Craggy Vegetation...

United States Department of Agriculture Forest Service July 2017

Geology Report Craggy Vegetation Management Project

Salmon/Scott River Ranger District, Klamath National Forest Siskiyou County, California

Prepared By: Angie Bell Klamath National Forest Headquarters 1711 S. Main Street, Yreka, CA 96097

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Table of Contents Geology Report............................................................................................................................ 1

Introduction ............................................................................................................................. 1 Methodology ........................................................................................................................... 1

Analysis Indicators.............................................................................................................. 1

Measures ............................................................................................................................. 1

Spatial and Temporal Bounding of Analysis Area ............................................................. 5

Affected Environment ............................................................................................................. 5 Environmental Consequences ................................................................................................. 7

Alternative 1........................................................................................................................ 7

Direct and Indirect Effects .............................................................................................. 7

Cumulative Effects.......................................................................................................... 8

Alternative 2........................................................................................................................ 8

Direct and Indirect Effects .............................................................................................. 8

Cumulative Effects........................................................................................................ 11

Alternative 3...................................................................................................................... 11

Direct and Indirect Effects ............................................................................................ 11

Cumulative Effects........................................................................................................ 11

Comparison of Alternatives .................................................................................................. 11 Compliance with law, regulation, policy, and the Forest Plan ............................................. 13 Literature Cited ..................................................................................................................... 14

List of Tables Table 1: Risk Matrix using Likelihood and Consequence to Assess the Risk Category of a Landslide

Event in a 7th Field Watershed .............................................................................................................. 5 Table 2: Landslide Likelihood under Current Conditions for the Analysis Watersheds .............................. 6 Table 3: Landslide Risk under Current Conditions for Analysis Watersheds .............................................. 7 Table 4: Summary of GEO Model Outputs and Percent of Watershed with High or Moderate Severity

Disturbance under Alternative 2 for Indirect Effects and Cumulative Effects ................................... 10 Table 5: Summary of GEO Model Outputs and Percent of Watershed with High or Moderate Severity

Disturbance under Alternative 3 for Indirect Effects and Cumulative Effects ................................... 11 Table 6: Summary of GEO Results for 7th Field Watersheds under Alternative 1 with a Modeled Wildfire

Event and Action Alternatives with a Modeled Wildfire Event for Zero to Five Years after Project Implementation ................................................................................................................................... 12

Table 7: Percent of Watershed that is Likely to Burn with High or Moderate Soil Burn Severity for all Alternatives ......................................................................................................................................... 12

Table 8: Summary of Effects to Landslide Risk with and without Wildfire Scenario ................................ 12


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Geology Report

Introduction The purpose of this report is to analyze the effects of the project alternatives on landslide rates and groundwater resources.

The Forest Service Manual Chapter 2880 (Geologic Resources, Hazards and Services) requires the assessment of the risk of safety, property and natural resources from both naturally-occurring and management-related landslides. The Klamath National Forest Land and Resource Management Plan (Forest Plan) directs the Forest to manage vegetation on unstable lands to maintain or enhance slope stability (Forest Plan Standard and Guideline 2-1). Project level review of the unstable lands is required to validate the current mapping (Forest Plan Standard and Guideline 2-2). Unstable lands are defined as active landslides, inner gorges, toe zones of dormant landslides and severely weathered and dissected granitic lands. These features are considered Riparian Reserves (Forest Plan Standard and Guideline - Management Area 10-2).

Methodology Analysis Indicators Landslide Risk. The Forest Plan guides projects to manage vegetation on unstable lands to maintain or enhance slope stability. Slope stability can be defined in terms of landslide risk. Landslide risk is the chance of effects of injury or loss as a measure of the probability and adverse consequences to safety, property or natural resources. Landslide likelihood is determined by geomorphic landform, disturbance, landslide modeling, and road density. Debris slide and debris flow processes are most likely to be influenced by the loss of root strength and interception as a result of timber harvest and prescribed burning versus deep-seated landslides which are not as vulnerable to vegetation changes. Deep-seated landslides such as the large dormant landslide features that exist in the project area are not likely to be reactivated as a result of the proposed activities (Benda et al. 2005, Reid 2010, Slaymaker 2001). Therefore, the focus of the landslide risk assessment is to analyze the indirect effects of the project alternatives on debris slide and debris flow processes.

Measures Landslide Risk A forest-wide goal is to promote slope stability on geologically unstable lands (Forest Plan, pages 4 to 5). Slope stability is indirectly affected by many land management practices. However, it is difficult to directly measure slope stability due to the stochastic (random) and complex nature of landslide processes in the Klamath Mountains. This analysis uses landslide risk as a proxy for slope stability. Landslide risk is a combination of the likelihood a landslide event may occur and the consequences of such an event.

