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{{bedakan|Bendung}}
[[Berkas:Scrivener Dam Canberra-01JAC.jpg|jmpl|ka|300px|Bendungan Scrivener, Canberra Australia, dibangun untuk mengatasi banjir 5000-tahunan.]]
'''Bendungan''' atau '''Empangan''' atau istilah pinjaman Inggris '''dam''' adalah konstruksi yang dibangun untuk menahan laju [[air]] menjadi [[waduk]], [[danau]], atau tempat rekreasi. Seringkali bendungan juga digunakan untuk mengalirkan air ke sebuah [[PLTA|Pembangkit Listrik Tenaga Air]]. Kebanyakan dam juga memiliki bagian yang disebut ''pintu air'' untuk membuang air yang tidak diinginkan secara bertahap atau berkelanjutan.
[[Kementerian Pekerjaan Umum Indonesia]] mendefinisikan bendungan sebagai "bangunan yang berupa [[tanah]], [[batu]], [[beton]], atau pasangan batu yang dibangun selain untuk menahan dan menampung air, dapat juga dibangun untuk menampung [[limbah]] tambang atau lumpur."<ref>{{cite web |url = http://www1.pu.go.id/uploads/berita/ppw110811dsda.htm |title = JUMLAH BENDUNGAN BESAR DI INDONESIA CAPAI 284 BUAH |website = pu.go.id |accessdate = 4 Oktober 2013 }}{{Pranala mati|date=Februari 2021 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
Bendungan (''dam'') dan [[bendung]] (''weir'') sebenarnya merupakan struktur yang berbeda.<ref>{{Cite news|url = http://megapolitan.kompas.com/read/2013/01/20/17484025/Bendung.Katulampa.Bukan.Bendungan |title = Bendung Katulampa Bukan Bendungan |work= [[Kompas.com]] |accessdate = 4 Oktober 2013|last = Mulyadi |first = Agus |editor-last = Mulyadi |editor-first = Agus }}</ref> Bendung (weir) adalah struktur bendungan berkepala rendah (''lowhead dam''), yang berfungsi untuk menaikkan muka air, biasanya terdapat di sungai. Air sungai yang permukaannya dinaikkan akan melimpas melalui puncak / mercu bendung (overflow). Dapat digunakan sebagai pengukur kecepatan aliran air di saluran / sungai dan bisa juga sebagai penggerak pengilingan tradisional di negara-negara Eropa. Di negara dengan sungai yang cukup besar dan deras alirannya, serangkaian bendung dapat dioperasikan membentuk suatu sistem transportasi air. Di Indonesia, bendung dapat digunakan untuk irigasi bila misalnya muka air sungai lebih rendah dari muka tanah yang akan diairi.
== Jenis bendungan ==
[[Berkas:Hoover dam.jpg|ka|jmpl|300px|Bendungan Hoover, sebuah bendungan beton lengkung di [[Black Canyon of the Colorado|Black Canyon]] di [[Sungai Colorado]].]]
Dam dapat diklasifikasikan menurut struktur, tujuan atau ketinggian.
Berdasarkan struktur dan bahan yang digunakan, bendungan dapat diklasifikasikan sebagai dam kayu, "embankment dam" atau "masonry dam", dengan berbagai subtipenya.
Tujuan dibuatnya termasuk menyediakan air untuk [[irigasi]] atau [[penyediaan air]] di perkotaan, meningkatkan navigasi, menghasilkan [[hidroelektrik|tenaga hidroelektrik]], menciptakan tempat rekreasi atau [[habitat (ekologi)|habitat]] untuk ikan dan hewan lainnya, [[pencegahan banjir]] dan menahan pembuangan dari tempat industri seperti [[pertambangan]] atau [[pabrik]]. Hanya beberapa dam yang dibangun untuk semua tujuan di atas.
Menurut ketinggian, ''dam besar'' lebih tinggi dari 15 [[meter]] dan ''dam utama'' lebih dari 150 m. Sedangkan, ''dam rendah'' kurang dari 30 m, ''dam sedang'' antara 30 – 100 m, dan ''dam tinggi'' lebih dari 100 m.
