(a) subdivision easements across lots or centered on rear or side lot lines shall be provided for water, sewage and drainage where necessary and shall be at least ten feet wide.

(b) Where a subdivision is traversed by a watercourse, drainageway, channel or stream, there shall be provided a stormwater easement or drainage right-of-way conforming substantially with the lines of such watercourse and such further width or construction or both as will be adequate for the purpose. Parallel streets or parkways may be required in connection therewith, except where fingers occur.