The process of applying EFM involves three basic phases: statistical analyses, river hydraulics modeling, and spatial analyses (Figure 2). Most user interfaces in EFM support the statistical phase where users identify the ecosystem restoration or water management scenarios (“flow regimes”) and the aspects of the ecosystem (“relationships”) to be investigated. Results from the statistical phase are then input to hydraulics models that generate layers of water depth, velocity, and inundation, which are then used in Geographic Information Systems (GIS) to investigate spatial criteria and results for the flow regimes and relationships.

Figure 2. Statistics, hydraulics, and spatial phases of the EFM process. GeoEFM is used in the spatial analyses phase to investigate habitat areas and habitat connectivity produced by different restoration or water management scenarios.
“Flow regime” and “relationship” are terms that appear frequently in this manual. An EFM "flow regime" is defined as two concurrent daily time series that reflect conditions for a study area. Typically, the two series are mean flows and mean stages of a water body. Multiple flow regimes can be activated for consideration in a single analysis, but only one may be identified as the reference, which is the flow regime that all other active flow regimes will be compared to when considering model outputs.
"Relationships" are links between characteristics of flow regimes and elements of the ecosystem. Individual relationships are defined by the user via combinations of statistical criteria (seasonality, flow duration, rate of change, and flow frequencies) and geographical criteria (suitable ranges of water depth and velocity). Statistical criteria are considered in the first phase of the EFM process. Geographical criteria are considered in the last.
As GeoEFM is used in the last phase (spatial analyses), much of the structure for data and modeling will already have been determined before beginning work with GeoEFM. It is important to remember that due to this sequence information such as names of flow regimes and relationships are always passed from EFM to GeoEFM.
For more information about EFM use and terminology, please refer to the user guidance for that software or visit HEC’s webpage (www.hec.usace.army.mil).