Asia – Monsoon AsiaM Meybeck, Universite Pierre et Marie Curie, Paris, France

ã 2009 Elsevier Inc. All rights reserved.

General Features of South and SoutheastAsian Drainages

The relief, climate, and lithological features of thisregion are summarized in Table 1 for 17 aggregatedcoastal catchments that link river networks to thecoasts of the Indian Ocean and of the South ChinaSea (Figure 1). The northern hydrographic limits ofthis drainage are the anti-Taurus (3500m) in Turkey,the Zagros Range in Iran (4070m), the Belutschistanmountains and Hindu Kush range in North Pakistan(7690m), the Karakorum (8600m) and Himalaya(8840m) ranges, the Tibetan Plateau (6000m), andfor Southeast Asia the Yunnan mountains in South-west China. As a whole, these rivers are thereforecharacterized by headwaters of very high elevationwith extended snow cover and permanent ice inareas exceeding 5000m in the Hindu Kush andKarakorum (Indus basin), in the Himalayans (Gangesand Brahmaputra basins), and in some parts of theTibet Plateau. These headwaters snow and ice coversprovide most of the water resources from Anatolia tothe Indus Valley and function as water towers inproviding water to lower elevations.The lithology of this region, a major controlling

factor of river chemistry, is characterized by mixedsedimentary and crystalline rocks folded in the alpineranges. An important volcanic plateau in CentralIndia (the Deccan Traps) must be mentioned; therest of Deccan and Sri Lanka have crystalline rocksoriginating from the former Gondwana continent.Sedimentary detrital rocks are found in all lowlandsas in the Shatt el Arab, Indus, Ganges, Irrawaddy, andMekong plains.Climates of South and Southeast Asia are greatly

dependent on elevation, which controls both temper-ature and precipitation, and by the presence of theAsian monsoon, which affects the central and easternparts of this region from the Indus Valley to the SouthChina Sea basin. The monsoon is characterized bywinter–spring dryness and summer rain (June andAugust) that accounts for 50–80% of the annualrain. In India, the monsoon starts abruptly in Junein the Western Ghats highlands, south of Mumbai,and progresses eastward during summer. The periodof maximum precipitation depends on station loca-tion, ranging from July (e.g., Mumbai) to November(Chennai). The annual rainfall varies between 660(Delhi) and 1700mm year�1 (Hanoi) with a localmaximum at 3000mm year�1 in the Western Ghats.

318

World extreme rainfall is recorded in the Khasi Hills(10 800mm year�1), north of Bangladesh in the upperMeghna basin, a tributary of the Ganges/Brahmaputracommon estuary (also termed Padma). Another pre-cipitation maximum (4800mm year�1) is observed inthe southeastern Salween basin (Myanmar). In thesouthern part of the South China Sea basin (Malaysia,Indonesia, Philippines), near the equator, the rainfall isnearly equally distributed throughout the year andreaches 3200mm in North Borneo. In the MiddleEast from the Indus Valley to the Persian Gulf Basin,annual precipitation reaches 500–800mm year�1 inthe mountains but barely exceeds 200mm year�1 in theShatt El Arab Valley (160mm year�1 in Baghdad) andin the Indus plain (180mm year�1).

In this region, river temperature, a major control ofaquatic species distribution, is very variable, includ-ing along the greatest basins that cross several cli-matic zones (Table 1). In high mountains, from theAnatolian Plateau to Tibet, rivers are commonly fro-zen during winter, while in equatorial catchments,from Sri Lanka to Philippines, thermal variationsare limited, and monthly temperatures may exceed22 �C. The greatest catchments, such as Shatt el Arab,Indus, Ganges, Brahmaputra, Irrawaddy, Salween, andMekong, are characterized by the greatest spatialand temporal thermal variability.