Watershed Modeling The risk assessment uses the cumulative watershed effects (CWE) model results for the GEO model. Although this model is labeled as a ‘cumulative watershed effects’ model, it does not measure cumulative effects as defined by the Council of Environmental Quality for NEPA


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analysis. Instead, it provides information on the effects of alternatives by adding the effects of various activities proposed for each alternative (i.e. road construction, landings, thinning, etc.) to result in a risk ratio for the process model. It also provides information on the added effects of past activities and events to provide a baseline risk ratio to which to compare the effects of proposed alternatives. For the GEO model the threshold of concern for the risk ratio is 1.0. A risk ratio greater than or equal to 1.0 is a yellow flag and calls for a closer look at mitigation opportunities. Cumulative Watershed Effects: the Abridged Version (Bell 2012) provides a more detailed description of the model.

The GEO model estimates the volume of sediment delivered to the mouth of a 7th field watershed due to all types of landsliding during a 10-year storm event. The coefficients in the mathematical equation were developed in the Salmon River basin and the model assumes the geomorphic landforms react identically regardless of elevation. The indirect effects of an alternative will be analyzed using the landslide volume estimates attributed to the alternative relative to the existing condition volume estimates. Changes to landslide volume between the different alternatives is apparent in the resulting risk ratio.

The GEO model was run for Alternative 1 (current condition) and Alternatives 2 and 3 for the proposed activities alone. It was also run under a wildfire scenario for Alternatives 1 and 3. We chose to model potential wildfire watershed effects for Alternative 3 and not Alternative 2 because the GEO results of Alternative 2 and 3 are relatively similar. Therefore, the amount of time that would be required to run the model for both action alternatives was not warranted because of the small differences between these alternatives. The modeling results for Alternative 3 under the wildfire scenario will be used as a proxy for the effects of Alternative 2 under a wildfire scenario. The modeling was generated using the FlamMap modeling for fire potential zero to five years after project implementation (see the Fire and Fuels report for detailed methods). The resulting flame lengths were used with the GEO modeling as a proxy for soil burn severity. It was assumed that flame lengths of less than four feet would have a low soil burn severity, between 4.1 and 8 feet would have a moderate severity and greater than 8 feet would have high severity. The purpose of combining a wildfire scenario and GEO results is to illustrate the benefits of the Alternative 2 and 3 treatments on watershed health over the long term. The detailed results of the GEO modeling can be found in the project record in the cumulative watershed effects analysis excel spreadsheet, available on the project website.

Mapping of geologic and soil resources has not been completed for the Rocky Gulch-Yreka Creek 7th field watershed (18010207050206) because of the small amount of public lands in the watershed. This mapping is a required input into the model so there are no model results for Rocky Gulch-Yreka Creek. The landslide likelihood reported in this analysis was estimated using Long Gulch as an analogy for the baseline. However, about 10 percent of Rocky Gulch-Yreka Creek was affected by a high and moderate severity wildfire in August 2016 (the Grade Fire). The GEO model risk ratio was estimated using Long Gulch as a baseline with the estimated effects of the Grade Fire added; it was assumed that 200 acres burned with moderate or high severity and the watershed is non-granitic with moderate slopes (less than 65 percent). Landsliding Likelihood

Landslide likelihood is determined by geomorphic landform, disturbance, vegetation condition, bedrock type, and groundwater conditions. The analysis uses existing field reviewed geomorphic mapping, field reviewed bedrock mapping and historical landslide information to determine the


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likelihood of landsliding. A majority of the west side of the Forest (in which the project area is located) is relatively unstable so the likelihood of having small localized landslides in any given 7th field watershed during any storm is highly probable with or without management activities. This analysis is focused on determining the likelihood of a landslide event. A landslide event is defined for this analysis as a large scale, extensive episode resulting in several landslides that could interrupt ingress and egress (road access) or fluvial processes on 3rd to 5th order streams, or damage major infrastructure across a 7th field watershed. (Dai et al. 2002, Wise et al. 2004, AGS 2007).

The likelihood of a landsliding event was analyzed at the 7th field watershed scale using a combination of the percent of the watershed that was harvested or burned within the last 10 years, the GEO risk ratio, and the percent of unstable lands. The likelihood categories are summarized below: (definitions of the risk categories referenced below (low to very high: in italics) may be found following Table 1).

1. Almost Certain – A landsliding event is expected to occur even under an average storm event (two-year storm event). A watershed in this category meets at least two of the following criteria: 1) greater than or equal to 25 percent of the watershed had high to moderate disturbance (based on soil burn severity, silviculture or fuels reduction prescriptions) in the past 10 years; 2) the GEO risk ratio is greater than or equal to 1.5; or 3) greater than or equal to 25 percent of area is designated as unstable lands (per definition in Forest Plan).

