APPLICATION OF MATHEMATICAL MODEL FOR STUDYING FLOOD INXEBANGHIENG RIVER BASIN
Oudomsack Philavong1), Oulaphone Ongkeo2), and Chanseng Phongpachith2)
1) Lao National Mekong Committee Secretariat,

Water Resources & Environment Administration (WREA)
Vientiane 01000, Lao PDR
2) Water & Environment Research Institute,Water Resources & Environment Administration (WREA)
Vientiane 01000, Lao PDR

INTRODUCTION
Introduction Study Area
Xebanghieng is one of major tributaries of Mekong River which has created livelihoodand colorful of ethnic-tribes of local for long time. The river of Xebanghieng begins in
Savannakhet province and flows with contribution of nine tributaries before confluence
into the Mekong River. Most of Xebanghieng River Basin is plateau and scattered ofmountainous area to the Lao-Vietnamese border, which cover by light forest and water
resources as well as variation of biodiversity. Its total common area of about 19,712 Km2,
the total length is about 370Km and the river discharges of 497m3/s (at Kengdone station
during 1960-1997).
Though there is high rate of poverty in this area, the Xebanghieng River Basin is strong
in that the basin is still rich in land, water, forest, biodiversities and other natural resource,and rich in cultures and colorful of ethnic-tribes. The use of water, land, forest and related
natural resources for economic development are un-sustainable due to poor management
and inadequate practice. The forest lost has been reported very high in this basin.
However, the government policy and regional cooperation for water resourcesmanagement study is ongoing. There are great opportunities for development in the basin,
including forestry development, agriculture and animal husbandry, fisheries, eco-tourism,
small scale of hydropower, river transports, multi-sector development. The more income
for local people through non-timber products trade and overall development facts will
help in poverty eradication of the region.
As water resources is the key factor for agricultural production in this river basin and in
the past there is no study in details on the potential of water resources and opportunities
for development in Xebanghieng Basin. Therefore this case study will provide knowledge
base and report for water resources planning and development in Xebanghieng RiverBasin.

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Figure 1: Overview map of Xebanghieng BasinObjectives of case study
The ultimate objectives of the case study are to build capacity of LNMC modelers inapplying the DSF in real case study.
• Assessment of available potential of water resources and hydrological regime ofNam Sebang Hieng River Basin• Assessment of hydropower developments and climate changes in Xebanghieng
River Basin• Application of DSF, models and tools to support water resources planning in theXebanghieng River Basin• To identify rooms for other supplementary models and tools•
Scope of the case study• Hydrological regime change of the basin using Soil Water Assessment Tool(SWAT)• Hydrological regime and water use of the basin using Integrated Quality &Quantity Model (IQQM)• Hydrodynamic (hydrological movement/flood) of the basin using
Hydrodynamic Model (ISIS)• Results interpretation using Impact Analysis Tool
• Reporting work
MODEL APPLICATION
Hydrological Model
Soil Water Assessment Tool (SWAT) is the hydrological model used for study onhydrological regime change against the development projects growth cause to thechanges of other factors in Xebanghieng basin.

Data used2

Requires rainfall data is collected from rainfall stations appear below:
Table 1: Rainfall data used

Rainfall data used
NoNameFrom MRC & DMH

1Seno

1985-04

2

Donghen1986, 88-05

3

Kongkok

1989-2005

4

Khemarat (Thailand)

1985-2004

5

Meuang Phine

1991-2005

6

Xepone1990-2005

7

Saravan

1987-2005

8

Khe Sanh (Vietnam)

1980-1995

The daily water level and run off of the basin is collected from hydrological station
located in and outside of basin “in case data gap filling is needed”. Data are obtained
from the Department of Hydrology & Meteorology, Ministry of Agriculture andForestry (now under the Water Resources & Environment Administration ‘WREA’),
Waterways Administration Division, Ministry of Communication, Transport, Post andConstruction (now Ministry of Communication & Transport). Besides the two mainagencies, most data were received from Mekong River Commission Secretariat“MRCS”.
Other data requirements for the study are as follow:
••
•
•
•

Geological map
Climatic and meteorological data: temperature, relative humidity, wind speed,solar radiation, evaporation…
Irrigation structures includes: existing and planning irrigation areas,irrigation’s schemes, pump capacity, water requirement in m3/ha…
Water supply
River long profiles & cross-sections

SWAT Model setup
The Xebanghieng Basin is delineated into 24 sub-basins with the total area of 19,712
Km2. The figure below shows the result of Xebanghieng Basin after delineation into.

