PG&E Transmission Lines Hazard Tree Removal and Salvage Project

Transcription

1 PG&E Transmission Lines Hazard Tree Removal and Salvage Project Hydrology Effects Analysis Report Zack Mondry, Hydrologist (PH) USFS ACT2 Enterprise Unit

2 Executive Summary Analysis of the proposed Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects action determined that no direct or indirect adverse effects to water quality are expected as a result of the small-scale project if Resource Protection Measures and Best Management Practices are implemented. Because no direct or indirect effects are anticipated there will also be no cumulative effects. Affected Environment Nearly all of the proposed Humboldt/Trinity transmission line hazard tree removal areas occur in the Lower South Fork Trinity River 5 th -field watershed with only approximately 18 acres in the Lower Hayfork Creek 5 th -field watershed (Table 1). At the 7 th -field scale most of the Humboldt/Trinity project acres are contained in the Big Slide Creek-South Fork Trinity River and Upper Eltapom Creek watersheds with additional minor acres occurring in Lower Eltapom and Middle Corral Creeks (Table 1). All of the proposed Bridgeville/Cottonwood transmission line hazard tree removal areas occur in the Middle South Fork Trinity River 5 th -field watershed and are contained in the Cave Creek-Swift Creek 7 th -field watershed (Table 2). Table 1 Humboldt/Trinity project acres by watershed. Humboldt/Trinity Line 5th- Field Projec t 7th- Field Projec t 5th-Field ID Acres Acres 7th-Field ID Acres Acres Lower South Fork Trinity 129, Big Slide Ck-South Fork Trinity 10, River 3 River Lower Eltapom Creek 5, Upper Eltapom Creek 6, Lower Hayfork Creek 142, Middle Corral Creek 8, Table 2 Bridgeville/Cottonwood project acres by watershed. Bridgeville/Cottonwood Line 5th- Project 7th- Project Field Field 5th-Field ID Acres Acres 7th-Field ID Acres Acres Middle South Fork Trinity River 118, Cave Creek-Swift Creek 9, Watershed Existing Conditions The Shasta-Trinity National Forest (herein SHF) employs a cumulative watershed effects (CWE) equivalent roaded area (ERA) model to assess watershed existing conditions and effects of past, present, and reasonably foreseeable activities. Potential hydrologic effects of activities such as timber harvest (including timber harvest plans on private land), thinning and fuels reduction, road construction, highand moderate-severity wildfire, and road decommissioning are incorporated in to the model assessments. Ground disturbing activities are assigned coefficients of disturbance in the ERA model in order to scale the activities to the disturbance created by an equal sized (area) road segment (Haskins 1986). Effects to hydrologic function from vegetation management and wildfire reduce over time based on recovery curves. Roads do not recover naturally over time although their coefficients of disturbance

3 can be reduced if road segments are restored by decommissioning. The SHF has established % ERA thresholds of concern (TOC) for 5 th -field watersheds. A watershed at or above the TOC is interpreted to be at increased risk for adverse effects to water quality. However, exceedance of the TOC does not necessarily manifest as impacts to water quality due to the influence of other variables such as vegetative recovery, storm magnitude and frequency, and sediment routing processes. Tables 3 and 4 display computed watershed % ERA values for the 5 th -field watersheds containing the Humboldt/Trinity and Bridgeville/Cottonwood transmission line hazard tree removal areas (D. Schmerge, Shasta-Trinity National Forest, personal communication). The 2016 % ERA value assesses baseline watershed disturbance levels, and disturbance is forecast through Table 3 Computed % ERA for 5 th -field watersheds containing proposed Humboldt/Trinity hazard tree removal areas. The 2016 value assesses baseline watershed disturbance levels. 5th-Field TOC Equivalent Roaded Area (%) 5th-Field ID Acres (% ERA) Lower South Fork Trinity River 129, Lower Hayfork Creek 142, Table 4 Computed % ERA for the 5 th -field watershed containing proposed Bridgeville/Cottonwood hazard tree removal areas. The 2016 value assesses baseline watershed disturbance levels. 5th-Field TOC Equivalent Roaded Area (%) 5th-Field ID Acres (% ERA) Middle South Fork Trinity River 118, The 5 th -field watersheds remain well below their TOC through the period. Activity acres of the Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects are included in the % ERA values in Tables 3 and 4 and they do not change computed % ERA at this scale. Tables 5 and 6 display % ERA values for the 7 th -field watersheds containing the project areas. The 2016 % ERA value assesses baseline watershed disturbance levels, and disturbance is forecast through Watershed TOC are not established at this scale however, computed % ERA values remain relatively stable for the 5 year period. Table 5 Computed % ERA for 7 th -field watersheds containing proposed Humboldt/Trinity hazard tree removal areas. The 2016 value assesses baseline watershed disturbance levels. 7th-Field Equivalent Roaded Area (%) 7th-Field ID Acres Big Slide Ck-South Fork Trinity River 10, Lower Eltapom Creek 5, Upper Eltapom Creek 6, Middle Corral Creek 8,