Drainage Network and River DischargeRegimes

Because of the predominance of mountainous regionsand of active tectonics, the drainage network of SouthAsia has not generated very large river basins com-pared with those found on other continents. The largestriver drainage area does not exceed 1.05million km2

(Ganges), while on islands (Sri Lanka, Indonesia,Philippines), peninsulas (Malaysia), and narrow coasts(Iran, Oman, W. Deccan, Annam), river basins donot generally exceed 20 000 km2. In the ArabianPeninsula and on the Iranian coast, medium-sizedriver networks are found, but they are mostly dryor flow only occasionally (desert wadis).

The major river systems from East to West are: theShatt el Arab, draining the Anatolian Plateau to thePersian Gulf; the Indus, which reaches the ArabianSea through one of the world’s largest deltas; theGanges (Ganga), which drains the southern side ofthe Himalayas; the Brahmaputra (named Tsang Po in

Table 1 General characteristics of South and Southeast Asian coastal catchments

Sea basin

name

Code

(a)

Principal

basins

Sea

basin

area

(Mkm2)

Runoff

(mm

year�1)

Population

density/

sea basin

(people

km�2)

Sediment

yield

(t km�2

year�1)

Relief Climate Geology

%

low

%

mid

%

high

%

polar

%

cold

%

temperate

% dry

< 3mm

(b)

% dry

�3mm

(b)

%

tropical

<680mm

(c)

%

tropical

� 680 mm

(c)

%

plutonic

metam.

%

volcanic

%

carbon.

%

other

rock

type

East South

China Sea

28 Kapuas,

Rajang,

Aguson

0.35 1824 115 512 21.7 77.3 1.0 0.0 0.0 10.3 0.0 0.0 0.0 89.7 8.3 15.5 4.5 24.8

West South

China Sea

19 Mekong,

Chao

Phraya,

Song Koi

1.49 1038 94 280 40.7 52.2 7.1 6.0 0.8 21.6 0.0 0.0 36.5 35.2 11.2 7.8 37.2 21.5

Sunda Strait 30 Barito,

Mahakam

0.55 1220 122 278 49.0 51.0 0.0 0.0 0.0 6.3 0.0 0.0 8.3 85.4 4.8 27.2 5.4 26.9

Sulu-

Celebes

Sea

31 Mindanao 0.36 1194 107 605 14.8 85.2 0.0 0.0 0.0 1.3 0.0 0.0 9.1 89.6 4.2 34.6 16.9 9.6

Banda Sea 32 No important

rivers

0.19 800 105 326 4.8 95.2 0.0 0.0 0.0 3.1 0.0 0.0 34.3 62.6 20.0 43.0 14.0 8.0

South Timor

Coast

33 No important

rivers

0.01 560 214 66 0.0 100.0 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0 25.0 49.9 0.0

Java Trench 34 Cinamuk,

Citanduy

0.17 1306 128 557 2.3 97.7 0.0 0.0 0.0 4.5 0.0 0.0 17.7 77.9 0.0 48.9 30.2 9.3

Andaman

Sea

35 Irrawaddy,

Salween,

Kelantan,

Musi

0.96 1106 79 652 18.7 64.1 17.1 16.1 1.5 37.6 2.5 2.1 10.9 29.3 12.7 9.7 35.0 14.6

Bengal Gulf 36 Ganges,

Damodar,

Pennar

1.82 820 261 612 48.7 23.6 27.6 22.2 2.2 60.9 3.3 3.4 5.0 3.0 24.7 3.1 17.7 40.7

East

Deccan

Coast

37 Godavari,

Krishna,

Mahanadi,

Cauweri,

Brahmani

1.12 273 315 355 45.8 54.2 0.0 0.0 0.0 11.2 17.0 12.0 55.5 4.3 53.9 23.0 8.4 10.6

Laccadive

Basin

38 Ponnani,

Payaswani,

Kalinadi

0.12 695 377 732 32.5 67.5 0.0 0.0 0.0 0.0 0.0 6.0 45.5 48.5 83.8 0.0 0.0 13.5

West

Deccan

Coast

39 Narmada,

Tapti, Mahi,

Rabarmati

0.34 498 297 441 47.3 52.7 0.0 0.0 0.0 16.6 6.2 33.6 26.4 17.2 21.4 51.3 6.1 19.4

