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HomeMy WebLinkAboutHohRiverwetlandmitigationmemo_08-29-2017 Memorandum DATE: August 29, 2017 TO: Steve Morrow Environmental Protection Specialist FHWA, Western Federal Lands FROM: Gray Rand Senior Scientist, PWS SUBJECT: Conceptual Wetland Mitigation Plan PROJECT: Upper Hoh River Road Bank Stabilization Project PROJECT NO.: FHAX0000-0242 COPIES: File INTRODUCTION This memorandum describes proposed conceptual wetland mitigation for an estimated 2,679 square feet of long term temporary or permanent wetland impact for the Upper Hoh River Road Project (project) proposed by the Western Federal Lands Highway Division of FHWA (WFLHD). This conceptual mitigation plan has been prepared for use by several regulatory agencies, including the U.S. Army Corps of Engineers (Corps), Washington State Department of Ecology (Ecology), and Jefferson County, as well as interested parties, which may include tribes or interested citizens. The proposed mitigation will be located near the west end of the proposed project, near Site C1 (Figure 1). The following sections describe the major elements of the conceptual mitigation plans. At the 70 percent design level, there is an estimated 2,679 square feet of long term temporary and permanent impacts to Category III wetland systems from the project. These wetland impacts are associated with systems largely along the Hoh River Road. Portions of these wetlands are associated with the road ditch and drainage system. The base mitigation ratios for Jefferson County include a 2:1 ratio for impacts to Category III wetland systems (JCC 18.22.350). Therefore, approximately 5,358 square feet of wetland creation would be required for compensatory mitigation. Efforts to reduce the project impacts will occur as the project design is advanced. Steve Morrow August 29, 2017 Page 2 Figure 1. Conceptual Wetland Mitigation Site 1 Steve Morrow August 29, 2017 Page 3 PROPOSED MITIGATION Following completion of installation of Site C1 engineered log jams (ELJ), WFLHD would construct a bench wetland (similar to Wetland 1) to provide compensatory mitigation for wetland impacts per Jefferson County mitigation ratios (JCC 18.22.350). This potential mitigation site is shown in Figure 2 below. This wetland would have the following characteristics:  Approximately 5,358 square feet in size  Hydrology supported by flow from Stream 9 and groundwater, encouraged by level flow spreader, berms, or similar methods.  HGM = Riverine  Wetland would be protected from erosion by ELJs  Planted with local native wetland plants typically observed in adjacent wetlands: o Slough sedge o Skunk cabbage o Lady fern o Small-fruited bulrush o Water parsley o Red alder o Salmonberry o Western red cedar o Sitka spruce MITIGATION GOALS AND PERFORMANCE STANDARDS The proposed wetland mitigation is intended to replace wetland acreage and functions lost or impacted by the proposed project. PERFORMANCE STANDARDS The performance standards described below provide benchmarks for measuring achievement of the goals and objectives of the mitigation site. Mitigation activities are intended to meet these performance standards within a specified time frame. The mitigation site will be deemed successful after achieving the approved performance standards described below in Table 1. A baseline evaluation should be conducted and will represent a baseline of conditions after mitigation is implemented (i.e. construction is competed). This Year 0 report provides a baseline to allow comparison of performance for subsequent years. Results of annual monitoring in Years 1, 3, and 5 will be compared with these standards. The following performance standards are based on conditions at and around the proposed mitigation site. The forested nature of the site will influence suitable plants and expected density of plant growth expected during the monitoring period. Methods to monitor each performance standard are described in general terms. Steve Morrow August 29, 2017 Page 5 Wetland Hydrology Performance Standard (Years 1, 3, 5) Within all intended wetland areas, the soil will be saturated, or a water table will be present, within 12 inches of the soil surface for at least 30 consecutive days during the growing season in years when rainfall meets or exceeds the 30-year precipitation average. Native Herbaceous Species in the Wetland Performance Standard (Year-1) One hundred percent survival of all installed herbaceous plants one-year post installation of all wetland restoration plants. At least three native herbaceous species will be present in