Whenever, after the determination of special benefits accruing from the maintenance of the district's system of improvements, it appears to the board from a petition filed by the affected property owner or owners or otherwise, that by reason of permanent improvements or additions made, removed, abandoned or destroyed by fire or other casualty, or of other changes in the character or condition of the property, the benefits theretofore determined in respect to any one or more pieces or parcels of property are no longer fair, just and equitable, then the board shall appoint three appraisers who shall qualify as in RCW 85.08.360 hereof. Said appraisers shall proceed immediately to carefully examine the pieces or parcels of property as to which since the last determination of special benefits thereto there have been permanent improvements or additions made, removed, abandoned or destroyed by fire or other casualty or other changes in the character or condition of the property. Said appraisers shall file their sworn report with the board setting forth the special benefits determined by them as accruing to each piece and parcel of property examined by them not less than ten days prior to the date of hearing. The board shall hold a hearing thereon at the county seat at the time of equalization of the real property assessment and shall give notice thereof as provided in RCW 85.16.070.