Development of Recommended Flow Targets to Support Biological Integrity Based on Regional Flow-ecology Relationships for Benthic Macroinvertebrates in Southern California Streams

Changes to instream flow are known to be one of the major factors that affect the health of biological communities. Regulatory, monitoring, and management programs are increasingly using biological community composition, particularly benthic invertebrates, as one measure of instream conditions, stormwater project performance, or regulatory compliance with NPDES or other requirements and regulations. Understanding the relationship between changes in flow and changes in benthic invertebrate communities is, therefore, critical to informing decisions about ecosystem vulnerability, causes of stream and watershed degradation, and priorities for future watershed management.

There are many approaches to developing flow-ecology relationships that relate hydrologic change to responses in instream biological communities that can be used to establish management targets. The Ecological Limits of Hydrologic Alteration (ELOHA) framework (Poff et al. 2010) provides a way to assess the effect of flow alteration on the condition of biological communities (vs. individual taxa) on a regional basis. Consequently, it is a useful approach for setting targets across a wide range of geographies and stream types where comprehensive detailed site-specific investigations are not practical. The framework includes elements of stream classification, estimation of flow alteration and development of flow ecology relationships based on the response of biological communities to changes in flow.