3 reiter deschutes_south_sound_symp2010

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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

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Page 1: 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

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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.

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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.

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Study Area (cont.)

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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

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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.

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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

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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

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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

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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

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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.

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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

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“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.

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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)

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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

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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

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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