4 Table 6 Computed % ERA for the 7 th -field watershed containing proposed Bridgeville/Cottonwood hazard tree removal areas. The 2016 value assesses baseline watershed disturbance levels. 7th-Field Equivalent Roaded Area (%) 7th-Field ID Acres Cave Creek-Swift Creek 9, Activity acres of the Humboldt/Trinity and Bridgeville/Cottonwood Transmission Lines Hazard Tree Removal and Salvage projects are included in the % ERA values in Tables 5 and 6. When the effects of proposed hazard tree removal acres on computed % ERA are isolated they produce a maximum increase of 0.3% in the Lower Eltapom Creek watershed (Table 5) in year-1 after implementation. This value is interpreted to be within the ERA model s level of sensitivity. Riparian Reserves Hydrologic Riparian Reserves Project activities are proposed along roads and transmission line corridors proximate to fish-bearing, permanently flowing nonfish-bearing, and seasonal streams. Riparian Reserves are established for all defined stream channels and unstable landforms in the project area per the Standards and Guidelines of the SHF Land Management Plan (herein LMP). Minimum Riparian Reserve widths are defined based on stream type per the LMP as displayed in Table 3. Table 7 Minimum Riparian Reserve widths based on stream type for the Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects. Fish-bearing streams Permanently flowing non-fishbearing streams Seasonally flowing or intermittent streams A distance equal to the height of 2 site potential trees or 300 feet slope distance (600 feet total, including both sides of the stream channel), whichever is greatest. A distance equal to the height of 1 site potential tree or 150 feet slope distance (300 feet total, including both sides of the stream channel), whichever is greatest. A distance equal to the height of 1 site potential tree or 100 feet slope distance (200 feet total, including both sides of the stream channel), whichever is greatest. A geographic information systems (GIS) analysis of the proposed hazard tree removal areas indicates that about 19 acres and 3 acres of the Humboldt/Trinity and Bridgeville/Cottonwood hazard tree removal areas, respectively, intersect Riparian Reserves. Figures 1 and 2 illustrate the location of the hazard tree areas that intersect Riparian Reserves primarily along fish-bearing and permanently flowing nonfish-bearing stream segments.

5 Figure 1 Map of proposed Humboldt/Trinity transmission line hazard tree removal areas and proximate streams and Riparian Reserves. Approximately 19 acres of proposed treatment areas intersect Riparian Reserves (yellow shading). Hyampom Mountain is at the right of the map for reference. Map scale is approximately 1:35,000. Figure 2 Map of proposed Bridgeville/Cottonwood transmission line hazard tree removal areas and proximate streams and Riparian Reserves. Approximately 3 acres of proposed treatment areas intersect Riparian Reserves (yellow shading). South Fork Trinity River is at the center of map for reference. Map scale is approximately 1:15,000. If stream channels are identified in the field that do not appear in the GIS data Riparian Reserves will also be established for the channels per the Standard and Guidelines of the SHF LMP (Table 3).

