Ecovalues are measures of how well flow regimes meet the needs of relationships. Users specify how seasonal and statistical results translate to ecovalues through the hypothesis tracking feature available as part of each relationship. Ecovalues can either be set equal to the flow result (i.e., when the “+” hypothesis tracking setting is active), the negation of the flow result (i.e., when the “-” setting is active), or interpolated based on the flow result and a table provided by the user (i.e., when the “Curve” setting is active). This interpolation option allows users to score the ecological success of different flow results. For example, a table could be applied that translates flow results for a relationship to ecovalues on a scale from 0 to 10.
Ecovalues are computed for each season within the period of record. Seasonal ecovalues are then used to compute a mean ecovalue for the whole flow regime (Figure 12). Mean ecovalues are used as a variable in the computations of Indices, as described later in this chapter.
Figure 12. Seasonal ecovalues shown as a time series (left) and in accordance with percent exceedance (right). Ecovalues are measures of how successfully the criteria for a relationship are met by a flow regime. Typically, increasingly positive ecovalues correspond to increasingly beneficial habitat conditions.
For flow regimes that are active and not the reference, seasonal ecovalue “shifts” are computed as a percent change in ecovalue from the reference flow regime. Seasonal ecovalues and seasonal ecovalue shifts are output as time series (one value per season per year) and as ranked data (Figure 13). Both offer insights regarding how successfully habitat is provided and how that success differs between flow regimes.
Figure 13. Ecovalue shifts provide insight regarding changes in success (left) and changes in the consistency of success (right) for a relationship. In HEC-EFM, “shifts” inherently compare an active flow regime with the reference flow regime. Ecovalue shifts are computed as the percent difference in ecovalue between active and reference flow regimes.