Managed Forest Practices Reduced Turbidity in Deschutes River
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1) The study analyzed 30 years of turbidity data from four locations in the Deschutes River basin in Western Washington to determine the effects of forest practices on water quality. 2) Analysis showed decreasing trends in winter turbidity levels, which were likely related to improvements in forest road construction and maintenance practices over time that reduced sediment input. 3) Additional factors like natural variations in precipitation and streamflow, as well as changes in forest harvesting levels, also influenced turbidity patterns in the watershed over the multi-decade study period.
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Managed Forest Practices Reduced Turbidity in Deschutes River
- 1. 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
- 2. 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.
- 3. Study Area 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- Weyerhaeuser ownership.
- 5. 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
- 6. 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.
- 7. 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 mainstem n=2164 0.284 < 0.0001 Thurston Creek n=1234 0.260 < 0.0001 Hard Creek n=161 0.343 < 0.0001 Ware Creek n=143 0.743 < 0.0001
- 8. 2000 1500 1000 500 1000 800 600 400 200 20041998199219861980 300 200 100 0 20041998199219861980 1000 800 600 400 200 Winter total precip. (mm) Year Medianseasonalflow(cms) 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
- 9. Trends in explanatory variables: streamflow 12 9 6 3 0 6 5 4 3 2 20041998199219861980 2.0 1.5 1.0 0.5 20041998199219861980 3 2 1 0 A. Winter median flow Year Medianseasonalflow(cms) B. Spring median flow C. Summer median flow D. Fall median flow Seasonal median flow through time for the Deschutes mainstem
- 10. 8 4 0 20041998199219861980 2 0 -2 20041998199219861980 2 0 -2 A. DRM w int er Year Unadjustedandflowadjustedturbdity(NTU)throughtime A. Hard Cr w int er A. Ware Cr w int er Flow adjusted Unadjusted Turbidit y t ype Trend analysis results: winter turbidity decrease
- 11. 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.
- 12. 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 -2 20041998199219861980 6 4 2 0 -2 A. DRM winter Year Unadjustedandflow-adjustedturbidity(NTU) B. DRM spring C. DRM summer D. DRM fall Seasonal median and flow-adjusted turbidity through time for the Deschutes
- 13. “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.
- 14. 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 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 Year DRMmedianwinterFAT(NTU) 0 3 6 9 12 15 Percentofwatershedharvested orroaded Annual % of watershed harvested Annual % of total road network constructed DRM winter median FAT (NTU)
- 15. Natural conditions influence on turbidity patterns Results (cont.) 0 2 4 6 8 10 12 14 1.D R M 2.M itch ellC r 3.H uckleberry C r 4.Joh nson C r 5.T hurston C r low er 6.L ittle D eschu tes 7.D esch blLin co ln 8.L ew is C r 9.D eschu tes 3350 B r 10.B uck C r 11.W estfork C r 12.W are C r 13.H ard C r 14.U pper D eschutes Medianwinterturbidity(NTU) 1981 median winter turbidity (NTU) 1997 median winter turbidity (NTU) Continental glaciation Resistant volcanic mountain slopes
- 16. 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 Key New water quality instruments only (2006) Old (1974) and new (2006) instruments Weather Station Traffic Counters
- 17. 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
Hinweis der Redaktion
- 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)