2. Highly Likely – A landsliding event will probably occur under an average storm event. A watershed in this category meets at least one of the following criteria: 1) greater than or equal to 25 percent of the watershed had high to moderate disturbance (based on soil burn severity, silviculture or fuels reduction prescriptions) in the past 10 years; 2) the GEO risk ratio is greater than 0.95; or 3) greater than or equal to 25 percent of the area is designated as unstable lands.

3. Likely – A landsliding event is likely to occur under a 10- to 20-year storm event. A watershed in this category meets at least one of the following criteria: 1) between 10 percent and 25 percent of the watershed had high to moderate severity disturbance (based on soil burn severity, silviculture or fuels reduction prescriptions) in the past 10 years; 2) the GEO risk ratio is between 0.75 and 0.95; or 3) between 10 percent and 25 percent of the area is designated as unstable lands.

4. Unlikely – Landsliding might occur under a 20- to 99-year storm event. A watershed meets this category if it is on the west side of the Forest and does not meet the criteria in above categories.

5. Rare – Landsliding is conceivable but only under a greater than or equal to100-year storm event. A watershed meets this category if it is on the east side of the Forest (with occasional exceptions).

Consequence Categories

The consequences of a landslide are based on the impacts to elements at risk. The elements at risk for this analysis are human safety, infrastructure, property, recreation and visitor use, and environmental resources. The consequences categories are summarized below:


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1. Catastrophic Consequences – In this category human health and safety are susceptible to landslide events. The presence of occupied structures (homes, businesses, work areas), campgrounds, or heavily used roads that are vulnerable to (in the path of) a potential landslide event meets the criteria for this category.

2. Major Consequences – In this category essential infrastructure such as main National Forest Transportation System (system) roads (maintenance levels 3, 4 and 5), power lines, pipelines, municipal water sources, and railroads are susceptible to (in the path of) landslide events and may be rendered inoperative as a result. This category is also used to describe the vulnerability of anadromous fish habitat to landslide events that lead to the complete loss of their habitat. This category also applies when stream channels are vulnerable to landsliding which leads to aggrading (depositing sediment) or degrading (removing sediment) the stream channel. Also, the reduction of shade and riparian vegetation over a large portion (greater than or equal to 50 percent) of late flowing intermittent or perennial streams is a major consequence. See the hydrology and aquatics resource reports for more information regarding the impacts of these effects on shade.

3. Moderate Consequences – In this category only non-essential infrastructure and property such campgrounds (unoccupied), trailheads, day use areas and system trails are vulnerable to landslide events and will be rendered inoperable. Landsliding debris will temporarily block major ingress and egress roadways. Anadromous fish habitat is vulnerable to a partial loss or short-term impairment. This category also applies when stream channels are vulnerable to aggradation, degradation or a reduction of shade over less than 50 percent of late-flowing intermittent and perennial streams.

4. Minor Consequences – In this category infrastructure is vulnerable to damage that does not render it inoperable but makes its operation unsafe but repairable or inconvenient (e.g. debris partially blocking a two-lane road) as a result of landslide events. The minor damage category applies to landsliding into streams that are vulnerable to a reduction of shade at the site scale or blocking the stream for the short term (less than six months).

5. Nuisance Consequences – In this category there is no infrastructure, fish habitat or stream shade vulnerable to landslide events.

Landslide Risk Matrix

The landslide risk matrix (Table 1) is the crosswalk between the likelihood, consequences, and the implications of landslide risk. Once the likelihood and consequences have been determined using the criteria above, the risk matrix is used to determine the risk category that fits that situation. For instance, you may have an area that is likely to experience landsliding during a 10-year storm event and the essential infrastructure is susceptible to landsliding; in this case the landslide risk is high. This risk has implications for forest management which are described in the section below.


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Table 1: Risk Matrix using Likelihood and Consequence to Assess the Risk Category of a Landslide Event in a 7th Field Watershed

Consequences/Likelihood Almost Certain Highly likely Likely Unlikely Rare

Catastrophic Consequences Very High Very High High Moderate Moderate

Major Consequences Very High High High Moderate Low

Moderate Consequences High High Moderate Moderate Very Low

Minor Consequences High Moderate Low Low Very Low

Nuisance Consequences Low Low Very Low Very Low Very Low

The Risk Category Implications

1. Very High - Health and human safety or essential infrastructure is at risk. There is an immediate and urgent need to reduce the likelihood of landsliding or mitigate the consequence to the elements at risk.

2. High - There is a reasonable probability that landsliding will impact essential infrastructure and may impact health and human safety. Non-essential infrastructure as well as recreation and visitor use may be impacted. Project-wide and global mitigations need to be in place to minimize impacts to landslide processes for actions in these watersheds.