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Figure 2: Delineation of Xebanghieng Basin into 24 sub-basins.

Figure 3: SWAT Calibration Result at Kengkok station

Hydrodynamic model

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ISIS is hydrodynamic model, it function is possible to use for calculation the inundatedarea (flood depth and duration) of Xebanghieng Basin,ISIS Model set up
Due to location of Xebanghieng, particularly Ban Kengdone and the neighbor villages isflat and the Luang pone connects to the Xebanghieng river by a small sub-tributary,
therefore this region have been flooding regularly. The study on the flood behavior of thisarea is referred to the flood map which was produced in 1996 by the Department ofIrrigation, Ministry of Agriculture and Forestry (MAF).

Figure 4: River cross-section (34- measured & 56-interpolated)
The study area covers from upper boundaries (Sechamphone, Sexamsay andXebanghieng) down to the junction with Mekong River. The derived river crosssections from the survey about 34 and from interpolation of about 56, in total of thewhole area is 90 cross-sections were applied to simulate the flood duration and flood
depth of the area. There is no gauging station for water level at the river mouth ofXebanghieng, therefore the calculation of water level by slope from Khemmalatstation, which is located upstream of the junction (Xebanghieng river mouth) about 15Km.

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Figure 5: ISIS Schematization.

ISIS model result
The model result by comparing the simulated and observe data at selected station, theresults hydrograph can show the differences between simulated water level and theobserve water of the year 1996.

Figure 6: Calibration results of ISIS

6Figure 7: Hydrograph of ISIS result compared between Base Line & Scenario @Kengdone

Figure 8: Hydrograph of ISIS result compared between Base Line & Scenario @Kengkok7

The purpose of ISIS application in Xebanghieng Basin is to analyze of flood behavior
flood this area, particularly flood duration and flood depth, using ISIS model result to
produce flood map by using Delta-Mapper and compare with the base line. Base line
condition is based on flood map of the year 1996, which produced by Department ofIrrigation, Ministry of Agriculture & Forestry.

Figure 9: Base line condition of ISIS Scenario (flood map)

Figure 10: Map of flood depth comparison between base line condition & climatechange scenario

8Table 2: Summary of flood depth Values
Depth(m)Area(ha)No.

% of Increased
BaselineScenario

1

1-3

15,78014,776(6.36)

2

3-5

10,0219,876(1.45)

3

5-7

6,869

14,022104.13

4>7

11,08233,036198.1143,752

71,71063.90

Total:

Figure 11: Map flood duration comparison between base line condition & climatechange scenario

Table 3: Summary of flood duration
No.

Duration

Area(ha)Baseline

Scenario% of Increased

1

1days

112,140

94,158(16.04)

2

7days

4,034

3,602

(10.71)

3

15days

4,255

5,282

24.14

4

1mths

5,541

5,847

5.52

52mths

6,656

14,323115.1963mths

3,508

8,050

129.4874mths

2,269

5,920

160.9185mths

2,508

4,984

98.72

9

6mths

867

3,364

288.00107mths

17,397

24,14338.78

159,175

169,673~7

Total:

9CONCLUSION1
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3Results obtained from the Xebanghieng Case Study can show the area under risk offlood in baseline, hydropower and climate change scenario.
Dam Scenario; by adding one dam at Xepone and two dams at Xelanong, the peakflow in the wet season is cut off natural flow regime, thus make opportunity offlood reduction for the risk area, and flow increase in the dry season, this mean theavailability of water use also increase due to the dam operation. The data use istaken from real development plan.
Similar case study in other river basin throughout the Lao PDR, namely NamNgum, Nam Ou, Xebangfai, Xekong and Xedone river basins were carried out by
national modeling team.

RECOMMENDATION
In order to make the flood hazard map, it is required to have satellite images of thestudy area. Further in-depth study of flood in the Xebanghieng Basin as well as
dissemination to local communities is recommended.

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