Kadang-kadang ada yang namanya ''Bendungan Sadel'' sebenarnya adalah sebuah [[dike (construction)|dike]], yaitu tembok yang dibangun sepanjang sisi danau untuk melindungi tanah di sekelilingnya dari banjir. Ini mirip dengan [[tanggul]], yaitu tembok yang dibuat sepanjang sisi sungai atau air terjun untuk melindungi tanah di sekitarnya dari ke[[banjir]]an.
Bendungan Pengecek ''check dam'' adalah bendungan kecil yang didisain untuk mengurangi dan mengontrol arus [[erosi]] tanah.
Bendungan kering ''[[dry dam]]'' adalah bendungan yang didisain untuk mengontrol banjir. Ia biasanya kering, dan akan menahan air yang bila dibiarkan akan membanjiri daerah dibawahnya.
=== Bendungan Separuh ===
Bendungan separuh [[diversionary dam]] adalah bendungan yang tidak menutup [[sungai]]. sebagian dari arus ditampuh di [[danau]] terpisah, di depan bendungan.
=== Bendungan kayu ===
Bendungan [[kayu]] kadang-kadang digunakan orang karena keterbatasan lokasi dan ketinggian di tempat ia dibangun. Di Lokasi tempat bendungan kayu dibuat, kayulah bahan yang paling murah, [[semen]] mahal dan sulit untuk diangkut. Bendungan kayu dulu banyak digunakan, tetapi kebanyakan sudah diganti dengan beton, khususnya di negara-negara industri. Beberapa bendungan dam masih dipakai. Kayu juga bahan dasar yang digunakan [[berang-berang]], sering juga ditambah lumpur dan bebatuan untuk membuat bendungan berang-berang.
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=== Embankment dams ===
Embankment dams are made from fill material not joined by mortar, and have two main types, rockfill and earth dams. Embankment dams rely on their weight to hold back water, like the gravity dams made from concrete.
==== Rock-fill dams ====
[[Berkas:Rockfill dam (Risdon).jpg|thumb|right|220px|A rockfill dam]]
[[Rock (geology)|Rock]]-fill dams are embankments of loose rock with either a watertight upstream face of [[concrete]] slabs or timber or a watertight core. Where suitable rock is at hand, a minimum of transportation of materials can be realized with this type of dam. Like the earth embankment, rock-fill dams usually resist damage from [[earthquake]]s quite well. However, water infiltration may cause [[Earthquake_liquefaction|liquefaction]] at embankment dams during an earthquake. This problem can be eliminated by keeping the susceptible material dry. [[New_Melones_Dam|New Melones Dam]] is a rock-fill dam.
==== Earth dams ====
[[Berkas:Dam.jpg|thumb|220px|right|A Farmer's Dam]]
Earth dams, also called earthen and earth-fill dams, are constructed as a simple homogeneous embankment of well-compacted earth, sometimes with a watertight concrete or [[clay]] core or upstream face, or sometimes with a [[hydraulic fill]] to produce a watertight core. A type of temporary earth dam occasionally used in high latitudes is the frozen-core dam, in which a coolant is circulated through pipes inside the dam to maintain a watertight region of [[permafrost]] within it. [[Oroville_dam|Oroville Dam]] is an earth dam.
=== Masonry dams ===
[[Masonry]] dams are of either the gravity or the [[arch]] type.
====Gravity dams ====
[[Berkas:Eder_dam.jpg|thumb|220px|right|The Eder dam in Germany, built around 1910.]]
In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. The dam will not overturn provided that the [[moment (physics)|moment]] around the turning point, caused by the water pressure is smaller than the moment caused by the weight of the dam. This is the case if the [[resultant force]] of water pressure and weight falls within the base of the dam. However, in order to prevent [[tensile stress]] at the upstream face and excessive [[compressive stress]] at the downstream face, the dam cross section is usually designed so that the resultant falls within the middle third at all elevations of the cross section (the [[core]]). For this type of dam, good impervious foundations are essential.
