The City Planning Commission may grant special permits to allow adjustments in the boundaries of the designated open space on a zoning lot provided that such adjustment will not place the new boundary closer than 60 feet to a watercourse. As a condition for such adjustment in the boundaries, the Commission shall find that such adjustment will:
(a) result in a substantial improvement in the quality and usefulness of the designated open space; or
(b) permit development which better satisfies the purposes of this Chapter and that the new features which will be added to the designated open space will be at least equal in quality to those which are displaced from it; and
(c) provide an equivalent area replacement for the area removed from the designated open space.