Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Functions of Forested Wetlands in the Delta Region of Arkansas, Lower Mississippi River Alluvial Valley, Version 2.0

摘要

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 is Version 2.0 of a Regional Guidebook that presents the HGM Approach for assessing the functions of most of the wetlands that occur in the Delta Region of Arkansas, which is part of the Lower Mississippi River Alluvial Valley. The report begins with an overview of the HGM Approach and then classifies and characterizes the principal wetlands that have been identified within the Delta Region of Arkansas. Detailed HGM assessment models and protocols are presented for six 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: Flat, Mid-gradient Riverine, Low-gradient Riverine Backwater, Low-gradient Riverine Overbank, Headwater Depression, Isolated Depression, and Connected Depression. 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. The appendices provide field data collection forms, spreadsheets for making calculations, and a variety of supporting spatial data intended for use in the context of a Geographic Information System.