Flood prone area delineation at the Tapi river basin, Thailand

Flooding is the most important catastrophe, ranking the first position among other natural disasters with the increasing trend of frequency and severity. Flooding has generated the devastating impacts on human lives and their belongings, especially in the flood prone areas all over the world. Flood prone areas are attractive places to settle due to their beneficial characteristics e.g. high soil fertility, convenient accessibility. Therefore people have to undertake all possible attempts to fight against flooding to keep themselves and their properties safely. There are two major distinctive measures distinguished: structural measure and non - structural measure.From the statistic, there is a remarkable aspect about the difference of the number of casualties and losses causing by flooding in Europe, America and Asia. This might be due to both structural and non - structural measures are applied together to mitigate flooding consequences in Europe and America while in Asia only structural measures are concentrated. Correspondingly, land use planning which is one of the primary causes of frequent and severe flooding becomes a more and more significant strategy. Flood prone area delineation is the beginning to achieve the land use planning and further development of sustainable flood mitigation strategies / policies.Subsequently, the flood prone area delineation is executed in the Tapi River Basin in the southern Thailandwhere more than 40% of total inundation in Thailand occurred. An assortment of tools were applied in the study: Arithmetic Average and Normal Ratio Method for data completion, Areal rainfall interpolation by Thiessen polygons, Rainfall Runoff analysis and Flow model simulation by SOBEK program and, lastly, Gumbel Type I distribution for extreme value analysis which would be later used to develop 3 initialconditions for further flood flow model.The Tapi River Basin has the area of 1.35 million ha, mostly is the river plain with the mountainous areas to the northwest and the east. Two major rivers flowing through the area converge together near three cities before cascading into the sea. Agriculture envelops the majority of the areas of which rubber trees, oil palm trees and orchards are predominant. The amount of rainfall is rather high due to its location and the influence of monsoon and depression.High intensity of rainfall is the main cause of flood in the area; in the meanwhile, a lack of maintenance of the floodway worsens the impact. The doubts of a sufficiency of drainage capacity and the water released from the dam are still existent among the stakeholders, therefore the further studies about these issues arerecommended. In case the capacity of the current drainage is not sufficient, from the preliminary study from the land use map, the expansion of existing drainage system including the natural floodway, by pass canal or retention basin are proposed for consideration.The results from the simulation can be concluded that the areas susceptible to flooding are along the riparian areas, particularly at the estuary downstream. This area can be considered as the sensitive areawhere the government and decision makers should pay more attention on due to high degree of urbanization and a lot of inhabitants. Although the quantity of runoff increases slightly, the flooded areasdownstream goes up significantly that can contribute to a higher degree of losses.The findings of vulnerable area to inundation from this study should be used as the basic information for the proper land use planning and zoning which should be applied in conjunction with the structural measures in order to achieve the sustainable mitigation strategies

Improving flood and drought management in agricultural river basins: An application to the Mun River Basin in Thailand

Agriculture productivity is regularly affected by floods and droughts, and the severity is likely to increase in the future. Even if significant efforts are spent on water development projects, ineffective project planning often means that they continue to occur or are only partly mitigated, for example, in the Mun River Basin, Thailand, where 1,000 s of water projects have been implemented. Despite this, the basin regularly experiences floods and droughts. In this study, an analysis of the adverse impacts of basin-scale floods and droughts on rice cultivation in the Mun River Basin is conducted, and an estimation of the coping capacity of existing measures. The results demonstrate that while the total storage capacity of in-situ and ongoing projects would be sufficient to tackle both hazards, it can only be achieved if the projects are effectively utilised. Based on this, proposed solutions for the region include small farm ponds, a subsurface floodwater harvesting system, and oxbow lake reconnections. The suggested measures are practicable, economical, environmentally low-impact, and their implementation (if executed with appropriate care) would reduce flood and drought problems in the basin. Notably, the measures and calculation methods proposed for this basin can also be applied to other crops and regions