Thursday, 7 April 2022

Rivers of Sri Lanka

Mahaweli Ganga
Sri Lanka's Rivers rise from the inland regions of the country such as the Central Highlands and flow towards the sea. According to traditional classification, there are 103 rivers (basins) in Sri Lanka and 16 of them are longer than 100 km in length while 12 of them carry about 75% of the mean river discharge in the entire country (Katupotha & Gamage, 2020; Weerasinghe, 2008). Their basins cover 90% of the island.

A river is a ribbon-like body of water that flows downhill from the force of gravity representing different drainage patterns (Katupotha & Gamage, 2020). It can be wide and deep or shallow enough for a person to wade across (Katupotha & Gamage, 2020). A river with a regular discharge, throughout the year is known in Sri Lanka as a Ganga while a smaller river that dries up during the dry season is called an Oya (De S. Hewavisenthi, 1997). Although there are 103 river basins in Sri Lanka only 29 of them can be identified as rivers (Katupotha & Gamage, 2020).

Most rivers in Sri Lanka are short (Katupotha & Gamage, 2020). However, a few rivers rise in the Central Highlands, from 2,400 m or more elevation and reach the sea passing a more than 100 km length (Katupotha & Gamage, 2020). Water from these rivers is utilized to fulfil the basic water requirements of the country.

River basins in Sri Lanka
A river basin is a natural unit and lends itself ideally for water resources studies concerning rainfall, streamflow water use, drainage etc (Arumugam, 1969). There are 103 river basins in Sri Lanka and many of them are located on the Intermediate, and Dry Zones below the 300 m and 150 m contour lines (Arumugam, 1969; Katupotha & Gamage, 2020; Hydrological Annual, 2011/2012). For the convenience of studies, each basin has been given a unique ID number ranging from 1 to 103. 
 
Of the river basins, ID nos. 2 (Bolgoda Lake), 5 (Madu Ganga), 6 (Madampe Lagoon), 7 (Telwatta Ganga), 8 (Ratgama Lake) and 10 (Koggala Lagoon)) are water bodies located in back-barrier of the coastal area (Katupotha & Gamage, 2020). Also, the ID nos 24 (Mahasilawa Oya), 27 (Katupila Ara), 66 (Palakutti Ara) and 101 (Ratmal Oya) are not connected directly with the sea but to a major river or a marsh (Katupotha & Gamage, 2020). The Mahasilawa Oya flows into a salt marsh, while Katupila Ara is connected to Menik Ganga. Palakutti Ara is connected to a lagoon and Ratmal Oya flows into the Gin Oya (Katupotha & Gamage, 2020).

Of the 103 flows, 64 rivers flow at lagoons or lakes while 29 rivers directly flow to the sea (Katupotha & Gamage, 2020). Only 8 rivers (Kelani Ganga, Kalu Ganga, Walawe Ganga, Kirindi Oya, Menik Ganga, Kumbukkan Oya, Gal Oya and  Mahaweli Ganga) start from the central highland and its adjacent areas [(>1200 m contour line) Katupotha & Gamage, 2020]. Mahaweli Ganga is the longest river in the country and its head-streams start from Central Highland. The head-streams of the other 3 major rivers namely Kelani, Kalu and Walawe begin from the western and southern flanks of the Samanala Mountain Range (Katupotha & Gamage, 2020). 
 
The list of river basins in Sri Lanka (103)
+ Rivers (29)                                                                * Water bodies (6)    
# Not connected with the sea (4)                             ! Connect to either lagoons or lakes (64)