3. Moderate - There is a moderate probability of impacts to essential or non-essential infrastructure or health and human safety as a result of landsliding. The cost and benefit of mitigations needs to be considered before actions are proposed for implementation. Strategic or localized mitigations need to be in place to minimize impacts to landslide processes for actions in these watersheds.

4. Low - There a low probability of impacts to elements at risk. Remediation of landsliding consequences may be the most cost effective method of dealing with these areas.

5. Very Low - There is almost no probability of impacts to elements at risk as a result of landsliding. Mitigations are rarely needed.

Spatial and Temporal Bounding of Analysis Area The spatial scale for landslide risk is the 7th field watershed scale for the direct and indirect effects and the cumulative effects. The models used for analysis are calibrated at a 7th field scale (Bell 2012). The temporal scale is zero to 10 years for short term and greater than 10 years for long term. Elevated landslide rates due to forest management have been shown to begin to decrease around seven to 12 years after disturbance in Northern California (Ziemer 1981).

Affected Environment Landslide Risk


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Upper Humbug and Middle Fork Humbug Creeks both have a highly likely likelihood of a landslide event occurring during an average storm event. This is mainly a result of the combination of high road densities and the steep, weathered granitic bedrock in the watersheds. Lower Humbug Creek, Clear Creek and Rocky Gulch are likely to have landslide events during a 10- to 20-year storm event. These watersheds have less area underlain by steep, weathered granitic bedrock than Upper and Middle Fork Humbug Creek. Greenhorn Creek, Yreka City-Yreka Creek, and Long Gulch are unlikely to experience a landsliding event even during a 20 year storm event.

Table 2: Landslide Likelihood under Current Conditions for the Analysis Watersheds

Watershed Code Watershed Name Existing

GEO model Risk Ratio

Unstable Lands (% Watershed)

Watershed Disturbance

(% Watershed)

Landslide Likelihood

18010206080101 Upper Humbug Creek 1.37 17% 0% Highly Likely

18010206080102 Middle Fork Humbug Creek 1.10 11% 0% Highly

Likely 18010206080104 Lower Humbug Creek 0.52 13% 0% Likely 18010206080103 Clear Creek 0.61 16% 0% Likely 18010207050203 Greenhorn Creek 0.49 9% 9% Unlikely 18010207050204 Yreka City-Yreka Creek 0.29 1% 0% Unlikely 18010207050205 Long Gulch 0.59 1% 0% Unlikely 18010207050206 Rocky Gulch-Yreka Creek 0.75 0% 0% Likely

Upper Humbug Creek would have moderate consequences as a result of a landslide event. The values at risk include endangered fish habitat and the potential for damage to private property with a low probability of a landslide affecting an occupied residence. Middle Fork Humbug and Lower Humbug Creek would have major consequences as a result of a landslide event mainly because of the primary ingress/egress roadways that could be affected by debris flows in the watershed. Lower Humbug Creek has year-round residences along its banks that are vulnerable to debris flow events. Clear Creek would have moderate consequences because of the potential for damage to private property with a low probability of a landslide affecting an occupied residence.

Greenhorn Creek would have nuisance consequences because the effects are restricted to interruptions of recreation at the city park including recreational fishing and effects to non-essential infrastructure such as bridges on the walking path. Yreka City-Yreka Creek, and Long Gulch will have minor consequences from a landslide event. The stream channels in the Yreka City-Yreka Creek watershed have been modified to carry flood events and debris flows. Long Gulch flows into Yreka Creek downstream of the City of Yreka; a large floodplain in that area provides defense against the effects of debris flows.

The Grade Fire burned with high and moderate severity in Rocky Gulch-Yreka Creek. This makes debris flow initiation locations less predictable because a landslide could be triggered on any portion of the fire area during an average storm event. Prior to the fire the primary landslide process was debris flow of material already in the stream channel. New debris sliding could occur anywhere in the drainage affected by moderate or high severity fire-generated debris flows


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from anywhere on the hillslope. This means that private land could be affected if a debris slide from the hillslope initiates a debris flow outside of existing stream channels. The most likely effect would be deposits of sediment on private property and superficial damage to private property. This means that the landslide consequence in Rocky Gulch-Yreka Creek is moderate.

Table 3: Landslide Risk under Current Conditions for Analysis Watersheds

Watershed Name Likelihood Consequence Risk Upper Humbug Creek Highly Likely Moderate High

Middle Fork Humbug Creek Highly Likely Major High

Lower Humbug Creek Likely Major High

Clear Creek Likely Moderate Moderate

Greenhorn Creek Unlikely Nuisance Very Low

Yreka City-Yreka Creek Unlikely Minor Low

Long Gulch Unlikely Minor Low

Rocky Gulch-Yreka Creek Likely Moderate Moderate

Upper, Lower and Middle Fork Humbug Creeks currently have high landslide risks. Clear Creek and Rocky Gulch-Yreka Creek have moderate risks. Greenhorn has a very low landslide risk. Yreka City-Yreka Creek and Long Gulch and have low landslide risks under current conditions.

