2020-2021 Executive Summary
Ecohydrology is the study of how changes to flow patterns impact the health of aquatic ecosystems. Streams, wetlands and other aquatic environments all experience routine natural variation in the timing, magnitude, duration and frequency of flows. While aquatic life has naturally adapted to these flow patterns, human activities can trigger significant disruptions to flows that alter the natural structure and composition of aquatic ecosystems. California’s water resources management community needs to understand the relationship between alterations to environmental flows and ecological impacts to make optimal decisions about how to impound, divert, recharge and otherwise control the release of water to serve a variety of societal needs – from flood control to agricultural irrigation to water recycling. SCCWRP research is helping water resources managers take science-informed approaches to solving complex flow management issues. By developing tools and strategies that help managers evaluate various potential options for offsetting threats to environmental flows, SCCWRP is poised to help bring greater consistency, standardization and coordination to the design of environmental flow management programs across California.
SCCWRP’s ecohydrology research is driven by three major objectives: (1) Understand and predict patterns in key drivers of hydrologic change (e.g., land use, climate change, water use practices), (2) develop tools including statistical and deterministic models to evaluate the relationship between key drivers, changes in flow, and related physical and biological responses, and (3) evaluate the effectiveness of various management actions (e.g., BMPs) and other efforts to reduce or mitigate the impacts of flow modification. Evaluating possible management actions includes developing mechanisms that enhance performance and that improve understanding of how multiple management actions, including stream restoration, can work synergistically across broad areas to improve the condition of receiving waters.
This year, SCCWRP will continue to focus on developing tools that can be used to predict how changes in flow translate to changes in physical structure and in biological community composition – and how these changes affect water resources management decisions. SCCWRP’s focus for 2020-21 will be on:
- Development of statewide framework for evaluating in-stream flow needs: SCCWRP has facilitated formation of a statewide workgroup under the California Water Quality Monitoring Council that is developing a tiered framework for assessing in-stream flow needs across California. The workgroup, which features partners from UC Berkeley, UC Davis, U.S. Geological Survey and The Nature Conservancy, is developing an environmental flows management framework that includes statewide hydrologic and geomorphic classification, coarse-level flow requirements for each hydrologic class in the state, and a framework for selecting the most appropriate site-specific tool based on consideration of stream type, biological endpoint, and management needs. The framework will be applied to support several needs related to flow management, including dam management, agricultural water withdrawals, and urban stormwater management.
- Applying flow-ecology to water resources management: SCCWRP will continue examining how to apply flow-ecology principles to optimally support water resources management, including urban stormwater management, evaluation of climate change effects, and evaluation of water use and reuse proposals. SCCWRP is conducting investigations of the effects of flow management in four southern California watersheds (Los Angeles River, San Gabriel River, San Juan Creek and Aliso Creek), with a goal of informing stormwater and wastewater management actions (including reuse) and stream restoration. These projects will help develop recommended environmental flow targets that sustain the health of freshwater fish, amphibians and riparian habitats, while also optimally balancing competing demands on finite water resources, especially reuse of treated wastewater effluent discharges and enhanced stormwater capture practices. These projects represent important early implementations of the recently developed California Environmental Flows Framework (CEFF) for southern California urban watersheds.
- Evaluating the effectiveness of hydromodification management: SCCWRP is developing an approach for evaluating the effectiveness of hydromodification management actions aimed at restoring and maintaining the physical and biological health of southern California streams. Given the hydromodification management plans that have been implemented over the past five years, sufficient management actions have occurred to begin evaluating the efficacy of approaches and the tools used to inform management decisions. Working with Orange and San Diego Counties, SCCWRP will explore ways to assess effectiveness of programs aimed at protecting and remediating streams of varying susceptibility. SCCWRP will also develop recommendations to standardize approaches for assessing performance effectiveness. Information compiled through these efforts will also be used to determine any necessary refinements to the hydromodification screening and assessment tools previously developed by SCCWRP and its partners.
- Advancing species modeling for informing environmental flow prescriptions: SCCWRP is advancing the science of species occurrence and distribution modeling by applying the science to several southern California case studies. SCCWRP will draw on previously developed statistical approaches that relate changes in flow to effects on biological communities (mainly using existing benthic invertebrate and algae indices). Given that current management decisions require the ability to evaluate proposed flow alterations on higher trophic communities such as fish, amphibians, and birds, SCCWRP will explore new hybrid statistical and mechanistic approaches for conducting these assessments and piloting their application to inform environmental flow decisions.