When situated on a suitable site, a gravity dam inspires more confidence in the layman than any other type; it has mass that lends an atmosphere of permanence, stability, and safety. When built on a carefully studied foundation with stresses calculated from completely evaluated loads, the gravity dam probably represents the best developed example of the art of dam building. This is significant because the fear of [[flood]] is a strong motivator in many regions, and has resulted in gravity dams being built in some instances where an arch dam would have been more economical.
Gravity dams are classified as "solid" or "hollow." The solid form is the more widely used of the two, though the hollow dam is frequently more economical to construct. Gravity dams can also be classified as "overflow" (spillway) and "non-overflow." [[Grand_Coulee_Dam|Grand Coulee Dam]] is a solid gravity dam and [[Itaipu|Itaipu Dam]] is a hollow gravity dam.
====Arch dams ====
[[Berkas:Jiroft_dam.jpg|right|thumb|220px|[[Jiroft]] Dam, [[Kerman Province]], [[Iran]].]][[Berkas:vidraru1.jpg|thumb|220px|right|The Vidraru dam, Arges, [[Romania]]]]
In the arch dam, stability is obtained by a combination of arch and gravity action. If the upstream face is vertical the entire weight of the dam must be carried to the foundation by gravity, while the distribution of the normal hydrostatic pressure between vertical [[cantilever]] and arch action will depend upon the [[stiffness]] of the dam in a vertical and horizontal direction. When the upstream face is sloped the distribution is more complicated. The [[normal]] component of the weight of the arch ring may be taken by the arch action, while the normal hydrostatic pressure will be distributed as described above. For this type of dam, firm reliable supports at the abutments (either [[buttress]] or [[canyon]] side wall) are more important. The most desirable place for an arch dam is a narrow canyon with steep side walls composed of sound rock. [[Parker_Dam|Parker Dam]] is an arch dam constructed of concrete.
Two types of single-arch dams are in use, namely the constant-angle and the constant-radius dam. The constant-radius type employs the same face radius at all elevations of the dam, which means that as the channel grows narrower towards the bottom of the dam the central angle subtended by the face of the dam becomes smaller. Jones Falls Dam, in Canada, is a constant radius dam. In a constant-angle dam, this subtended angle is kept a constant and the variation in distance between the abutments at various levels is are taken care of by varying the radii. [[New_Bullards_Bar_Dam|New Bullards Bar Dam]] is a variable radius arch dam. The safety of an arch dam is dependent on the strength of the side wall abutments, hence not only should the arch be well seated on the side walls but also the character of the rock should be carefully inspected. The multiple-arch dam consists of a number of single-arch dams with concrete buttresses as the supporting abutments. The multiple-arch dam does not require as many buttresses as the hollow gravity type, but requires good rock foundation because the buttress loads are heavy. See [[Geotechnical engineering]].
=== Cofferdams ===
A cofferdam is a sometimes temporary barrier constructed to exclude water from an area that is normally submerged. Made commonly of wood, [[concrete]] or steel sheet [[pile|piling]], cofferdams are used to allow construction on the foundations of permanent dams, bridges, and similar structures. When the project is completed, the cofferdam may be demolished. See also [[causeway]] and [[retaining wall]].
== Spillways ==
[[Berkas:Llyn_Brianne_spillway.jpg|right|thumb|300px|Spillway on Llyn Brianne dam, [[Wales]] soon after first fill]]
A ''spillway'' is a section of a dam designed to pass water from the upstream side of a dam to the downstream side. Many spillways have gates designed to control the flow through the spillway.
A ''service spillway'' or ''primary spillway'' passes normal flow. An ''auxiliary spillway'' releases flow in excess of the capacity of the service spillway. An ''emergency spillway'' is designed for extreme conditions, such as a serious malfunction of the service spillway. A ''fuse-plug spillway'' is a low embankment designed to be overtopped and washed away in the event of a large flood.
Any [[cavitation]] or [[turbulence]] of the water flowing over the spillway slowly eats the dam.
To minimize that [[erosion]] (especially with maximum water elevation at the crest), the downstream face of the spillway is ordinarily made an [[ogee curve]].
It was the inadequate design of the spillway that caused the overtopping of a dam that caused the infamous [[Johnstown Flood]].