6 Geologic Riparian Reserves In addition to Riparian Reserves designated for defined stream channels policy also requires Riparian Reserves be established unstable lands. Within the SHF active landslide and inner gorge terranes are considered unstable lands and are designated Riparian Reserves. An assessment of SHF GIS data indicates that only a minor part of the hazard tree removal areas proposed for the Humboldt/Trinity transmission line intersects unstable lands. This preliminary determination should be verified by a project geologist or earth scientist. Aquatic Conservation Strategy Shasta-Trinity National Forest policy under the Northwest Forest Plan requires that the Forest manage the riparian-dependent resources to maintain existing conditions, or implement actions to restore conditions. The SHF must comply with the Aquatic Conservation Strategy (ACS) objectives that are as follows: 1. Maintain and restore the distribution, diversity, and complexity of watershed and landscapescale features to ensure protection of the aquatic systems to which species, populations and communities are uniquely adapted. 2. Maintain and restore spatial and temporal connectivity between watersheds. 3. Maintain and restore the physical integrity of the aquatic system, including shorelines, banks, and bottom configurations. 4. Maintain and restore water quality necessary to support healthy riparian, aquatic, and wetland ecosystems. 5. Maintain and restore the sediment regime under which aquatic ecosystems evolved. Elements of the regime include the timing, volume, rate, and character of sediment input, storage, and transport. 6. Maintain and restore in-stream flows sufficient to create and sustain riparian, aquatic, and wetland habitats, and to retain patterns of sediment, nutrient, and wood routing. The timing, magnitude, duration, and spatial distribution of peak, high, and low flows must be protected. 7. Maintain and restore the timing, variability, and duration of floodplain inundation and water table elevation in meadows. 8. Maintain and restore the species composition and structural diversity of plant communities in riparian areas. 9. Maintain and restore habitat to support well-distributed populations of native plant and invertebrate riparian dependent species. Direct and Indirect Effects Treatments with Potential Impacts Mechanical Treatments The Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects will be implemented with mechanized equipment (skidders or tractors) wherever possible on slopes less than about 40 %. Slash produced by hazard tree removal and salvage operations will be treated at least in part by machine piling and burning or mastication. Total acres of proposed treatment by watershed are displayed in Tables 1 and 2. The potential impacts of mechanical treatments include the following:

7 Water quality pollution by spilled petroleum fuel or lubricants Soil displacement and compaction, and potential associated erosion and sedimentation Erosion and sedimentation from the burned pile areas Riparian Reserves along all perennial (fish-bearing and nonfish-bearing) streams are designated as equipment exclusion zones (EEZ). Hazard trees will be directionally felled towards channels but not removed from perennial nonfish-bearing Riparian Reserves. Hazard trees are allowed to be felled and endlined from the outer half (150 ) of Riparian Reserves along fish-bearing streams. The GIS analysis of proposed activity acres determined that the above-described treatments would occur on the less than 25 acres (see Figures 1 and 2). All activities within Riparian Reserves must not retard or prevent attainment of ACS objectives. Resource Protection Measures Resource protection measures (RPM) for the projects follow those established for the Trinity Post Fire Hazard Reduction and Salvage project that is currently under analysis on the SHF. The primary water quality RPM for the projects is establishment of the EEZ along all defined stream channels (fish-bearing, permanently flowing non-fish-bearing, and intermittent). The following RPM were specified for the Trinity Post Fire Hazard Reduction and Salvage project at the time of this reporting: Riparian Reserve Areas In the Eltapom and Corral planning watersheds, imminent hazard trees/snags would be felled along roads, but no logs would be removed from Riparian Reserves unless the log falls within 200 feet upstream of a culvert and threatens stability of road infrastructure. No treatments beyond mitigating hazard trees (felling and leaving onsite) along any road segment would occur in the East Fork New River planning watershed. Riparian Reserves along perennial flowing streams will be Equipment Exclusion Zones. Trees within 150 feet will be felled towards the stream and left onsite. Trees within the outer 150 feet of fish-bearing stream Riparian Reserves may be removed by endlining to the road if more than 20 tons/acre of LWD occurs. In the outer 150 feet, 20 tons/acre of the largest LWD will be left. In Riparian Reserves where a road runs parallel to a perennial stream and/or bisects the Riparian Reserve by winding in and out, trees uphill of the road may be removed until 20 tons/acre of the largest LWD is left. Equipment used to remove trees from the uphill of the road will remain on the existing roadbed. Riparian Reserves along intermittently flowing streams will be comprised of two zones: the inner Equipment Exclusion Zone (EEZ) and the outer Riparian Reserve treatment zone. When water is flowing within intermittent streams, the EEZ will be 100 feet on each side of the channel. When the stream is not flowing, the EEZ will be 50 feet on each side of the channel. All heavy equipment is excluded from EEZs, except at designated crossings. All EEZs will be identified as "streamside buffer" on project maps. Wetlands (including wet meadows, seeps, fens, and springs), stream inner gorges and unstable land features are also EEZs. Where stream inner gorges are wider than the EEZ, the EEZ is extended to include the entire inner gorge plus the addition of a 50-foot buffer beyond the inner gorge feature. Unstable land features (active landslides) are also protected by a 50 EEZ buffer. Hand treatments are permissible in EEZs up to the high water mark; no green vegetation would be treated. Hand treatments will have limited ground disturbance in the EEZ and will

