**3.3 Hydrogeomorphic methodology**

180 Studies on Environmental and Applied Geomorphology

river. Dam effects on the Illinois River are exhibited by much larger and permanent backwater lakes compared to isolated lake and channel networks present at low flow prior

Fig. 8. Simulated floodplain inundation (bottom) and levee distribution by river mile.

Levees impede the flooding simulated above and prevent floodwater distribution in the floodplain south of river mile 450 (Figure 8). Most UMRS levee districts were established more than 100 years ago, and they occur as independent, quasi-political entities that have taxation and other authority for residents within their boundaries (Thompson., 2002). They

to development (Mills et al., 1966).

Our HGM maps are relatively simple deterministic models that select various combinations of hydrology, geomorphology, and soil to map individual community distribution (Figure 9) which are integrated to produce potential vegetation estimates (Figure 9). Potential vegetation (HGM) maps (Figure 10) have been produced for several Mississippi River Reaches (Heitmeyer, 2008a; 2010) and many individual refuges or restoration sites

Fig. 9. Hydrogeomorphic Data layers and examples of deterministic model results.

Hydro-Geomorphic Classification

collaboratively between managers and scientists.

improving the odds of successful restoration.

feature in a separate data layer.

**4. Discussion** 

and Potential Vegetation Mapping for Upper Mississippi River Bottomland Restoration 183

environmental benefits that may accrue from restoration and management actions. Ultimately, these plant community models may be used in more comprehensive ecosystem services models that incorporate dynamic hydrology and ecosystem feedback loops that

There are many environmental and economic management needs that can be addressed with ecosystem modeling. Hydraulic models have become so precise that their results are routinely used for engineering design to simulate alternative design features (Silberstein, 2006). We believe the HGM approach for potential vegetation community assessment can achieve a similar standard for ecosystem restoration alternative analysis. The methods are not precise to species levels, nor very small spatial scale, at this stage of development but they do match well with the scale of most wildlife refuges and management areas that are the focus of most natural resource management and restoration activity. They also scale nicely for landscape ecology metrics and regional ecosystem management (USACE, 2011). HGM models have been developed for many floodplain systems (Klimas et al. 2009; U.S. Army Corps of Engineers, 2010), and they gain wide agency acceptance when developed

These HGM methods for the UMRS are still quite simple in their statistical capacity and ability to model land cover occurrence. Future work will explore more rigorous landscape metrics that examine adjacency of land cover classes and associations with physical landscape features. The fundamental premise of the Hydrogeomorphic Method (HGM) is that vegetative communities segregate according to a single, or some combination of landscape features (e.g. geomorphology, hydrology, soil type). Indeed floodplain topography influences the frequency and duration flooding, which both directly influences plants via control over the length of oxic and anoxic phases, and indirectly influences plant communities by changing the physical properties of the soil (e.g. texture, pH, fertility). However, few studies have quantified the degree to which different plant communities segregate along key environmental gradients. By quantifying nonrandom associations among hydrology, soils and vegetation, land managers can increase their odds of successfully matching species and community types to suitable site conditions, thereby

To test the hypothesis that various plant communities segregate according to a given landscape feature or some combination of landscape features, an electivity index can be used (Jacobs, 1974; Jenkins, 1979; Pastor and Broschart, 1990). An electivity index calculates the juxtaposition of one cover type from one GIS data layer with some other landscape

These methods allow one to empirically test the hypothesis that a particular vegetation cover class 'elects' for a given landscape feature. If a particular cover class indeed elects for a given landscape feature, then it provides land managers with a prescription of broad-scale conditions that may be required for successful establishment of a given plant community under a given set of environmental conditions (Dr. Nathan DeJager, U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, contributed text).

simulate complex functional processes of riverscapes (Thorp et al., 2006, 2008).

(Heitmeyer and Westphal, 2007; Heitmeyer, 2008b). Each HGM evaluation is much more than simply combining GIS layers. An HGM evaluation reviews the physical setting, climate and hydrology, and the distribution and characteristics of presettlement habitats to establish a potential natural landscape. The HGM then reviews changes due to development and succession to make restoration and management decisions based on the likelihood of natural communities to recover from disturbance and in light of future disturbances. Potential vegetation maps assembled from hydrologic, geomorphic, and soils data are simply tools to visualize and quantify landscape response to management actions.

Fig. 10. A portion of a HGM map for the St. Louis region.

The near term intent is to complete an initial set of potential natural vegetation maps to help inform forest and land management plans for the entire UMRS (National Great Rivers Research and Education Center, 2010). The hydrology and geomorphology base layers described above were an important precursor to the rapid completion of the project. When the initial potential vegetation maps are complete, or as project needs dictate, potential vegetation maps for alternative floodplain management plans can be modeled to estimate environmental benefits that may accrue from restoration and management actions. Ultimately, these plant community models may be used in more comprehensive ecosystem services models that incorporate dynamic hydrology and ecosystem feedback loops that simulate complex functional processes of riverscapes (Thorp et al., 2006, 2008).