the emergent plant communities. Performance Standard (Year-3) Cover of native wetland herbaceous plant species (planted and volunteer) will be at least 30 percent in the emergent communities. At least three native herbaceous species will be present in the emergent plant communities. Performance Standard (Year-5) Cover of native wetland herbaceous plant species (planted and volunteer) will be at least 50 percent in the emergent communities. At least three native herbaceous species will be present in the emergent plant communities. Year of Monitoring Percent Coverage Year-3 30 percent Year-5 50 percent Native Trees and Shrubs in the Wetland Performance Standard (Year-1) One hundred percent survival of all installed native trees and shrubs one-year post installation of all wetland restoration plants. At least two species of native tree and three species of native shrubs will be present in the forested and scrub-shrub areas. Performance Standard (Year-3) Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 30 percent in the combined scrub-shrub and forested communities. At least two species of native trees and three species of native shrubs will be present in the forested and scrub-shrub areas. Performance Standard (Year-5) Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 60 percent in the combined scrub-shrub and forested communities. At least two species of native trees and three species of native shrubs will be present in the forested and scrub-shrub areas. Steve Morrow August 29, 2017 Page 6 Year of Monitoring Percent Coverage Year-3 30 percent Year-5 60 percent Invasive Species Performance Measure (Years 1, 3, and 5) Washington State-listed or county-listed noxious weeds observed in any area of the mitigation site must be eradicated. (Eradicating weeds means getting rid of the plants altogether, including plant roots). All occurrences shall be reported to the site manager. Class B and C weed species designated for mandatory control in Jefferson County include the following:  Yellow archangel (B) (Lamiastrum galeobdolon)  Scotch broom (B) (Cytisus scoparius)  Butterflybush (B) (Buddleja davidii)  Reed canarygrass (C) (Phalaris arundinacea)  Common fennel (B) (Foeniculum vulgare)  Knotweeds (B) (Polygonum spp.) (non‐native)  Poison hemlock (B) (Conium maculatum)  Tansy ragwort (B) (Senecio jacobaea)  Perennial sowthistle (C) (Sonchus arvensis)  Common teasel (C) (Dipsacus fullonum)  Ravenna grass (C) (Saccharum ravennae) Designated noxious weeds or other species of concern will include less than 10% cover in all intended wetland zones. Other weeds of concern include Himalayan blackberry, herb Robert, English ivy, and Canada thistle. Upland Buffer Vegetation Performance Criteria Existing upland vegetation around the proposed mitigation area will be left intact with existing vegetation. No buffer vegetation performance criteria are proposed. Steve Morrow August 29, 2017 Page 7 Table 1. Performance Standards Performance Standards Monitoring Methods Monitoring Intervals 1. Wetland Hydrologic Characteristics present Inundation at the soil surface or at least saturation within 12 inches of soil surface at least 30 consecutive days during the growing season, in years when rainfall meets or exceeds the 30-year precipitation average. Year 1, 3, 5. 2. 100% survival of all installed native herbaceous plant one-year post installation herbaceous plants. Total plant count of all installed herbaceous plants Years 1 3. Annual monitoring for cover of all installed herbaceous plants. Volunteer native herbaceous plants in mitigation area will be included. herbaceous plant cover: 30% by Year 3, 50% by Year 5. At least 3 native herbaceous plants shall be present in the mitigation area Percent cover of installed herbaceous plant shall be measured by an approved monitoring technique such as line intercept method and/or sample plots. Tally species in restoration areas Years 3, and 5 Years 1, 3 and 5 4. 100% survival of all installed native trees and shrubs one-year post installation. Total plant count of all installed trees and shrubs. Year 1. 