TURBIDITY
and
THE EFFECT OF SCALE
Joseph C. Greene, Research Biologist
Claudia J. Wise, Physical Scientist
Flood Stage, Klamath River above Portuguese Creek, 2005
“Mining debris is chemically inert, makes no oxygen demand on
the stream and therefore takes away from the flowing water
nothing which the fish require. This is equally true of this
material whether placed in transit by nature or by man since the
products are alike in nature and comes from the same sources…”
Swartley, A. M. Appendix A. In: Ward, H. B. 1938. Placer Mining on the Rogue River, Oregon, in Its Relation to the Fish and
Fishing in that Stream. Department of Geology and Mineral Industries, State of Oregon, Portland, OR
Klamath River water: The left vial was allowed to settled for 24hours, the right vial was shaken to re-suspend the particulates. The
sample was measured at 656 NTU.
Cross-sectional measurements of turbidity at various distances downstream from
an 8-inch suction dredge in the Fortymile River, Alaska. The dredge was operating
approximately 7 m from the right bank at the time of sample collection.
16 ft.
33 ft.
66 ft.
1,050 ft.
Royer et al,,1999. Impact of Suction Dredging on Water Quality, Benthic Habitat, and Biota in Fortymile River, US EPA Final Report.
Unfiltered concentrations of copper and zinc measured in the
Fortymile River, AK collected at locations upstream of the 8-inch
dredge; the dredge was located at zero on the x-axis.
131 ft
131 ft
263 ft.
394 ft.
Royer et al,,1999. Impact of Suction Dredging on Water Quality, Benthic Habitat, and Biota in Fortymile River, US EPA Final Report.
Temperature
of
the
Sacramento River is of
concern for the wellbeing of migrating fish
such as salmon.
The concentrations of
trace elements, including
mercury, were always
below
any
existing
drinking water standards.
Mercury concentrations
frequently exceeded the
standards
for
the
protection of aquatic life,
and
the
exceedances
always happened during
the late fall to early
spring rainy season.
Domagalski, J. L., and Peter D. Dileanis, 2000. Water-Quality
Assessment of the Sacramento River Basin, California –
Water Quality of Fixed Sites, 1996-1998, U.S. GEOLOGICAL
SURVEY, Water-Resources Investigations Report 00-4247
Research to Support the
Siskiyou National Forest DEIR
The SNF engaged Dr. Peter B. Bayley, Dept. Fisheries & Wildlife,
Oregon State University, to conduct a “Cumulative Effects Analysis” on
the effects of suction dredging forest-wide
Dr. Bayley concluded:
"The statistical analyses did not
indicate that suction dredge mining
has no effect on the three responses
measured, but rather any effect that
may exist could not be detected at
the commonly used Type I error rate
of 0.05."
(In other words, if there are effects, they are so small they can't be measured.)
Bayley, P.B., 2003, Response of fish to cumulative effects of suction dredge and hydraulic mining in the Illinois subbasin, Siskiyou National Forest,
Oregon, Dept. Fisheries & Wildlife, Oregon State University, Corvallis OR 97330
Dr. Bayley continued…
"The reader is reminded of
the effect of scale.
Localized, short-term effects of suction dredge
mining have been documented in a qualitative
sense.
However, on the scales occupied
by fish populations such local
disturbances would need a strong
cumulative intensity of many
operations to have a measurable
effect."
Bayley, P.B., 2003, Response of fish to cumulative effects of suction dredge and hydraulic mining in the Illinois subbasin, Siskiyou National Forest,
Oregon, Dept. Fisheries & Wildlife, Oregon State University, Corvallis OR 97330
THE ROGUE RIVER AS IT FLOWS PAST THE GRANTS
PASS, OREGON, SEWAGE TREATMENT PLANT, MAY 10,
2005.
ACCORDING TO THE GRANTS PASS DAILY
COURIER, TURBIDITY IN THE RIVER DUE TO RECENT
RAINS MEASURED AT APPROXIMATELY 54-61 NTUs.
APPROXIMATE SIZE OF
A 4” SUCTION DREDGE
A report from the Siskiyou National Forest answered the
question, “How much material is moved by annual mining suction
dredge activities and how much does this figure compare with
the natural movement of such materials by surface erosion and
mass movement?”
The movement rate by suction dredge mining would equal
about 0.7% of natural rates.
Cooley, M.F. 1995. Forest Service yardage Estimate. U.S. Department of Agriculture, U.S. Forest Service, Siskiyou National Forest, Grants Pass, OR.
The total acreage of all analyzed claims related to the total
acres of watershed is about 0.2 percent.