Basin
ID
River name
(length)
Origin
(elevation)
Drainage area
Sq. km
Runoff (Annual total)
1000 Ac. ft.
1 Kelani Ganga (+)
>2,400 m
2,340
5,807
2 Bolgoda Lake (*)
<150 m
396
669
3 Kalu Ganga (+)
1,200-2,400 m
2839
6,294
4 Bentota Ganga (+) 150-300 m
667
1,427
5 Madu Ganga (*)
69
137
6 Madampe Ganga (*)
90
205
7 Telwatta Ganga (*) <150 m
41
120
8 Ratgama Lake (*) <150 m
13
23
9 Gin Ganga (+)
600-1,200 m
915
1,550
10 Koggala Lake (*) <150 m
55
137
11 Polwatta Ganga (+)
150-300 m
232
255
12 Nilwala Ganga (+)
600-1,200 m
1043
1,210
13 Sinimodara Oya (+)
<150 m
35
46
14 Kirama Oya (+)
150-300 m
183
168
15 Rekawa Oya (!)
<150 m
70
55
16 Urubokka Oya (!)
300-600 m
373
206
17 Kachigal Ara (!)
150-300 m
208
100
18 Walawe Ganga (+)
>2,400 m 2424
1,784
19 Karagan Oya (!)
<150 m
60
20
20 Malala Oya (!)
150-300 m
409
131
21 Embilikala Oya (!)
<150 m
69
19
22 Kirindi Oya (+)
1,200-2,400 m
1156
537
23 Bambawe Ara (!)
<150 m
66
26
24 Mahasilawa Oya  (#)
<150 m
13
3
25 Butawa Oya (!)
<150 m
37
14
26 Menik Ganga (+)
1,200-2,400 m
1301
524
27 Katupila Ara  (#) <150 m
111
36
28 Kurunda Ara (!)
<150 m
99
52
29 Namadagas Ara (!)
<150 m
110
43
30 Karambe Ara (!)
<150 m
54
33
31 Kumbukkan Oya (+)
1,200-2,400 m
1,227
586
32 Bagura Oya (!)
<150 m
93
55
33 Girikula Oya (!)
<150 m
14
6
34 Helawa Ara (!)
<150 m
38
8
35 Wila Oya (!)
150-300 m
472
192
36 Heda Oya (+)
150-300 m
615
302
37 Karanda Oya (!)
150-300 m
425
196
38 Seymena Ara (!)
<150 m
72
27
39 Tandiadi Ara (!)
<150 m
20
14
40 Kangikachchi Ara (!)
<150 m
78
27
41 Rufus Kulam Aru (!)
<150 m
27
14
42 Pannel Oya (!)
<150 m
195
116
43 Ambalan Oya (!)
150-300 m
112
70
44 Gal Oya (+)
1,200-2,400 m
1,911
1,418
45 Andella Oya (!)
300-600 m
534
324
46 Tumpan Keni Tank (!) <150 m
18
3
47 Namakada Aru (!) <150 m
12
6
48 Mandipattu Aru (!) <150 m
90
64
49 Pathantoppu Aru (!) <150 m
101
64
50 Vedi Aru (!) <150 m
22
21
51 Magalavatavan Aru (!) <150 m
304
153
52 Mundeni Aru (!) 150-300 m
1373
609
53 Miyangolla Ela (!) <150 m
228
101
54 Maduru Oya (!) 150-300 m
1,439
1,133
55 Pulliyanpota Aru (!) <150 m
87
27
56 Kirimechchi Odai (!) <150 m
89
72
57 Bodigoda Aru (!) <150 m
132
144
58 Mandan Aru (!) <150 m
26
16
59 Makarachchi Aru (!) <150 m
59
39
60 Mahaweli Ganga (+)
>2,400 m 10,266
4,306
61 Kantale Aru (!) 150-300 m
437
221
62 Palapotta Ara (!) <150 m
97
49
63 Panna Oya (!) <150 m
164
90
64 Pankulam Aru (!) 150-300 m
377
223
65 Kunchikumban Aru (!) <150 m
245
71
66 Pulakutti Aru  (#) <150 m
8
8
67 Yan Oya (+)
150-300 m
1,518
636
68 Mee Oya (!) <150 m
89
36
69 Ma Oya (!) <150 m
1,042
384
70 Churiyan Aru (!) <150 m
105
30
71 Chavar Aru (!) <150 m
35
12
72 Palladi Aru (!) <150 m
66
26
73 Manal Aru (!) <150 m
194
90
74 Kodalikallu Aru (!) <150 m
92
42
75 Per Aru (!) <150 m
392
185
76 Palu Aru (!) <150 m
70
44
77 Maruthapillay Aru (!) <150 m
36
23
78 Thoravil Aru (!) <150 m
104
39
79 Piramanthal Aru (!) <150 m
91
41
80 Netheli Aru (!) <150 m
114
51
81 Kanakarayan Aru (!) <150 m
604
337
82 Kalwalappu Aru (!) <150 m
68
34
83 Akkarayan Aru (!) <150 m
244
107
84 Mandekal Aru (+)
<150 m
208
121
85 Pallavarayankaddu Aru (+)
<150 m
311
51
86 Pali Aru (+)
<150 m
451
163
87 Chippi Aru (+)
<150 m
79
18
88 Parangi Aru (+)
<150 m
770
266
89 Nay Aru (+)
<150 m
717
145
90 Malwathu Oya (+)
150-300 m
3,291
1,004
91 Kal Aru (+)
<150 m
210
94
92 Moderagama Aru (!)
<150 m
1,001
252
93 Kala Oya (+)
300-600 m
2,526
859
94 Moongil Aru (!) <150 m
78
11
95 Mi Oya (!) <150 m
1,555
121
96 Madurankuli Aru (!) <150 m
128
7
97 Kalagamu Oya (!) <150 m
169
12
98 Rathambala Oya (!) <150 m
244
104
99 Deduru Oya (+)
600-1,200 m
2,622
1,222
100 Karambala Oya (+)
<150 m
693
292
101 Ratmal Oya  (#)
<150 m
341
143
102 Maha Oya (+) 600-1,200 m
1,470
1,570
103 Attanagalu Oya (+)
150-300 m
811
618
.
Attribution

References
1) Arumugam, S., 1969. Water resources of Ceylon: its utilisation and development. Water Resources Board. pp.1-6.
2) De S. Hewavisenthi, A.C., 1997. Management of the Mahaweli, a river in Sri Lanka. Water international, 22(2), pp.98-107.
3) Hydrological Annual, 2011/2012. Hydrology Division. Irrigation Department. Ministry of Irrigation and Water Resources Department. pp.4-6.
4) Katupotha, J.; Gamage, S., 2020. Understanding the river basin classification of Sri Lanka. Wildlanka, 8 (4). Department of Wildlife Conservation, Sri Lanka. pp.175-197.
5) Weerasinghe, S.M., 2008. North-Western Province Biodiversity Profile and Conservation Action Plan. The Biodiversity Secretariat. Ministry of Environment and Natural Resources. ISBN: 978-955-0033-01-0. p.30.


This page was last updated on 16 September 2022

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