(1) This chapter applies to public surface waters of the main stem Columbia River in Washington state and to any groundwater the withdrawal of which is determined by the department of ecology to have a significant and direct impact on the surface waters of the main stem Columbia River.

The extent of the "main stem" Columbia River shall be the Columbia River from the upstream extent of tidal influence (Bonneville Dam-River Mile 146.1) upstream to the United States-Canada border (River Mile 745) and including those areas inundated by impounded waters at full pool elevations.

(2) Chapter 173-500 WAC, the general rules of the department of ecology for the implementation of the comprehensive water resources program mandated by RCW 90.54.040, applies to this chapter.

(3) Nothing in this chapter shall affect existing water rights, riparian, appropriative, or otherwise, existing on the effective date of this chapter, including existing rights relating to the operation of any navigation, hydroelectric, or water storage reservoir, or related facilities. This exemption includes rights embodied in all water right permits and certificates existing on the effective date of this chapter.

(4) The instream flows established and implemented by this chapter for instream and out-of-stream uses, and the average weekly flows applied by this chapter to out-of-stream uses do not apply to any application for water from the main stem Columbia River on which a decision is made by the department of ecology on or after July 27, 1997. Any water right application considered for approval or denial after that date will be evaluated for possible impacts on fish and existing water rights. The department will consult with appropriate local, state, and federal agencies and Indian tribes in making this evaluation. Any permit which is then approved for the use of such waters will be, if deemed necessary, subjected to instream flow protection or mitigation conditions determined on a case-by-case basis through the evaluation conducted with the agencies and tribes.

(5) Waters withdrawn by the United States pursuant to RCW 90.40.030 prior to the effective date of this rule relating to the second half of the Columbia basin project, and water right permits and certificates hereafter issued by the department of ecology pertaining to such withdrawn waters, are not subject to the provisions of this chapter.

(6) For the purposes of this chapter, average weekly flows shall be the average of the daily average flows reported in the Columbia River operational hydromet and management system (CROHMS) for a seven-day period beginning at 12:01 a.m. Monday and ending at midnight on Sunday. When the beginning of the seven-day period defined in this section does not correspond to the dates on which flows are established in WAC 173-563-040, the flow requirements for that week shall be the arithmetic average of the required flows listed in WAC 173-563-040 for each of the seven days, rounded to the nearest 1,000 cfs.