== Other considerations ==
The best place for building a dam is a narrow part of a deep river valley; the valley sides can then act as natural walls. The primary function of the dam's structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a [[masonry]] dam flanked by earth embankments. The current use of the land to be flooded should be dispensable.
Significant other [[engineering]] considerations when building a dam include
* permeability of the surrounding rock or soil
* earthquake faults
* peak flood flows
* reservoir silting
* environmental impacts on river fisheries, forests and wildlife (see [[fish ladder]])
* impacts on human habitations
* compensation for land being flooded as well as population resettlement
* removal of toxic materials and buildings from the proposed reservoir area
[[Berkas:Teton_Dam_failure.jpg|thumb|right|The reservoir emptying through the failed Teton Dam]]
[[Kenneth E. Boulding]]'s [[poem]] ''The Ballad of Ecological Awareness'' (see Pranala luar) discusses the social and ecological impact of dam-building, beginning: "The cost of building dams is always underestimated" and concluding: "...cost-benefit analysis is nearly always sure/To justify the building of a solid concrete fact/While the Ecologic Truth is left behind in the Abstract."
Dam failures are generally catastrophic if the structure is breached or significantly damaged. Routine monitoring of seepage from drains in, and around, larger dams is necessary to anticipate any problems and permit remedial action to be taken before structural failure occurs. Most dams incorporate mechanisms to permit the reservoir to be lowered or even drained in the event of such problems. Another solution can be rock grouting - pumping cement slurry into weak fractured rock under pressure.
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== Contoh bendungan ==
* [[Bendungan Tiga Jurang]], [[Cina]]
* [[Itaipu|Bendungan Itaipu]], [[Brasil]]/[[Paraguay]]
* [[Bendungan Aswan]], [[Mesir]]
* [[Bendungan Benmore]], [[Selandia Baru]]
* [[Bendungan Glen Canyon]], [[Amerika Serikat]]
* [[Bendungan Grand Coulee]], [[Amerika Serikat]]
* [[Bendungan Hoover]], [[Amerika Serikat]]
* [[Bendungan Hume]], [[Australia]]
* [[Danau Pedder]] - [[Danau Gordon]], [[Australia]]
* [[Bendungan Kariba]], [[Zambia]]/[[Zimbabwe]]
* [[Bendungan Vishvesvaraya]], [[India]]
* [[Bendungan Mactaquac]], [[Kanada]]
* [[Bendungan Inga]], [[Republik Demokratik Kongo]]
* [[Bendungan Sepaku Semoi]], [[Indonesia]]
=== Bendungan gagal ===
* [[Johnstown Flood|South Fork Dam]] - [[1889]]
* [[St. Francis Dam]] - [[1928]]
* [[Vajont Dam]] - [[1961]]
* [[Baldwin Hills, Los Angeles, California|Baldwin Hills Dam]] - [[1963]]
* [[Buffalo Creek Flood]] - [[1972]]
* [[Banqiao Dam|Banqiao]] and [[Shimantan Dam]]s - [[1975]]
* [[Teton Dam]] - [[1976]]
* [[Kelly Barnes Dam]] - [[1977]]
* [[Lawn Lake Dam]] - [[1982]] <!-- In Rocky Mountain National Park -->
* [[Opuha Dam]] - [[1997]]
* [[Camará Dam]] - [[2004]]
== Lihat pula ==
{{portal|Pertanian}}
{{commons|Dam}}
* [[Berang-berang]], binatang pengerat pembuat bendungan
* [[Waduk]]
== Referensi ==
{{reflist}}
== Pranala luar ==
* [http://www.icold-cigb.org/ International Commission On Large Dams (ICOLD)]
* [http://www.structurae.de/en/structures/stype/s3.cfm Structurae: Dams and Retaining Structures]
* [http://www.iucn.org/themes/ceesp/Publications/SL/CT/Ballad%20-%20Part%202.pdf The Ballad of Ecological Awareness] {{Webarchive|url=https://web.archive.org/web/20061211151508/http://www.iucn.org/themes/ceesp/Publications/SL/CT/Ballad%20-%20Part%202.pdf |date=2006-12-11 }} ([[Portable Document Format|pdf]])
[[Kategori:Bendungan dan waduk| ]]
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