Section 173-183-620. Habitat index.

(1) Most state freshwaters vary to some degree from the natural condition as increased activities within individual watersheds have decreased stream, river, and/or lake habitat quality. In order to account for that degradation prior to assessing damages using the compensation schedule, a habitat index (HI) is calculated to represent existing stream conditions prior to the oil spill.

(2) For each stream, river, or lake impacted by an oil spill where the preassessment screening committee determines that the compensation schedule shall be used, a habitat index (HI) shall be calculated following an oil spill using the following methodology. The HI measures the amount of stream degradation from natural conditions and shall be calculated using the following formula:

Habitat Index (HI) = [(P1+P2+P3+P4+P5+P6)÷Np] x f1 x f2 x f3

(3) The RDA committee shall determine which of the habitat quality parameters described in subsection (2) of this section are applicable to the particular spill under consideration. If a parameter is not applicable to the spill under consideration, the parameter shall not be included in the formula provided in subsection (2) of this section.

(4) Habitat quality parameters (P).

(a) Barriers to natural fish movement (P1). Barriers, to some degree, limit the free passage of fish upstream thus limiting the ability of streams to recover. The scoring of this parameter is based on the influence of barriers in the natural dispersal of fish populations as follows:

Table 12. Scoring of Barriers to Natural Fish Movement (P1).

(b) Urbanization (P2). Urban development has historically had negative habitat effects on freshwater ecosystems. The percent of urban development in a watershed directly influences siltation, riparian abuse, and water quality deterioration. The scoring of this parameter is based on the percent of urbanization in the stream watershed.

Table 13. Scoring of Urbanization (P2).

(c) Condition of riparian vegetation (P3). Riparian vegetation is important to seventy percent of the animal and bird species in Washington for some part of their life cycle. It also exerts thermal regulatory and thermal controls for the aquatic system. The scoring of this parameter is based on the percent of banks that are protected by effective riparian vegetation.

Table 14. Scoring of Condition of Riparian Vegetation (P3).

(d) Condition of the flood plain (P4). The condition of the flood plain forecasts the amount of sedimentation and erosion in the watershed and as such is a primary predictor of stream degradation. The rating of this parameter is as follows:

Table 15. Scoring of the Condition of the Flood Plain (P4).

(e) Land use of the watershed (P5). Land use practices exert a great deal of influence on the quality of the aquatic habitat. The rating of this parameter is as follows:

Table 16. Scoring of Land Use of the Watershed (P5).

(f) Flow alteration (P6). Alteration of the natural flow regime can frequently alter habitat conditions that are necessary for certain behavioral and ecological needs of species. The rating of this parameter is as follows:

Table 17. Scoring for Flow Alteration (P6).

(5) Habitat alteration functions (F). Each habitat alteration function has the power to reduce the habitat quality rating, dependent on the type and extent of alteration. Functions are expressed on a scale of 0 to 1.0.

(a) Channel modification (F1). Channel modification can have a dramatic effect of the ability of a stream to provide for a diversity of habitats. This parameter is rated as follows:

Table 18. Scoring for Percent Fish Reduction (FR).

(b) Water quality (F2). Water quality exerts a variety of detrimental and/or beneficial on the aquatic ecosystem. This parameter is rated as follows:

Table 19. Scoring for Water Quality (F2).

(c) Streambed condition (F3). The condition of the substrate habitat can be altered in such a way as to reduce the effective habitat available to the aquatic community as a whole. This parameter is ranked as follows:

Table 20. Scoring of Streambed Condition.

[Statutory Authority: Chapter 90.48 RCW. WSR 92-10-005 (Order 91-13), § 173-183-620, filed 4/23/92, effective 5/24/92.]

Reviser's note: The brackets and enclosed material in the text of the above section occurred in the copy filed by the agency.

Chapter 90.48 RCW. WSR 92-10-005 (Order 91-13), § 173-183-620, filed 4/23/92, effective 5/24/92.