Geographic information systems are technologies used to store, manage, edit, analyze, and display data that are spatially referenced to the earth.  Using GIS in an application of HEC-EFM allows users to analyze data layers produced by HEC-RAS as well as any external data sets that have ecological significance.  The following sequence of figures is an example of how GIS can be used to investigate ecosystem response spatially.  Results are shown for Riparian tree establishment dynamics in the Natural flow regime.  Depth grids were initially created for recruitment (Figure 52) and inundation (Figure 53).  The inundation layer was then placed on top of the recruitment layer (Figure 54).

Figure 52.  Depth grid created for Riparian tree recruitment.  The green area shows where stage recession creates suitable conditions for seedlings to begin to grow.


Figure 53.  Depth grid created for Riparian tree inundation.  This blue area shows where any new seedlings will be drowned by prolonged inundation.


Figure 54.  Overlay of Riparian tree recruitment and Riparian tree inundation depth grids.


In accordance with the combo relationship for Riparian tree establishment (Figure 7), the inundation depth grid was clipped from the recruitment depth grid.  The resulting layer shows the area where HEC-EFM predicts Riparian tree establishment (Figure 55). 

Figure 55.  Depth grid created by clipping the inundation depth grid from the recruitment depth grid.  The resulting area shows where HEC-EFM predicts Riparian tree establishment.


Information for the Riparian tree inundation relationship mentioned that seedlings were more likely to survive if sustained inundation did not exceed 0.5 ft.  Delineating the area of inundation less than or equal to 0.5 ft shows the portion of Riparian tree inundation that may not lead to seedling mortality (Figure 56).  This Riparian tree inundation fringe can then be layered with the clipped layer to create a new view of predicted and possible (due to the shallow depths) Riparian tree establishment (Figure 57).

Figure 56.  The yellow fringe shows areas of the Riparian tree inundation depth grid that are less than or equal to 0.5 ft, which may not be deep enough to drown new seedlings.


Figure 57.  Potential recruitment sites for the Rolling River's Natural flow regime as computed using statistical and geographical queries in HEC-EFM, water surface profiles computed by HEC-RAS, and depth grids produced by HEC-GeoRAS. 


So far the demonstration project has focused on comparing flow regimes with different hydrologic scenarios (Natural vs. Gaged).  HEC-EFM can also be used to look at changes in topography, which will change the stage time series without changing the flow.  Figure 58 shows a comparison of the current topography and a planned restoration project that increases stream meander.  The same flows (Natural) are used for each of the channel topographies.

Figure 58.  Comparison of Riparian tree establishment in existing and restored topographic conditions.


The following progression of tasks for the demonstration project has now been completed: 1) building relationships, 2) setting up an HEC-EFM project and computing statistical results, 3) simulating the statistical results with a hydraulic model, and 4) use of GIS to investigate ecosystem responses spatially.

Statistical results in HEC-EFM are computed as flows and stages, percent exceedances, index values, and directions of ecosystem change.  Spatial results are shown as combinations of map layers with each combination presenting a snapshot of an ecosystem dynamic.  Layers are typically translated to areas for spatial comparisons of different flow regimes and channel topographies.  Working with GIS allows use of other ecologically relevant data.  For example, a soils map for Rolling River could be used to intersect the Riparian tree establishment layer (Figure 55) with the extent of suitable soils for riparian trees.