The operator of a gas pipeline (DN 150; put into operation in 1962; burial depth of more than 1 m) located 100 m from the river Gave de Pau, which was flooding at the time, detected several problems (pressure fluctuations) on the Pierrefitte-Nestalas station at around 3:00 a.m. The firefighters were alerted at around 3:20 a.m. At around 4:00 a.m., on-call technicians reported that access to the pipeline was hampered (flooded roads, etc.). The pressure continued to drop and the leakage rate was estimated at 9000 Nm³/h at 8:30 a.m. A strong smell of gas was reported in the surrounding area. The monitoring and response plan was implemented at 9:00 a.m.

A discharge point was reported upstream of the Beaucens block valve station at around 10:00 a.m. The discharge occurred when the bank in which the pipeline was buried was swept away by the fast-moving current. The bare section of pipeline then broke off, folded in half due to the force of the water, and was carried away. The flooded areas were then surveyed by helicopter for other hazardous situations between the towns of Tarbes et Lacq from 10:00 a.m. to noon.

Once the flood had receded, a secure excavation area was created and work was started at around 7:30 p.m. to isolate the leaky section of the pipeline. This work was finished at 1:30 a.m. on 20 June. A dished bottom was placed on the depressurised section.

Natural gas is being piped in from other parts of the network to meet customer demand, especially for the coming winter. In light of this degraded operating mode, the gas pipeline will be rebuilt several hundred metres away from its original site. It is expected to be put back into operation in late 2014.

The operator of the pipeline estimates that 233,000 Nm³ of natural gas leaked out over the course of 17 hours.

The flooding of the Gave de Pau was notable for the extent of damage caused in the area, due not only to the heights reached but also to the change in the river’s bed and thus the course of its flows