Canche

The river Canche (; ) is one of the rivers that flow from the plateau of southern Boulonnais and Picardy, into the English Channel, of which the Somme is the largest example. It is long. The basin of the Canche extends to and lies in the south of the département of Pas-de-Calais. Forming an alluvial valley from wide, the Canche valley also contains marshes, meadows and small woods. The gentle gradient, averaging 1.5 percent, gives the river a meandering course.

The river rises at Gouy-en-Ternois and passes Frévent, Hesdin, and Montreuil-sur-Mer before leaving the chalk to flow to the coast between Étaples and Le Touquet-Paris-Plage. Its principal tributaries are the Ternoise, the Planquette, the Créquoise, the Bras de Bronne, the Course, the Dordogne (not to be confused with the Dordogne) and the Huitrepin which all join on its right bank, i.e. to the north of the Canche. The lie of the land means there is no notable tributary from the south until the Grande Tringue, which flows from marshland into the small, dredged estuary.