Publication Summary

This report presents data on flood events, channel scour, and chinook redd characteristics for rivers in the Upper White watershed of the Puyallup Basin. The primary focus of the report is a baseline study of channel and redd survival conditions for the Greenwater River. This will be used as a benchmark from which to measure progress in restoring aquatic system health based on watershed restoration (to be carried out through a TMDL for aquatic habitat, and a companion USFS Water Quality Restoration Plan. In addition, documentation of channel effects from two winter 1995 to 1996 flood events are reported for the Clearwater River.

From the fall of 1995 to the spring of 2001, spring chinook redds, channel scour and surface elevations were investigated in the Upper White watershed of western Washington. The primary purpose for this work was to document current conditions in spring chinook habitat to establish a baseline for monitoring changes resulting from watershed restoration. The study included a first- year reconnaissance study of channel cross-sections and scour monitors in the Clearwater River, and, a five-year study on redd disturbance from gravel scour and changes in channel morphology associated with peak discharges primarily in the Greenwater River, but including the Clearwater and White Rivers in 1996.

Two large floods in the Clearwater River during the first-year study caused major channel realignments and habitat changes that indicated a high end of poor survival for salmonid incubation. The focus of the Clearwater study was adjusted to provide documentation of the nature and extent of changes associated with the flood events. In the five-year long Greenwater study, redd results indicated that during 2 of 5 years 92% of redds had a good likelihood of survival. During the other 3 years redd results showed likelihood of good survival for 79%, 72% and 50% of redds. However, redd data includes only scour of the surface bed; bed scour monitor data for 2 of 4 years in the Greenwater indicated a greater level of redd loss was occurring with greater than 50% of monitors scouring to the top of egg pocket depth.

Scour monitor and redd site data for fall 1996 to late winter 2001 for the Greenwater River show a strong negative correlation between increasing annual peak incubation discharge and scour depth. There was also a strong positive relationship between the maximum annual incubation peak discharge and percent of sites scoured to 15 cm (the top of chinook egg pocket depth), and for the maximum annual incubation peak discharge and percent of redds with a poor likelihood of embryo and alevin survival to emergence. Based on the relationship between peak discharge and scour level, flows of 1235 cfs (2-year return interval) are predicted to scour 25% of scour monitors to =15 cm; flows of 2073 cfs (4-year return interval) scour 50% of monitors to =15 cm; and, flows of 2912 cfs (7- year return interval) are predicted to scour 75% of monitors to =15 cm.

Historically, (pre-1970, n=41 years), discharges predicted to have scoured = 50% of monitor sites in spawning habitat to =15 cm occurred at a 5.9-year frequency. Currently (1970 ? 2000, n=16 years) these discharges are expected to occur at a 3.0-year frequency, nearly twice as often. This difference is significant with a p-value of 0.0826. This research supports the need for restoration of watershed processes (e.g. hydrology and sediment production) that affect depth of gravel scour in chinook spawning habitat.