8 not disturb riparian plant species such as big leaf maple (Acer macrophyllum), willow (Salix spp.) and alder (Alnus spp.). When snags are felled within the intermittent stream EEZ, they will be left unless there is a site specific reason for removing them, such as desired coarse woody debris levels are met and heavy fuel loading occurs (greater than 20 tons/acre), or the tree is within 200 feet upstream of a culvert and threatens stability of road infrastructure. Riparian Reserves that are unmapped will be identified and protected, prior to and/or during implementation, in accordance with appropriate protection measures (see Table 7 above). Upon field review, if ephemeral streams show no sign of annual scour or deposition (i.e., upland swales) they do not meet the Forest Plan definition of a seasonal or intermittent channel (they are not Riparian Reserves). Hand piling and pile burning will not occur within the EEZs. However fire may be allowed to back into these areas, providing the fire spread will not cause holding problems. Landings, skid trails and crossings within Riparian Reserve Existing landings within the Riparian Reserve can be reused; however, the area of disturbance will not be increased and these features will be tilled and seeded following use where they do not need to be retained as part of the road system. No new landings will be constructed within the Riparian Reserve. No existing landings within EEZs will be used unless they are connected to a system road. No full bench skid trails will be constructed within the Riparian Reserve. Any intermittent stream equipment crossings (except Forest Service system roads) will be field reviewed and approved by an earth scientist, fish biologist or designee prior to use, and will avoid unstable areas. These features will be rocked crossings designed to maintain fish passage on existing and potential fish-bearing streams. They will be reshaped and stabilized following use. If intermittent stream crossings are left in place for wet weather operations, they will be removed during the following dry season. During construction of temporary stream crossings disturbance to existing live vegetation will be minimized to the maximum extent possible. When the crossing is rehabilitated, fill will be pulled back from the crossing so that the original stream level is re-established when the culvert is removed. Water drafting Water drafting will occur at existing sites with existing access and will be located to minimize adverse effects on stream channel stability, sedimentation and instream flows needed to maintain riparian resources, channel conditions and fish habitat. Water drafting sites that are not within habitat that is accessible to anadromous salmonids will be identified first and will be given priority for use. When needed, water drafting may occur in habitat accessible by anadromous salmonids. In all cases where water drafting occurs within anadromous salmonid habitat, 2001 National Marine Fisheries Service s (NMFS) Water Drafting Specifications will be adhered to. In addition, when drafting water the following rules apply. o Allow drafting from fish bearing streams only where immediate downstream discharge is maintained at 1.5 cubic feet per second (CFS) or greater (and is not greater than 10 percent of the stream flow). o Allow drafting from ephemeral streams, intermittent streams, wetlands or constructed ponds provided that sufficient water quantity and quality remains to support associated wildlife species and riparian values. o Never allow drafting to remove more than 75 percent of constructed pond water.

