Published online 20 August 2010 | Nature | doi:10.1038/news.2010.424

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Pakistan faces long-term damage to irrigation system

Second wave of flooding overloads canals.

floodPakistan's floods have already displaced millions of people.Picture Alliance/DPA/Photoshot

Pakistan faces a critical week as flood surges continue to destroy homes and farmland. In a desperate effort to prevent further damage, water is being diverted from the swollen Indus River into irrigation canals. But engineers are warning that these canals are becoming swamped, threatening the infrastructure that will be crucial to the country's recovery.

The unrelenting, intense rainfall over the past three weeks has resulted in two surges of floodwater. These have flowed from the high ground in the north of the country along the Indus River tributaries, gaining momentum and volume as they make their way to the Arabian Sea.

The first surge caused vast damage because "the ground was so hard and dry — when the first rains fell, the runoff was huge," explains James Dalton, Water Management Advisor for the International Union for Conservation of Nature Water Programme, headquartered in Switzerland.

As the first surge travelled south, it gave northern regions some respite from the fast-flowing floods as the ground began to absorb some of the water. But "now the ground and soils are saturated and the waters have nowhere to go apart from across the surface," says Dalton.

Last week, the northwest Khyber Pakhtunkhwa region was the worst hit (see 'Pakistan's floods: is the worst still to come?'). Now, more southerly provinces have been inundated, with the Pakistan Meteorological Department reporting that flood surges have arrived in the southeastern Sindh province.

There, "the second flood wave has merged with the first flood wave," says M. Akram Anjum, chief meteorologist of the Pakistan Meteorological Department. "The second flood wave is likely to create exceptionally high flood levels over the next three to four days in and around the Kotri area [in Sindh], and the high flood situation will remain until the end of this month."

flood mapLatest map of flooded areas in Pakistan. Click for larger image.JRC

The surges are putting intense pressure on the embankments along the Indus and the barrage gates that control the flow of the river. The Pakistan Irrigation and Power Department has declared many embankments along a 160-mile stretch of the Indus in the Sindh province to be in danger of breaking.

But experts believe that the management of the flood waters may present a longer-term problem. Chris Davey, project director for Mott Macdonald, a British management, engineering and development consultancy specializing in water and resource management, is leading an irrigation project in Sindh. Based on conversations with his engineers currently working in Pakistan, he says that "the main barrages have all stood up to failures". "But the way the authorities have controlled the flood water is different to normal."

The first signs that something strange was happening were measurements earlier this week from the Guddu and Sukkur barrages, two of the largest barrages in the Sindh province, where more than 25,000 cubic metres per second of water was flowing down the river. But at the Kotri barrage, just a few hundred kilometres downstream, the flow was much lower. That's because the excess water is being diverted into the canals.

"Officials have been opening gates to canals in an attempt to pass water down the canal system to relieve pressure on the barrages," says Davey. "The problem is that flooding the canal system is not normal practice during the monsoon."

When the canals themselves show signs of breaking, controlled breaching is the only solution. In Jacobabad in Sindh, 300,000 people were evacuated on 13 August before a controlled breaching of part of the canal system, resulting in the surrounding area being flooded.

Those canals that are not breached still face problems from the silt-laden waters. "If too much silt is deposited the flow will be reduced along the canal gradients, and this will affect normal irrigation once waters recede," says Davey.

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Without adequate irrigation, severe food shortages will become even more likely over the coming months. The Asian Development Bank, which is leading the first assessment of the flooding, says that 80,000 livestock have already perished and that 2 million hectares of crops are still underwater.

Farmland will likely not be ready for rice planting later this year, adds Etienne Labande, deputy chief of the Preparedness and Response Branch at the UN World Food Programme, and food stocks are running short. "Millions of families may have lost their personal grain stores in the flood water and chaos." 

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