For the purpose of determining said ratios of benefits, said board of appraisers shall segregate the acreage of the respective lands within the district into such number of classes as in the sole judgment of the members of the board of appraisers shall fairly represent the manifest degrees of benefits, including benefits from better sanitation, easier accessibility, facility of drainage, promotion of land development as well as from minimization of flood damages and from actual flood protection, accruing to the several lands from the organization and operation of the district and the construction and maintenance of the district works in accordance with the comprehensive plan therefor adopted by the directors of the district.