9 Soils and Hydrology Retain downed logs in decay classes 3 and 4 (Maser and Trappe 1984) for soil fertility purposes whenever possible. Landings and skid trails Mechanical skidding equipment is generally restricted to slopes less than 40 percent. On short steep pitches (less than 45% slope, and less than 100 ft in length), mechanical skidding equipment is restricted to slash covered primary skid trails using flexible track skidders with low ground pressure equipment. Wet weather logging is permitted on soils with compaction hazard rating of moderate or less with restrictions (see Field Guide to Soil Moisture Conditions for Operability of Logging Equipment (Rust 2015) and Shasta-Trinity Wet Weather Soil Compaction Hazard Rating (Rust 2008)). Ground-based mechanical equipment will only operate on fine-textured soils (identified as medium and heavy soils in the Field Guide to Soil Moisture Conditions for Operability of Logging Equipment (Rust 2015)) when the top 8 inches of soil are dry (identified as slightly moist soils in the Field Guide), as evaluated by Forest soil scientist or designee. Areas along roads proposed for treatments that have this soil type will be identified on a map for use by the Timber Sale Administrator. Post-treatment total soil cover should be between 50 and 70 percent averaged across the treatment area on metamorphics with at least 50 percent cover as fine organic matter (duff, litter, plant leaves/needles, fine slash (<3 inch material), etc.). On granitics, soil cover should be greater than 90 percent with at least 50 percent cover as fine organic matter. In some cases in this project area, soil cover has been removed by high intensity fire conditions; in these areas, soil cover will be retained to the extent practicable during implementation and in some cases will be increased by treatments. Areas along roads proposed for treatments that have this soil type will be identified on a map for use by the Timber Sale Administrator. Treatment areas susceptible to logging-based soil displacement (shallow granitic soils) will keep skidders (rubber tired or fixed track) on slopes less than 35%. Avoid displacing topsoil (typically 2 to 4 inches) and exposing erosive subsoils on areas greater than 15 by 15 feet outside of skid trails, unless mulched. Only operate on these soils when soil is no wetter than the moist category identified in the Field Guide to Soil Moisture Conditions for Operability of Logging Equipment (Rust, 2015) down to 8 inches. Areas along roads proposed for treatments that have this soil type will be identified on a map for use by the Timber Sale Administrator. All material will be skidded with one end suspended, where possible. No skid trails will be built on active landslides or inner gorges, and no existing skid trails on active landslides or inner gorges will be used. Reuse existing primary skid trails and landings where available and practical to minimize soil displacement and concentrated surface flow. Skid trails will not run along the axis of intermittent channels or swales. Till (subsoil to 18 inches) all landings identified for rehabilitation, temporary roads, and main skid trails (up to 200 feet entering landings) that have fine textured soils with a wingedsubsoiler following completion of all management activities. Tillage will be completed outside of the tree drip-line so as not to impact root systems. For rocky soil, scarification will be used to restore sites. These areas should be mulched (weed free straw, wood chips or on-site organic material) at a rate of 1.5 to 2 tons per acre (approximately 4 to 6 inches in depth) over a minimum of 75 percent of the exposed soils, where necessary to prevent erosion.

