**2.5 Hydro-geomorphic methodology**

The HGM process of evaluating ecosystem restoration and management options relies heavily on eight types of data, most of which require geospatial digital information usable in an ArcGIS/ArcMAP format. These data include historic and current information about: 1) soils, 2) geomorphology, 3) topography/elevation, 4) hydrology/flood frequency, 5) aerial photographs and cartography maps, 6) land cover and vegetation communities, 7) presence and distribution of key plant and animal species, and 8) physical anthropogenic features.

The three-stages of HGM are as follows: first, the historic condition and ecological processes of an area and its surrounding landscapes are determined from a variety of historical and current information such as geological, hydrological, and botanical maps and data. Public Land Survey (PLS) maps and notes are especially useful to understand historic vegetation composition and distribution. A key element of HGM is developing a "matrix" of understanding of which plant communities historically occurred in different geomorphological, soil, topographic, and flood-frequency settings (Table 1). For example, in the Mississippi-Missouri River Confluence Area, wet bottomland prairie that was dominated by prairie cordgrass historically occurred at elevations greater than 417 feet, on relict alluvial floodplain terrace surfaces, on silt loam soils, and between the two- and fiveyear flood frequency zones (Heitmeyer and Westphall, 2007). Contemporary areas that offer these conditions, especially surface, soil, and flood frequency attributes now offer the best edaphic conditions for restoring wet bottomland prairie communities.

Second, alterations in hydrological condition, topography, vegetation community structure and distribution, and resource availability to key fish and wildlife species are determined by comparing historic vs. current landscapes. This analyses is essentially a qualitative "best professional judgment" assessment of current condition and the types and magnitudes of changes, including assessment of which communities are most resilient and which types of change are the most/least reversible.

Third, options and approaches are identified to restore specific habitats and ecological conditions. The foundation of ecological history coupled with assessment of current conditions helps to determine which system processes (e.g., periodic dormant season flooding) and habitats (e.g., forest composition) can be restored or enhanced, and where this is possible, if it is at all. Obviously, some landscape changes are more permanent and less reversible (e.g., mainstem levees on the Mississippi and Illinois rivers) than others (e.g., clearing of bottomland forest). Through development of the HGM matrix conservation planners can identify: 1) which, and where, habitat types have been lost or altered the most and establish some sense of priority for restoration efforts; 2) where opportunities exist to restore habitats in appropriate geomorphic, soil, hydrological, topographic settings including both public and private lands; 3) how restoration can replace lost functions and values including system connectivity; and 4) what management types and intensity will be needed to sustain restored communities. HGM can be an iterative process that is well-coupled with adaptive ecosystem management (Christensen et al., 1996; Palmer et al., 2005) because new monitoring and research can be used to refine HGM models and restoration plans.


Table 1. Hydrogeomorphic matrix of historic distribution of major vegetation communities/habitat types in the American Bottoms geomorphic reach (near St. Louis, Missouri) in relation to geomorphic surface, soils, and flood frequency.
