Thai-German Climate Programme – Water: Feasibility study on the use of oxbow lakes for EbA solutions

General information

Client: GIZ/Thai-German Climate Programme (TGCP)
Location: Thailand,Phrae Province
Project duration: 01/2021 - ongoing
Key characteristics: Flood management, 2D hydraulics with HEC-RAS

Project description

SYDRO Consult has been contracted by GIZ Thailand to provide technical guidance on the development and implementation of Ecosystem-based adaptation (EbA) measures in the Thai water sector with a specific focus on oxbow lake ecosystems.
The objective of this study was to determine and assess the most suitable techniques to include oxbow lakes as an ecosystem-based adaptation option for a climate sensitive river basin management, taking into account of hydrological and ecological conditions of selected oxbow lakes in Yom basin.
The primary goal was to prevent and solve water- related problems. So the specified objective was the identification of alternative water sources in areas that lack water sources, develop new water reservoirs and water delivery system to the fullest potential and finding water sources for agricultural areas to expand the opportunities
Oxbow lake restoration responds to this need by accessing additional water sources for the time of the dry season due to the increase of the available storage volume. Together with managed abstraction the benefit for riparian water users can be maximized.

In the course of such study both 2D hydraulic modeling and hydrological modeling are key elements in assessing hydraulic processes, the impact of measures and water availability. It is an integral element of any oxbow lake restoration.
The 2D- hydraulic modeling software used for the feasibility studies is HEC-RAS 2D.

The resulting design concept provides the inlet resp. the intake structure as a key element for restoration, reconnecting the Yom River to an oxbow lake. It is composed of an intake basin as part of the Yom River cross-section, a rock ramp as outlet of the intake basin, a regulated weir connecting the intake basin with the oxbow lake and a levee protecting the oxbow lake during high flows in the Yom River.
Moreover the design concept of the oxbow lake consists of planned terraces for enhanced retention volume to provide more storage, a low flow channel as well as the outlet structure with a rock ramp which raises water levels in the oxbow lake, thereby increasing the available storage volume. A natural river stretch is located before the confluence with the main river.

In the case of this study the goal was to enhance water availability for users locating along the oxbow lakes.
Therefore, the approach chosen in this study differs from a purely nature-based solution and incorporates typical water management features. Water abstraction is the main purpose followed by enhanced infiltration, groundwater recharge and structured cross-sections to enable a hybrid use of flood terraces for more storage and adopted agriculture.

Services

• Communication with Thai authorities and stakeholders
• On-site drone surveys and bathymetric surveys for detailed orthophotos, DSM and topography
• Selection of suitable oxbow lakes as a result of site selection
• Setup of hydraulic models for each selected oxbow lake pilot site without measures (current state scenario).
• Setup of hydraulic models for each selected oxbow lake pilot site with measures: this results in restoration scenarios with different designs of connections of the inlet and outlet to the main river.
• Extensive elaboration of the feasibility report

Skills

• Hydraulic 2D modeling with HEC-RAS 2D and its evaluation
• Hydrological analyses and evaluations

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