The writer is a freelance columnist.
As floods in Punjab and Azad Jammu & Kashmir for the fourth consecutive year leave behind harrowing tales of loss of life, destruction of infrastructure, livestock, property and cash crops, the debate amongst academics has veered towards a narrative that increasingly questions the utility and usefulness of dams and barrages. As the Multi-Sector Initial Rapid Assessment (MIRA) gets underway in collaboration with the United Nations Office for the Coordination of Humanitarian Affairs (UN-OCHA) to ascertain the exact damages caused by floods, the loss to the national economy is likely to be between $10 billion and $15 billion, more than what was caused by the 2010 flooding.
Those who advocate an approach of non-structural measures to contain floods base their opposition to dams and barrages on the phenomenon of sedimentation, massive investments on building of water reservoirs, embankments and dykes coupled with loss of natural sponges due to deforestation and drainage of wetlands.
All projects involving water storage and change in the courses of rivers are inherently controversial because they entail displacement of people, and destruction of inhabitation adversely impacting the ecosystem. The fact of the matter is that dams have traditionally proven their usefulness by virtue of their multipurpose role in water storage so critical to the economy, the populace and industry, inexpensive power generation and mitigation of flood hazards.
So far as sedimentation is concerned, it is a natural phenomenon which occurs in water courses whether dams are built or not. Siltation in reservoirs though, reduces their capacity but in no way exacerbates floods. Had there been no reservoirs, then the river beds would have risen due to years of siltation, and flooding would have increased because specifically in Sindh, the Indus flows at a higher level than the adjacent ground and is contained within bunds. So water courses/ rivers are prone to accumulate silt that cause the floodwater to rise in river beds thereby aggravating the severity of the flood. Negating the importance of dams on the basis of this phenomenon does not make much sense as the world has explored ways and means to control the phenomenon of sedimentation.
As for the massive investment involved in the building of dams/ barrages/ dykes and embankments, it is a globally accepted fact that the construction of dams/ water reservoirs requires huge funding; but they pay back their cost after a period of time. The decision to breach embankments/ dykes during peak floods depends on simple logic of minimizing losses as efforts are made to protect populated areas from flooding. Most of the barrages have been built for 100 year floods and fuse plugs have been incorporated in the side embankment to blow off in case the flood exceeds the safe design of the barrage. Normally, water is directed to less inhibited areas so that damages are less.
As the said story has pointed out, it is not necessary that dams mitigate floods. In the same way, there is no reason why dams cannot mitigate floods. Dams can only mitigate flood hazards if they have enough storage capacity. In the absence of dams/water reservoirs that trap a huge quantum of floodwater depending upon their storage capacity, flood losses are sure to grow manifold. Flood mitigation in two mega dams of Pakistan is incidental i.e. they can absorb the flood peak when they are not full. Even when they are full, they still dampen the flood peak by calculated surcharge in the reservoir when all outlets are open. Pakistan’s storage is less than 11% of average annual flows against 40% of the world average.
Chenab River enters the plain areas of Pakistan and does not have any storage along its route because construction of reservoirs is subject to certain geological and technical conditions. Marala and Trimmu barrages have small storage which cannot absorb floods. During floods, canals are also closed to save them from siltation and breaches. Trimmu barrage passed flood of about 6 lac cusecs equal to its design discharge. Proposed Chiniot Dam Project, if constructed on River Chenab, cannot play an effective role in flood mitigation as it has storage capacity of merely 1 million acre feet. Besides, it will cause a huge displacement of people.
In recent floods, the role played by the raised Mangla dam in taming peak floodwater, storing much of water inflows from River Jhelum and releasing only a small quantity merits special mention. Had the raised Mangla dam not been there to store peak inflows, floodwater of Jhelum and Chenab Rivers would have merged to cause a greater havoc at Trimmu and downstream than what has been witnessed now.
The role played by dams in flood mitigation can be measured from the example of China’s Three Gorges Dam that has saved the lives of 15 million people and protected 1.5 million acres of farmland in areas of the Yangtze River. In the absence of Three Gorges Dam, China experienced devastating floods after every ten years. The last such flood in 1998 caused the deaths of 14,000 people, left 14 million people homeless and dented the Chinese economy with a loss of $24 billion. Besides flood control, the Dam is also being used for the generation of hydroelectric power and navigation.
Unlike devastating floods in 2010 flowing down from Rivers Swat, Kabul and Indus, the recent flooding in Chenab and Jhelum Rivers was caused by cloud bursts and heavy rains in their catchment areas. Even areas of the country which normally record low rainfall experienced cloud bursts and thus recorded heavy rains. Floods can only be controlled and their consequent losses minimized if there are dams to trap their water. In case there is no dam in the way of floodwater, the magnitude of destruction can be too horrendous to imagine.
Building water reservoirs/barrages does not mean that non-structural measures cannot be adopted. Non-structural measures like monitoring precipitation, river and reservoir storages and flow measurements, forecasting, early warning, appropriate disaster warnings and strategy are important in flood management.
However, it is an internationally accepted norm to take structural measures such as construction of levees and embankments in addition to non-structural measures such as supplying timely information to people and evacuating them. In Pakistan, people dwell in the riverine areas in violation of laws. It is not the fault of the dams but the inability to adhere to the laws and orders of local authorities which is responsible for flood ravages.
In addition to flood mitigation, dams have played a key role in the sustainability of development by serving communities’ needs for fast-paced socio-economic growth. They have generated employment, decreased poverty and arrested the urbanization trend besides ensuring food security and the generation of the cleanest and cheapest power.http://nation.com.pk/columns/30-Sep-2014/to-dam-or-not-to-dam
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