The Nairobi River is a river that flows across Nairobi , the capital city of Kenya . It is the main river of the Nairobi River Basin, with several parallel streams flowing eastward. All of the Nairobi basin rivers join east of Nairobi and meet the Athi River , which eventually flows into the Indian Ocean . The rivers are mostly narrow and highly polluted, though recent efforts to clean the rivers have improved water quality.
82-627: The main stream, the Nairobi River, bounds the northern city center, where it is partly canalized . The Nairobi River originates from the Ondiri Swamp in Kikuyu . The Nairobi River has several tributaries : The Motoine River flows to Nairobi Dam , an artificial lake meant to provide potable water to the residents of Nairobi. The stream continues as the Ngong River. Gatharaini stream originates in
164-399: A lock has to be provided alongside the weir, or in a side channel, to provide for the passage of vessels. A river is thereby converted into a succession of fairly level reaches rising in steps up-stream, providing still-water navigation comparable to a canal; but it differs from a canal in the introduction of weirs for keeping up the water-level, in the provision for the regular discharge of
246-491: A waterwheel to power the bellows of a blast furnace producing cast iron . Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation . In ancient Sri Lanka, hydraulics were widely used in the ancient kingdoms of Anuradhapura and Polonnaruwa . The discovery of the principle of the valve tower, or valve pit, (Bisokotuwa in Sinhalese) for regulating
328-431: A flood-dam or confined within continuous embankments on both sides. By placing these embankments somewhat back from the margin of the river-bed, a wide flood-channel is provided for the discharge of the river as soon as it overflows its banks, while leaving the natural channel unaltered for the ordinary flow. Low embankments may be sufficient where only exceptional summer floods have to be excluded from meadows. Occasionally
410-429: A high flood to places on the lower river, weir-keepers are enabled to fully open the movable weirs beforehand to permit the passage of the flood, and riparian inhabitants receive timely warning of the impending inundation. Where portions of a riverside town are situated below the maximum flood-level, or when it is important to protect land adjoining a river from inundations, the overflow of the river must be diverted into
492-402: A large scale to prospect for and then extract metal ores . They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae . Hydraulic mining was used in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold-mine of Las Medulas was one of the largest of their mines. At least seven long aqueducts worked it, and
574-399: A moderate fall and a fair discharge at their lowest stage, for with a large fall the current presents a great impediment to up-stream navigation, and there are generally great variations in water level, and when the discharge becomes very small in the dry season. It is impossible to maintain a sufficient depth of water in the low-water channel. The possibility to secure uniformity of depth in
656-508: A reciprocating device with hinged valves. The earliest programmable machines were water-powered devices developed in the Muslim world. A music sequencer , a programmable musical instrument , was the earliest type of programmable machine. The first music sequencer was an automated water-powered flute player invented by the Banu Musa brothers, described in their Book of Ingenious Devices , in
738-407: A river by lowering the shoals obstructing the channel depends on the nature of the shoals. A soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. The lowering of such
820-476: A shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. The removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. Where, however, narrow rocky reefs or other hard shoals stretch across
902-440: A stream's natural bottom lands so that the bulk of such lands can be made available for agriculture. A third reason is flood control, with the idea of giving a stream a sufficiently large and deep channel so that flooding beyond those limits will be minimal or nonexistent, at least on a routine basis. One major reason is to reduce natural erosion ; as a natural waterway curves back and forth, it usually deposits sand and gravel on
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#1732844630947984-579: A watering channel for Samos , the Tunnel of Eupalinos . An early example of the usage of hydraulic wheel, probably the earliest in Europe, is the Perachora wheel (3rd century BC). In Greco-Roman Egypt , the construction of the first hydraulic machine automata by Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10 – 80 AD) is notable. Hero describes several working machines using hydraulic power, such as
1066-434: Is a technology and applied science using engineering , chemistry , and other sciences involving the mechanical properties and use of liquids . At a very basic level, hydraulics is the liquid counterpart of pneumatics , which concerns gases . Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics
1148-399: Is avoided, as is the danger of breaches in the banks from an unusually high flood-rise and rapid flow, with their disastrous effects. A most serious objection to the formation of continuous, high embankments along rivers bringing down considerable quantities of detritus, especially near a place where their fall has been abruptly reduced by descending from mountain slopes onto alluvial plains,
