East Fork Illinois River Channel and Floodplain Restoration Project

Transcription

1 East Fork Illinois River Channel and Floodplain Restoration Project Wild Rivers Ranger District, Rogue River-Siskiyou National Forest /s/ Joni D. Brazier Date: February 20, 2015 Joni D. Brazier, Forest Soil Scientist

2 Soils Introduction This report analyzes the effects of the East Fork Illinois River Channel and Floodplain Restoration Project on soil productivity, erosion, large woody debris and slope stability within the analysis area. It analyzes the effects of the following proposed activities: the placement of large wood instream structures, construction of stream side channels, and revegetation of riparian upland sites. Background and Affected Environment Management Direction Land management direction is contained in the Siskiyou National Forest (SNF) Land and Resource Management Plan (LRMP) (UDSA Forest Service 1989) as amended by the Northwest Forest Plan (USDA Forest Service and USDI Bureau of Land Management 1994). The authorities governing Forest Service soil management are outlined in Forest Service Manual (FSM) 2550 Soil Management (WO Amendment , Effective November 23, 2010). Regional direction for maintaining and protecting the soil resource from detrimental disturbance to soil productivity is given in FSM 2500 Watershed Protection and Management, Region 6 Supplement No The Siskiyou National Forest (SNF) LRMP provides standards and guidelines (S&Gs) for soil and water resources on pages IV-44 through IV-48. In regard to soils and geology, they include S&Gs for detrimental soil conditions, soil erosion, mass movement, and large woody material. Detrimental soil conditions include compaction, displacement, puddling, and severely burned soil conditions. Detrimental soil conditions are further defined in FSM 2500, Region 6 Supplement No On the Siskiyou National Forest, the total area of detrimental soil conditions should not exceed 15 percent of the total acreage within the activity area, including roads and landings (S&G 7-2, page IV-44) (Siskiyou National Forest, 1989). Surface organic matter (duff, litter) is vital for protecting surface soils from erosion. Mineral soil exposure (loss of duff and litter) should not exceed the following limits (ibid.): o o o 40% mineral soil exposed on soils classed low-to-erate erosion hazard; 30% mineral soil exposed on soils classed erosion hazard; 15% mineral soil exposed on soils classed very erosion hazard. Standards and Guidelines for large woody material stress the importance of addressing sitespecific needs that will maintain a healthy forest ecoystem. In general, five to twenty pieces of large woody material per acre should remain on each site; material should be from a range of decomposition classes; each piece should be at least 20 inches in diameter at the large end and contain at least 40 cubic feet volume (ibid.). In addition, the Northwest Forest Plan requires that all areas and potentially areas be managed as Riparian Reserve. 1

3 Affected Environment The analysis area is in the Klamath Mountains physiographic province, and within the Siskiyou Mountains, which is a mountain range within the Klamaths that runs west-east roughly straddling the Oregon-California border. The Klamath-Siskiyous are known for their blocks and bands of peridotite and serpentine rock, which is the dominant geologic parent material in the analysis area. Gabbros (an intrusive rock), and metavolcanics are also present. The Dunn Creek and upper East Fork Illinois River drainages have been shaped by past glaciation, based on landform association interpretation done by Professor Jay Noller at Oregon State University (GIS files in Region 6 data, dated April 2014). The remnants of this past glacial activity likely contribute in part to the general instability of the landscape today. Soils have been mapped as part of the Soil Resource Inventory for the Siskiyou National Forest (Meyer and Amaranthus 1979), and are listed in Table 1 by general location in the analysis area. Overall soil productivity in the analysis area has not been impacted by any past management or other human activities, as much of the terrain is rugged and fairly inaccessible. There have been scattered mining impacts within and immediately adjacent to stream channels throughout the project area but nothing widespread enough to be considered detrimental to long-term soil productivity in the area. Table 1. Soil map units present in sections of the analysis area. Project Location Side Channel Construction Area Dunn, NF Dunn, Poker Creek Wood Placement Areas EF Illinois River & Bybee Gulch Wood Placement Areas Soil Map Units Present 15 (stream channel alluvium) 4, 15, 31, 36, 314, 812, 818, 978 5, 12, 15, 31, 96 Soils in the analysis area are naturally prone to erosion when vegetative cover and litter is removed, and when subsurface soils are exposed (refer to Table 2). This is due in large part to the steep terrain in much of the area, but also considers other characteristics such as soil texture and structure, permeability, and bedrock. As a result, these soils are also prone to contributing sediment to adjacent stream systems. Effective groundcover is very important for minimizing surface erosion and sedimentation in the analysis area. Much of the analysis area exhibits various levels of instability as well, much of it due to steep slopes and ly fractured nature of underlying bedrock. Much of the slope instability in the area manifests itself as shallow debris slides or small slumps, and channel (refer to Table 2). The landscape also exhibits deep-seated landflow and landslump terrain, which either is or has been active during the past history of the slope. These locations vary from shallow to very deep soils, and have soils with very slow infiltration rates (hydrologic group D). Movement of these slopes most typically re-activate during very wet periods with soil water saturation. A review of the analysis area in Google Earth revealed three active landslide locations within the analysis area. All three appear to be caused by the undermining of the steep toe slopes by Dunn Creek in serpentine geology, and contribute chronic ravel to the stream, and as well as likely larger pulses of rock and fines during flow events. The largest of these, labelled Landslide #1 located on the west bank of Dunn Creek in section 2, appears in particular to be due to the large landflow feature on the opposite mountainside, pushing Dunn Creek into the opposite hillside. This may also be what is triggering the smaller landslide #2 on Dunn Creek. Refer to Figure 1. 2

