Executive Summary

Disaster signifies extreme impacts suffered when hazardous physical events interact with vulnerable social conditions to severely alter the normal functioning of a community or a society (high confidence). Social vulnerability and exposure are key determinants of disaster risk and help explain why non-extreme physical events and chronic hazards can also lead to extreme impacts and disasters, while some extreme events do not. Extreme impacts on human, ecological, or physical systems derive from individual extreme or non-extreme events, or a compounding of events or their impacts (for example, drought creating the conditions for wildfire, followed by heavy rain leading to landslides and soil erosion). [1.1.2.1, 1.1.2.3, 1.2.3.1, 1.3]

Management strategies based on the reduction of everyday or chronic risk factors and on the reduction of risk associated with non-extreme events, as opposed to strategies based solely on the exceptional or extreme, provide a mechanism that facilitates the reduction of disaster risk and the preparation for and response to extremes and disasters (high confidence). Effective adaptation to climate change requires an understanding of the diverse ways in which social processes and development pathways shape disaster risk. Disaster risk is often causally related to ongoing, chronic, or persistent environmental, economic, or social risk factors. [1.1.2.2, 1.1.3, 1.1.4.1, 1.3.2]

Development practice, policy, and outcomes are critical to shaping disaster risk (high confidence). Disaster risk may be increased by shortcomings in development. Reductions in the rate of depletion of ecosystem services, improvements in urban land use and territorial organization processes, the strengthening of rural livelihoods, and general and specific advances in urban and rural governance advance the composite agenda of poverty reduction, disaster risk reduction, and adaptation to climate change. [1.1.2.1, 1.1.2.2, 1.1.3, 1.3.2, 1.3.3]

ABSTRACT

There are nearly 40,000 large dams in the world, increasing around 250 a year. More reservoirs need to be built, in developing countries, for anticipated population growth, upgrading standard of living, urbanization, flood control, hydroelectric energy, and so on. In developed countries, however, instead of reservoir construction, more emphasis will be placed on demand management and efficient use and reuse of water to meet higher environmental quality needs. Climate change would increase the importance of reservoirs but societal adaptation measures should precede the physical counteractions. The average sedimentation rate to fill reservoirs in the world may not be very high, but the rate is much higher in East and Southeast Asia where many reservoirs would suffer from sedimentation problems in the latter part of the twenty-first century. Reservoirs are the most important component for risk and uncertainty management of water resources systems. But for a reliable and robust water resources system, an integrated management and the administrative structure that makes it possible are most important. The integrated management is also the key strategy for sustainable reservoirs and water resources management.

INTRODUCTION

Reservoirs are indispensable to utilize running water for sustaining life and civilized activities. They must have been built ever since the beginning of human history and clearly since the emergence of irrigated agriculture. The oldest ruin of a dam may be the Sad el-Kafara Dam, 30km south of Cairo, Egypt (length 104m, height 11m and storage capacity 0.57 · 106m3), that was built around 2800 B.C. for water supply, and believed to be destroyed by the first hit of a flood (Biswas 1970).