Section A: Identify ecological flow criteria using natural functional flows
The goal of Section A is to identify ecological flow criteria – expressed as quantifiable metrics – that must be maintained to support the five functional flow components of a healthy stream ecosystem in California (Figure A.1). These ecological flow criteria – which correspond to flow metrics describing the magnitude, timing, duration, frequency, and/or rate-of-change of flow – are based on expected values of these metrics occurring in the absence of human activities. The predicted values of functional flow metrics are obtained from an existing statewide database. Once the ranges for these metrics have been identified, the user evaluates whether the range of natural flow metrics for a functional flow component would fail to support ecosystem functions due to the alteration of physical, biological or water quality factors. The outcome of that analysis determines whether the user proceeds to Section C to develop environmental flow recommendations, or proceeds to Section B to develop ecological flow criteria for the subset of functional flow components for which natural flows are unlikely to support essential ecosystem functions.
Figure A.1. Steps in Section A of the California Environmental Flows Framework
Section A has four steps (Figure A.1). In Step 1, the user defines the study area and locations of interest (LOIs) for establishing flow criteria, determines ecological management goals, and identifies the specific ecosystem functions that must be supported by ecological flow criteria to satisfy those goals. In Step 2, the user characterizes natural functional flows at their LOIs by obtaining predictions of the natural ranges of flow metrics from the California Natural Flows Database. In Step 3, the user evaluates whether there are any physical, biological, or water quality factors that may limit the ability of natural functional flows to support ecosystem functions and thus require additional consideration. In Step 4, the user selects ecological flow criteria for the functional flow components that do not require additional consideration. If non-flow factors have the potential to limit the effectiveness of the natural range of flow metrics to support ecosystem functions for any flow component, further analysis is required in Section B to define ecological flow criteria for these focal flow components.