User:Dr.Rivers/sandbox

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Slope stability and effects of logging
Numerous parties have raised the question as to whether logging was a contributing factor to the 2014 Oso (aka Hazel) mudslide. Past logging on the Whitman Bench above the Hazel Landslide has been correlated to past slide events, and this has lead to concerns that recent logging may have been a contributing factor to the 2014 slide event. Further, logging activities have long been known to trigger landslides, and in the past decade, a series of spectacular landslides that followed timber harvest have heightened public awareness of linkages between logging and landslides in Washington state. Such events include the 2007 Stilllman Creek landslides, the 2007 Highway 6 landslide , and the 2009 Whatcom County landslides.

Scientists have published several reports and papers that assess the potential impact of logging on the stability of the Hazel landslide. Below is a synopsis of their findings, with emphasis on the peer-review article.

In their 1998 peer-review article on the Hazel Landslide, Miller and Sias describe the mechanisms through which timber harvest can affect the stability of the Hazel Landslide, as paraphrased below :

Timber harvest reduces the amount of water that trees remove from the soil by evapotranspiration (ET). When water accumulates in the soil, it adds mass to the soil and it reduces frictional resistance between soil (e.g. clay) layers, both of which increase the potential for slope failure. Forests reduce soil moisture both by withdrawing water from the soil through their roots, and intercepting rainfall with their canopies such that it never reaches the soil. In a warm, low elevation site such as the Hazel Landslide, conifers actively transpire throughout the year, including winter. So as rainstorms increase soil moisture levels, conifers reduce soil moisture levels, and the relative magnitude of these two dynamic opposing factors influences the potential for slope failure. Because most rainfall occurs in the late fall, winter and early spring, the ability of forests to remove water during this time is critical to reducing landslide risk. Average annual conifer forest ET at Hazel is between 45-75% of annual rainfall, and winter ET accounts for 50% or more of annual ET. Clearcuts (and hardwood forests) have almost no ability to remove water during the winter.

The underlying geology (and hence groundwater hydrology) of the glacial deposits on the Whitman Bench is complex, making it difficult to accurately differentiate between slide-prone areas, areas where forest removal would affect landslide hydrology (e.g. groundwater recharge areas) and areas where forest removal would have no effect on landslide hydrology. As an example, based on the complex hydrology-slope stability-groundwater recharge model that Miller and Sias constructed for the Hazel Landslide, the Department of Natural Resources (which regulates logging in Washington) delineated a area above as a “groundwater recharge” area. However, recent maps published in newspapers show that much of this recharge area failed during the 2014 event, indicating that it was part of the landslide itself rather than a recharge area to the slide. Miller and Sias noted the limitations of models in accurately delineating groundwater recharge areas and suggest that field measurements of water table elevations would be useful for testing the model.

Thus, while there is little disagreement as to the mechanisms whereby forest removal can affect deep-seated landslides such as the Hazel slide, there is less consensus as to the extent of the areas around such slides that should be protected from logging. As of March 31, 2014, a review of recent news articles suggests there is not yet consensus among experts as to whether the existing protective measures were sufficient to eliminate logging as a contributing factor to the 2014 landslide.

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Numerous parties have raised the question as to whether logging was a contributing factor to the 2014 Oso (aka Hazel) mudslide. Past logging on the Whitman Bench above the Hazel Landslide has been correlated to past slide events, and this has lead to concerns that recent logging may have been a contributing factor to the 2014 slide event. Further, logging activities have long been known to trigger landslides, and in the past decade, a series of spectacular landslides that followed timber harvest have heightened public awareness of linkages between logging and landslides in Washington state. Such events include the 2007 Stilllman Creek landslides, the 2007 Highway 6 landslide , and the 2009 Whatcom County landslides.

Scientists have published several reports and papers that assess the potential impact of logging on the stability of the Hazel landslide. Below is a synopsis of their findings, with emphasis on the peer-review article.

In their 1998 peer-review article on the Hazel Landslide, Miller and Sias describe the mechanisms through which timber harvest can affect the stability of the Hazel Landslide, as paraphrased below :

Timber harvest reduces the amount of water that trees remove from the soil by evapotranspiration (ET). When water accumulates in the soil, it adds mass to the soil and it reduces frictional resistance between soil (e.g. clay) layers, both of which increase the potential for slope failure. Forests reduce soil moisture both by withdrawing water from the soil through their roots, and intercepting rainfall with their canopies such that it never reaches the soil. In a warm, low elevation site such as the Hazel Landslide, conifers actively transpire throughout the year, including winter. So as rainstorms increase soil moisture levels, conifers reduce soil moisture levels, and the relative magnitude of these two dynamic opposing factors influences the potential for slope failure. Because most rainfall occurs in the late fall, winter and early spring, the ability of forests to remove water during this time is critical to reducing landslide risk. Average annual conifer forest ET at Hazel is between 45-75% of annual rainfall, and winter ET accounts for 50% or more of annual ET. Clearcuts (and hardwood forests) have almost no ability to remove water during the winter.

The underlying geology (and hence groundwater hydrology) of the glacial deposits on the Whitman Bench is complex, making it difficult to accurately differentiate between slide-prone areas, areas where forest removal would affect landslide hydrology (e.g. groundwater recharge areas) and areas where forest removal would have no effect on landslide hydrology. As an example, based on the complex hydrology-slope stability-groundwater recharge model that Miller and Sias constructed for the Hazel Landslide, the Department of Natural Resources (which regulates logging in Washington) delineated a area above as a “groundwater recharge” area. However, recent maps published in newspapers show that much of this recharge area failed during the 2014 event, indicating that it was part of the landslide itself rather than a recharge area to the slide. Miller and Sias noted the limitations of models in accurately delineating groundwater recharge areas and suggest that field measurements of water table elevations would be useful for testing the model.

Thus, while there is little disagreement as to the mechanisms whereby forest removal can affect deep-seated landslides such as the Hazel slide, there is less consensus as to the extent of the areas around such slides that should be protected from logging. As of March 31, 2014, a review of recent news articles suggests there is not yet consensus among experts as to whether the existing protective measures were sufficient to eliminate logging as a contributing factor to the 2014 landslide.

heading3
Numerous parties have raised the question as to whether logging was a contributing factor to the 2014 Oso (aka Hazel) mudslide. Past logging on the Whitman Bench above the Hazel Landslide has been correlated to past slide events, and this has lead to concerns that recent logging may have been a contributing factor to the 2014 slide event. Further, logging activities have long been known to trigger landslides, and in the past decade, a series of spectacular landslides that followed timber harvest have heightened public awareness of linkages between logging and landslides in Washington state. Such events include the 2007 Stilllman Creek landslides, the 2007 Highway 6 landslide , and the 2009 Whatcom County landslides.

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Numerous parties have raised the question as to whether logging was a contributing factor to the 2014 Oso (aka Hazel) mudslide. Past logging on the Whitman Bench above the Hazel Landslide has been correlated to past slide events, and this has lead to concerns that recent logging may have been a contributing factor to the 2014 slide event. Further, logging activities have long been known to trigger landslides, and in the past decade, a series of spectacular landslides that followed timber harvest have heightened public awareness of linkages between logging and landslides in Washington state. Such events include the 2007 Stilllman Creek landslides, the 2007 Highway 6 landslide , and the 2009 Whatcom County landslides.

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