(a) Terms used in this article shall have the meaning set forth in Subpart 645-2 and section 646-4.4 of this Title except the following terms, as used in this Subpart, shall mean:
(1) Designated stream corridor means the stream bed and the area extending 35 feet from the high water mark on each side of a stream.
(2) Existing development means buildings, structures, impervious areas, landscaped areas, utilities, and accessory structures present on the effective date of this Subpart.
(3) High Water Mark (HWM) of a stream means a line along the banks of a stream that is the approximate seasonal peak water level as indicated by the cut of the bank and the demarcation between terrestrial and aquatic vegetation. For the purpose of determining the high water mark, ponds of one acre or less within the stream shall be included.
(4) Landscaped area means an area of vegetation which has been actively maintained as a lawn, garden, hedge, or planting bed.
(5) Stream means an AA-special perennial stream designated or mapped by the department.
(6) Stream bed means the flow area of a stream at and below the high-water mark of a stream.