BASIN WIDE STREAM DEGRADATION LIMITS SPAWNING AND REARING FOR SALMONID

Reckendorf & Tice in 1998 & 1999 assessed 88.4 miles of streams (Robinson Fk., South Touchet, North Fk., Wolf Fk., Touchet Ri., Walla Walla Ri., Pattit Cr., Upper Dry Cr., Yellowhawk Cr., and Mill Cr.) in Walla Walla Basin for physical & biological habitat. Assessed were 14 to 26 items, which reflect stream (st.) geometry & are used in mgt. decision. Average (av.) bankfull (bkf.) width (wd.) for 12 st. reaches varied from 118 ft. on Walla Walla Ri. to 44 ft. on Pattit Cr. South Touchet, Wolf Fk, Robinson Cr., Lower North Fk., Upper Touchet & Lower Touchet had av. bkf. wd. of 77, 70, 60, 59, 73, 69 ft. respectively. Streams were mostly C4 & pool/riffle with many reaches in stage II and III of CEM. Downcutting and widening has resulted in many reaches of mixed C4, F4, C1, F1, degraded C4, and occas. C4/D4 channels. The av. dist. between pools for the 13 st. av. 273 ft. but varies by locat., & LWD, which is locally limiting. Upper Touchet & Wolf Fk. have 277 & 225 ft. respect. between pools, vs. a portion of Walla Walla Ri. with 457 ft. between pools. In contrast, Upper Dry Cr, & Pattit Cr. had 135 &155 ft. respect. between pools. The st. av. of 22.1 pools/mile, but the range was 11.6 to 39.1. The av. freq. of pools varied from 2.7 to 6.3 bkf. wd. on 12 st., and is locally limiting. The av. pieces of LWD/mile varied from 5.5 to 15.2 pieces/mile on 11 st. Some LWD variation is reflected in % of streambank er. and bkf. wd. Erosion of both streambanks was evaluated & was site specific. Robinson Fk. had a riparian quality of 6.2 (1- 10 with 10 worst). However the er. was only 10.8 % assoc. with an av. bkf. wd. of 45 feet. In contrast Wolf Fork with higher riparian qual. of 3.8 also had high er. of 33.0 %, assoc, with an av. bkf. wd. of 70 ft. Channel straightening has increased streambank er., st. temp., sed. yield, & sed. intrusion into spawning gravels, and is limiting spawning & rearing. We made an evaluation of downcutting to bedrock on 49.2 miles on 4 streams. Eleven miles of streams (26 %) were downcut with Wolf Fk. being the highest (37 %). There are numerous migrating headcuts & hanging channels indicating a regional problem. Past straightening on the Walla Walla River to develop agricultural land, and perceived flood control, may be a major cause of upstream headcut migration. Reaches downcut at or near bedrock reflect the limiting of habitat for spawning, or rearing.