1230-399: Is held back and released more slowly. The removal of obstructions, natural or artificial (e.g., trunks of trees, boulders and accumulations of gravel) from a river bed furnishes a simple and efficient means of increasing the discharging capacity of its channel. Such removals will consequently lower the height of floods upstream. Every impediment to the flow, in proportion to its extent, raises
1312-482: Is liable to be stopped during the descent of high floods, which in many cases rise above the locks; and it is necessarily arrested in cold climates on all rivers by long, severe frosts, and especially by ice. Many small rivers, like the Thames above its tidal limit, have been rendered navigable by canalization, and several fairly large rivers have thereby provided a good depth for vessels for considerable distances inland. Thus
1394-401: Is loss of wetlands . Wetlands are an excellent habitat for many forms of wildlife, and additionally serve as a "filter" for much of the world's surface fresh water. Another is the fact that channelized streams are almost invariably straightened. For example, the channelization of Florida's Kissimmee River has been cited as a cause contributing to the loss of wetlands. This straightening causes
1476-432: Is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. Accordingly, in large basins, rivers in most cases begin as torrents with a very variable flow, and end as gently flowing rivers with a comparatively regular discharge. The irregular flow of rivers throughout their course forms one of
1558-458: Is the branch of hydraulics dealing with free surface flow, such as occurring in rivers , canals , lakes , estuaries , and seas . Its sub-field open-channel flow studies the flow in open channels . Early uses of water power date back to Mesopotamia and ancient Egypt , where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include
1640-535: Is the danger of their bed being raised by deposit, producing a rise in the flood-level, and necessitating a raising of the embankments if inundations are to be prevented. Longitudinal sections of the Po River, taken in 1874 and 1901, show that its bed was materially raised during this period from the confluence of the Ticino to below Caranella , despite the clearance of sediment effected by the rush through breaches. Therefore,
1722-480: Is the study of how rivers change their form over time. Fluvial geomorphology is the cumulation of a number of sciences including open channel hydraulics , sediment transport , hydrology , physical geology, and riparian ecology. River engineering practitioners attempt to understand fluvial geomorphology, implement a physical alteration, and maintain public safety. The size of rivers above any tidal limit and their average freshwater discharge are proportionate to
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#17328446309471804-448: Is thought to occur because of reduction in habitat, elimination of riffles and pools, greater fluctuation of stream levels and water temperature, and shifting substrates. The rate of recovery for a stream once it has been dredged is extremely slow, with many streams showing no significant recovery 30 to 40 years after the date of channelization. For the reasons cited above, in recent years stream channelization has been greatly curtailed in
1886-399: Is transmitted undiminished throughout the fluids. A French physician, Poiseuille (1797–1869) researched the flow of blood through the body and discovered an important law governing the rate of flow with the diameter of the tube in which flow occurred. Several cities developed citywide hydraulic power networks in the 19th century, to operate machinery such as lifts, cranes, capstans and
1968-436: Is used for the generation, control, and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, and they cover concepts such as pipe flow , dam design, fluidics , and fluid control circuitry. The principles of hydraulics are in use naturally in the human body within the vascular system and erectile tissue . Free surface hydraulics
2050-456: The Chariton River in northern Missouri , United States, found that the channelized section of the river contained only 13 species of fish, whereas the natural segment of the stream was home to 21 species of fish. The biomass of fish able to be caught in the dredged segments of the river was 80 percent less than in the natural parts of the same stream. This loss of fish diversity and abundance
2132-891: The Qanat system in ancient Persia and the Turpan water system in ancient Central Asia. In the Persian Empire or previous entities in Persia, the Persians constructed an intricate system of water mills, canals and dams known as the Shushtar Historical Hydraulic System . The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I , has been referred to by UNESCO as "a masterpiece of creative genius". They were also
2214-603: The Rhine , the Danube and the Mississippi . River engineering works are only required to prevent changes in the course of the stream, to regulate its depth, and especially to fix the low-water channel and concentrate the flow in it, so as to increase as far as practicable the navigable depth at the lowest stage of the water level. Engineering works to increase the navigability of rivers can only be advantageously undertaken in large rivers with
