Authors
Dale A. McCullough, Ph.D.
M. Jonas Greene
Report Reference
#05-1
Publication Date
April 2005
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Monitoring Fine Sediment:
Grande Ronde and John Day Rivers
Abstract |
Fine
sediment trends were evaluated by monitoring percentage surface fine
sediment as well as fine sediment infiltration into cleaned spawning
gravels embedded into spawning reaches in plastic buckets. The threshold
fine sediment particle size was ≤ 6.35 mm; however, fines were
recorded in three size fractions—0.0-0.85 mm, 0.85-2.0 mm, and
2.0-6.35 mm.
Overwinter fine sediment (for fines <0.85 mm and <6.35 mm) infiltration
monitoring in the cleaned gravels of “artificial redds”
indicated no significant 4-year trend for any stream, except for the
<6.35 size fraction in the NFJDR. In 2001, the NFJDR had the highest
level of infiltrated fines (16.4%) less than 6.35 mm. Variation in
infiltration of fines <0.85 mm produced fewer significant differences
among streams within a single year than did fines <6.35 mm.
Statistical comparison of 4-year mean overwinter fines infiltration
among study streams revealed that for fines <6.35 mm, percentage
infiltration for NFJDR and GR were 12.6 and 12.1%, respectively; for
CC and GT infiltration was 7.8 and 7.5%, respectively. Percentage
surface fines were estimated using three independent methods. Mean
fine sediment infiltration rates for each stream and year were regressed
against mean surface fine sediment. Surface fine sediment conditions
in the summer preceding emergence were more effective in explaining
the variation in infiltration rates in the following overwinter incubation
period than was the surface fine sediment condition in the summer
following emergence. Surface fine sediment conditions are a statistically
significant predictor of the likelihood that cleaned spawning gravels
will be filled with fines <6.3 mm. The greater the level of surface
fines, the greater the degree of infiltration. Infiltration, then,
occurs under all flow years to a level primarily dictated by level
of surface fines.
Other studies have shown that surface fine sediment levels are significantly
related to average survival-to-emergence of Chinook salmon. Also,
surface fine sediment levels tend to indicate fines levels that would
be equaled or exceeded in the subsurface spawning gravels, thereby
representing a minimal estimate of conditions to which eggs/alevins
are subjected. |
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