The Pakistani Spectator

This article will present analysis of flood which caused 1589 causalities left 2344 injured and 1,236,256 private house destruction.  The main emphasis would be at effective flood risk management measures to reduce flood damages.

The monsoonal storm forcing induced severe flood, hit Pak Himalayan and Karakoram Range, which form the collective watershed for Kabul, Indus, Jhelum and Chenab Rivers. Hitting of storm forcing to Indus and Kabul water shed coupled with almost 3000 mm rainfall in 6 days, make it highly unusual and exceptional event in the historical time line. The return period of such flooding is estimated of 500 years.

Pakistan is being fed by four major rivers; Kabul, Indus (Swat is tributary to Indus), Jhelum and Chenab located from west to east respectively and flow from north to south. These rivers normally receive moderate flow in winter due to snow and glacial melt, whereas, high flows in summer monsoon month; Late June to October due to storm system moving from Arabian sea to the mountains.

The flooding is not uncommon in these Rivers but the calamity worsened this year due to magnitude of flood and unavoidable flood wave synchronization at the confluence of Kabul with Indus and Jhelum Chenab with Indus. To make the situation further worse, the hill torrent hit the western cities of Punjab and Khaibar Pukhtonkhow, making them sandwich between Indus on one side and torrential flows on other side. Baluchistan mainly effected due to torrential flows. The problem of huge flooding in Sindh is due to the capacity constraint of channel to sustain the huge influx of flood wave within its banks.

The science of flood risk management is a strategy, to reduce the damages of floods while keeping its benefits. It include pre flood, during flood and post flood phases. The pre flood stage includes planning structure to cope with potential upcoming severe floods. The studies are conducted on all major rivers to determine the probability of flood occurrence. This yield the results in terms of 2 to 1000 or 10,000 year return period flood. On the basis of this statistics of flood discharges, the flood risk zoning maps are prepared which indicate the potential effected areas by each category flood. This risk maps are supposed to be the public document, therefore delivered to all potentially affected communities to give them an idea of risk in the area of their settlement and cropping.

In order to cope with this various category floods, the studies are conducted in planning phase to determine their impact on strategic assets, for example dams barrages and main bridges etc and the process to save them in case of flooding. The embankments are made to contain flood within certain periphery in the case of flood over flow channel banks. However, certain sections are marked along the river as breach sections. The breach sections are meant to breach the section in case of flooding to reduce the flood peak which may affect any strategic structure downstream are any major city along the River Bank. Normally the breach sections should have to be in the scarcely populated area with the proper warning to the settlers of breaching points. This phase normally determine that which cities and villages you want to keep safe in the case of flooding. However in the case of severe flooding the planner left with minimum options in developing countries because it need really big infrastructure to save every city in the case of severe floods. But the guide lines are easy to issue for new settlement of comparatively flood safe areas.

The flood phase includes the early warning bulletin much ahead of flood wave arrival. The flood warning lead time determine the time of evacuation. Normally this warning time vary from couple of days to week or even more depending on the location. This warning is effectively communicated to civil authorities to convey to general public. The communication method of flood warning and communication time is dominant factor in flood phase. In most countries all means of communication and propagation are used to inform the people of upcoming flood warning. The local civil services should have to be prepared to cope with the evacuation of big chunk of population as big as whole city in few days and should have to be aware of their resettlement locations in the pre flood phase.

In flooding, the decisions are made by decision support system to keep the damages of floods to minimum level by accepting one kind of damages and rejecting others to yield optimization with respect to social and economic impacts.

The post flood phase normally includes the assessment of damages and planning & operational mistakes. The valuation of damages is normally conducted by surveys, interviews and form filling from the effecters of their personal damage. Whereas, the public sector damage is assessed by comparison of the public sector infrastructure of pre flood stage with post flood stage.

Normally, the help is taken from GIS imagery of pre flood and post flood detailed high resolution satellites images and revenue records to assess the damage to live stalk, crops and houses.

The compensation mechanism to damage differs from country to country. In developed countries, the normal houses are normally ensured. Whereas, in other countries, sometimes government give subsidies on taxes etc, in order to contribute to the relief of the flood victims.

However, one question is vital in flood risk management and that is the avoidable damage. It the question at planning stage and to the policy makers that how much damage they are willing to take against each category flood. It is obvious that no one afford to build huge infrastructure to prevent entirely from 1000 year flooding but the floods of less magnitude could be planned to dealt effectively by keeping much damage in avoidable domain.

If the dams could contribute to reduce the flood damages? The answer is big yes. It would be certainly realized in post flood studies that Tarbela and Mangla would had played big role in attenuating flood peaks and buying more time for evacuation. The condition could have been much better if we had more dams at our disposal to further reduce the flood peak. The small dams on hill torrents could not only had saved lot of human casualties rather also brought sufficient water storage for next cultivation season.