As used in this chapter:

"District" means a diking, drainage or sewerage improvement district organized under chapter 85.08 RCW.

"Maintenance" means and includes not merely operating expenses and such upkeep and other work commonly classed as maintenance as shall be necessary to restore and preserve the district's systems of improvement and the machinery and equipment operated in connection therewith in the same or as good condition as when originally constructed and installed, but also the making of such changes in and betterments to the original works, improvements and installations as shall, subject to approval of the board of county commissioners, be by the board deemed necessary to put the systems of improvements into such condition as will provide protection and services as contemplated and intended by the original construction and any enlargement and extensions thereof thereafter made.