10 Minimize soil erosion by water-barring skid trails. Install waterbars on contour at major breaks in slope along the skid trails. New landings will be located on gentle slopes (<20%) to minimize earthwork, and will avoid unstable areas, steep slopes below landslide benches, and slope positions where they could deliver sediment to streams. Cuts and fills would not exceed 5 feet in height, unless field reviewed and approved by an earth scientist beforehand. Pull organic materials out of fill slope of landings to prevent collapse. Landings will have natural, non-constructed designs. If non-constructed design is not feasible, landings will be constructed to adequately drain through crowned surface and directed drainage with catchment structures (rock armoring and/or silt fences with straw bales may be used as necessary). All new landing fill slopes and access road fill slopes (>100 sq. ft.) would be mulched initially, and then the mulch would be maintained throughout the life of the project; mulch may be weed-free straw, or landing slash. Areas with new road and landing fill will be rehabilitated after treatments are complete. New landings will occur in areas that are generally open or fire deforested, whenever possible. General road measures Purchaser or contractor-utilized roads rutted by purchaser/contractor operations shall be spot rocked or otherwise suitably repaired. Drainage structures shall be protected or repaired as necessary. Road surfaces expected to be used during wet weather, in areas crossing serpentine soils, should be rocked to prevent roadbed deformation (rutting) during wet conditions. Dispose of unsuitable slide and excess fill in stable, non-floodplain sites. Fill material will be inspected by a botanist, weed specialist, or designee prior to moving for presence of noxious weeds. If noxious weeds are present, they will be treated prior to moving the fill, and the disposal site will be monitored in the future and treated as necessary. Best Management Practices As with the RPM, Best Management Practices (BMP) for the transmission line hazard tree removal projects follow those established for the Trinity Post Fire Hazard Reduction and Salvage project. The following BMP with their associated objectives are prescribed from the National Core BMP Technical Guide (2012): Veg-2. Erosion Prevention and Control Objective: Avoid, minimize, or mitigate adverse effects to soil, water quality, and riparian resources by implementing measures to control surface erosion, gully formation, mass slope failure, and resulting sediment movement before, during, and after mechanical vegetation treatments. Veg-3. Aquatic Management Zones Objective: Avoid, minimize, or mitigate adverse effects to soil, water quality, and riparian resources when conducting mechanical vegetation treatment activities in the AMZ. Veg-4. Ground-Based Skidding and Yarding Operations

11 Objective: Avoid, minimize, or mitigate adverse effects to soil, water quality, and riparian resources during ground-based skidding and yarding operations by minimizing site disturbance and controlling the introduction of sediment, nutrients, and chemical pollutants to waterbodies. Veg-6. Landings Objective: Avoid, minimize, or mitigate adverse effects to soil, water quality, and riparian resources from the construction and use of log landings. Road-10. Equipment Refueling and Servicing Objective: Avoid or minimize adverse effects to soil, water quality, and riparian resources from fuels, lubricants, cleaners, and other harmful materials discharging into nearby surface waters or infiltrating through soils to contaminate groundwater resources during equipment refueling and servicing activities. Please refer to the Trinity Post Fire Hazard Reduction and Salvage project Environmental Impact Statement and the National Core BMP Technical Guide for specific BMP practices to be undertaken. No Effect Analysis No direct, indirect, or cumulative adverse effects to water quality are anticipated from implementation of the Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects. The analysis supporting this determination is based on the scale of the proposed activities and prescribed RPM and BMP. Scale of Disturbance The Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage projects should have little to no influence on water quality because of the limited total activity acres (Tables 1 and 2). The maximum treatment acres (108 acres) will occur in the Upper Eltapom Creek 7 th - field watershed (6,836 acres) comprising approximately 1.5 % of the total watershed area. Cumulative Watershed Effects Because no direct or indirect adverse effects to water quality are expected from implementation of the Humboldt/Trinity and Bridgeville/Cottonwood Transmission Line Hazard Tree Removal and Salvage project no adverse cumulative effects are anticipated. Computations in the SHF ERA model indicate that the entire acreage of the projects is undetectable when modeling at the 5th-field watershed scale and within model sensitivity at the 7th-field watershed scale (Tables 3 and 4). Activity acres of the transmission line hazard tree removal projects do not change computed % ERA at these scales. References Haskins, D.M A Management Model for Evaluating Cumulative Watershed Effects. California Watershed Management Conference, November 18-20, West Sacramento, California. Schmerge, D Shasta-Trinity National Forest, South Fork Management Unit. USDA National Best Management Practices for Water Quality Management on National Forest System Lands, Volume 1: National Core BMP Technical Guide. USDA Forest Service, National Headquarters. Washington, DC.