In the 14th century (1310? or 1330?) , the combination of heavy snowmelt , major rainfall and a terrible storm in front of Capbreton accumulated masses of sand on the coast to the point of forming a bar facing the river Adour blocking suddenly the exit in this place . The Adour then rushes north over a width of 400 m , snatching everything in its path, crossing Ondres and the country of Labenne upstream , engulfing the neighboring ponds , absorbing the lake of Hossegor , ravaging the territory of Soustons to finally find in Plecq (now Vieux-Boucau: boucau = “mouth” in Gascon) an outlet on the ocean .
A new port is created : it is Port d'Albret . A secondary arm remains which joins the ocean at Capbreton , but it is impracticable for the not small vessels .
The people of Bayonne , who were saved in this way from a catastrophic flood , then found themselves about thirty kilometers from the mouth of their river . The port is in decline with competition from the ports of Port d'Albret and Capbreton , very active and close to the sea , even if Bayonne levies taxes on goods in transit on the river .FWIKI
King Charles IX ordered in 1562 to give the river a mouth in Bayonne . We begin to dig a direct channel from the city to the sea . Faced with the difficulty of this work , on February 8, 1571 , Charles IX appoints the engineer Louis de Foix to direct it .
Louis de Foix draws up a very complete estimate of the work to be carried out and obtains from Paris a provision of 30,000 pounds tournaments . We will soon be finishing the digging of the channel towards the Atlantic through the sand dunes . A dam and a new harbor were built at Trossoat , three kilometers from Bayonne , where the river then turned at right angles to the north .
These works continued under the reign of Henry III according to a plan providing that “[…] the closure of the river will have a width of one hundred and fifty toises [290 m] . It will be necessary to make a good carpentry capable of bearing the burden of the said river . It will include three rows of squared trees , shoed at the end , which will be sunk a fathom into the ground , or more if the ground permits . Seventy-five pillars per row , ending in a dovetail , to easily enter the male […]” . Also planned is the digging of a canal 900 fathoms long (1,800 meters) and 12 meters wide towards the ocean .
This dam was quickly replaced by a solid stone wall , the centerpiece of the new port of Bayonne . Difficulties of all kinds arise , Capbretonnais and Boucalais on their side do the impossible to thwart the work . The people of Bayonne are also worried about the increasing cost of the project and the requisitioning of labour .
It's a violent storm that will settle everything : the river Nive breaks in a sudden flood , threatens to engulf the whole city of Bayonne , but by a formidable flushing effect pushes the Adour which opens the new passage towards the ocean . It was on October 25, 1578 that Louis de Foix succeeded in “diverting” the Adour .
But the new estuary in Bayonne turns out to be unstable . It first drifts towards the south and Anglet , to form several winding passes near the "Chambre d'Amour" . Very quickly , a sandbank forms , a real shoal right across the estuary itself : the "bar of the Adour" .