The Mahakam River
is in Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. It flows 980 km from the district of Long Apari in the highlands of Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
, to its mouth at the Makassar Strait
Makassar Strait is a strait between the islands of Borneo and Sulawesi in Indonesia. To the north it joins the Celebes Sea, while to the south it meets the Java Sea.The Mahakam River of Borneo empties into the strait....
The city of Samarinda
Samarinda is the capital of the Indonesian province of East Kalimantan on the island of Borneo. The city lies on the banks of the Mahakam River. It is the most populous city in East Kalimantan with a population of 726,223...
, the provincial capital of East Kalimantan
East Kalimantan is the second largest Indonesian province, located on the Kalimantan region on the east of Borneo island. The resource-rich province has two major cities, Samarinda and Balikpapan...
, lies along the river 48 km (30 mi) from the river mouth.
The Mahakam River is the largest river in East Kalimantan, Indonesia, with a catchment area of approximately 77,100 km2
. The catchment lies between 2˚N to 1˚S latitude and 113˚E to 118˚E longitude. The river originates in Cemaru from where it flows south-eastwards, meeting the River Kedang Pahu at the city of Muara Pahu. From there, the river flows eastward through the Mahakam lakes region, which is a flat tropical lowland area surrounded by peat land. Thirty shallow lakes are situated in this area, which are connected to the Mahakam through small channels http://www.water.wur.nl/NR/rdonlyres/23DA3991-9116-4399-BAE8-03FDDEA07D6C/79521/FactsheetMahakamLR.pdf
. Downstream of the connection with the Semayang and Melintang lakes, the Mahakam meets three other main tributaries - the rivers Belayan, Kedang Kepala, and Kedang Rantau - and flows south-eastwards through the Mahakam delta distributaries, to the Makassar Strait.
Kalimantan, where the Mahakam lies, is part of the Sunda Continental Plate
The Sunda Plate is the tectonic plate on which the majority of Southeast Asia is located. It was formerly considered a part of the Eurasian Plate, but GPS measurements have confirmed its independent movement at 10 mm/yr eastward relative to Eurasia...
. The large island has mountain ranges between Indonesia and Malaysia, however, volcanism is absent in this island. As described by van Bemmelen (1949), River Mahakam rises in Cemaru (1,681 m) in the centre of Kalimantan, from there it cuts through the pre-tertiary axis of the island east of the Batuayan (1,652 m) and then reaches the tertiary basin of Kutai. Its middle course traverses a lowland plain with many marshy lakes. This intermontane depression is separated from the neighboring basin, the Barito depression, by a broad hilly tract of less than 500m altitude. After this region, the Mahakam cuts through the Samarinda anticlinorium and reaches its alluvial delta, which spreads like a broad fan over the shelf-sea, with a base of 65 km and a radius of about 30 km.
Upstream of Long Iram (upstream part of Mahakam river basin) the river is flowing in tertiary rocks (Voss, 1983). Between Long Iram and Muara Kaman (middle Mahakam area) the river is flowing in quaternary alluvium, while in the downstream area between Muara Kaman and the coast including the Mahakam delta, tertiary rocks are again present. The presence of the large delta is explained by the formation and rejuvenation of the hilly region near Samarinda.
The Mahakam catchment is around the equator. According to Köppen climate classification
The Köppen climate classification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936...
, this area belongs to type Af (tropical rainforest) that has a minimum temperature ≥18o
C and precipitation of the driest month in normal year ≥60 mm Transfer of mass and energy in the tropical zone occurred through general air circulation known as the Hadley cell
The Hadley cell, named after George Hadley, is a circulation pattern that dominates the tropical atmosphere, with rising motion near the equator, poleward flow 10–15 kilometers above the surface, descending motion in the subtropics, and equatorward flow near the surface...
. According to Seidel et al. (2008) the precipitation
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
pattern in this area is largely determined by this large-scale atmospheric wind patterns, which is observable in several ways throughout the atmosphere. This circulation carries moisture into the air, generating rainfall in equatorial regions, whereas at the edges of the tropical belt are drier. Within this circulation, evaporation is intensively occurred around the equator on the centre of low pressure called the Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....
(ITCZ), characterized by accumulation of cloud in the area. The ITCZ moves following the pseudo-motion of the sun within 23.5o
N and 23.5o
S zone, therefore its position always changes according to this motion.
The ITCZ drives the Indo-Australian monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
phenomena which influence the regional climate including the Mahakam catchment. In December, January, February (winter in northern hemisphere) the concentration of high pressure in Asia and low pressure in Australia make the west wind blows in Indonesia (west monsoon). In June, July, August concentration of low pressure in Asia (summer in northern hemisphere) and concentration of high pressure in Australia make the east wind blows in Indonesia (east monsoon). Due to the global air circulation and the regional climate mentioned above, the Mahakam catchment which is located around the equator has a bimodal rainfall pattern with two peaks of rainfall, which are generally occurred in December and May. This is because the ITCZ passed through the equator twice a year, from the northern hemisphere in September and from the southern hemisphere in March.