The percentage of land area within riparian zones on the
Siskiyou National Forest occupied by mining claims is estimated
to be only 0.1 percent.
SNF, 2001. Siskiyou National Forest, Draft Environmental Impact Statement: Suction Dredging Activities. U.S. Department of Agriculture,
U.S. Forest Service, Siskiyou National Forest, Medford, OR.
The area or length of river or streambed worked by a single
suction dredger, as compared to total river length, is relatively
small compared to the total available area.
CDFG, 1997. draft Environmental Impact Report: Adoption of Amended Regulations for Suction Dredge Mining. State of California,
The Resource Agency, Department of Fish and Game
CONCLUSION
Small-scale gold suction
dredging temporarily
effects a very small
area in the environment
relative to the entire
area in which all
dredges operate.
Salmon River Dredge Pit and Spoils Survey
260 ft
10/13=76.9%
Leroy Cyr, Fish Biologist, 2005, Interoffice Memorandum to Jerry Boberg, Fish and Watershed Program Manager, Six Rivers National Forest.
Leroy Cyr, Fish Biologist, 2005, Interoffice Memorandum to Jerry Boberg, Fish and Watershed Program Manager,
Six Rivers National Forest.
442 ft
11/26=42.3%
Leroy Cyr, Fish Biologist, 2005, Interoffice Memorandum to Jerry Boberg, Fish and Watershed Program Manager,
Six Rivers National Forest.
364 ft
6/14=42.9%
Salmon River Study Conclusions
Measured
dredge holes cover a total length of
1,066 ft. The entire 79 miles of the Salmon
River covers a length of 417,120 linear feet.
Therefore, suction dredge holes disturbed
0.26% of the area, calculated on a linear basis.
The length of the dredge holes is actually
<0.26% because the data does not allow for
calculation of area disturbed vs linear area
disturbed. The total dredge hole area of the
Salmon River is less than that calculated
because the dredge holes did not extend to both
margins of the river.
Salmon River Study Conclusions
Refugia has been defined, in the literature,
as any hole in a river bottom that is 3 feet
or deeper.
This study identified 27 potential refugia
created by suction dredging.
All of the suction dredge holes disturbed
<0.26% of the river bottom.
27 of the 53 holes dredged, or 51%, have
the potential of improved habitat for the
survival of species in the Salmon River.
Positive Effects of Suction Dredging
Excavations from dredging operations can result in
temporarily formed pools or deepen existing pools which may
improve fish habitat.
Deep scour may intersect subsurface flow creating pockets of
cool water during summer which can provide important
habitat for fish.
Nielsen, J. L., T. E. Lisle, and V Ozaki. 1994. Thermally stratified pools and their use by steelhead in northern California streams.
Trans. Am. Fish. Soc. 123:613-626.
During times of low flow in a river or stream, increased water
depth can provide a refuge from predation by birds and
mammals
Harvey, B. C., and A. J. Stewart. 1991. Fish size and habitat depth relationships in headwater streams. Oecologia. 87:336‐342.
Pools created by abandoned dredger sites can provide holding
and resting areas for juvenile and adult salmonids.
Stern, G. R. 1988. Effects of suction dredge mining on anadromous salmonid habitat in Canyon Creek, Trinity County, California.
M.S. Thesis, Humboldt State University, Arcata, California, 80 pp.
CUMULATIVE EFFECT OF
MULTIPLE DREDGE OPERATIONS
“No additive effects were detected on the Yuba River
from 40 active dredges on a 6.8 mile stretch”.
Harvey, B.C., K. McCleneghan, J.D. Linn, and C.L. Langley, 1982. Some physical and biological effects of suction dredge mining.
Lab Report No. 82-3. California Department of Fish and Game. Sacramento, CA.
“Six small dredges (<6 inch nozzle) on a 1.2 mile stretch
had no additive effect
Harvey, B.C. 1986. Effects of suction gold dredging on fish and invertebrates in two California streams.
North American Journal of Fisheries Management 6:401-409.
The Chugach National Forest, Alaska found that, “The
results from water quality sampling do not indicate any
strong cumulative effects from multiple placer mining
operations within the sampled drainages.”
“Several
suction
dredges
probably
operated
simultaneously on the same drainage, but did not affect
water quality as evidenced by above and below water
sample results.
Huber and Blanchet, 1992. Water quality cumulative effects of placer mining on the Chugach National Forest, Kenai Peninsula, 1988-1990.
Chugach National Forest, U.S. Forest Service, Alaska Region, U.S. Department of Agriculture.
In
the
recreational
mining
area
of
Resurrection Creek, five and six dredges
would be operating and not produce any
water quality changes.