2296-477: The ancient Near East in the 4th century BC, specifically in the Persian Empire before 350 BCE, in the regions of Iraq , Iran , and Egypt . In ancient China there was Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 – 139 AD), and Ma Jun (200 – 265 AD), while medieval China had Su Song (1020 – 1101 AD) and Shen Kuo (1031–1095). Du Shi employed
2378-454: The force pump , which is known from many Roman sites as having been used for raising water and in fire engines. In the Roman Empire , different hydraulic applications were developed, including public water supplies, innumerable aqueducts , power using watermills and hydraulic mining . They were among the first to make use of the siphon to carry water across valleys, and used hushing on
2460-604: The "alteration of the hydrologic characteristics of coastal and non-coastal waters, which in turn could cause degradation of water resources." River engineering has often resulted in unintended systematic responses, such as reduced habitat for fish and wildlife, and alterations of water temperature and sediment transport patterns. Beginning in the late 20th century, the river engineering discipline has been more focused on repairing hydromodified degradations and accounting for potential systematic response to planned alterations by considering fluvial geomorphology . Fluvial geomorphology
2542-401: The 9th century. In 1206, Al-Jazari invented water-powered programmable automata/ robots . He described four automaton musicians, including drummers operated by a programmable drum machine , where they could be made to play different rhythms and different drum patterns. In 1619 Benedetto Castelli , a student of Galileo Galilei , published the book Della Misura dell'Acque Correnti or "On
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2624-455: The Army Corps with EPA participation. Rivers whose discharge is liable to become quite small at their low stage, or which have a somewhat large fall, as is usual in the upper part of rivers, cannot be given an adequate depth for navigation purely by works which regulate the flow; their ordinary summer level has to be raised by impounding the flow with weirs at intervals across the channel, while
2706-580: The Islamic world, including fulling mills, gristmills , paper mills , hullers , sawmills , ship mills , stamp mills , steel mills , sugar mills , and tide mills . By the 11th century, every province throughout the Islamic world had these industrial mills in operation, from Al-Andalus and North Africa to the Middle East and Central Asia . Muslim engineers also used water turbines , employed gears in watermills and water-raising machines, and pioneered
2788-657: The Measurement of Running Waters," one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e., management of rivers in the Papal States, beginning in 1626. The science and engineering of water in Italy from 1500-1800 in books and manuscripts is presented in an illustrated catalog published in 2022. Blaise Pascal (1623–1662) studied fluid hydrodynamics and hydrostatics, centered on
2870-476: The U.S., and in some instances even partially reversed. In 1990 the United States Government published a " no net loss of wetlands" policy, whereby a stream channelization project in one place must be offset by the creation of new wetlands in another, a process known as "mitigation." The major agency involved in the enforcement of this policy is the same Army Corps of Engineers, which for many years
2952-500: The available fall is exceptionally small, as in land originally reclaimed from the sea, such as the English Fenlands , and where, in consequence, the drainage is in a great measure artificial, straight channels have been formed for the rivers. Because of the perceived value in protecting these fertile, low-lying lands from inundation, additional straight channels have also been provided for the discharge of rainfall, known as drains in
3034-416: The basic principles of hydraulics, some teachers use a hydraulic analogy to help students learn other things. For example: The conservation of mass requirement combined with fluid compressibility yields a fundamental relationship between pressure, fluid flow, and volumetric expansion, as shown below: Assuming an incompressible fluid or a "very large" ratio of compressibility to contained fluid volume,
3116-406: The bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. The capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in
3198-404: The canalized Seine has secured a navigable depth of 10 1 ⁄ 2 feet (3.2 metres) from its tidal limit up to Paris, a distance of 135 miles, and a depth of 6 3 ⁄ 4 feet (2.06 metres) up to Montereau, 62 miles higher up. As rivers flow onward towards the sea, they experience a considerable diminution in their fall, and a progressive increase in the basin which they drain, owing to
3280-405: The channel as a whole, and in the case of a large river with a considerable flow it is very difficult to maintain a straight cut owing to the tendency of the current to erode the banks and form again a sinuous channel. Even if the cut is preserved by protecting the banks, it is liable to produce changes shoals and raise the flood-level in the channel just below its termination. Nevertheless, where
3362-480: The channel at the low stage by low-dipping cross dikes extending from the river banks down the slope and pointing slightly up-stream so as to direct the water flowing over them into a central channel. The needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary . The interaction of river flow and tide needs to be modeled by computer or using scale models, moulded to
