2018-2019 Executive Summary
Ecohydrology is the study of how changes in the frequency, magnitude, and duration of flow affect ecosystem structure and composition. As water runs off land surfaces with varying frequency, magnitude, and duration, these flows can not only directly affect biological communities, but also trigger erosion and deposition that alters the physical structure of water bodies, which, in turn, affects the ability of aquatic systems to support desired plant and animal communities. Past SCCWRP research has focused on predicting changes in water chemistry in response to specific anthropogenic actions, and on developing management measures – including best management practices (BMPs) – aimed at offsetting the effects of these chemical changes. Substantially less effort has been devoted to relating hydrologic and physical (or geomorphic) alterations to how biological communities respond to these alterations. As regulatory programs increasingly rely on biological endpoints to assess compliance and the effectiveness of mitigation efforts, SCCWRP is working to develop and improve tools that can help environmental managers better understand and ultimately predict the relationship between flow (and its associated hydrologic and geomorphic impacts) and ecosystem health. Better tools will better inform management actions aimed at reducing and mitigating the impacts of flow alterations, especially human-induced alterations associated with flood control, stormwater capture, and water reuse practices.
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 and changes in flow and related physical and biological responses in the stream, 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 BMPs 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 – changes that are ultimately linked to ecosystem health. SCCWRP’s focus for 2018-19 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.
- Application of flow-ecology to water resources management:: Past SCCWRP research has produced flow-ecology relationships that linked changes in flow to changes in stream condition as indicated by benthic macroinvertebrate community composition. SCCWRP is now pursuing development of flow targets based on algal communities, freshwater fish and riparian habitats. This broader suite of tools will be applied to support applications that include urban stormwater management, evaluation of climate change effects, and evaluation of water use and reuse proposals.
- Development of site-specific and watershed-scale BMPs: To facilitate BMP implementation to achieve physical and biological targets, SCCWRP is focusing on a combination of local and watershed-scale strategies, both of which are required for effective flow management. SCCWRP is partnering with members of the Southern California Stormwater Monitoring Coalition (SMC) to investigate performance of low-impact development (LID) practices under a range of design and implementation scenarios, including developing recommendations for standard monitoring and data management approaches. LID practices, which are one of the main tools used to meet stormwater runoff, hydromodification, and water-quality requirements, operate by capturing, retaining, detaining, or infiltrating runoff from developed land uses. LID performance can be affected by a variety of factors, such as influent concentrations, rainfall intensity, design attributes, and maintenance history. The results of this work will ultimately be used to support development of mechanistic models of LID performance. Separately, SCCWRP is working with local partners on developing technical approaches to determine optimal placement of hydromodification and water-quality management measures to achieve agreed-upon, watershed-scale objectives. These approaches include helping to develop a system that can determine appropriate offsets between BMPs and impacts along different portions of a watershed.