Huber and Blanchet, 1992. Water quality cumulative effects of placer mining on the Chugach National Forest, Kenai
Peninsula, 1988-1990. Chugach National Forest, U.S. Forest Service, Alaska Region, U.S. Department of Agriculture.
“Department regulations do not currently limit
dredger densities but the activity itself is
somewhat self-regulating. Suction dredge
operators must space themselves apart from
each other to avoid working in the turbidity
plume of the next operator working upstream.
Suction Dredging requires relatively clear
water to successfully harvest gold.
CDFG, 1997. draft Environmental Impact Report: Adoption of Amended Regulations for Suction Dredge Mining. State of California,
The Resource Agency, Department of Fish and Game
The streams in Alaska have tremendous
populations of char, Arctic Grayling, and
various species of salmon.
The
environment that sustains these
native populations has had intense
suction dredging activities that have
been ongoing for decades.
Other
problems
must
be
more
detrimental to fish and their freshwater
habitat.
Harvey and Lisle “measured scour of Chinook
salmon redds on dredge tailings and natural
substrates in Elk Creek, South Fork Salmon River,
and Scott River, California.”
They “measured maximum scour with scour
chains and net scour by surveying before and
after high winter flows.
Scour of chinook salmon redds located on dredge
tailings exceeded scour of redds on natural
substrates, although the difference varied among
streams.”
HARVEY, B. C. and T. E. LISLE. 1999. Scour of Chinook Salmon Redds on Suction Dredge Tailings. North American Journal of Fisheries Management 19:613-617
“The significance of dredge tailings to salmon
populations may vary even among streams
with similar patterns of scour.
The proportion of Chinook salmon that spawn
on dredge tailings would influence the
population level effect of tailings and
depend, in part, on the availability of
spawning sites on natural substrates.
If
natural spawning sites were relatively
abundant and tailings were not strongly
selected, a small fraction of redds would be
located on tailings.”
Approximately 60 salmonid redds were observed in a
study on Canyon Creek, CA. None of the redds
were found within dredge tailing piles.
Stern, G. R. 1988. Effects of Suction Dredge Minin on Anadromous Salmonid Habitat in Canyon Creek, Trinity County, California.
Masters Degree Thesis, Humbolt State University, 80p.
“In the lower 6.8 mi of the Scott River in 1995, only 12
of 372 (3.2%) redds were located on tailings because
much more natural substrate than dredge tailings
provided spawning habitat and fish exhibited no strong
preference for either substrate.”
J. Kilgore, U.S. Forest Service, unpublished data
During 1996-98 23.3 miles of the Trinity River was
surveyed for fall Chinook salmon redds. Of the 1,717
redds found 23 (1.3%) were built on dredge tailings.
Quihillalt, R.R. 1999. Mainstem Trinity River Fall Chinook Salmon Spawning Redd Survey, U.S. Fish & Wildlife Service, Arcata Fish & Wildlife Office, California
► In 2001 there were 1,578 fall chinook redd counted in
the Klamath River mainstem from the I-5 Bridge to
Happy Camp. Two redd (0.127%), were observed on
suction dredge tailings.
► In 2002 there were 4,652 fall chinook redd counted in
the Klamath River mainstem from the I-5 Bridge to Happy
Camp. One redd (0.02%) was observed on suction dredge
tailings.
Magneson, M., P. McNeil , and T. Shaw. 2001. Mainstem Klamath River fall Chinook salmon spawning survey 2001. U. S. Fish and Wildlife Service,
Arcata Fish and Wildlife Office, Arcata Fisheries Data Series Report 2006-02, Arcata, California.
► In
2006 there were 1,186 fall Chinook salmon redds counted
in the mainstem Klamath River between Iron Gate Dam and the
confluence of Indian Creek. No redds were observed on suction
dredge tailings.
Magneson, M., R. Studebaker, and J. Ogawa. 2008. Mainstem Klamath River Fall Chinook Salmon Spawning Survey 2006. U. S. Fish and Wildlife Service,
Arcata Fish and Wildlife Office, Arcata Fisheries Data Series Report Number DS 2008-13, Arcata, California.
 Turbidity does not cause the water to warm and takes





away nothing fish require.
Chemicals suspended in water fall out of suspension a
short distance below the dredge.
Small-scale gold suction dredging temporarily effects a
very small area in the environment relative to the
entire area in which all dredges operate.
Excavations from dredging can result in temporarily
formed pools (refugia) or deepen existing pools which
may improve fish habitat.
Studies do not indicate any strong cumulative effects
from multiple placer mining operations.
Few redds are constructed upon suction dredge tailings
and usually only when natural substrates are in short
supply.