with time.
The main difference between natural and anthropogenic eutrophication is that the natural process is slow, occurring on geological time scales. Eutrophication is a common phenomenon i
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
Crocodile River (Limpopo)
The Crocodile River is a river in South Africa. After its confluence with the Marico River, both rivers form the Limpopo River; the Crocodile River has its source in the Witwatersrand mountain range, originating in Constantia Kloof, Gauteng province. The first dam it fills is the Lake Heritage Dam just west of the Lanseria Airport. Just north of this airport is its confluence with the Jukskei River. Further downstream into the North West two large dams are located in the river, namely Hartbeespoort Dam and Roodekoppies Dam. Beyond the Hartbeespoort Dam, it passes the town of Brits; the Elands River joins downstream from the Vaalkop Dam, about 20 km further the Pienaars River joins its right bank, shortly after exiting the Klipvoor Dam. In the Limpopo Province, about 35 km further, the Crocodile River passes the town of Thabazimbi and meanders for many miles through a sparsely inhabited area before joining the Marico River just west of Rooibokkraal at the limit of North West Province to form the start of the Limpopo River.
The tributaries of the Crocodile River include the Bloubankspruit, Hennops River, Jukskei River, Magalies River, Sterkstroom River, Skeerpoort River, Elands River, Bierspruit River and Sundays River. The Crocodile River is one of the most pressured river systems in South Africa; the effects of pollution from two of South Africa's metropolitan areas and Tshwane, has been detrimental to the ecology of the system. Untreated industrial, mining and household waste has deteriorated the water quality throughout most of its course and led to massive algal blooms in the Hartbeespoort Dam and Roodekoppies Dam. Invasive plant species have negatively affected the integrity of the system. Unsustainable farming practices have led to sediment overloads and erosion further harming the river; the Crocodile River is part of Marico Water Management Area. Dams in the river basin are: Hartbeespoort Dam Roodekoppies Dam Rietvlei Dam, in the Rietvlei River Bon Accord Dam and Leeukraal Dam, in the Apies River Klipvoor Dam and Roodeplaat Dam, in the Pienaars/Moretele River Vaalkop Dam, in the Elands River Bospoort Dam, in the Hex River Drainage basin A List of rivers of South Africa List of reservoirs and dams in South Africa Overview of the Crocodile /Marico Water Management Area Natural and anthropogenic influences on water quality: an example from rivers draining the Johannesburg Granite Dome A river runs through Limpopo Province The influence of land use on water quality and diatom community structures in urban and agriculturally stressed rivers
Asphalt concrete is a composite material used to surface roads, parking lots, airports, as well as the core of embankment dams. It consists of mineral aggregate bound together with asphalt, laid in layers, compacted; the process was refined and enhanced by Belgian inventor and U. S. immigrant Edward de Smedt. The terms asphalt concrete, bituminous asphalt concrete, bituminous mixture are used only in engineering and construction documents, which define concrete as any composite material composed of mineral aggregate adhered with a binder; the abbreviation, AC, is sometimes used for asphalt concrete but can denote asphalt content or asphalt cement, referring to the liquid asphalt portion of the composite material. Mixing of asphalt and aggregate is accomplished in one of several ways: Hot-mix asphalt concrete This is produced by heating the asphalt binder to decrease its viscosity, drying the aggregate to remove moisture from it prior to mixing. Mixing is performed with the aggregate at about 300 °F for virgin asphalt and 330 °F for polymer modified asphalt, the asphalt cement at 200 °F.
Paving and compaction must be performed. In many countries paving is restricted to summer months because in winter the compacted base will cool the asphalt too much before it is able to be packed to the required density. HMA is the form of asphalt concrete most used on high traffic pavements such as those on major highways and airfields, it is used as an environmental liner for landfills and fish hatchery ponds. Warm-mix asphalt concrete This is produced by adding either zeolites, asphalt emulsions, or sometimes water to the asphalt binder prior to mixing; this allows lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide and vapors. Not only are working conditions improved, but the lower laying-temperature leads to more rapid availability of the surface for use, important for construction sites with critical time schedules; the usage of these additives in hot mixed asphalt may afford easier compaction and allow cold weather paving or longer hauls.
Use of warm mix is expanding. A survey of US asphalt producers found that nearly 25% of asphalt produced in 2012 was warm mix, a 416% increase since 2009. Cold-mix asphalt concrete This is produced by emulsifying the asphalt in water with soap prior to mixing with the aggregate. While in its emulsified state, the asphalt is less viscous and the mixture is easy to work and compact; the emulsion will break after enough water evaporates and the cold mix will, take on the properties of an HMA pavement. Cold mix is used as a patching material and on lesser trafficked service roads. Cut-back asphalt concrete Is a form of cold mix asphalt produced by dissolving the binder in kerosene or another lighter fraction of petroleum prior to mixing with the aggregate. While in its dissolved state, the asphalt is less viscous and the mix is easy to work and compact. After the mix is laid down the lighter fraction evaporates; because of concerns with pollution from the volatile organic compounds in the lighter fraction, cut-back asphalt has been replaced by asphalt emulsion.
Mastic asphalt concrete, or sheet asphalt This is produced by heating hard grade blown bitumen in a green cooker until it has become a viscous liquid after which the aggregate mix is added. The bitumen aggregate mixture is cooked for around 6–8 hours and once it is ready, the mastic asphalt mixer is transported to the work site where experienced layers empty the mixer and either machine or hand lay the mastic asphalt contents on to the road. Mastic asphalt concrete is laid to a thickness of around 3⁄4–1 3⁄16 inches for footpath and road applications and around 3⁄8 of an inch for flooring or roof applications. High-modulus asphalt concrete, sometimes referred to by the French-language acronym EMÉ This uses a hard bituminous, sometimes modified, in proportions close to 6% on the weight of the aggregates, a proportion of mineral powder high, between 8–10%, to create an asphalt concrete layer with a high modulus of elasticity, of the order of 13000 MPa being possible to reduce the thickness of the base layer up to 25% depending of the temperature in relation to conventional bitumen, as well as high fatigue strengths.
High-modulus asphalt layers are used both in reinforcement operations and in the construction of new reinforcements for medium and heavy traffic. In base layers, they tend to exhibit a greater capacity of absorbing tensions and, in general, better fatigue resistance. In addition to the asphalt and aggregate, such as polymers, antistripping agents may be added to improve the properties of the final product. Asphalt concrete pavements—especially those at airfields—are sometimes called tarmac for historical reasons, although they do not contain tar and are not constructed using the macadam process. A variety of specialty asphalt concrete mixtures have been developed to meet specific needs, such as stone-matrix asphalt, designed to ensure a strong wearing surface, or porous asphalt pavements, which are permeable and allow water to drain through the pavement for controlling stormwater. Different types of asphalt concrete have different performance characteristics in terms of