Indus Delta

Coast

40 Indus 1.39 111 191 195 47.2 23.0 29.8 12.4 7.4 10.5 58.4 9.7 1.6 0.0 22.7 4.5 11.9 44.6

Oman Gulf 41 No important

rivers

0.26 2 45 10 9.7 90.3 0.0 0.0 0.0 0.0 87.9 12.1 0.0 0.0 6.6 5.5 19.9 6.7

Persian Gulf 42 Shatt el Arab,

Dawasir

2.47 48 28 122 45.1 52.3 2.7 0.0 6.4 10.0 79.4 4.2 0.0 0.0 13.2 3.4 50.6 29.6

South

Arabian

Coast

43 Muqshin 0.80 2 18 1 34.5 64.0 1.5 0.0 0.0 0.0 97.6 2.4 0.0 0.0 9.2 2.5 59.1 27.1

East Red

Sea

44 No important

rivers

0.44 0 36 1 0.7 97.1 2.2 0.0 0.0 0.0 100.0 0.0 0.0 0.0 52.9 23.3 4.0 8.8

(a) See location in Figure 1. (b) Annual runoff. (c) Annual precipitation.

Meybeck M, Durr HH, and Vorosmarty CJ (2006) Global coastal segmentation and its river catchment contributors: a new look at land-ocean linkage. Global Biogeochem. Cycles, 20, GB IS 90, doi 10.1029/2005 GB 002540.

Rivers

andStre

ams_A

sia

–MonsoonAsia

319

Figure 1 Major rivers South Asia and South-East Asia and regional coastal catchments as defined by Maybeck et al. (2006).

320 Rivers and Streams _ Asia – Monsoon Asia

Tibet, Jamuna in Bangladesh), which drains thenorthern side of the Himalayas and forces its wayeastward across this range near the Namtcha BarwaPeak (7758m) between Tibet and Assam, and finallyflows south and shares the Bengal Delta with theGanges, forming the Padma River or estuary;the Meghna, a relatively small basin in Bangladeshwith an enormous discharge (3500m3 s�1 for only80000km2); the Irrawaddy (Ayerarwady inMyanmar);and the Salween (Thanlwin in Myanmar), which origi-nates from the Tibet Plateau at 6000m, where it isnamed Nag Chu then Lukiang, both of which have avery narrow and elongated basin caused by tectonicforcing; the Mekong (Dza Chu in China), also ori-ginating from the Tibetan Plateau with an extremelynarrow upper course down to Vientiane (Laos) thena wider lower and middle course; the Song Koi or redriver (Yunnan, China, and Vietnam). Other middle-sized basins include the Godavari, Krishna,Mahanadi,Narmada, Tapti in Deccan, and the Chao Phraya inThailand. In deserts (Arabian Desert, Rajasthan Des-ert between Pakistan and India), ephemeral or occa-sional rivers (wadis) flow only during rare rain events.Internal regions in Iran and Afghanistan also have verylimited river networks, excepted for the HelmandRiver (Afghanistan).

The Mekong river system has a unique hydro-logical feature, the Tonle Sap, or Great Lake, inCambodia. This important lake is fed by the Mekongduring its high water stage (June to November). Atthis period the lake progressively deepens and extendsto a maximum size of 15 000 km2. Then the connec-tion between the Tonle Sap with the Mekong isreversed and the lake recedes to 3000 km2 (annualdepth variation: 9m). A very diverse and abundantaquatic life is in equilibrium with this pulsing system,which also provides essential food and fibre resourcesto the riparian populations well adapted to thischanging environment (e.g., floating villages). Otherexamples of such seasonal wetlands can also beobserved on other continents as for the Niger, Nile,Senegal, Okavango in Africa and upper Parana inSouth America, although the Tonle Sap is the greatestpulsing lake.

