According to Bernier, what were the extensive canals in Bengal primarily used for?

Navigation and irrigation

The French traveller, Bernier, described seventeenth century Bengal in the following way: “The knowledge I have acquired of Bengal in two visits inclines me to believe that it is richer than Egypt. It exports, in abundance, cottons and silks, rice, sugar and butter. It produces amply — for its own consumption — wheat, vegetables, grains, fowls, ducks and geese. It has immense herds of pigs and flocks of sheep and goats. Fish of every kind it has in profusion. From rajmahal to the sea is an endless number of canals, cut in bygone ages from the Ganges by immense labour for navigation and irrigation.”