Environmental Consequences Alternative 1

Direct and Indirect Effects No treatment in the project area would lead to decreased tree vigor and in some stands increased tree mortality due to competition in the timber stands over time. Without treatment the species diversity of the timber stands would decrease, making the stand more likely to be impacted by highly intense and severe wildfires (see the Fire and Fuels report and the Silviculture report). The increased tree mortality would increase landslide likelihood by reducing root cohesion (Swanston and Dryness 1973) and precipitation interception (Reid 2010). Alterations to evapotranspiration and precipitation interception processes due to tree loss would also increase landslide likelihood across the watersheds. High severity wildfire, which is associated with tree mortality, would increase the landslide likelihood should an event occur.

If no wildfire should occur within the spatial and temporal boundaries of this analysis the landslide likelihood will decrease slightly overtime as the areas effected by past disturbances recover. This recovery outweighs the decreased forest health in the watershed for landslide risk reduction. One of the primary drivers of the high landslide risks in the Humbug Creek area is the high road density. The decision made regarding travel management reduced the administrative road density and the unauthorized route (previously non-system road) density; these roads and routes are passively recovering in the watershed. This would reduce the landslide risk over time. However, the risk would remain high for Upper, Middle and Lower Humbug because of the high road densities in the watersheds.


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Under a Wildfire Scenario If a wildfire should occur in the project area and no treatment is implemented the GEO risk ratios will be increased to well over the threshold of concern of 1.0 for Upper, Middle, and Lower Humbug, Clear Creek, Long Gulch and Rocky Gulch-Yreka Creek. The model results for Greenhorn Creek and Yreka City-Yreka Creek are likely an overestimate considering great lengths would be implemented to prevent a wildfire from entering or spreading in these watersheds, however even with the overestimation they would remain close to or below the threshold of concern for the GEO model.

It is assumed in this analysis that a high intensity wildfire in any of the 7th field watersheds in the Humbug 5th field watershed are likely to result in at least 20 to 25 percent of the watershed having high or moderate soil burn severity. This is based on information from previous wildfires including the 2008 wildfires, the Salmon Complex Fires in 2013 and the 2014 wildfires. Greenhorn Creek, Yreka Creek and Long Gulch are likely to have a lower percent of high and moderate severity fire given the proximity to the city of Yreka, priority of firefighting resources, and access to the area. If 25 percent or more of the watersheds have high or moderate soil burn severity, this indicates that the landslide likelihood would increase to almost certain for Upper, Middle Fork and Lower Humbug Creek and Clear Creek. Based on increases in the GEO model, Long Gulch will move into a highly likely landslide likelihood. Rocky Gulch-Yreka Creek will go to a highly likely landslide likelihood because of the current conditions created by the Grade Fire. If the model results are not an overestimate, Greenhorn will move to a highly likely category and Yreka City-Yreka Creek to likely.

This would lead to landslide risk for Middle and Lower Humbug Creek moving from a high landslide risk to a very high landslide risk. It would also lead to Clear Creek moving from a moderate landslide risk to a high landslide risk. Upper Humbug Creek would continue to have a high landslide risk even with a wildfire event. Greenhorn Creek would move to low. Yreka City-Yreka Creek would remain at low. Long Gulch would move to moderate. Rocky Gulch-Yreka Creek would have a high landslide risk if the rest of the watershed were to burn as the fuels model predicts. To see the change in risk ratio for the analysis area under Alternative 1 with or without a wildfire event, see Table 6.

Cumulative Effects The only action considered a reasonably foreseeable event that will have an effect on landslide risk is a timber harvest plan on private land in Lower Humbug Creek. The timber harvest plan covers a small area and will only increase the risk ratio in the watershed by 0.01. This is not enough to increase the landslide risk for the watershed. This means that the cumulative landslide risk remains the same for all watersheds in the analysis area as described in the direct and indirect effects section above.

Alternative 2

Direct and Indirect Effects The direct and indirect effects of Alternative 2 will not measurably affect (change) the current landslide risk ratio of any of the watersheds (Table 6). The silvicultural prescriptions are mainly thinning from below in plantations which will have little effect on the root support in the


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watershed. The logging systems are a combination of tractor logging and skyline and have been designed either with project design features or project design components (i.e. silvicultural prescriptions, location of new landings, fuels treatment placement, etc.) to minimize effects to landslide processes.