Natural hydrologic regimes, as described bymonthly long-term specific runoff (l s�1 km�2), reflectclimatic control factors. They are presented inTable 2on the basis of river discharges prior to dammingaccording to the earliest records and from west toeast. The natural Shatt el Arab regime, here reconsti-tuted from Tigris plus Euphrates discharges, iscontrolled by winter rains and snowmelt from the

Table 2 Flow regimes of South Asian rivers before damming presented from west to east

River Station Country Jan

(l s�1

km�2)

Feb

(l s�1

km�2)

Mar

(l s�1

km�2)

Apr

(l s�1

km�2)

May

(l s�1

km�2)

Jun

(l s�1

km�2)

Jul

(l s�1

km�2)

Aug

(l s�1

km�2)

Sep

(l s�1

km�2)

Oct

(l s�1

km�2)

Nov

(l s�1

km�2)

Dec

(l s�1

km�2)

Year

(l s�1

km�2)

A (103

km2)

Period

Euphrates DS Baghdad Iraq 3.5 4.8 6.95 10.35 11.1 6.1 2.65 1.5 1.12 1.18 1.6 1.6 4.42 398 1932/66

Narmada Garudeshwar India 1.75 1.3 0.90 0.66 0.41 2.2 24.0 52.5 62 16.8 4.9 2.3 14.1 89.3 1949/62

Damodar Rhondia India 1.8 1.8 1.4 1.1 1.75 10.7 39 59.8 49.8 22.0 4.8 2.5 16.5 19.9 1934/61

Mahamadi Kaimundi India 1.07 0.80 0.76 0.78 0.57 1.7 31.3 58.3 43.1 12.1 4.5 1.4 12.9 132.1 1947/61

Godavari Dowlaishwaram India 0.81 0.65 0.47 0.38 0.24 3.1 26.6 39.8 35.5 14.2 3.7 1.35 10.6 299 1901/60

Krishna Vijayawada India 0.44 0.27 0.17 0.15 0.77 2.38 21.9 26.1 17.3 10.9 4.0 1.0 6.9 251 1961/60

Pennar Nellore India 0.47 0.24 0.28 0.17 0.82 0.28 0.88 1.74 3.2 4.4 5.2 3.5 1.8 53.3 1934/47

Kelani Nagalagam Sri Lanka 51.8 48.0 51.3 63.3 123.7 129.4 88.7 77.2 76.7 127.5 109.3 70.5 84.9 2.085 1924/60

Chao

Phraya

Nakohn S. Thailand 2.1 1.4 1.0 0.86 1.61 4.3 5.94 11.8 19.6 26.5 15.3 4.75 7.9 111.4 1905/66

Mekong Kratie Cambodia 4.45 3.25 2.5 2.4 4.5 14.1 38.5 58.7 64.8 40.0 19.8 9.7 22.0 646 1933/53

Se Ban Ban Komphun Cambodia 9.9 6.8 5.2 5.6 14.0 25.3 58.5 83.4 74.7 55.2 25.7 17.2 31.7 48.2 1961/66

Kelantan Guillemard Malaysia 77.5 44.3 33.0 27.5 36.8 33.4 28.1 29.2 39.5 55.9 69.6 87.4 47.0 11.9 1949/64

Agusan Poblacion Philippines 139 173 105.9 60.7 53.7 57.7 54.0 60.6 62.1 66.2 65.0 125 81.9 7.39 1955/63

UNESCO (1969) Discharges of selected rivers of the world. Studies and reports in Hydrology, no. 5, p. 70. Paris: UNESCO.

UNESCO (1996) Global river discharge database (Riv Dis), Technical Documents in Hydrology, p. 41. Paris: UNESCO.

A: River basin in area.

