Dr David Petley’s report on the Attabad landslide lake

March 31, 2010 - PRLog -- This report provides a summary of the key findings of a visit to Pakistan, including a short field visit to the landslide dam at Attabad in Hunza. A full report will be available within a few days. This report makes a series of recommendations regarding management of the hazard at Hunza, and both upstream and downstream, for consideration.
Key recommendations include (NB this list is not exhaustive):

There is a substantive risk of an outburst event caused by the landslide dam in Hunza;
An outburst event is most likely during or shortly after water flows across the spillway. However, such an event could be triggered by a range of other processes, some of which may provide little warning;

If such an event occurs, there is the potential for a large flood wave to travel downstream as far as Tarbela Dam. This wave would greatly endanger the downstream population and could cause damage to infrastructure;

The safe level is considered to be 60 m above the current river level, although further, more details work should be undertaken to verify this. Populations located between the river level and the safe level should be evacuated prior to the arrival of the wave. This will require precautionary evacuations for those people living immediately downstream of the dam; and emergency evacuation plans for those further downstream.

There is also substantive risk to people living close to terrace edges and on unstable slopes; these populations should also be protected through evacuation;
A flood wave would also cause substantive damage to infrastructure downstream, and the impact of the flood will pose problems in terms of livelihoods and welfare.
If the dam does not breach in the initial flow event, an expert group needs to be convened to determine the point at which an all clear can be given. This group must be convened before the overtopping event starts.

If the dam does not breach there will be a long term hazard at the site that will continue to threaten downstream communities. This will require a long term monitoring effort and a disaster plan to move the affected population at short notice. Management of this hazard will require considerable investment;

There will be substantive impacts on the upstream communities regardless of the future state of the dam. The nature of these impacts depends upon whether a collapse event does occur;

Whilst constructing the spillway is undoubtedly an appropriate first step, a great deal more work is urgently required in terms of the management of the hazard, in particular outside of the area between Attabad and Gilgit, which Focus are working upon. The downstream communities are facing a level of risk that is not tolerable – immediate action is required at national level to protect the population between Attabad and Tarbela Dam.
Thought is needed regarding the decision to protect the dam against erosion. Consideration should be given to intentionally allowing an outburst event with an evacuated population in order to manage the landslide hazard;

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