2 August 2010

Pakistan floods – the progression of the flood wave down the Indus River

Posted by Dave Petley

The floods in Pakistan appear to be starting to generate substantial interest in the UK, although this may in part be a result of the perhaps surprising decision of the Pakistan president to travel to London today.  Whilst the crisis continues to develop in the north of the country, of equal concern now must be the progression of the flood wave down the Indus River.  Of course Pakistan is a country built around the Indus – the green swathe that cuts north-south across the deserts of central and southern Pakistan (see image below) is essentially defined by the Indus and its tributaries.  The Google Earth image shows Pakistan with the various gauging stations and other larger settlements on the Indus:

The passage of the flood wave is rather well illustrated by this series of hydrographs, from the Flood Forecasting Division website.  The units are cubic feet per second – there are 35.3 cubic feet in a cubic metre.

The hydrograph for Besham, in the north looks like this.  The peak occurred around about midnight on 29th July.

A little further downstream lies Tarbela, whose hydrograph looks like this.  The peak occurred early on 30th July.  Note that Tarbela is a (very) large dam, so will probably have modified the flow somewhat.

 Further downstream lies Chsashma (see the map above), whose hydrograph looks like this.  Note that here the peak occurred late on 1st August:

And downstream again is Taunsa (see map above), where the hydrograph looks like this.  In this case the peak flood has yet to arrive.  However, already the flood is defined as “extremely high”.

Taunsa is 800 km from the mouth of the river as the crow flies (so over 1000 km along the length of the river), so it will take some days for the flood wave to reach the sea.  These lower reaches are mostly surrounded low lying land – the fabulous image below, by Najamuddin Bhatti, shows Sukkur on the banks of the Indus for example:

The reasons for concern about the potential impact of this flood wave downstream are clear.