For purpose of preserving the integrity of the Official Map of the Borough, no permit shall be issued for any building or structure in the bed of any street or public drainageway, flood control basin or public area reserved pursuant to N.J.S.A. 40:55D-32 et seq. as shown on the Official Map, or shown on a plat filed pursuant to this chapter before adoption of the Official Map, except as herein provided. Whenever one or more parcels of land, upon which is located the bed of such a mapped street or public drainageway, flood control basin or public area reserved pursuant to N.J.S.A. 40:55D-32 cannot yield a reasonable return to the owner unless a building permit is granted, the Planning Board, may, in a specific case, by an affirmative vote of a majority of the full authorized membership of the Board, direct the issuance of a permit for a structure in the bed of such mapped street or public drainageway or flood control basin or public area reserved pursuant to N.J.S.A. 40:55D-32 which will as little as practicable increase the cost of opening such street, or tend to cause a minimum change of the Official Map, and the Board shall impose reasonable requirements as a condition of granting the permit so as to promote the health, morals, safety and general welfare of the public.