4 The vegetation in the analysis area has not been heavily manipulated by management actions and therefore it is assumed that the levels of large woody debris are within the natural range that would be expected for this area. Table 2. Soil characteristics of map units in the analysis area (from Meyer and Amaranthus 1979). Map Unit (Complex) Acres Surface erosion potential Moderate to severe Subsurface erosion potential 5 8 Severe 12 9 Mod Mod Sediment yield potential Mod Mod Mod Severe to High 36 2 Severe Severe High (31 & 34) 812 (81 & 82) 818 (81 & 18) 978 (97 & 98) Very severe Severe to Severe or 1 Severe 9 Severe to High High or High to High to High Mod Expected sediment size Silt, Gravel, sand, silt Gravel, sand silt Gravel, sand, silt Gravel, sand, silt Natural stability Unstable to locally very Unstable to very Stable to stable to to to or to Nature of mass movement Slumps Slumps, channel small slumps Creek bank ravel debris slides debris slides & slumps debris slides & channel Debris slides & channel Slumps, occasional debris slides, channel Debris slides & channel debris slides & channel, slumps 3

5 Figure 1. Map showing locations of natural landflows, landslumps, and active landslides. 4

6 Environmental Consequences Alternative 1 (No-Action) Direct and Indirect Effects; Cumulative Effects There would be no direct or indirect effects to soil productivity, soil erosion processes, large woody debris, or slope stability with no action. Natural soil productivity, erosion, large wood, and slope stability/mass wasting processes would continue on their current trajectory. There would therefore be no cumulative effects with the no action alternative. Alternative 2 (Proposed Action) Design Features and Mitigation Measures The following design features and mitigation measures are recommended for the East Fork Illinois River Channel and Floodplain Restoration Project, to minimize impacts to the soil resource and slope stability. Effects of the proposed action are based on the assumption that these design features and mitigation measures are employed appropriately for proposed action activities. National Core BMP Tech Guide: Follow Best Management Practices for Operations in Aquatic Ecosystems (AqEco-2), when implementing ground-disturbing stream restoration activities. In particular for minimizing short and long-term impacts to the soil resource: Clearly delineate the geographic limits of any areas to be cleared, to minimize unnecessary ground disturbance. o Locations of where heavy equipment can operate will be clearly defined and limited to the minimal area needed to complete the project. o The total area of detrimental soil conditions (compaction, displacement, puddling, and severely burned soil conditions), should not exceed 15% of the total acreage of the activity area, including roads and landings (Siskiyou NF LRMP, 7-2, pg. IV-44). Avoid or minimize unacceptable damage to existing vegetation. Conduct operations during dry periods. o Heavy equipment operations outside the footprint of channel construction (such as in staging areas and access routes) will take place when soils are dry to prevent undue soil compaction and displacement. Dry conditions refer to soil moistures of approximately 25% or less. If heavy equipment operations create ruts greater than 4-6 inches, soil caking and/or smearing, soils are too wet. Stage construction operations as needed to limit the extent of disturbed areas without installed stabilization measures. Promptly install and appropriately maintain erosion control measures, such as silt fence, wattles, and mulch. 5

