A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland Functions of Forested Wetlands in the West Gulf Coastal Plain Region of Arkansas

Abstract : The Hydrogeomorphic (HGM) Approach is a method for developing and applying indices for the site-specific assessment of wetland functions. The HGM Approach was initially designed to be used in the context of the Clean Water Act Section 404 Regulatory Program permit review process to analyze project alternatives, minimize impacts, assess unavoidable impacts, determine mitigation requirements, and monitor the success of compensatory mitigation. However, a variety of other potential uses have been identified, including the design of wetland restoration projects and management of wetlands. This Regional Guidebook presents the HGM Approach for assessing the functions of most of the wetlands that occur in the West Gulf Coastal Plain Region of Arkansas. The report begins with an overview of the HGM Approach and then classifies and characterizes the principal wetlands that have been identified within the Coastal Plain Region of Arkansas. Detailed HGM assessment models and protocols are presented for nine of those wetland types, or subclasses, representing all of the forested wetlands in the region other than those associated with lakes and impoundments. The following wetland subclasses are treated in detail: Pine Flat, Hardwood Flat, Low-gradient Riverine Backwater, Low-gradient Riverine Overbank, Mid-gradient Riverine, Unconnected Depression, Connected Depression, Bayhead, and Seep. For each wetland subclass, the guidebook presents (a) the rationale used to select the wetland functions considered in the assessment process, (b) the rationale used to select assessment model variables, (c) the rationale used to develop assessment models, and (d) the functional index calibration curves developed from reference wetlands that are used in the assessment models. The guidebook outlines an assessment protocol for using the model variables and functional indices to assess each of the wetland subclasses.