Mekong River Commission


  Khmer | Lao | Thai | Vietnamese | | Contact Us | Feed Back | FAQ | Site Map  
 

2. The flood hydrology of the major tributaries in the Lower Mekong Basin (Continue)

2.7 Vientiane to Pakse - the regional tributary systems



Figure 18. Vientiane to Pakse - schematic of the major Mekong tributary systems
indicating the sites at which discharge data are available. (Numbers refer to those
in Table 6.)

In this reach the large left bank tributaries in Lao PDR begin to exert their dominant influence on the flood hydrology of the Mekong, starting with the entry of the Nam Ngum 50 km downstream of Vientiane. The combined mean annual flow of all tributaries between Vientiane and Pakse is 171 km3, almost 40% of the Mekong total. The major contributions to this figure are made from the left bank by the Nam Ngum, Nam Kading/Nam Theun and the Se Bang Hieng, while the Mun – Chi Basin accounts for by far the greater part by far of the floodwater arising from the right bank in Thailand. The major tributary systems are indicated schematically in Figure 18, which also shows the functional hydrometric network. Tables 5 and 6 provide further summary information.

Within this reach:

  • The tributary catchment areas are generally very large such that flash floods do not dominate the flood hydrology as they do in the tributaries upstream of Vientiane. They are locally important on some of the smaller, steeper tributaries and in the upper reaches of the larger rivers and conditions can arise on the larger tributaries of extremely rapid increases in discharges, followed by equally fast flood recessions.
  • In their lower reaches backwater effects from the confluence with the Mekong mainstream can extend very considerable distances upstream and exacerbate the depth and duration of inundation during extreme events.
  • The accelerating development of hydropower schemes in this sub-region of the LMB will in time significantly modify the flood regime of many of the major tributaries. The impact upon flood peaks and volumes will depend upon the scale of reservoir development and whether any such storages are operated in a way that mitigates the flood hazard, by the provision of operational flood storage during the flood season, for example.
  • It is anticipated that one of the major changes to the flood regime will be a delay in the start of the flood season and the onset of the higher discharges associated with it. Early season flood water will be withheld in the reservoirs which will typically be drawn down at the end of the dry season.
  • The cumulative impacts of the numerous proposed schemes will in time modify the flood regime of the Mekong mainstream itself.

Table 5. Major tributaries to the Mekong mainstream — Vientiane to Pakse.

 

Table 6. Vientiane to Pakse — tributary sites at which functional hydrometric data are available.
(Sequence numbers refer to those in Figure 18.)

Sketch Station
No.
River Site
 Area
 (km2)
Mean annual flow
(cumecs)
1 230205 Nam Lik Muong Kasi
375
 
15
 
2 230201 Nam Lik Ban Hin Heup
5115
 
265
 
3 230401 Nam Song Vang Vieng
865
 
50
 
4 230110 Nam Ngum Ban Na Luong
5220
 
130
 
5 230104 Nam Ngum Ban Tha Lat
8280
 
590
 
6 230101 Nam Ngum Ban Pak Kanhong
14,300
 
600
 
7 230102 Nam Ngum Tha Ngon
21,995
 
680
 
8 250101 Nam Nhiep Muong Mai
4305
 
170
 
9 260101 Nam Sane Muong Borikhane
2230
 
130
 
10 270101 Nam Kading Ban Phone Si
14,200
 
340
 
11 270901 Nam Theun Kham Kheut
5650
 
290
 
12 270903 Nam Theun Ban Signo
3370
 
220
 
13 290102 Nam Songkhram Ban Tha Kok Daeng
4650
 
150
 
14 310201 Nam Pung Ban Tham Hai Br
1070
 
10
 
15 320107 Se Bang Fai Mahaxai
4520
 
230
 
16 320101 Se Bang Fai Se Bang Fai
8560
 
440
 
17 330103 Huai Bang Sai Ban Na Khom Noi
1220
 
15
 
18 350105 Se Bang Hieng Tchepon
3990
 
170
 
19 350101 Se Bang Hieng Ban Keng Done
19,400
 
520
 
20 350301 Se Pon Ban Muong Chan
1980
 
65
 
21 350401 Se Thamouak Highway Br
636
 
20
 
22 350201 Se La Nong Muong Nong
2,010
 
80
 
23 350501 Se Xangxoy Ban Phalane
880
 
25
 
24 350602 Se Champone Dong Hen
1525
 
45
 
25 350601 Se Champone Ban Keng Kok
2640
 
60
 
26 370210 Nam Pong Si Chompu
1260
 
10
 
27 370805 Lam Choen Ban Tha Dua
1500
 
10
 
28 371101 Huai Rai Ban Non Kiang
1370
 
15
 
29 371203 Huai Pa Thao Ban Tad Ton
326
 
4
 
30 371509 Nam Yang Ban Na Thom
3240
 
30
 
31 370122 Nam Chi Ban Chot
10,200
 
55
 
32 370104 Nam Chi Yasothon
43,100
 
230
 
33 380134 Nam Mun Rasi Salai
44,600
 
175
 
34 380103 Nam Mun Ubon
104,000
 
610
 
35 380127 Nam Mun Kaeng Saphu Thai
116,000
 
770
 
36 380111 Nam Mun Pak Mun
117,000
 
backwater
 
37 381206 Huai Khayuong Ban Huai Khayuong
2900
 
35
 
38 381503 Lam Dom Yai Ban Fang Phe
1410
 
20
 

 

 

 


E-Newsletters

Choose a newsletter: