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:
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 |