The process of determining annual recession rates shall include preparation of recession-line base maps, measurement of recession distances on the recession-line maps, and calculation of annual recession rates.
(A) Recession-line maps shall be prepared using the following procedure.
(1) Base maps shall be constructed using the most currently available imagery. Types of base-map imagery may include, but are not limited to, aerial photographs, remote sensing imagery, digital data, or some combination thereof. Criteria used to select base-map imagery shall include, but are not limited to, complete synoptic coverage of the Ohio shore where the shore is centrally located on the images, adequate geographic reference points, and resolution that is adequate to map a base recession line and identify cultural and physiographic features on the imagery.
(2) The resulting base maps shall be produced at a nominal scale of one inch equal to two hundred feet; the scale of the base maps shall be verified with field measurements not less than five hundred feet in length, and the true scale in feet shall be noted on each individual base map.
(3) A base recession line shall be mapped on the recession-line base maps as described in paragraph (R) of rule 1501-6-10 of the Administrative Code.
(4) Historical imagery used to prepare recession-line maps shall be selected from charts, aerial photographs, or other imagery of the shore which are on file at the department of natural resources, division of geological survey. Criteria used to select this imagery for recession-line mapping shall include but are not limited to those criteria listed in paragraph (A)(1) of this rule. Imagery shall be acquired within a time period of not less than ten years nor greater than thirty years prior to the year that the base-map imagery was acquired.
(5) Recession lines from charts, aerial photographs, or other imagery shall be projected or digitally transferred onto the base maps.
(B) Recession distances shall be measured at points uniformly spaced along the base recession line. The recession distance at each point shall be measured from the base recession line along a transect oriented at a right angle to the general trend of the base recession line (figure 1). Each transect shall be uniquely identified and the measured recession distance shall be recorded and used to calculate the annual recession rate.
(C) For each transect, the annual recession rate in feet per year shall be calculated by dividing the measured recession distance by the time period in years between the recession lines. The minimum annual recession rate shall be zero feet per year.