Chatwin (1994) found scheduling activities with the use of wet weather operation standards and normal operating seasons was effective at reducing negative effects to hillslope hydrology especially on the occurrence of rilling and gullying, which will indirectly minimize negative effects to landslide risk. Cristan et al. (2016) concluded that roads, skid trails and stream crossings have the highest impact on hillslope hydrology changes including rilling and gullying. These activities should be given the most attention while planning best management practices for timber harvest in order to be effective in reducing effects.

Madej et al. (2012) found that most sediment delivered to the streams in the Panther Creek basin (Northwestern California) was from landslides originating on landings and roadbeds. This rate was reduced by improved road and landing construction standards, reduced ground disturbance from tractors for ground-based harvest and from treating legacy sediment sources. Litschert and MacDonald (2009) found that using best management practices meant only 19 of 200 sites that had undergone timber harvest had rills or gullies in the Sierra Nevada Forest Service lands. They attributed this low rate to the installation of effective waterbars on skid trails and the proper closing of skid trails before winter weather set in.

There are more than 20 project design features that are intended to reduce the probability of hillslope hydrology changes and changes to root support. The protection of riparian reserves including landslides, inner gorges and swales, in combination with partial harvest techniques that leave some understory vegetation intact have been found to substantially reduce the increase in landslide probability after timber harvest (Sidle 1992; Dhakal and Sidle 2003). Sidle (1992) found that partial cuts that retain the integrity of the understory vegetation maintain enough root strength to balance stand health needs and slope stability concerns. Cristan et al. (2016) concluded that implementation of best management practices was most effective in reducing effects to watershed processes when implemented both during treatment activities and at the close of the project.

There are project design features and design components that minimize the effects to root strength. The project design components include the silvicultural prescriptions and the prescribed fire prescriptions. The silvicultural prescriptions are essentially thinning from below and the prescribed fire is intended to have low to moderate burn severity in a mosaic pattern. These silvicultural and burning prescriptions will have an extremely high effectiveness of maintaining sufficient root support across the watershed. The overall effectiveness of project design to maintain sufficient root strength for slope stability is extremely high (See Forest Plan Monitoring Reports on the Forest website: http://www.fs.usda.gov/main/klamath/landmanagement/planning).

http://www.fs.usda.gov/detail/klamath/landmanagement/planning/?cid=fsm8_049843

http://www.fs.usda.gov/detail/klamath/landmanagement/planning/?cid=fsm8_049843

http://www.fs.usda.gov/main/klamath/landmanagement/planning


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Table 4: Summary of GEO Model Outputs and Percent of Watershed with High or Moderate Severity Disturbance under Alternative 2 for Indirect Effects and Cumulative Effects

7th Field Watershed Name Alt. 2 Risk Ratio (Indirect Effects)

Alt. 2 Watershed Disturbance

Indirect Effects (% Watershed)

Alt. 2 Cumulative Risk Ratio


Cumulative Effects (% Watershed)

Upper Humbug Creek 1.29 0% 1.29 0%

Middle Fork Humbug Creek 0.89 0% 0.89 0%

Lower Humbug Creek 0.47 0% 0.48 1%

Clear Creek 0.62 0% 0.62 0%

Greenhorn Creek 0.49 9% 0.49 9%

Yreka City-Yreka Creek 0.29 0% 0.29 0%

Long Gulch 0.59 0% 0.59 0%

Rocky Gulch-Yreka Creek 0.75 0% 0.75 0%

If a wildfire occurs in the project area after Alternative 2 treatments, the negligible negative effects in some of the 7th field watersheds (some don’t have a measurable effect) will be easily outweighed by the benefits to the landslide processes, by reducing the greater negative effects from a wildfire event. The assumption is that in any place where treatment occurs, the flame lengths will be less than four feet until about 10 to 15 years after treatment (see the fire and fuels report).

The assumption used to get results from the fire effects model is that a watershed is expected to have 25 percent of its area burn with moderate or high severity in a wildfire event under no action and under Alternative 2 about nine percent of the watershed will burn with high or moderate severity under Alternative 2. This is a reduction of the original percent expected to have high or moderate soil burn severity relative to the percent of the watershed treated.

With these assumptions that are dependent on a wildfire event occurring in the project area, Alternative 2 is expected to have overall less negative effects on landslide processes than Alternative 1. As far as the analysis indicators of this analysis are concerned, Alternative 2 will reduce the landslide likelihood for Upper, Middle and Lower Humbug Creeks and Clear Creek from almost certain to highly likely. Greenhorn and Long Gulch will both go from highly likely down to likely. Yreka City-Yreka Creek will go from likely to unlikely. Rocky Gulch-Yreka Creek will stay the same as described under Alternative 1. For Alternative 2, Middle Fork and Lower Humbug Creek will move to a high landslide risk instead of going to a very high risk as it would under Alternative 1 if a wildfire event takes place. Greenhorn Creek will move to a very low risk; the landslide risks for the other watersheds remain the same as in Alternative 1 with a wildfire.