There are about 76 lakes spread in the Mahakam river basin and about 30 lakes are located in the middle Mahakam area including the three main lakes (Lake Jempang 15,000 Ha; Lake Semayang 13,000 Ha; Lake Melintang 11,000 Ha). The lakes levels are seasonally fluctuated from 0.5m – 1m during dry period to seven meters during rainy season. The Mahakam lakes and surrounding wetlands act as a trap of sediment contained in the water flowing into the lakes which are now known to become shallower, presumably as a result of an imbalance between sediment input and slow subsidence.http://www.eastkalimantan.org/projects/wp4.html
Fishing is the primary source of livelihood in the Mahakam lakes area, most of the people around the lakes are fishermen. The middle Mahakam lake area is an area of intensive fishing activity with a productivity of 25,000 to 35,000 metric tons per year since 1970.http://globalnature.org/docs/02_vorlage.asp?id=12726&domid=1011&sp=E&m1=11089&m2=28219&m3=11178&m4=12726&addhilite=mahakam
The Mahakam delta is a mixed fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
-tidal dominated delta. The delta covers about 1800 km2, consisting of mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
areas near the shore, Nypa
Nypa fruticans, known as the attap palm , nipa palm , and mangrove palm or buah atap , buah nipah , dừa nước , Ging Pol in Sinhala in Sri Lanka and gol pata , dani . It is the only palm considered a mangrove in the Mangroves Biome...
swamps in the central areas, and lowland forest near the apex, corresponding to the first bifurcation,http://www.eastkalimantan.org/projects/wp5.html
however, recent fishery development in this area has converted a vast area of mangrove into shrimp ponds (tambak). The delta has three main distributaries
A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. They are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary is a tributary...
system directed Northeast, Southeast and South. The area between distributaries consists of a series of tidal channels generally unconnected to the main distributaries. The distributary channels are narrow and rectilinear with the depth ranging from 8 to 15 m and distributary channel bifurcations appear every 10 to 15 km.
This lower Mahakam area is the second most productive hydrocarbon basin of Indonesia which contains around 3 billion barrels of oil and 30 Tcf of gas reserves. Field geological investigations in this area was started in 1888 and in 1897 exploration drilling discovered oil at shallow depth of 46 m on the Louise structure. Production started in 1898 followed by expansion of exploration to the entire Mahakam.
Mahakam and its floodplain is an ecologically important region. A total of 147 indigenous freshwater fish species had been identified from the Mahakam. The Mahakam hosts the freswater dolphin Irrawaddy Dolphin
The Irrawaddy dolphin is a euryhaline species of oceanic dolphin found in discontinuous subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.-Etymology and taxonomic history:...
; called Pesut by local people) a critically Endangered fish species, which is included on CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) Appendix I.http://www.globalnature.org/bausteine.net/file/showfile.aspx?downdaid=6866&sp=E&domid=1011&fd=2
The Mahakam river basin is also an important breeding and resting place for 298 bird species, among them 70 protected and five endemic species: Borneo Dusky Mannikin (Lonchura fuscans
), Borneo Whistler (Pachycephala hypoxantha
), Bornean Peacock-pheasant (Polyplectron schleiermacheri
), Bornean Blue-flycatcher (Cyornis superbus
) and Bornean Bristlehead (Pityriasis gymnocephala
A Research Cluster (http://www.eastkalimantan.org
): "Upsetting the balance in the Mahakam Delta: past, present and future impacts of sea-level rise, climate change, upstream controls and human intervention on sediment and mangrove dynamics" extensively carry out research on the Mahakam. The cluster's objective is to study the impact of external forcing factors such as sea-level rise, climate change, upstream sediment, as well as human interference on past, present and future development of the Mahakam delta in different time scales.
The River Mahakam is an economic resource for fishermen and farmers, and as freshwater source, as a waterway since ancient time until today. It is in this river basin where the Kutai
Kutai is the traditional name of a historic region in East Kalimantan in Indonesia on Borneo, a Dayak people of the region with a language of the same name and their historic states. Today the name is preserved in the names of three regencies in East Kalimantan, the Kutai Kartanegara Regency, the...
kingdom evolved. The Kutai history is divided into two periods, Kutai Martadipura (around 350-400) and Kutai Kartanegara period (around 1300). Kutai Martadipura, a Hindu kingdom founded by Mulawarman at Muara Kaman, is regarded as the oldest kingdom in Indonesia. Kutai Kartanegara was founded by settlers from Java at Kutai Lama near the mouth of Mahakam. In around 1565, Islam was extensively spread in Kartanegara by two Moslem preachers from Java, Tunggang Parangan and Ri Bandang.
The Dayak or Dyak are the native people of Borneo. It is a loose term for over 200 riverine and hill-dwelling ethnic subgroups, located principally in the interior of Borneo, each with its own dialect, customs, laws, territory and culture, although common distinguishing traits are readily...
are the indigenous people inhabiting Kalimantan beside the Kutais and the Banjars. Since 1970s transmigration
The transmigration program was an initiative of the Dutch colonial government, and later continued by Indonesian government to move landless people from densely populated areas of Indonesia to less populous areas of the country...
of people to East Kalimantan was organised by the Indonesian government especially in areas near River Mahakam. Transmigration aims to migrate people from overpopulated Java
Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...
Bali is an Indonesian island located in the westernmost end of the Lesser Sunda Islands, lying between Java to the west and Lombok to the east...
, and Madura
Madura is an Indonesian island off the northeastern coast of Java. The island comprises an area of approximately 4,250 km². Madura is administered as part of the East Java province. It is separated from Java by the narrow Strait of Madura.-History:...
islands to stimulate greater agricultural productivity in outer islands. By 1973, almost 26% of the land under cultivation in East Kalimantan was being worked by transmigrants.