Sedimentation in three small forested drainage basins in the Alsea River basin, Oregon

Circular 490




A multidiscipline investigation to determine the effects of logging on the ecology of three small forested tributary basins is a part of an overall study of the Alsea River basin in the Coast Range of Oregon. The investigation of these small basins will be to (1) establish pre-logging conditions, (2) determine the effects of different logging methods, and (3) study the rate of recovery after the timber harvest. This report presents results of sedimentation in the basins, Deer and Flynn Creeks and Needle Branch, for the first 2 years of study (1959 and 1960 water years). Rainfall, runoff, and sediment discharge are seasonal for the Coast Range of western Oregon. About 95 percent of the rainfall and runoff occurs during the period October to May, but nearly 100 percent of the suspended-sediment discharge occurs during the same period. For Deer Creek, in the 1960 water year, 23 percent of the annual suspended-sediment discharge occurred on 1 day, 58 percent during the 10 days of greatest discharge, and 78 percent during the 38 days of greatest discharge. Rainfall is practically equal for all three of the basins. The runoff of the Deer and Flynn Creek basins is about equal, but that of the Needle Branch basin averaged 8 percent less. Sediment yield varies considerably for the three basins. The suspended-sediment yield of the Deer Creek basin is almost twice that of the Needle Branch basin and almost 1? times that of the Flynn Creek basin. Water temperature of the three streams varied only 22?F during the 2 water years. The greatest variation between streams was 3?F in the minimums. Water temperature effect can be neglected in comparing the sediment yields of the basins. The aquifers of the basins have low storage capacities as illustrated by the very low, late summer flow. A study of a midwinter freshet period for the Deer Creek basin showed that virtually all the rainfall left the basin as runoff within 4 days; the period of significant sediment transport was thus very short.

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Sedimentation in three small forested drainage basins in the Alsea River basin, Oregon
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U.S. Dept. of the Interior, Geological Survey,
iii, 16 p. :ill. ;27 cm.