WEAP modelling for understanding river basin dynamics

By Tho Nguyen, ISET-Vietnam

There a many facets to the existing problems facing Da Nang city and Quang Nam province of Vietnam related to their shared Vu Gia – Thu Bon river basin. These range from changed patterns of flooding, increased water shortage, to elevated surface water pollution and salinization, all of which can be connected to a certain extent to the development and operation of hydropower reservoirs upstream of this cross-boundary river system.

A Prime Minister decision was issued in September 2015, providing rules for the operation of the multiple reservoirs in this river system (Decision 1537), but this operation protocol seems not effective enough. As Quang Nam and Da Nang continue to struggle with water management challenges, the damages and risks to people, property and production continue to expand in the context of climate change, population growth and economic development.

The official establishment of the Coordination Board for Integrated Management of the Vu Gia – Thu Bon river basin and Quang Nam – Da Nang coastal areas earlier in August 2017 was a major milestone in the two provinces’ collaborative effort for resolving their existing water conflicts. It was based on the understanding of their inter-connected development risks and challenges, threaded together by the flows of the Vu Gia, the Thu Bon and their many branches.

A focus area of action of the newly formed river basin organization (RBO) was the construction of a Water Evaluation and Planning (WEAP) model for the entire Vu Gia – Thu Bon river basin. This activity was initiated by a project led by ISET under the Global Resilience Partnership (GRP) program in the months leading to the RBO’s official establishment, and will be strengthened with the support of the operating RBO. A versatile river basin model not only looking at water supply, demand, and infrastructure, but also hydrologic interactions to describe runoff and irrigation dynamics, the WEAP model is expected to capture the complicated nature of the inter-dependence of the Quang Nam and Da Nang, provide nuanced analysis of different water management options, through which to build understanding and inform policies and decisions for integrated management of the river basin.

The standing working group under the RBO, consisting of technical staff from key departments and agencies in the two provinces (especially Da Nang Department of Meteo-Hydrology and Climate Change, and Quang Nam Division of Sea and Islands), is charged with the responsibility to work with ISET experts on the WEAP model development and analysis. A great advantage for this work is the expertise and WEAP modelling results that Da Nang city had inherited from a water assessment project funded by the Rockefeller Foundation, finished in 2016. The WEAP model for the Vu Gia – Thu Bon basin is being built upon this existing model of Da Nang.

An extensive three-day training was organized in Tam Ky city of Quang Nam from September 11-13, in which Dr David Yates—ISET’s consultant from the National Centre for Atmospheric Research (NCAR) and an experienced WEAP specialist—provided the working group members, especially those from Quang Nam who are less familiar with this modelling tool, with both detailed theoretical background of WEAP’s functionalities, and opportunities to play around with the tool’s applications for the practical problems of their own river basins.

Following this training workshop, on September 15, 2017, ISET and the RBO organized a shared learning dialogue (SLD), its first major event since official establishment in August, and the third in a series of such events under the GRP project. A key objective of this SLD is to share and initiate discussion over initial WEAP modelling work. In this workshop, Dr David Yates presented the Vu Gia – Thu Bon-level WEAP model, in which four scenarios related to the inter-reservoir operation protocol was integrated:

• Scenario A: Pre-development (no reservoir storage or diversion)
• Scenario B: Reservoir management according to current (Decision 1537) protocol
• Scenario C: Wet Protocol Sensitivity (increase the maximum flood Level to near capacity)
• Scenario D: Dry Protocol Sensitivity (triple the Dak Mi 4 release for both intensive and normal period)

Many of the resulted model outputs are consistent with actual data, as confirmed by participants at the workshop, suggesting the model’s credibility in reflecting actual water dynamics in the river basin. However, it was emphasized by the WEAP expert that the model is still in an early phase of its development, and that the presentation is merely to illustrate what the model can and cannot do, through which to generate discussions on how the model can be useful in assisting related water management strategies. It is therefore premature to make any conclusions or draw any recommendations from the current model outputs.

Discussions by the working group members and project experts resonated on the need for further model refinement and filling of data gaps, especially on historic reservoir storage, rainfall (especially upstream of reservoirs), and historical inundation in downstream floodplains. In addition, one of the important questions for the model to answer will be related to the water diversion structure at the Dak Mi 4 reservoir on the Thu Bon River, an issue of great concerns of both provinces. The modelling team will take all of these points forward for further refinement and framing of the model to best suit the project’s objectives—which are to best understand the different trade-offs facing Quang Nam and Da Nang in the management of their flooding and water resource risks, and to promote new policies and courses of actions to manage these risks and promote sustainable and inclusive development in both provinces.

In addition to discussions on the WEAP model, the SLD also discussed results of community vulnerability assessments conducted by CARE International experts in five communes of Da Nang and Quang Nam, with the purpose of understanding specific historical events and their impacts, improving flood and drought responses, and formulating risk reduction plans for the communities and its most vulnerable members. The local working group also presented a proposed project for installing water quality monitoring facilities in the Vu Gia – Thu Bon river system.

The next shared learning dialogue event of this project is planned for the end of October 2017.