Wash. Rev. Code § 86.09.622
Flood control districts may be dissolved upon a favorable sixty percent vote of the electors voting at an election for that purpose called, noticed, conducted and canvassed in the manner provided in this chapter for special elections and no further district obligations shall thereafter be incurred: PROVIDED, That the election shall not abridge or cancel any of the outstanding obligations of the district, and the county legislative authority of the county within which the major portion of the district is situated shall each year at the time and in the manner provided in this chapter for the levy of district assessments, levy assessments against the lands in the district and the same shall be collected and enforced in the manner provided herein, until the outstanding obligations of the district are fully paid.
RCW 86.09.622
Dissolution of districts: Chapter 53.48 RCW.