What is the importance of reservoirs to water management?
Without a water supply from reservoirs, many of our agriculture based and industrial communities would have drastically reduced populations and economic activity. Management of reservoirs in many systems is a compromise between low flow augmentation and flood protection. In water-short areas, there is no compromise, only conservation.
How are the floods caused?
The floods are generally caused due to heavy concentrated rainfall in the rivers catchments, during monsoon season, which is sometimes augmented by snow melt flows. Monsoon currents originating from Bay of Bengal and resultant depressions (weather system) often result in heavy downpour in the Himalayan foothills, which occasionally generate destructive floods in main rivers and their tributaries. Sometimes exceptionally high flood flows in major rivers are generated due to formation of temporary natural dams by landslide or glacier movement (Glacier Lakes) and their subsequent collapse.
What are the flash floods?
The riverine floods take hours or even days to develop, giving ample reaction time to locals to prepare/evacuate. However, flash floods occur suddenly and unexpectedly and for a short duration. They are usually generated quickly with little warning/reaction time for locals. Flash floods can be extremely dangerous, instantly turning a babbling brook into a thundering wall of water and sweeping everything on its way downstream.
 Which organizations are involved in flood management?
Flood management is a multifunctional process involving a number of organizations. The government organizations, which play major role in the flood management, are the Provincial Irrigation Departments (PIDs), GB-PWD, Irrigation Directorate FATA, Irrigation & Small Dams Organization, Government of AJ&K, PMD/Flood Forecasting Division, WAPDA, CIW, Federal Flood Commission, Pak Army, NHA, Pakistan Railways, NDMA, Provincial Disaster Management Authorities, GB-DMA, FDMA, SDMA & DDMAs/District Administrations.
What is a recurrence interval?
Disaster experts classify floods according to their likelihood of occurring in a given time period which is called recurrence interval. A hundred-year floods, for example, is an extremely large, destructive event that would theoretically be expected to happen only once every century. But this is a theoretical number. In reality, this classification means there is a one-percent chance that such a flood could happen in any given year. Statistical techniques, through a process called frequency analysis, are used to estimate the probability of the occurrence of a given event. The recurrence interval is based on the probability that the given event will be equaled or exceeded in any given year.
Over recent decades, possibly due to global climate change, hundred-year floods have been occurring worldwide with frightening regularity. The effects of development (conversion of land from forested or agricultural uses to commercial, residential, or industrial uses) on peak flows is generally much greater for low-recurrence interval floods than for high-recurrence interval floods. During these larger floods, the soil is saturated and does not have the capacity to absorb additional rainfall. Under these conditions, essentially all of the rain that falls, whether on paved surfaces or on saturated soil, runs off and becomes streamflow. When a major flood occurs, you might have heard that the stream stage reached the “100-year flood level”. This means that a flood of that magnitude has a 1 in 100 chance of occurring in any year.