The council of any county or county borough shall, in relation to any area within the county or borough and .not within a drainage district, have all the powers conferred on drainage boards by the last three foregoing sections, and accordingly those sections shall have effect as if—
(a)any reference therein to a drainage board included a reference to any such council; and
(b)any reference therein to a district of a drainage board included a reference to so much of a county or county borough as is not comprised in a drainage district.