Surface water balance and future water demands under environmental flow requirements, Nam Xong Watershed, Laos

Author: Phousavanh Fongkhamdeng

Fongkhamdeng, Phousavanh, 2019 Surface water balance and future water demands under environmental flow requirements, Nam Xong Watershed, Laos, Flinders University, College of Science and Engineering

Terms of Use: This electronic version is (or will be) made publicly available by Flinders University in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. You may use this material for uses permitted under the Copyright Act 1968. If you are the owner of any included third party copyright material and/or you believe that any material has been made available without permission of the copyright owner please contact with the details.


The abundant water resources in the Nam Xong Watershed of Laos is readily available for the multiple uses of both socio-economic development and the environment. The competitive demands, land use, and climate change constraints are key challenges to sustainability of the water resources and its associated functions in the watershed. Therefore, this research paper aimed at studying the surface water balance and projection of the future demands as well as minimum environmental flow requirement for effective water governance. To achieve this aim, the rainfall runoff method in the Water Evaluation and Assessment Planning (WEAP) model package was employed in this study. Three predicted scenarios were constructed for the future water demands projection, namely increases of the irrigated agriculture, population (domestic use), and industrial production units. The current account year was set in 1997, and the future projection period was from 1998 until 2040. The paper then presented and discussed the results of the model simulation and analysis to enable understanding of the watershed water resources conceptualisation. The surface water resource in the Nam Xong Watershed is relatively abundant in terms of its total water inflows into the watershed system every year. The total water availability amounts to approximately 25.5 billion m3 per annum, while the total current water demand is approximately 135.88 million m3/y. Of the primary users, the agriculture sector shows the highest water demand of approximately 129.84 million m3/y, and 4.94 million m3/y and 1.09 million m3/y for the domestic and industry sectors, respectively. However, by the year 2040, the average annual water demands are expected to have dramatically increased, especially in the agriculture and industry sectors. The agricultural water demand is anticipated to increase from the current use of about 129.84 million m3/y to about 159.73 million m3/y, or an increase of 1.2 times from present levels. Notably, according to the study scenarios, the industry water demand will also significantly increase from 1.09 million m3/y to approximately 146.86 million m3/y, or an increase of 135 times. Furthermore, the domestic water demand would also increase from 4.94 million m3/y to about 125.06 million m3/y or equivalent to an increase of 25 times over the present extraction rate. However, although the total water availability is enough to supply the growing needs of water users, inadequacies might potentially occur in some areas during the dry season, for instance February and March. In addition, the minimum environmental flow requirement was also defined for the study area. The potential minimum flow requirement for the Nam Xong mainstream is approximately 9.6 m3/s. This was determined by analysing the observed mean minimum and maximum flow at the Nam Xong dam station (upstream station), which considered as the most natural flow station at the most downstream of the watershed. Therefore, this minimum requirement is very important for the downstream livelihood of Lao communities, freshwater ecosystems, and environmental functions of the river. Although the available water resource in the watershed is relatively abundant and sufficient to meet the current and future water demands of Laos, including the environmental requirement, there are challenges and uncertainties of the increasing demands, land use changes, and climatic condition changes, which may pose some significant impacts on the watershed. Consequently, integrated water resource management and sustainable allocation is crucial, as is recognising the importance of capacity building and climate change adaptation, for the future of the watershed and equitable use of the water resources. Therefore, further research is needed to contribute to a better understanding of the water resource assets in the Nam Xong Watershed.

Keywords: Water balance, Water demands, Water availability, IWRM, Environmental flow, WEAP model, Nam Xong Watershed, Laos

Subject: Water Resources Management thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Strategic Professor Okke Batelaan