5. Annual monitoring for cover of all installed trees and shrubs. Volunteer native trees and shrubs in the mitigation area will be included. Tree and shrub cover: 30% by Year 3, 60% by Year 5. At least 2 native tree species and 3 native shrub species shall be present Percent cover of installed trees and shrubs shall be measured by an approved monitoring technique such as line intercept method and/or sample plots. Years 3 and 5 Years 1, 3 and 5 5. No more than 10% cover of non-native or other invasives, e.g., Himalayan blackberry, evergreen blackberry, reed canarygrass, scots broom, English ivy, morning glory, etc. Percent cover of non-native or invasive species shall be measured by an approved monitoring technique such as line intercept method and/or sample plots. Years 1, 3, and 5 Steve Morrow August 29, 2017 Page 8 MONITORING AND MAINTENANCE The wetland mitigation site will be monitored for a minimum of five years. Formal monitoring procedures will be performed in years one, three, and five after initial acceptance of the mitigation construction. The site should be evaluated for baseline conditions the summer following plant installation to evaluate survival rates and document the presence of non-native invasive species. A baseline monitoring report should document post construction conditions and characteristics. Monitoring reports will be submitted to the Corps and Jefferson County for review and comment. Monitoring reports will be completed by December of each monitoring year. Mitigation success will be measured by the attainment of performance standards. The actual monitoring methods used to monitor the site will be determined and documented in annual monitoring reports. CONTINGENCY PLAN It is anticipated that the mitigation goals will be accomplished with the construction and installation of the mitigation design as shown on the grading and planting plans. Contingency actions, however, may be needed to correct unforeseen problems. Contingency revisions typically require coordination with the permitting agencies. As necessary, contingency measures (site management or revisions to performance criteria with permitting agency agreement) will be implemented to meet performance measures and performance standards. The following describes potential situations that may occur and the potential contingencies that might be implemented to correct the problem. Because not all site conditions can be anticipated, the contingencies discussed below do not represent an exhaustive list of potential problems or remedies. Hydrology Hydrologic problems occurring on a mitigation site are typically the result of either insufficient water or excessive water. Insufficient water can occur seasonally during drought conditions or can be a long-term problem. Long-term problems can be the result of altered surface water flows for mitigation sites reliant on surface water flows as the primary source of hydrology. For groundwater driven mitigation sites, typical long-term hydrologic problems that result in either excessive or insufficient hydrology can occur from a design based on insufficient groundwater data, th e establishment of incorrect final grade elevations, or an unperceived soil condition that alters groundwater flows. Hydrologic contingency measures will be implemented based on observed conditions or monitoring data. Steps to address insufficient or excessive hydrology are:  Clearly identify the source of the problem.  Consult with the mitigation design team and the resource agencies to determine an appropriate course of action.  Adjust elevations or install water management structures to achieve appropriate hydrologic conditions. Steve Morrow August 29, 2017 Page 9 Vegetation Problems related to vegetation include plant mortality, and poor growth resulting in low plant cover. These problems could be the result of insufficient site management, particularly watering in the first few growing seasons, animal browse, competition from invasive species, incorrect plant selection, altered site conditions, and vandalism. Contingencies for plant mortality and poor plant cover may include:  Plant replacement – Additional planting may be required to meet plant survival and plant cover requirements. Plant species will be evaluated in relation to site conditions to determine if plant substitutions will be required.  Weed control – Control of non-native invasive species may be required to meet survival and plant cover requirements. Weed control methods could include mechanical or hand control, mulching, or herbicide application.  Review and revise performance criteria with permitting agency agreement. SITE MANAGEMENT The applicant, or its agent, will manage the site annually for the first 5 years. Site management activities shall include noxious weed control and may include mulching, fertilizing, supplemental watering, maintaining access, correcting erosion or sedimentation problems, or litter pickup. The first year of plant establishment includes supplemental water and care of all replacement plants installed during the first year. Enclosures: Conceptual Wetland Mitigation Plan