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3444-496: The channel at the lowest stage. The problem in the dry season is the small discharge and deficiency in scour during this period. A typical solution is to restrict the width of the low-water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. This can be effected by closing subsidiary low-water channels with dikes across them, and narrowing
3526-490: The completion of the embankments, together with their raising, would only eventually aggravate the injuries of the inundations they have been designed to prevent, as the escape of floods from the raised river must occur sooner or later. In the UK, problems of flooding of domestic properties around the turn of the 21st century have been blamed on inadequate planning controls which have permitted development on floodplains. This exposes
3608-553: The configuration of the estuary under consideration and reproducing in miniature the tidal ebb and flow and fresh-water discharge over a bed of very fine sand, in which various lines of training walls can be successively inserted. The models should be capable of furnishing valuable indications of the respective effects and comparative merits of the different schemes proposed for works. Hydraulics Hydraulics (from Ancient Greek ὕδωρ ( húdōr ) ' water ' and αὐλός ( aulós ) ' pipe ')
3690-480: The course, characteristics, or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and behaviour of rivers since before recorded history—to manage the water resources , to protect against flooding , or to make passage along or across rivers easier. Since the Yuan Dynasty and Ancient Roman times, rivers have been used as a source of hydropower . From
3772-406: The difference in pressure is proportional to the difference in height, and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force. This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other end in the container, i.e., any change in pressure applied at any point of the liquid
3854-422: The embankments are raised high enough to retain the floods during most years, while provision is made for the escape of the rare, exceptionally high floods at special places in the embankments, where the scour of the issuing current is guarded against, and the inundation of the neighboring land is least injurious. In this manner, the increased cost of embankments raised above the highest flood-level of rare occurrence
3936-478: The escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, several large-scale irrigation works had been completed. Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya , Sri Lanka. The coral on
4018-471: The extent of their basins and the amount of rain which, after falling over these basins, reaches the river channels in the bottom of the valleys, by which it is conveyed to the sea. The basin of a river is the expanse of country bounded by a watershed (called a "divide" in North America) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on
4100-476: The far slope of the watershed flows away to another river draining an adjacent basin. River basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground very near the coast and flowing straight down into the sea, up to immense tracts of great continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching
4182-554: The fens. Even extensive modification of the course of a river combined with an enlargement of its channel often produces only a limited reduction in flood damage. Consequently, such floodworks are only commensurate with the expenditure involved where significant assets (such as a town) are under threat. Additionally, even when successful, such floodworks may simply move the problem further downstream and threaten some other town. Recent floodworks in Europe have included restoration of natural floodplains and winding courses, so that floodwater
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#17328446309474264-402: The flood-level upstream. Regulations for the management of rivers may include stringent prohibitions with regard to pollution , requirements for enlarging sluice-ways and the compulsory raising of their gates for the passage of floods, the removal of fish traps , which are frequently blocked up by leaves and floating rubbish, reduction in the number and width of bridge piers when rebuilt, and
4346-445: The flow, primarily for navigation purposes, although power generation is often an important factor. The former is known in the US as channelization and the latter is generally referred to as canalization . Reducing the length of the channel by substituting straight cuts for a winding course is the only way in which the effective fall can be increased. This involves some loss of capacity in
4428-458: The gradient or slope. When two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. The fall available in a section of a river approximately corresponds to the slope of the country it traverses; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall
4510-400: The gradual reduction in fall, and, consequently, in the transporting force of the current. Accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods; the size of the materials forming the bed of the river or borne along by
