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HEC-EFM analyses involve: 1) statistical analyses of relationships between hydrology and ecology, 2) hydraulic modeling, and 3) use of Geographic Information Systems (GIS) to display results and other relevant spatial data.

Most features in the main interface of HEC-EFM focus on the first step in this process (statistical analyses). The main interface has four tabs: Properties, Relationships, Tables, and Combo Relationships.

Properties Tab

The Properties Tab contains information relevant to the model as a whole and is where the user identifies the hydrologic data and time window to be analyzed. In the figure above, there are two HEC-EFM “flow regimes”: Natural and Gaged. Each is defined by concurrent records of daily mean flow and daily mean stage data at a single location in the study area. HEC-EFM accepts input data in several text formats (i.e., comma, space, and tab delimited) and from the HEC Data Storage System (HEC-DSS), which is the database used by HEC models for storage of time series and other data.

Relationships Tab

HEC-EFM "relationships" are statistical representations of links between hydrology and ecology. Relationships are typically developed by teams of scientists and engineers using a combination of expert knowledge and scientific literature. The Relationships Tab is where the user specifies the statistical and geographical queries that define each relationship. The figure above shows queries for the spawning season of the Little Minnow, which is the first of six standard relationships in the HEC-EFM demonstration project (Rolling River.efm).

Tables Tab

	The Tables Tab presents statistical results (as in figure above) for flow regime and relationships as well as project reports and output files.

Combo Relationships Tab

	Combo relationships are used to group two or more individual relationships to represent a single ecosystem dynamic. In the figure above, Riparian tree establishment is defined as Riparian tree recruitment minus Riparian tree inundation.

Hydraulic Modeling and Use of GIS

	Statistical results computed by HEC-EFM are translated to water surface profiles, water depths, and water velocities by hydraulic modeling packages like HEC-RAS and GeoRAS. These data can be viewed in GIS and overlaid with other spatial data sets that have ecological significance (land use, soils, and vegetation mapping) to gain more insight about important ecosystem dynamics.
	The figure above shows areas where HEC-EFM predicts recruitment of Riparian tree seedlings (green layer) and loss of that recruitment to prolonged inundation (blue layer). The visible portion of the recruitment layer reflects predicted establishment of Riparian tree seedlings, in accordance with the combo relationship discussed above.