At 9.4 mi upstream from the mouth of the Muddy River is the tributary, Clearwater Creek, where the 1980 eruption blast felled trees and deposited tephra in the upper part of the drainage basin. A gaging station was established 3 mi upstream from the mouth of Clearwater Creek in 1981. Access to this remote site was usually by helicopter on a monthly or twice monthly schedule. Cross-section samples were seldom collected during storm flows due to the limited access. Daily sediment-discharge records are available for January 28, 1982 (date of automatic sampler installation), to January 9, 1990 (date of damage to gaging station during storm flow) ( fig. 43 ).
Simulated rainfall on a test hillslope plot also was measured in the upper part of Clearwater Creek (Leavesley and others, 1989). Infiltration rates for the coarse tephra deposits were one-half to one-third the estimated pre-eruption rates. As hypothesized for the Green River basin, erosion rates in the Clearwater Creek basin during 1980 could have been much higher than measured in subsequent years. The three highest sediment concentrations ever sampled at Clearwater Creek were collected in November 1980, indicating high sediment discharges in that year.
