The Ecosystem Functions Model (HEC-EFM) is a planning tool that aids in analyzing ecosystem response to changes in flow regime. The Hydrologic Engineering Center (HEC) of the U.S. Army Corps of Engineers is developing HEC-EFM to enable project teams to visualize existing ecologic conditions, highlight promising restoration sites, and assess and rank alternatives according to the relative change in ecosystem aspects.
Central to HEC-EFM analyses are "functional relationships". These relationships link characteristics of hydrologic and hydraulic time series (flow and stage) to elements of the ecosystem through combination of four basic criteria: 1) season, 2) duration, 3) rate of change, and 4) percent exceedance.
After relationships are developed, HEC-EFM performs statistical computations to analyze flow and stage time series for the specified criteria and produces a single flow value for each relationship. This process can then be repeated for alternative flow regimes to compare different project scenarios and indicate directions of changes to ecosystem health (Figure 1).
In addition to the statistical computations, HEC-EFM analyses typically involve hydraulic modeling (performed outside of HEC-EFM), which can translate statistical results to water surface profiles and spatial layers of water depth, velocity, and inundation areas. Geographic Information Systems (GIS) can then be used to display these generated layers as well as other relevant spatial data (i.e., soils, vegetation, and land-use maps).
Data requirements of HEC-EFM are related to the level of detail desired by the modeler. If only statistical results are desired, then required data consists of the flow regimes to be analyzed and the eco-hydro relationships. If the user intends to visualize statistical results spatially, data (and software) requirements increase significantly to include flow and stage time series, eco-hydro relationships, digital topography, a geo-referenced hydraulic model, and any other spatial data relevant to the ecosystem investigations.
This quick start guide provides an overview of the software (User Interface), a description of the numerical processes performed by the software (HEC-EFM Math), examples that demonstrate its use (Demonstration Project), information about application at different scales (Applying HEC-EFM), details about multivariate analyses (Multivariate Analyses), and language support (Language Support). Text has been formatted to help readers keep track of the different types of information presented. Italics are used to identify software features that are available through the user interfaces of HEC-EFM. Underlines are used to identify model input data, which includes the names of flow regimes and relationships used in the demonstration project. Bold is used to highlight key information for individual sections of text.
Figure 1. The process of applying HEC-EFM involves statistical analyses, river hydraulic modeling, and spatial analyses. Key inputs are hydrologic time series and ecological information such as the life history requirements of species of interest (e.g., seasons, durations, and frequencies).