4592-418: The height of the floods at these places, can be ascertained. With the help of these records, and by observing the times and heights of the maximum rise of a particular flood at the stations on the various tributaries, the time of arrival and height of the top of the flood at any station on the main river can be predicted with remarkable accuracy two or more days beforehand. By communicating these particulars about
4674-558: The influx of tributaries subject to different conditions, so that the Rhone below Lyon has a more uniform discharge than most rivers, as the summer floods of the Arve are counteracted to a great extent by the low stage of the Saône flowing into the Rhone at Lyon, which has its floods in the winter when the Arve, on the contrary, is low. Another serious obstacle encountered in river engineering consists in
4756-409: The inside of the corners where the water flows slowly, and cuts sand, gravel, subsoil , and precious topsoil from the outside corners where it flows rapidly due to a change in direction. Unlike sand and gravel, the topsoil that is eroded does not get deposited on the inside of the next corner of the river. It simply washes away. Channelization has several predictable and negative effects. One of them
4838-591: The inventors of the Qanat , an underground aqueduct, around the 9th century BC. Several of Iran's large, ancient gardens were irrigated thanks to Qanats. The Qanat spread to neighboring areas, including the Armenian highlands . There, starting in the early 8th century BC, the Kingdom of Urartu undertook significant hydraulic works, such as the Menua canal . The earliest evidence of water wheels and watermills date back to
4920-531: The large quantity of detritus they bring down in flood-time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. The power of a current to transport materials varies with its velocity , so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones , which are by degrees ground by attrition in their onward course into slate , gravel , sand and silt , simultaneously with
5002-529: The late 20th century, the practice of river engineering has responded to environmental concerns broader than immediate human benefit. Some river engineering projects have focused exclusively on the restoration or protection of natural characteristics and habitats . Hydromodification encompasses the systematic response to alterations to riverine and non-riverine water bodies such as coastal waters ( estuaries and bays ) and lakes. The U.S. Environmental Protection Agency (EPA) has defined hydromodification as
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#17328446309475084-470: The level of the river above it so as to produce the additional artificial fall necessary to convey the flow through the restricted channel, thereby reducing the total available fall. Human intervention sometimes inadvertently modifies the course or characteristics of a river, for example by introducing obstructions such as mining refuse, sluice gates for mills, fish-traps, unduly wide piers for bridges and solid weirs . By impeding flow these measures can raise
5166-614: The like. Joseph Bramah (1748–1814) was an early innovator and William Armstrong (1810–1900) perfected the apparatus for power delivery on an industrial scale. In London, the London Hydraulic Power Company was a major supplier its pipes serving large parts of the West End of London , City and the Docks , but there were schemes restricted to single enterprises such as docks and railway goods yards . After students understand
5248-458: The low-lying riverbanks flood. Kenya has a second river named Nairobi that starts on Mount Kenya and is a tributary of the Sagana and Tana , the country's longest river. 1°11′59″S 37°09′26″E / 1.19972°S 37.15722°E / -1.19972; 37.15722 Canalized River engineering is a discipline of civil engineering which studies human intervention in
5330-565: The lower sections of Githurai and Zimmerman, the stream is characterized by coffee farming, intensive mixed farming, and industry such as the Kamiti Tannery Factory. The lower stream waters are brackish and foul. In the past, riverine subsistence agriculture of arrowroots and kale was common throughout the area. Efforts to conserve and preserve this river are yet to be initiated. Nairobi's rivers are contaminated due to agriculture, slums, and industry. During rainy seasons , rivers on
5412-466: The main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. In tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in
5494-630: The marshes of the lower reaches of the Aberdare mountains and flows through various populated areas. The stream is impacted by human activities along its channels and in its catchment. In the upper sections of Kiambaa and Kanunga, the stream passes through swampy and marshy areas, with subsistence agriculture and human settlement as the main types of land use. In the midsections of Kiambu, are extensive coffee crops and mixed farming . In Eastern Nairobi it passes through Nairobi Sewerage Company in Ngundu, Kamulu In
5576-452: The massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa (King Dhatusena), Parakrama Samudra (King Parakrama Bahu), Tisa Wewa (King Dutugamunu), Minneriya (King Mahasen) In Ancient Greece , the Greeks constructed sophisticated water and hydraulic power systems. An example is a construction by Eupalinos , under a public contract, of