Rivers

andStre

ams_A

sia

–MonsoonAsia

321

322 Rivers and Streams _ Asia – Monsoon Asia

Anatolian Plateau (maximum discharge in April andMay, low flows from July to December). The upperIndus and its tributaries (Jhellum, Ravi, Sutlej, andChenab, which altogether represent 40% of thedrainage basin, are mainly fed by the Hindu Kushand Karakorum snow and ice melt. After their con-fluence, the Indus River crosses a very dry region anddoes not receive any other important tributary; it is atypical ‘allogenic’ river in which the mountain watertower allows the river to make its way through desert,as is also true for the Nile River. The upper Indusbasin now has several major dams in Kashmir andPakistan used for hydropower, irrigation, and watersupply of downstream users.The Narmada River, south of Mumbai, is character-

istic of the West Deccan monsoon regime. From Juneto August the average specific discharge increases from2.2 to 53.8 l s�1 km�2 and 82% of the annual flow isdischarged from July to September. East Deccanregimes, from the Damodar River in the North BengalGulf to the Pennar in the south (Table 2), are muchdryer but also very seasonal. It must be noted thatthe average specific discharge in monsoon-fed riverscan be quite variable: 1.8 l s�1 km�2 for the Pennarcompared with 31.7 l s�1 km�2 for the Se Ban (a lowerMekong tributary) and much more in some parts ofthe Meghna and in the lower Salween basins.Ganges, Brahmaputra, Salween, and Mekong

headwaters are fed by late spring snowmelt and byice melt for their higher tributaries, after which theirmiddle and lower basins receive the monsoon rains(July–September). The result is a mixed regime with awell-marked summer maximum (‘monsoon period’)and an extended low flow period from Decemberto May (‘pre-monsoon period’), as for the Mekong(Table 2). River basins near the equator, in westernSri Lanka (e.g., Kelani), Malaysia (e.g., Kelantan), thePhilippines (e.g., Agusan), and Indonesia are charac-terized by minor seasonal discharge variations andby very high annual specific runoff (84.9, 47, and81.9 l s�1 km�2, respectively, Table 2), which isamong the world’s highest. Regional variability canbe important: there is a 50-fold difference betweenthe dry Pennar basin of Southeast Deccan and theKelani basin, and a 250-fold difference between theirminimum monthly runoff (0.17 and 48 l s�1 km�2,respectively) over a distance of only 600km.

Suspended Loads and Water Chemistry

South Asian rivers are much more turbid and erosivethan world average because their headwaters arelocated in areas of very high relief, and because mon-soon and snowmelt regimes are very seasonal, gener-ating peak runoff with high velocities. Also, in some

regions basin rock types are very erodible (e.g., vol-canic ashes in Java).

The average concentrations of suspended particu-late matter (SPM), calculated as the ratio of annualsediment loads over annual water volumes at the rivermouth, are here presented for a selection of large andmedium rivers, prior to damming (Table 3). All docu-mented rivers have SPM concentrations higher thanthe world median of about 200mg l�1. SPM concen-trations are much higher in headwaters, as in theupper Mekong, the upper Brahmaputra, and upperIndus, or in the Himalayan tributaries of the GangesRiver, such as the Kosi River.

Small coastal rivers in tectonically active regions(e.g., Indonesia and the Philippines) also are veryturbid and erosive (e.g., Cimanuk, Citanduy, andCitarum in Java, Table 3). As a result, the majorpart of the global sediment fluxes to oceans is gener-ated by the South and East Asian rivers.

Dissolved solids in South and Southeast Asian riv-ers are generally close to or slightly higher than theworld median, with a dominance of calcium andbicarbonate ions, as in most world rivers.

Because of the weathering of the volcanic DeccanTraps and the high evapotranspiration rate, Deccanrivers have a high ionic content (2000–5400meq l�1

for the cation sum (TZþ)), as in the Damodar,Godavari, Krishna, Narmada, and Tapti rivers(Table 3). Rivers draining the Himalayan and otheralpine ranges (Indus, Ganges, Mekong, Brahmaputra,Irrawaddy) are less mineralized, with TZþ from 1180(Mekong) to 2350 meq l�1 (Irrawaddy). The Salweenis an exception, possibly linked to the presence ofcarbonate rocks.