However, the risk ratios with Alternative 2 treatments and then a wildfire event are much lower than is described for Alternative 1 with a wildfire (see Table 6). When you consider the reduction in risk ratio between Alternative 1 and Alternative 2 under the wildfire scenario compared to the small increase in risk ratio (less than 0.01) that is a result of implementing Alternative 2 with a wildfire event, the benefits are clear. See Table 7 for results that compare Alternative 1 to Alternatives 2 and 3 for burn severity percentages.


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Cumulative Effects The only action considered a reasonably foreseeable event that will have an effect on landslide risk is the same timber harvest plan mentioned in Alternative 1 and it will have the same effects on Alternative 2. The 0.01 increase to the risk ratio is not enough to increase the landslide risk for the watershed. This means that the cumulative landslide risk remains the same for all watersheds in the analysis area as described in the direct and indirect effects section above.

Alternative 3

Direct and Indirect Effects The effects on landslide risk of Alternative 3 are the same as for Alternative 2.

Table 5: Summary of GEO Model Outputs and Percent of Watershed with High or Moderate Severity Disturbance under Alternative 3 for Indirect Effects and Cumulative Effects

7th Field Watershed Name Alt. 3 Risk

Ratio (Indirect Effects)


Indirect Effects (% watershed)

Alt. 3 Cumulative Risk Ratio

Alt. 3 Watershed Disturbance Cumulative

Effects (%Watershed)

Upper Humbug Creek 1.28 0% 1.28 0% Middle Fork Humbug Creek 0.89 0% 0.89 0% Lower Humbug Creek 0.47 0% 0.48 1% Clear Creek 0.62 0% 0.62 0% Greenhorn Creek 0.49 9% 0.49 9% Yreka City-Yreka Creek 0.29 0% 0.29 0% Long Gulch 0.59 0% 0.59 0% Rocky Gulch-Yreka Creek 0.75 0% 0.75 0%

Cumulative Effects The cumulative effects are the same as described in Alternative 2.

Comparison of Alternatives Implementation of the action alternatives do not measurably change the landslide risk in a negative manner. The increase in risk ratios from the implementation of either Alternative 2 or 3, compared to Alternative 1, result in no more than a 0.01 increase. On average there is a substantially increased landslide risk if no action is taken and a wildfire event occurs compared to the risk if the action alternatives are implemented and then a wildfire event takes place.


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Table 6: Summary of GEO Results for 7th Field Watersheds under Alternative 1 with a Modeled Wildfire Event and Action Alternatives with a Modeled Wildfire Event for Zero to Five Years after Project Implementation

7th Field Watershed Name Existing Risk Ratio

Alt. 2 or 3 Risk Ratios

(Indirect Effects)

Alt. 1 Risk Ratio with

Wildfire

Alt. 2 or 3 Risk Ratio

with Wildfire

Reduction in Risk

Ratio from Fire Effects Under Alt.2

or 3

Upper Humbug Creek 1.37 1.28 4.23 1.97 53%

Middle Fork Humbug Creek 1.10 0.89 2.48 1.54 38%

Lower Humbug Creek 0.52 0.47 1.82 1.09 40%

Clear Creek 0.61 0.62 1.86 1.10 41%

Greenhorn Creek 0.49 0.49 1.12 0.53 52%

Yreka City-Yreka Creek 0.29 0.29 0.77 0.25 68%

Long Gulch 0.59 0.59 2.16 1.38 36%

Rocky Gulch-Yreka Creek 0.75 0.75 2.94 2.06 30%

Table 7: Percent of Watershed that is Likely to Burn with High or Moderate Soil Burn Severity for all Alternatives

7th Field Watershed Name Alt. 1 Percent of Watershed Likely to Burn With High or Moderate Soil Burn Severity

Alt. 2 or 3 Percent of Watershed Likely to Burn

With High or Moderate Soil Burn Severity

Upper Humbug Creek 25% 9%

Middle Fork Humbug Creek 25% 18%

Lower Humbug Creek 25% 20%

Clear Creek 25% 16%

Greenhorn Creek 10% 9%

Yreka City-Yreka Creek 1% 1%

Long Gulch 10% 9%

Rocky Gulch-Yreka Creek 10% 9%

Table 8: Summary of Effects to Landslide Risk with and without Wildfire Scenario

Indicator Alternative 1 Alternative 2 Alternative 3

Landslide Risk with no wildfire scenario

There are three 7th field watersheds with high landslide risk (Upper, Middle Fork, and Lower Humbug Creek), two with a moderate risk (Clear Creek and Rocky Gulch-Yreka Creek), two with a low risk (Yreka City-Yreka Creek and Long Gulch), and one with a very low risk (Greenhorn Creek).

