The Sitka Spruce boundary layer was created to satisfy the Forest Practices Emergency Rules of March 20, 2000. The Franklin and Dyrness, 1973, "Generalized vegetation map of Oregon and Washington" (at a scale of approximately 1:2,000,000) was digitized to create the current sitka spruce zone. According to Forest Practices Rules, if the uppermost point of perennial flow cannot be identified with standard observations (see board manual, section 23), then type 4 Waters begin at a point along the channel where the contributing basin area is at least 13 acres in the Sitka Spruce Zone.