In very wet regions, where the effect of evaporationon ionic content is quite limited, water chemistry isdirectly controlled by the presence or absence of eas-ily weathered minerals. In the Mahakam River, whichdrains only crystalline rocks in Western Borneo, TZþ

can be as low as 392 meq l�1, while it ranges from 800to 1700 meq l�1 for rivers of Java. In central Thailand,the Chi andMun rivers, which drain evaporitic rocks,are naturally very high in Naþ and Cl�.

Human Effects on South Asian Rivers

South Asian rivers, with the exception of the Irra-waddy, Salween, Brahmaputra, and Middle andLower Mekong, are now extensively dammed. Thisgreatly fragments the river courses, modifies the flowregimes, and decreases the downstream fluxes of par-ticulate matter. In addition, reservoirs are generallyassociated with extensive irrigated areas where thewater is lost by evaporation. As a result, the discharge

Table 3 Water chemistry and suspended sediments before damming for South Asian rivers

River Station Country L(km)

A (103

km2)Q (km3

year�1)SPM(mg l�1)

SiO2

(mg l�1)Ca2þ

(mg l�1)Mg2þ

(mg l�1)Naþ

(mg l�1)Kþ

(mg l�1)Cl�

(mg l�1)SO4

2�

(mg l�1)HCO3

�

(mg l�1)TZþ

(meq l�1)

Brahmaputra Bangladesh (a) 3000 580 510 1058 7.8 14 3.8 2.1 3.9 1.1 10 58 1200

Cauweri India 800 88 20.9 19 28 24 60 5.5 50 32 177 6120

Chao Phraya Thailand 1200 111.4 27.8 395 15.8 22 6.3 4.0 8.4 76 1615

Cimanuk Java (Indonesia) 3.7 4.45 5600 19.2 16 6.2 9.0 2.0 4 19 81 1726Citanduy Java (Indonesia) 3.6 5.3 1800 13.3 6.7 3.2 4.3 1.1 3.3 4.7 36 812

Citarum Java (Indonesia) 5.9 4.9 30 11 3.9 8 2 5 13 52 1267

Damodar India 20 10 2800 22 8.2 15 3 9.7 45 62 2500

Ganges India/Bangladesh 2525 1050 493 1055 11.7 23.2 6.5 9.6 2.6 5.0 8 119 2177Godavari India 1500 313 105 1619 21.1 30.2 2.4 8.1 2.2 14.1 10 105 2113

Indus Pakistan 3180 916 90 26 6 9 2 7 26 90 2221

Irrawaddy Myanmar 2300 410 486 535 10 10 6 30 2 18 5 120 2350

Krishna India 1290 259 30 2130 5 27.5 13.5 42.5 3.0 37 63 125 4409Mahakam Borneo (Indonesia) 65.3 87 11.8 3.2 1.0 2.9 0.95 1.0 2.8 18.0 392

Mahanadi India 858 141.6 66 9.0 10.4 9.5 10.2 1.5 30.9 15 60.9 1783

Mekong Cambodia/Vietnam (b) 4850 795 467 321 8.9 14.2 3.2 3.6 2.0 5.3 3.8 57.9 1180Musi Sumatra (Indonesia) 57 80 24.5 3.2 1.1 4.6 1.1 4 5.2 15.5 470

Narmada India 1300 99 40.7 3071 25 19.2 35 17 5 175 4350

Salween Myanmar (c) 2820 325 211 46 16 10 1 20 1 212 4070

Shatt el Arab Turkey/Syria/Iraq 2760 541 45.7 6.9 52 22 31 3 32 73 180 5830Tapti India 724 65 18 49.6 30.4 8.3 3 44 39.4 242 5415

Meybeck M and Ragu A (1996) River discharges to the oceans. An assessment of suspended solids, major ions and nutrients. Environnement Information and assessment Rpt., 250 p. Nairobi: UNEP (loadable from

Gems Water:http://www.gemsstat.org/descstats.aspx)

A, basin area; Q, mean annual discharge; SPM, discharge weighted suspended particulate matter; TZþ, sum of cations; L, river length.

