Ecosystem-based flood and drought management in river basins

The vulnerability assessment approach allows to find the biggest problems in river basins. For this assessment the approach was based on GIWA (Global International Water Assessment Methodology) & HSAP (Hydropower Sustainability Assessment Protocol) and follows a 6 step approach including the following: 1) geographical scaling (mapping of hot spots) defines the geographic boundaries of the pilot areas to be analysed; sub-regions are identified within each project area and major hydro system features and economic activities are mapped out; 2) scoping by assessing environmental and socio-economic impacts and establishing priorities among the major concerns and issues as well as tracing the root causative factors behind the selected concerns and issues; 3) data collection; 4) modeling for verification and quantification of root-cause relationships with either physically deterministic or conceptual models covering a) hydrologic modeling with TalsimNG software, b) erosion and sedimentation modeling with Modified Uniform Soil Loss Equation (MUSLE), c) water quality modeling with GISMO software; 5) assessment to identify risks and uncertainties and to prioritize vulnerabilities; 6) Identification and ranking of potential EbA measures.

The living weir concept is an EbA Measure, which is based on the knowledge of the local communities in the river basin and in line with the King of Thailand’s Sufficiency Economy Philosophy to apply technologies based on local resources and know-how. In a first stage a bamboo grid construction is constructed in the river providing structure for degradable sand bags containing a mixture of sand, coconut coir and manure. Along the riverbanks a combination of Banyan trees (Ficus bengalensis) and other leguminous plants is planted to stabilize soils. The wide rooting banyan trees are planted on both side of the weir, The roots that they are forming will nurture from the manure and will penetrate in the bamboo construction over the next decades to form a “living weir”. This technology entails several benefits such as improving ground water recharge, which can increase the crop yields, increasing biodiversity, such as increasing in fish habitat, variety of plants etc. and strengthen unity among related stakeholders. Terraces also allow fish to move upstream. Maintenance costs and efforts for this methodology are low and can be easily conducted by the local communities.

The set-up of river basin committees, representing the population within a river basin as well as academia, government and others is crucial for the success of river management. The connection between the local population and the water resources, especially in the Tha Di river basin, is very strong. Within the local communities knowledge on changes in climate and natural disasters (flood and drought events) has been passed down from generation to generation without much written documentation. The concept of flood protection via living weirs originated from the local riparian communities and strong leaders with innovative ideas and the willingness to experiment different approaches for flood and drought protection. Combining this strong ownership with hydrological data from local universities and the administrative capacity from the regional governing institutions allows for a holistic water management approach. All these actors are represented within the river basin committees.

The set-up of site visits and exchange of stakeholders and decision makers between the three different pilot river basins was a great method to foster exchange and mutual learning on potential EbA measures across river basins and across institutions. This exchange triggered important exchange on the feasibility of measures, their application in different locations and the possibilities for upscaling. Further, on one hand a friendly competitive spirit could be sensed in regards to which river basin would have the better ecosystem-based water management sooner. On the other hand, institutions which are in competition to each other came together and started cooperating.

Key capacities for setting-up a sustainable river management, namely hydrological modeling, vulnerability assessments on future floods and droughts and economic valuation methods for identifying suitable ecosystem-based adaptation measures were built on the local and national level. The project introduced drone technology for monitoring the watershed and to improve modeling of future flood risks. A series of trainings, developed together with German research institutes and practitioners, was conducted, containing both theoretical background and practical application in the river basins.