The assessors shall, in the case of all assessments of the drainage district which may hereafter be levied by the board and all assessments which have heretofore been commenced but on which the assessment lists have not been made to conform with the decision of the board after equalization hearings held pursuant to the provisions of this part, state, as information for the board, in addition to the amount assessed by reason of the flood control features, opposite each sum assessed for each particular tract of land, in a separate column, the amount that they determine each tract is so assessed by reason of the severance of any lands not included in the assessed area which would have been included but for the location of a by-pass channel or channels provided for by another separate portion or project of the drainage district, adopted by the board.