(a) With headwaters in Tibet and India. (b) With headwaters in China and Laos. (c) With headwaters in China.

Rivers

andStre

ams_A

sia

–MonsoonAsia

323

324 Rivers and Streams _ Asia – Monsoon Asia

of many rivers in this region has decreased, as in theShatt el Arab, the Indus, and the East Deccan riversdischarging to the Bay of Bengal. Impoundments arestill created in India and in the upper Mekong Basin.The Shatt el Arab headwaters (Tigris and

Euphrates) also are extensively impounded in Turkey,the regional water tower of the Middle East (e.g.,Attaturk Dam, one of the world’s largest), and againin Syria and Iraq. The lower reaches of the Shatt elArab and the Karun River in Iran form an extensivewetland that has been greatly affected by conflicts,oil drilling, and drainage. The restoration of thisworld-class wetland remains uncertain.The upper Indus and its tributaries are impounded,

and the Kotri dam in the lower reach also takes waterfor irrigation. As a result, the Indus water dischargeto the Arabian Sea has been decreased by 80%, andits sediment load has been reduced even more. Theupper Mekong, in China also, is now dammed infive places, as are some of its Thai tributaries. In thelower Mekong, a major tributary in Laos is beingimpounded. The water quality evolution influencedby irrigation is not much documented, but someincrease of salt content is likely to occur in Pakistanand Iraq.In South and Southeast Asia, the degradation of

river quality is particularly caused by faecal contam-ination and by organic pollution, which depends onpopulation density and on the degree of urban andindustrial sewage collection and treatment. The pres-sure on water quality is therefore very high duringthe pre-monsoon period in densely populated regionswhere urban development is growing faster thansewage collection and treatment. Such a situation isfound in most of the Indian subcontinent (Himalayanheadwaters excepted), in Sumatra and Java, and inpopulated lowlands of Myanmar, Thailand, andViet Nam, and is likely to occur in the lower ShattEl Arab.Some of the largest and fastest growing cities are

located in South Asia. Many of them are locatedinland on relatively small river courses with limiteddilution or self-purification capacity, particularlyduring the pre-monsoon period, as is the case forHyderabad (Pakistan) on the Indus; Lahore on theRavi River; Hyderabad (India) on the Krishna Riverheadwaters; Bangalore on Ponnayar River head-waters; New Delhi, Allahabad, and Varanasi on theYamuna River, a Ganges tributary; Nagpur onthe Godavari headwaters; Poona on the Bima head-waters, a branch of the Krishna River; Calcutta onthe Hoogly, a branch of the Ganges Delta; Ahmedabadon the Sabarmati River; Dacca in the Bengal Delta;Baghdad on the Tigris; Ho Chi Minh City on theSaigon River; and Hanoi on the Song Koi (Red River).

Industrial activities are developing rapidly in theIndian subcontinent and in Southeast Asia. Theymay result in hotspots of pollution involving heavymetals already evidenced on the Yamuna River fromDelhi to Varanasi, and on the Gomati River and onthe Loni River at Lucknow, both Ganges tributaries,on Saigon River and delta branches of Song Koi River(Viet Nam).

Other possible threats are associated with conflicts(e.g., defoliant use in Viet Nam, leakage fromdestroyed industrial facilities in Iraq). However, thelevels of toxic contaminants remain largely undocu-mented (see GEMS Water, a global program on riverquality). The effect of rapid deforestation in South-east Asia (e.g., Malaysia, Indonesia, Thailand) onwater quality and aquatic species biodiversity shouldalso be assessed.