5658-527: The most heavily channelized areas in the United States is West Tennessee , where every major stream with one exception (the Hatchie River ) has been partially or completely channelized. Channelization of a stream may be undertaken for several reasons. One is to make a stream more suitable for navigation or for navigation by larger vessels with deep draughts. Another is to restrict water to a certain area of
5740-407: The ocean. The size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. The rate of flow of rivers depends mainly upon their fall, also known as
5822-417: The principles of hydraulic fluids. His discovery on the theory behind hydraulics led to his invention of the hydraulic press , which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure (or exact change of pressure) at both locations. Pascal's law or principle states that for an incompressible fluid at rest,
5904-600: The properties on the floodplain to flood, and the substitution of concrete for natural strata speeds the run-off of water, which increases the danger of flooding downstream. In the Midwestern United States and the Southern United States the term for this measure is channelization. Much of it was done under the auspices or overall direction of the United States Army Corps of Engineers . One of
5986-450: The river at the weirs, and in the two sills of the locks being laid at the same level instead of the upper sill being raised above the lower one to the extent of the rise at the lock, as usual on canals. Canalization secures a definite available depth for navigation; and the discharge of the river generally is amply sufficient for maintaining the impounded water level, as well as providing the necessary water for locking. Navigation, however,
6068-617: The rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. The only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the Rhône above the Lake of Geneva , and the Arve which joins it below. But even these rivers are liable to have their flow modified by
6150-463: The stream is gradually reduced on proceeding seawards, so that in the Po River in Italy, for instance, pebbles and gravel are found for about 140 miles below Turin , sand along the next 100 miles, and silt and mud in the last 110 miles (176 km). Improvements can be divided into those that are aimed at improving the flow of the river, particularly in flood conditions, and those that aim to hold back
6232-541: The streams to flow more rapidly, which can, in some instances, vastly increase soil erosion. It can also increase flooding downstream from the channelized area, as larger volumes of water traveling more rapidly than normal can reach choke points over a shorter period of time than they otherwise would, with a net effect of flood control in one area coming at the expense of greatly aggravated flooding in another. In addition, studies have shown that stream channelization results in declines of river fish populations. A 1971 study of
6314-414: The substitution of movable weirs for solid weirs. By installing gauges in a fairly large river and its tributaries at suitable points, and keeping continuous records for some time of the heights of the water at the various stations, the rise of the floods in the different tributaries, the periods they take in passing down to definite stations on the main river, and the influence they severally exercise on
6396-411: The successive influx of their various tributaries. Thus, their current gradually becomes more gentle and their discharge larger in volume and less subject to abrupt variations; and, consequently, they become more suitable for navigation. Eventually, large rivers, under favorable conditions, often furnish important natural highways for inland navigation in the lower portion of their course, as, for instance,
6478-435: The use of dams as a source of water power, used to provide additional power to watermills and water-raising machines. Al-Jazari (1136–1206) described designs for 50 devices, many of them water-powered, in his book, The Book of Knowledge of Ingenious Mechanical Devices , including water clocks, a device to serve wine, and five devices to lift water from rivers or pools. These include an endless belt with jugs attached and
6560-516: The water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content. In the Muslim world during the Islamic Golden Age and Arab Agricultural Revolution (8th–13th centuries), engineers made wide use of hydropower as well as early uses of tidal power , and large hydraulic factory complexes. A variety of water-powered industrial mills were used in
6642-455: The winter months, so that the rivers fall to their low stage in the summer and are very liable to be in flood in the winter. In fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from May to October and from November to April in the Northern hemisphere respectively; the rivers are low and moderate floods are of rare occurrence during the warm period, and
6724-731: Was the primary promoter of wide-scale channelization. Often, in the instances where channelization is permitted, boulders may be installed in the bed of the new channel so that water velocity is slowed, and channels may be deliberately curved as well. In 1990 the U.S. Congress gave the Army Corps a specific mandate to include environmental protection in its mission, and in 1996 it authorized the Corps to undertake restoration projects. The U.S. Clean Water Act regulates certain aspects of channelization by requiring non-Federal entities (i.e. state and local governments, private parties) to obtain permits for dredging and filling operations. Permits are issued by
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