7 Promptly rehabilitate or stabilize disturbed areas following construction or maintenance activities. o Effective groundcover of 85% or greater needs to be re-established at the end of the project (Siskiyou NF LRMP, 7-4, pg. IV-44-45). Utilize locally generated forest slash materials where available first and supplement as needed with other mulch materials such as wood chips, straw, etc. Stockpile and protect topsoil as much as possible for reuse in site revegetation. Minimize bank and riparian area excavation during construction to the extent practicable. Properly compact fills to avoid or minimize erosion. Contour site to disperse runoff, minimize erosion, stabilize slopes, and provide favorable environment for plant growth. Design log structure features and placement to avoid aggravating the three existing and naturally occurring, active shallow landslides that are present on Dunn Creek. Direct and Indirect Effects Side channel construction is expected to be the most ground-disturbing activity. Construction activities would be occurring on stream channel alluvium, which is a mix of stream deposited sands, silts, gravels and cobbles. In addition, much of this area appears to have been disturbed from historic mining activities. During construction activities, soils would be displaced and compacted. There would be an increased potential for erosion and sedimentation off of disturbed sites during precipitation events. The side channel construction location is considered to be erately stable, and is only subject to creek bank ravel. Design criteria and mitigation measures listed above are expected to effectively minimize the risk of erosion and sedimentation during and after project completion, assuming they are implemented appropriately. Disturbed areas would be effectively rehabilitated at completion of the project to promote revegetation of the site to a healthy riparian upland forest (refer to Revegetation Plan). Large woody debris would be protected and re-scattered across the site. These activities would meet the Forest Plan standards and guidelines for the soil resource. Where large wood instream structures are placed using ground-based equipment due to adequate road access, effects to soil productivity, erosion, sedimentation and large woody debris would be very similar to the stream channel construction site. Where large wood instream structures would be placed using a helicopter, there would be very little ground disturbance outside the stream channel. No effects to soil productivity would be expected, and if any ground does become disturbed during log placement, emitigation measures to restore effective groundcover would be employed to minimize or avoid the potential for erosion and sedimentation. Where large wood instream structures are placed could potentially have an effect on slope stabilities immediately adjacent to the stream channel, depending on how the structures influence the direction and velocity of stream flows towards or away from toeslopes. However, it is not expected that these structures would be large enough to initiate new instability where none currently exists. The design of the structures is to mimic the composition and distribution of naturally occurring structures in similar stream systems, and because they are lacking in these proposed locations. Therefore it is not expected that implementation of large wood instream structures would exacerbate slope instabilities outside the natural range that is found in the analysis area. It is also not expected that any project activities would have any measurable 6

8 impact to the landflow/landslump locations since these are deep-seated areas of instability and affected more by landscape level soil saturation. Revegetation of upland riparian sites have beneficial effects to long-term soil productivity, prevention of erosion and sedimentation, supplementation of large woody debris over time, and slope stability, directly through planting, seeding, and mulching of sites, and indirectly over time with contributions to litter, root structure, and nutrient enhancement. Cumulative Effects The 1987 Longwood Fire is the only other action in the analysis area that has the potential to have cumulative effects with the proposed action. The wildfire killed large sections of overstory vegetation (contributing beneficially to large downed wood), and is assumed to have increased the rate of erosion and sedimentation off of steep hillslopes for a period of time until ground vegetation reestablished enough to provide effective groundcover. Based on the amount of vegetation and groundcover within the burned area, it is assumed now that erosion and sedimentation rates are within the pre-fire range of variability. The wildfire did not appear to have measurably affected slope stabilities in the area, based on a review of aerial photography. Based on this information, there is not expected to be any measurable cumulative effect between impacts from the Longwood Fire, and the East Fork Illinois River Channel and Floodplain Restoration Project. Literature Cited (I NEED TO COMPLETE THIS) (BLM and USFS) United States Department of the Interior, Bureau of Land Management, and United States Department of Agriculture, Forest Service Southwest Oregon Late- Successional Reserve Assessment. USDI Bureau of Land Management, Medford District, Medford, Oregon; and USDA Forest Service, Pacific Northwest Region, Siskiyou National Forest, Grants Pass, Oregon. Available online at: (BLM and USFS) United States Department of the Interior, Bureau of Land Management, and United States Department of Agriculture, Forest Service Southwest Oregon Late- Successional Reserve Assessment, 12 May 2004 Update. USDI Bureau of Land Management, Medford District, Medford, Oregon; and USDA Forest Service, Pacific Northwest Region, Siskiyou National Forest, Grants Pass, Oregon. Available online at: (USFS) United States Department of Agriculture, Forest Service. 1989a. Siskiyou National Forest Land and Resource Management Plan. USDA Forest Service, Pacific Northwest Region, Siskiyou National Forest, Grants Pass, Oregon. (style: Citation) (USFS) United States Department of Agriculture, Forest Service. 1989b. Siskiyou National Forest Land and Resource Management Plan. USDA Forest Service, Pacific Northwest Region, Siskiyou National Forest, Grants Pass, Oregon. Available online at: (USFS and BLM) United States Department of Agriculture, Forest Service, and United States Department of the Interior, Bureau of Land Management. 1994a. Final Supplemental Environmental Impact Statement on Management of Habitat for Late-Successional and Old-Growth Forest Related Species Within the Range of the Northern Spotted Owl. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. 7

9 (USFS and BLM) United States Department of Agriculture, Forest Service, and United States Department of the Interior, Bureau of Land Management. 1994b. Record of Decision for Amendments to Forest Service and Bureau of Land Management Planning Documents Within the Range of the Northern Spotted Owl. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. Available online at: (USFS) United States Department of Agriculture, Forest Service Rogue River-Siskiyou National Forest Roads Analysis. USDA Forest Service, Pacific Northwest Region, Rogue River-Siskiyou National Forest, Medford, Oregon. 8