3 reiter deschutes_south_sound_symp2010
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Transcript of 3 reiter deschutes_south_sound_symp2010
Maryanne Reiter, Hydrologist Weyerhaeuser Company
South Sound Symposium October 27, 2010
Temporal and spatial turbidity patterns over 30 years in a managed forest of Western
Washington
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 Deschutes drainage”
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.
Study AreaWeyerhaeuser 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-
Weyerhaeuser ownership.
Study Area (cont.)
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 photosynthesis, sight–feeding organisms and drinking water quality.
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
10 NTU
3 NTU
Methods
1)Ensure that data meets requirements for trend analysis.
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 turbidity trends,
4)Conduct tests for monotonic trends in the turbidity data
5)Examine the relationship between turbidity and forest management.
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 samples
Turbidity and SSC
Deschutes River mainstemn=2164
0.284< 0.0001
Thurston Creekn=1234
0.260< 0.0001
Hard Creekn=161
0.343< 0.0001
Ware Creekn=143
0.743< 0.0001
2000
1500
1000
500
1000
800
600
400
200
20041998199219861980
300
200
100
020041998199219861980
1000
800
600
400
200
Winter total precip. (mm)
Year
Media
n s
easo
nal f
low
(cm
s)
Spring total precip. (mm)
Summer total precip. (mm) Fall total precip. (mm)
Total seasonal rainfall through time for the DeschutesTrends in explanatory variables: rainfall
Trends in explanatory variables: streamflow
12
9
6
3
0
6
5
4
3
2
20041998199219861980
2.0
1.5
1.0
0.520041998199219861980
3
2
1
0
A. Winter median flow
Year
Media
n s
easo
nal f
low
(cm
s)
B. Spring median flow
C. Summer median flow D. Fall median flow
Seasonal median flow through time for the Deschutes mainstem
8
4
0
20041998199219861980
2
0
-2
20041998199219861980
2
0
-2
A. DRM winter
Year
Unadju
sted a
nd flo
w a
dju
sted t
urb
dit
y (
NTU
) th
rough t
ime
A. Hard Cr winter
A. Ware Cr winter
Flow adjustedUnadjusted
Turbidity type
Trend analysis results: winter turbidity decrease
Turbidity parameter
DRM Hard Creek
Ware Creek
Spring median X
Summer median X
Fall median X X X*
Spring median FAT X
Summer 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
8
4
0
4
2
0
-2
20041998199219861980
4
2
0
-220041998199219861980
6
4
2
0
-2
A. DRM winter
Year
Unadju
sted a
nd flo
w-a
dju
sted t
urb
idity (
NTU
)
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.”
July, 1948 Water and Sewage Works
Why the decline?
We believe the decrease in turbidity is related to the improvement in roads.
Management and Turbidity
Red boxes indicate periods of similar levels of management. Red arrow indicates change in road practices.
-4
-3
-2
-1
0
1
2
3
4
Year
DR
M m
ed
ian
win
ter
FA
T (
NT
U)
0
3
6
9
12
15
Pe
rce
nt
of
wa
ters
he
d h
arv
es
ted
o
r ro
ad
ed
Annual % of watershed harvested Annual % of total road network constructed
DRM winter median FAT (NTU)
Natural conditions influence on turbidity patterns
Results (cont.)
0
2
4
6
8
10
12
14
Med
ian
win
ter
turb
idit
y (
NT
U)
1981 median winter turbidity (NTU) 1997 median winter turbidity (NTU)
Continental glaciation Resistant volcanic mountain slopes
Deschutes Update
In 2006 we installed new water quality sampling equipment that utilizes the latest technology for automated turbidity monitoring and sampling streamwater.
Little Deschutes
Upper Deschutes
KeyNew water quality instruments only (2006) Old (1974) and new (2006) instrumentsWeather StationTraffic Counters
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 watershed.
This study has shown decreasing trends in winter turbidity for at the small and large watershed scale.
The decreasing trends in turbidity in the mainstem Deschutes appeared to be most directly related to improvements in road construction and maintenance practices.
Summary