E.     The commission shall determine, at the conclusion of a hearing, whether a proposed district is necessary and desirable. In making its determination of the necessity of a proposed district and in defining district boundaries, the commission shall consider:   

(1)     the need for the proposed district and its probable effect upon the public health, safety and welfare;   

(2)     the topography and composition of soils comprising the area of the proposed district;   

(3)     the distribution of erosion within the proposed district and within surrounding lands;   

(4)     the prevailing land-use practices; and   

(5)     the probable effect of the proposed district upon, and its relation to, watersheds, agriculturally productive lands and other extant or proposed districts.   

F.     The findings of the commission and its final determination shall not be limited solely to an evaluation of the facts adduced at the hearing or those set forth in a petition, but shall be predicated upon all reliable information available to the commission, including reports, studies and other authoritative publications.   

G.     If the commission finds that a proposed district is necessary and desirable, it shall approve the petition, enter and record its final determination and define the district by legal description. If the commission finds no need for a proposed district, it shall deny the petition and enter and record its final determination. A geographical area or a substantial portion of it may not be the subject of a petition submitted for consideration by the commission more than one time in any calendar year.