567—75.6 (455B) Preexisting nonconforming development and associated uses. Regulations established by a department flood plain management order or an approved local ordinance shall identify the conditions under which nonconforming development and associated uses which lawfully existed prior to the effective date of the regulations may continue. The conditions shall include criteria for additions, reconstruction, replacement and changes in use. The criteria should generally encourage improvements or replacement construction which would provide an adequate degree of flood protection commensurate with the damage potential. The criteria should prohibit the improvements or replacement only where extension of the useful life of the structure by improvement or replacement would contribute to: perpetuation of an individual or collective obstruction which causes a significant increase in the level of Q100; perpetuation of a significant hazard to health or safety during floods; or perpetuation of the potential for significant flood damages to property and associated public costs.