Background on why the upper Deschutes In 1951 Capitol Lake (Olympia, WA) was created by the construction of an earthfill dam. By 1973 most of the impounded basin had filled with sediment. The source of the sediment was questioned in an attempt to determine liability for dredging costs. Increased sediment from logging and forest roads in the headwaters was identified at the time as one potential source of the sediment. In addition to sediment, flooding and impacts to fish habitat were also raised as concerns. In response to these concerns, Weyerhaeuser foresters, hydrologists and geologists developed the Deschutes Watershed Plan in 1974 which called for reducing sediment inputs and other environmental risks arising from forest management. To evaluate the effectiveness of changes in forest practices Weyerhaeuser Company began collecting hydrology data in the headwaters of the Deschutes River in 1974.
Timber harvest began in the Deschutes River study area in the 1950s and continues today. By the time the study started in the early 1970s, approximately 30 percent of the basin had already been harvested. The pattern of harvest has changed from big blocks in one area to more dispersed units.
While turbidity is not a direct measurement of suspended sediment (e.g., Anderson and Potts, 1987) and can be influenced by colloidal material (both organic and inorganic), water color and sediment particle size distribution (e.g., Hudson, 2001; Madej 2002), it still provides an easy-to-obtain indication of the relative concentration of suspended material in stream water (Beschta, 1980; Davies-Colley and Smith, 2000; Harris et al., 2007; Minella, 2007). Although there is uncertainty associated with using turbidity values to represent suspended sediment concentrations, the relationship between the two parameters is generally strong enough that turbidity is a more reliable index of suspended sediment concentration than flow (e.g., Beschta, 1980; Lewis, 1996; Christensen, 2002).
The statistical analyses consisted of several components: Ensuring that data meets requirements for trend analysis. no serial correlation and constant variance conducting correlation analysis to establish the appropriateness of using turbidity as a surrogate or index of SSC examining the temporal patterns of exogenous variables, such as discharge, that may influence turbidity trends, conducting tests for monotonic trends in the turbidity data examining the relationship between turbidity and forest management. Spatial patterns in winter median grab sample turbidity were examined using only graphical methods.
Tau is less than r-square
Even though there are no statistically significant monotonic trends in flow based on the Mann-Kendall test, there is variability in seasonal flow with some higher winter flows in the mid to late 1990s
* Due to non-constant variance results from Ware Cr must be interpreted with caution
Deschutes River mainstem showed decreasing trends in turbidity for the winter (both) and spring (flow adjusted only).
Periods of similar harvest/road building rates earlier in the record were associated with winter flow-adjusted turbidities higher than for periods with similar levels of harvest later in the record.
Those areas underlain by continental glaciation had higher turbidity as compared to volcanic areas, regardless of management intensity (1981 was high intensity and 1997 was low)
3 reiter deschutes_south_sound_symp2010
Maryanne Reiter, Hydrologist
South Sound Symposium October 27, 2010
Temporal and spatial turbidity
patterns over 30 years in a
managed forest of Western
Background and Objective
Photo credit: accessibletrails.com
To determine if forest practices were contributing to
the sediment Weyerhaeuser developed a watershed
plan in 1974. The goal was “to estimate the effects of
company operations on the water quality in the Upper
In the early 1970s there was concern over sediment
filling Capitol Lake which was created in 1951. The
source of the sediment was questioned in an attempt
to determine liability for dredging costs.
Weyerhaeuser has been measuring suspended sediment,
turbidity, stream flow and air and water temperature at four
locations in the upper Deschutes River basin since mid-1970s.
Precipitation was collected at one location.
75. Harvest for those basins was completed by the early 1990s.
Figure 2. Spatial distribution of stand ages (by birth year grouping) within the study area. White area indicates non-
Turbidity expresses the optical
property of water that causes light
to be scattered and absorbed by
particles. It is an important water
quality parameter that can affect
organisms and drinking water
Focus on Turbidity
We used turbidity as a surrogate for SSC because
our turbidity record is more complete than that for
SSC. While turbidity is not a direct measurement of
SSC, it does provide a relative indication of SSC.
Turbidity as a surrogate for suspended sediment
1)Ensure that data meets requirements for trend
2)Conduct correlation analysis to establish the
appropriateness of using turbidity as a surrogate or
index of SSC
3)Examine the temporal patterns of exogenous
variables, such as discharge, that may influence
4)Conduct tests for monotonic trends in the turbidity
5)Examine the relationship between turbidity and forest
Turbidity as a surrogate for suspended sediment
Daily turbidity and SSC were significantly correlated for
all permanent stations (p < 0.0001).
Station name and number of
Turbidity and SSC
Deschutes River mainstem
Winter total precip. (mm)
Spring total precip. (mm)
Summer total precip. (mm) Fall total precip. (mm)
Total seasonal rainfall through time for the Deschutes
Trends in explanatory variables: rainfall
Trends in explanatory variables: streamflow
A. Winter median flow
B. Spring median flow
C. Summer median flow D. Fall median flow
Seasonal median flow through time for the Deschutes mainstem
A. DRM w int er
A. Hard Cr w int er
A. Ware Cr w int er
Turbidit y t ype
Trend analysis results: winter turbidity decrease
Spring median X
Summer median X
Fall median X X X*
Spring median FAT X
Fall median FAT X X
Trend Analysis Results: Other Seasons
Trends in other seasons for the stations were not
consistent. X indicates statistically significant trend.
FAT is flow-adjusted turbidity.
Trend Analysis Results: Deschutes Seasonal
Red squares are unadjusted median turbidity and black circles
are flow-adjusted turbidity
A. DRM winter
B. DRM spring
C. DRM summer D. DRM fall
Seasonal median and flow-adjusted turbidity through time for the Deschutes
“For the most part, the difficulties of harvesting
wood products from areas of high watershed
values center around the general problem of
transporting the forest products out of watershed
onto main roads.”
Water and Sewage Works
Why the decline?
We believe the
related to the
Management and Turbidity
Red boxes indicate periods of similar levels of management.
Red arrow indicates change in road practices.
Annual % of watershed harvested Annual % of total road network constructed
DRM winter median FAT (NTU)
Natural conditions influence on
1981 median winter turbidity (NTU) 1997 median winter turbidity (NTU)
Continental glaciation Resistant volcanic mountain slopes
In 2006 we installed new
water quality sampling
equipment that utilizes the
latest technology for
monitoring and sampling
New water quality
Old (1974) and new
Since the Deschutes River study was initiated,
there have been several changes in forest
practices as well as natural disturbances that have
influenced sediment and turbidity patterns in the
This study has shown decreasing trends in winter
turbidity for at the small and large watershed
The decreasing trends in turbidity in the mainstem
Deschutes appeared to be most directly related to
improvements in road construction and