(1) To support the development of new water supplies in the Columbia river and to protect instream flow, the department of ecology shall work with all interested parties, including interested county legislative authorities and watershed planning groups in the Columbia river basin, and affected tribal governments, to develop a Columbia river water supply inventory and a long-term water supply and demand forecast. The inventory must include:

(a) A list of conservation projects that have been implemented under this chapter and the amount of water conservation they have achieved; and

(b) A list of potential water supply and storage projects in the Columbia river basin, including estimates of:

(i) Cost per acre-foot;

(ii) Benefit to fish and other instream needs;

(iii) Benefit to out-of-stream needs; and

(iv) Environmental and cultural impacts.

(2) The department of ecology shall complete the first Columbia river water supply inventory by November 15, 2006, and shall update the inventory annually thereafter.

(3) The department of ecology shall complete the first Columbia river long-term water supply and demand forecast by November 15, 2006, and shall update the report every five years thereafter.