Wash. Rev. Code § 86.18.010
Economic development and growth of the state is dependent on the control of flood waters. The legislature declares, in the exercise of its sovereign and police powers, that the purpose of this chapter is to provide for contributions of funds for assisting political subdivisions of the state in the protection of lands from inundation; the protection of public highways; the control of storm drainage; the maintenance of stream channels and water courses; and the protection of life and property.
It is the intent of the legislature that funds be provided to political subdivisions of the state to assist in the development of those flood control improvements and projects, which cannot be reasonably and practicably financed through the normal methods of financing available to such political subdivisions.
RCW 86.18.010