Moving Forward From the Flood – II

By Arif Belgaumi for The Express Tribune

The Indus, like the other rivers that originate in the Himalayas, carries an enormous sediment load — something in the order of 300 tons per square kilometre per year. The Himalayas, a relatively young mountain range, is comprised of soft rocks which are highly susceptible to erosion by the monsoon rains. In the past – every spring and summer – the Indus would bring the waters of melted snow and rains from the mountains, as well as millions of tons of sediment to the plains and eventually to its delta at the Arabian Sea. The sediment would be deposited along the river banks as the river flooded, and in the delta, in a vast fan that stretches several hundred kilometres out into the Arabian Sea.

In the last 150 years, with the construction of numerous levees, barrages and dams on the Indus and its tributaries, the natural flow of the river has been dramatically altered. To bring more land under cultivation, the course of the Indus has been restricted within its banks. Huge quantities of water – nearly 75 per cent of the total – are drawn off from the Indus for crop irrigation. Unfortunately, water management projects are engineered to control the flow of water and are rarely designed to address the enormous sediment load. Large amounts of water, drawn from the Indus for irrigation, limit the river’s ability to carry the sediment which settles in the river bed. Over the years this has resulted in raising the river bed well above the surrounding land. Even higher levees are then built to contain the river within its banks.

In its constrained state, the Indus is incapable of handling flood surges. Once the flood waters breach the levees there is no way for the flood waters to drain back into the river. This year, the flood itself was a short event; we have spent most of the last several weeks moving the water from one area to another, trying to spread it out and minimise its damage. The Indus and its tributaries naturally drain a vast area of this country. Our water management infrastructure has rendered them incapable of performing that function. In trying to convert the Indus into the equivalent of a vast domestic water system, whereby with the turn of a switch water can be tapped off as and when needed, we have severely compromised its ability to drain its watershed.

Similarly, dams will do little in the long run to control floods or even store extensive amounts of water for irrigation. Again, the sediment in the river is the determining factor. The Tarbela Dam, which was completed in the mid 70s and was a major engineering achievement for Pakistan, has already lost about 28 per cent of its reservoir capacity due to silting. In another generation, it is quite likely that the Tarbela’s water storage capacity will be reduced to nothing and it will simply function as a run-of-the-river hydroelectric power generator. That seems like an extremely short lifespan for a major infrastructure project which, during its construction, was responsible for an enormous socio-cultural and environmental impact on the surrounding region.

The Kalabagh Dam, or any other dam on the Indus, will likely face the same choice of a very high initial cost in terms of financial investment, population displacement and environmental cost, for diminishing returns over a relatively short lifespan. This is not to say that dams do not have their utility. The Tarbela Dam has been instrumental in revolutionising agriculture in Pakistan. But the benefits of large dams need to be weighed against the huge costs paid by the affected people and by the environment.

A balance needs to be struck between the needs for agriculture and domestic use and the need for the river system to sustain itself and its delta. New thinking on water management strategies must be introduced in Pakistan. More thought and effort must be expended on water conservation, reduction of wastage, and careful selection of low-water-consuming crops. This public discourse is sorely missing in Pakistan and needs to be initiated at the earliest so that we move forward from this calamity and establish a more productive relationship with the river that sustains our country.

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