Mekong River Commission

1.1 Introduction

This Annual Flood Report for 2006 represents the second such document produced within the framework of the MRC’s Flood Management and Mitigation Programme (FMMP). The first Report for 2005 should be regarded as exploratory in that it uncovered the constraints and challenges that inevitably arise when seeking to produce a consistent and coherent account of each year’s Mekong flood regime and its impacts. Through discussion and feedback, this earlier account has helped to sharpen awareness of precisely what the objectives are and the document content and structure required to achieve them.

It now seems clear that the Annual Flood Report should aim to fulfil two primary roles. It should at one and the same time:

• Provide a sound summary overview of the flood conditions over the year in question. This material should be presented in a way that strikes a balance between technical and quantitative detail and the needs of the wider target audience, a large part of which will be non-technical. The text should realise the first objective of providing a prompt retrospective of the foregoing flood season and setting it within its historical context.
• The second role of the report is a longer term one. It should act as a repository for the appropriate data, which would cover the geophysical (hydrology, meteorology), geospatial (maps, GIS material, satellite images) and socio-economic (flood inundation, agricultural, damage surveys ) aspects of the flood regime and its impacts. These data will in time accumulate to provide a primary regional resource for flood research and the collation of historical reference material. Such data should be clearly set out in appendices and might also be stored digitally.

It is self evident that any appraisal of flood conditions in a given year must be considered within their historical context. This 2006 Report therefore gives this aspect very particular attention and presents a number of ways of setting out the data in the form of summary graphics that, it is suggested, are a far more effective means of gaining insight than simply tabulating the unprocessed data and information. If the structure and content of the Flood Report from year to year is to be consistent, it is also the case that a number of these graphics will need to be adopted as a standard.

A final theme needs to be emphasised at this point. Conventionally, floods and flooding are perceived as geophysical hazards within a common framework of natural disasters that also covers storms and hurricanes, earthquakes, volcanic eruptions, landslides and tsunami. In each case, socio-economic losses and damage increase exponentially with event magnitude and as a function of civil exposure and vulnerability. Such hazards are perceived as random events with entirely negative impacts, ignoring the fact that floods also have a positive ecological and socio-economic function and that great civilizations have developed within flood plains,

where on the face of it, exposure and vulnerability have been high. Such societies have included Sumerian Mesopotamia along the Lower Tigris and Euphrates Rivers, the founding cultures of China in the Yellow River Valley and the Angkor civilization of the Lower Mekong Basin itself. Exploiting the benefits and avoiding the risks of the annual flood stimulated such societies to put greater efforts into social organisation and water management systems, which endorsed them as landmark civilisations.

Historical cultures that exploited the benefits of floodplains and contemporary societies that continue to do so, such as those in the Lower Mekong, therefore face a ‘two-tailed’ flood hazard. (see Webby et al, 2006). Either the annual flood is too small, leading to reduced agricultural output or too large, resulting in inundation, crop losses and general socio-economic damage. The dis-benefits arising from the ‘failure’ of the flood season must not therefore be ignored or even made light of. As will be seen, historically some of these deficiencies in the flood season hydrology of the Mekong have been quite spectacular.

1.2 Report Structure and Summary of Contents

The main text of the Report is laid out in such a way that there is a logical progression from the creation of an awareness of the nature and history of the flood regime of the Mekong towards a specific evaluation of events in 2006 and how they lie within this historical context. The causes and impacts of flood conditions during the 2006 season are evaluated, with the Country Reports, providing the major sources of information and data. The main text focuses on the interpretation and summary of this material, which is collectively presented in detail in the Appendices for reference purposes. An objective has been to keep the length of the main text modest and tabulate the minimum amount of data required, leaving it for presentation in the Appendices. The appendices also provide the results of a statistical analysis of the discharge data at the major hydrometric stations on the mainstream and the water level data in the Tonle Sap system, the flood plain regions and the delta. There is, in addition, a summary tabulation of the key quantitative features of the major historical flood events at each site, along with the current rating equations, specifying the relationship between water level and depth. The assembly of such material in the Appendices broadens the utility of this Annual Report to provide a basic source of reference.

  

Figure 1. Comparative hydrological regimes of temperate (left) and monsoonal (right) river systems.