Perspectives

River basins and water resources of South and South-east Asia region are changing very rapidly in responseto increasing water demand. From Turkey toPakistan, shared basins, already sensitive to climatevariations, are exposed to regional water manage-ment conflicts between water-rich upstream countriesand water-poor downstream users. In this region,most of the river water is already being used forirrigation and water supply for large cities. Theupper river courses are heavily fragmented by largedams and seasonal drought can now be observed inthe lower courses, such as the lower Indus.

Although human influences on river quality are notyet adequately documented with regard to the wateruse and demand, the fast growth of urbanization,intensive agriculture, and industrialization couldcause important problems in the future, particularlyin densely populated floodplains (Ganges, Meghna,Irrawaddy, Chao Phraya, Mekong, Song Koi), andwhere water resources have already been much used(Shatt El Arab, Indus).

Glossary

Allogenic river – Any river the main stem of which issustained almost entirely by waters derived fromthe uppermost regions of the drainage basin, be-cause the upper part of the drainage basin is wellwatered, whereas the lower part of the basin is arid.

Water tower – In a hydrologic context, a water toweris a large source of water that feeds the lower reachesof a river, often because the upper reaches are moun-tainous and receive abundant precipitation.

Rivers and Streams _ Asia – Monsoon Asia 325

Suspended particulate matter – Suspended particulatematter (SPM), which is also referred to as totalsuspended solids (TSS), consists of all material car-ried by water that can be separated from the waterby use of a filter. SPM consists of both inorganic andorganic particles.

TZþ – Sum of cations dissolved in water, expressed asmicroequivalents per liter (meq l�1). TZþ is an indexof total salinity or total dissolved solids.

See also: Africa; Asia – Eastern Asia; Flood Plains; FluvialExport; South America.

Further Reading

Ansari AA and Singh B (2000) Importance of geomorphology and

sediment processes for the metal dispersion in sediments and soils

of the Ganga Plain. Chemical Geology 162: 245–266.

Carbonnel JP and Guiscafre (1965) Grand Lac du Cambodge,Sedimentologie et Hydrologie, 1962–1963, 401pp. Paris: Rap-port de Mission , Ministere des Affaires Etrangeres.

Jennerjahn T, et al. (2004) Biogeochemistry of a tropical river

affected by human activities in its catchment: Brantas Riverestuary and coastal waters of Madura Strait, Java, Indonesia.

Est. Coastal Shelf Science 60: 503–514.

Korzun VI (ed.) (1978)World Water Balance and Water Resourcesof the World. Studies and Reports. Hydrology vol. 25, 663 pp.Paris: UNESCO (þatlas).

Le Thi Phuong Q, Garnier J, Billen G, Thery S, and ChanVan M

(2007) Hydrological regime and suspended load of the Red River

(Viet Nam), observation and modelling. Journal of Hydrology334: 199–214.

Meybeck M, Durr HH, and Vorosmarty CJ (2006) Global coastal

segmentation and its river catchment contributors: A new look at

land-ocean linkage.Global Biogeochemical Cycles 20, GB IS 90,doi 10.1029/2005 GB 002540.

Milliman JD and Syvitski JPM (1992) Geomorphic/tectonic control

of sediment discharge to the oceans, the importance of small

mountains. Journal of Geology 95: 751–762.SalomonsW, Kremer HH, and Turner RK (2006) The catchment to

coast continuum. In: Crossland CJ, et al. (eds.) Coastal Fluxes inthe Anthropocene, pp. 145–200. Springer.

UNESCO (1969)Discharges of selected rivers of the world. Studiesand reports in Hydrology, no. 5, 70pp. Paris: UNESCO.

UNESCO (1996) Global river discharge database (Riv Dis), Tech-nical Documents in Hydrology, 41pp. Paris: UNESCO.

Relevant Website

http://www.gemsstat.org/descstats.aspx – Gems Water program

UNEP, global river water quality data.