Causation and avoidance of catastrophic flooding along the Indus River, Pakistan
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The catastrophic flood of 2010 along the Indus River began in July with unusually intense but not unprecedented rainfall in the upland catchment. During four months, close to 2,000 fatalities occurred and ~20,000,000 inhabitants were displaced. The meteorological events triggered but did not cause this “natural” disaster. Analysis of multi-temporal remote sensing and topography instead indicates that most damage was caused by dam and barrage-related backwater effects, reduced water and sediment conveyance capacity, and multiple failures of irrigation system levees. The numerous failures extended from upstream areas, where some record discharges occurred, to downstream reaches and the delta, where peak discharges were not extreme. In Sindh, Pakistan, two major river avulsions (sudden changes in flow location) occurred. At one of these (the northern avulsion), Indus water flooded ~8,000 km2 of agricultural land to depths of 1–3 m; part of the river flowed 50–100 km west of its pre-flood location. The avulsion was caused by breaching of the Tori Bund, an artificial levee upstream of Sukkur Barrage, on 6–7 August, two days before arrival of the first flood crest and long before attainment of peak river flow at Chacharan, 100 km upstream, on 24 August. The early breach, during the rising stages of the flood, permitted much of the incoming flood wave to feed the avulsion over a sustained period.
As was the case for the dramatic and temporary avulsion of the Kosi River, India, in 2008, the lack of planned accommodation to the river’s high sediment load and its super-elevation above the surrounding terrain set the stage for exceptionally dangerous levee failures and channel avulsions. Major translocations of river flow will continue to occur during large flood events whether flood warning is improved or not. The observed dynamics indicate that reinforcing the existing engineering structures is not a sustainable strategy for avoiding future flood catastrophes. Instead, planning for major water and sediment flow diversions is required for effective flood control along the Indus and other sediment-rich and avulsion-prone rivers.
Manuscript received 30 Aug. 2012; accepted 3 Oct. 2012