US Army Corps of Engineers
Galveston District

Why Assess Function?

The district engineer must determine the compensatory mitigation to be required in a DA permit, based on what is practicable and capable of compensating for the aquatic resource functions that will be lost as a result of the permitted activity. The purpose of a functional assessment is to evaluate current wetland functions and predict potential changes to a wetland's functions that may result from proposed activities. A wetland is compared to similar wetlands that are relatively unaltered. The approach is based on combining variables that are typically structural measures or indicators that are associated with one or more ecosystem functions. Functions normally fall into one of three major categories: (1) physical (e.g., storage of surface water), (2) chemical (e.g., removal of elements and compounds), and (3) biological (e.g., topography, depth of water, number and size of trees).

The HGM approach to functional assessment estimates the change in functioning induced by alteration of a wetland, either positive or negative. Negative effects (i.e, reductions in sustainable levels of functioning) are normally determined in association with dredge-and-fill permits. The permit review process could use output from an assessment as one tool to determine if the project results in significant degradation. Output from HGM models can also be used to determine the amount of positive effects (i.e., increases in sustainable levels of functioning) associated with compensatory mitigation requirements, normally through restoration of previously altered wetlands of the same type.

For more information on the Galveston District's iHGM policy, please see our Standard Operating Procedure.

Galveston's Wetland Functional Assessments

Assessment Class  Description
SWG Forested Riverine iHGM The Forested Riverine iHGM model is limited to forested wetlands that are located along floodplains and/or floodways located along riverine system. These wetlands share a surface hydrology connection with the waters of the riverine system at least for a portion of the season. This model should be used for a rapid non-controversial estimate of the potential impacts to forested riparian wetlands and to see if the proposed mitigation will adequately address the wetland functions that are being impacted.
SWG Herbaceous Riverine iHGM  The Herbaceous Riverine iHGM model is limityed to herbaceous wetlands that are located along floodplains and/or floodways located along a riverine system. These wetlands share a surface hydrology connection with the waters of the riverine system for at least a portion of the season. This model is to be used for a rapid non-controversial estimate of the potential impacts to herbaceous riparian wetlands and to see if the proposed mitigation will adequately address the wetland functions that are being impacted.
SWG Tidal Fringe iHGM The Tidal Fringe iHGM is limited to the tidally influenced wetlands in the Galveston District. This model is to be used for a rapid non-controversial estimate of the potential impacts to tidally influenced wetlands and to see if the proposed mitigation will adequately address the wetland functions that are being impacted.
SWG Lucastrine iHGM  The Lucastrine iHGM model is designed to be used in wetlands found in the lakes of Texas. A lake is defined as a body of open water that greater than five-acres in size. This model is to be used for a rapid non-controversial estimate of the potential impacts to lacustrine wetlands and to verify that the proposed mitigation will adequately compensate for the wetland functions that are being impacted.