Same as Alternative 1. Same as Alternative 1.


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Indicator Alternative 1 Alternative 2 Alternative 3

Landslide Risk with wildfire scenario

There are two 7th field watersheds with a very high landslide risk Middle Fork and Lower Humbug Creek), three with high risk (Upper Humbug Creek, Clear Creek and Rocky Gulch-Yreka Creek), and three with low risk (Greenhorn Creek, Yreka City-Yreka Creek, and Long Gulch).

There are five 7th field watersheds with high landslide risk (Upper, Middle Fork, and Lower Humbug Creek, Clear Creek and Rocky Gulch-Yreka Creek), two with a low risk (Yreka City-Yreka Creek and Long Gulch), and one with a very low risk (Greenhorn Creek).

Same as Alternative 2.

Compliance with law, regulation, policy, and the Forest Plan Existing mapping was field verified by the Forest Geologist and unstable lands were removed from treatment areas where slope stability was not benefited. The landsliding magnitude and risk were analyzed for all of the alternatives in the project. The risk associated with the direct and indirect and cumulative effects of the project have been minimized by project design features and best management practices. The project is consistent with Forest Plan standards and guidelines as described in the Forest Plan Consistency Checklist in the project record, which is available on the project website.


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Literature Cited (AGS) Australian Geomechanics Society. 2007. Practice Note Guidelines for Landslide Risk

Management 2007. Journal and News of the Australian Geomechanics Society. Vol. 42, Issue 1.

Bell, A. 2012. Cumulative Watershed Effects Modeling: The Abridged Version. Prepared for the Klamath National Forest.

Benda, L., Hassan, M., Church, M., May, C. 2005. Geomorphology of Steepland Headwaters: The Transition from Hillslopes to Channels. Journal of American Water Resources Association.

Chatwin, S. 1994. Measures for Control and Management of Unstable Terrain. In: A Guide for Management of Landslide-prone Terrain in the Pacific Northwest, edited by S. Chatwin, D. Howes, J. Schwab, and D. Swanston. Land Management Handbook No. 18. British Columbia Ministry of Forestry, Crown Publications Inc., Victoria, Canada.

Cristan, R., Aust, W., Bolding, M., Barrett, S., Munsell, J., Schilling, E. 2016. Effectiveness of Forestry Best Management Practices in the United States: Literature Review. Forest Ecology and Management. 133-151.

Dai, F., Lee, C., Ngai, Y. 2002. Landslide Risk Assessment and Management: an Overview. Engineering Geology. Vol 64.

Dhakal, A, and Sidle, R. 2003. Long-term Modeling of Landslides for Different Forest Management Practices. Earth Surface Processes and Landforms. Issue. 28.

Litschert, S.E., MacDonald, L.H. 2009. Frequency and Characteristics of Sediment Delivery Pathways from Forest Harvest Units to Streams. Forest Ecology and Management. 259 (2), 143–150.

Madej, M.A., Bundros, G., Klein, R., 2012. Assessing effects of changing land use practices on sediment loads in Panther Creek, North Coastal California. In: Proceedings of Coast Redwood Forests in a Changing California: A Symposium for Scientists and Managers. USDA Forest Service General Technical Report. Pacific Southwest-GTR-238, pp. 101–109.

Reid, L. 2010. Cumulative Watershed Effects of Fuel Management in the Western United States: Chapter 6 – Cumulative Effects of Fuel Treatments on Channel Erosion and Mass Wasting. Rocky Mountain Research Station, General Technical Report. RMRS-GTR-231.

Sidle, R. 1992. A Theoretical Model of the Effects of Timber Harvesting on Slope Stability. Water Resource Research. Vol. 28, Issue 7.

Slaymaker, O. 2001. Geomorphic Impacts of Timber Harvest. Chinese Science Bulletin.

Swanston, D., Dyrness, C. 1973. Stability of Steep Land. Journal of Forestry.


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USDA Forest Service. 1995 (updated through 2010). Land and Resource Management Plan: Klamath National Forest (Forest Plan). Yreka, CA.

USDA Forest Service. 2008. Forest Service Manual 2880 – Geologic Resources, Hazards and Services.

Wise, M., Moore, G., and VanDine, D. (eds.). 2004. Landslide Risk Case Studies in Forest Development Planning and Operations. Land Management Handbook 56, British Columbia Ministry of Forestry Publication.

Ziemer, R. 1981. The Role of Vegetation in the Stability of Forested Slopes. Pacific Southwest Research Station. Arcata, CA.

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