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Using remotely sensed data to detect changes of riverbank in Mekong River, Vietnam
Results and discussions
- Results
Results of analysis and interpretation of time series data were compared to each other indicating spatial changes of shorelines. There are two main parts of changes as the following.
Shoreline erosion mainly occurred in Tien River from Tan Chau area to lower stream My Thuan, while in Hau river the phenomenon was less severe from Can Tho upwards Chau Doc.
- Tien River
Great changes are distributed in Tien river where there are many meander bends making river flow direction changed continuously (figure2), extended from 4 to 10 km in length, eroded into land from 100 to 1,000 meters. The eroded areas are presented in table 2.
Table.2 Location of erosion areas in Mekong River
within period 1966 - 1999
| River branch |
Areas |
Length (km) |
Width (m) |
| Tien river- Left bank |
Thuong Phuoc-Thuong Thoi Tien |
6 |
1,000 |
| |
Hong Ngu |
8 |
100 |
| |
An Phong |
4 |
120 |
| |
Tan Thanh |
4 |
130 |
| |
My Xuong |
9 |
250 |
| |
Chau Thanh-Sa Dec-My Thuan |
6 |
100-350 |
| |
Cho Lach-Ben Tre |
3.5-4.5 |
250-400 |
| - Right bank |
My Luong-Long Dien |
4 |
120 |
| Sa Dec |
10 |
1,100 | |
| Hau river- Left bank |
Nhon Hoa-An Chau |
4.5 |
200-800 |
| - Right bank |
An Chau-Long Xuyen |
2.6 |
100 |
| Binh Thuy-Can Tho |
2.8 |
150 | |
Within period 1966 - 1990, in Thuong Thoi Tien - Long Son area (Phu Chau - Tan Chau), erosion at left bank and accretion at right bank made the river channel almost shifted leftward and narrowed. Flow direction also changed. Gentle bends tend to be more meandered before flowing into Tan Chau area. Flow in Lower Tan Chau area (Thuong Thoi Tien - Hong Ngu) kept changing from 1990 to 1995 and 1999. Similarly, in Sa Dec area this phenomenon also occurred and spread from My Thuan upward Tan Qui Dong-Sa Dec in about 20 km. The river was narrower and new "bottle necks" appeared in Sa Dec, Tan Qui Dong, My Thuan (fig. 3). From 1995 to 1999, the situation was more complex. Bottle-necks changed in both their upper and lower parts, while relatively stable banks in previous period began to be affected by the changes.
Fig.2 Flow directions of Tien river
- Hau River
Here changed areas are not as large as in Tien River. They extend from 2.5 to 4.5 km and 100 to 1,000 meters in length and width. Narrow river segments were eroded in upper part and accreted in lower part as in Long Xuyen and Can Tho area (Binh Thuy - Phu An). Especially, stream in An Chau area became more straight because of erosion and accretion in both sides of riverbank, making the channel sifted leftward. At contiguous lower stream, the bend at Ong Ho islet (figure 3) was expanded as deposition at the slipoff slope side.
- Aits (islet)
Aits on Mekong River almost are natural bars or dunes. Naturally, their occurrence and distribution depend on river discharge and transported matter in stream (suspended load). Analyzing images also indicated spatial change of aits in shape resulting from erosion and accretion at both tips of them. This made a shift almost down stream. In some areas, these changes made streams narrower.
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