by Sarah Yarnell, Diego Rivera Salazar, Camila Boettiger, and Jay Lund
Countries, regions, and river basins globally are struggling to provide and manage flows in rivers for ecosystems. One approach, of many, is a Functional Flows approach, because it seeks to provide a range of streamflows over the year and between years to support fundamental functions of river ecosystems and the ecosystem services for society. These streamflows include seasonal base flows that vary from wet to dry seasons and interannually across wet to dry years as well as short-term flood flows that mobilize and scour bed sediments, recreate aquatic, riparian, and floodplain habitat, and support seasonal wetlands. The approach also involves a process for balancing multiple human and ecological objectives for river systems through broad engagement of multiple interests. In their challenge to maintain riverine ecosystem services, Chile and California can benefit from this dynamic approach to managing instream flows.
- Similar geography and activities
Chile is in the Southern hemisphere on the Pacific Ocean west of the Andes mountains. Chile’s geography, climate, and ecology are similar to California. The most populous areas in both regions span latitudes from 32 – 38 degrees dominated by a strongly seasonal Mediterranean climate with cool wet winters and warm dry summers, as well strong interannual and decadal variability. Both regions are on the west coast of the Americas, with the Pacific Ocean to the west and large high-elevation mountains running north-south inland to the east. Both regions have smaller coastal mountains paralleling the ocean’s edge, with a ‘Central Valley’ between these mountain ranges. These Central Valleys have rich productive agricultural lands, including some of the finest vineyards exporting wines globally, within which large populations and communities are economically sustained. The geographic diversity of each region supports a rich and vulnerable biodiversity of native and endemic species, many of which rely on healthy freshwater ecosystems. Major geographic differences are the mirrored effect of being either north or south of the equator: Chile’s summer peaks in January-February and its most arid regions are to the north, while California’s summer temperatures are highest in July-August and aridity increases to the south (Figures 2 and 3).
With such similarities, it is not surprising that in both Chile and California, like most populous regions globally, the increased harnessing of river flows for agriculture, hydropower, industry, and urban water supply has led to economic growth and prosperity. However, human development sustained by surface water sources has drastically reduced freshwater biodiversity and ecosystem services, risking the sustainability of fresh water supplies.
- A functional flows approach for instream flows
Environmental flows allocate some water for instream ecological purposes, supporting freshwater dependent ecosystems and improving river health (Horne et al., 2017). Implementing environmental flows has direct positive effects for biota in the river and can also improve water quality for recreation, drinking, and municipal uses. Instream flows do not attempt to restore the full “natural” or unimpaired flow of the river, rather they aim to support and maintain desired ecological conditions in regulated and diverted watercourses. Over time, the philosophy and practice of defining an environmental flow regime has advanced from static minimum instream flows protecting selected life history stages of specified aquatic species (e.g., Bovee, 1982) to environmental flow determinations that consider the natural variability of streamflows into which native species and ecosystems have evolved (e.g., Poff et al., 2010) and support river ecosystem functions (Palmer and Ruhi, 2019). In short, healthy river ecosystems provide a broad range of benefits to society, and environmental flows seek to maintain and support healthy streams.
One avenue for improving the ecosystem functionality of regulated rivers is a Functional Flows approach to river management (Yarnell et al., 2015; Stein et al., 2021). This approach focuses on identifying functional flow components, discrete aspects of the flow regime with documented importance for ecological, geomorphic or biogeochemical processes in riverine systems (Yarnell et al., 2015). Environmental flow management in regulated rivers then seeks to retain these key flow components, such as flooding overbank flows and spawning migration pulse flows to support biophysical processes needed to maintain a river’s ecological structure and function upon which native biological communities depend (Bestgen et al., 2020; Yarnell et al., 2020).
In California, five functional flow components have been identified that support critical physical, biogeochemical, and biological functions that maintain river ecosystem health and satisfy life history requirements of native species (Figure 2):
- Fall pulse flow: Following first major storm event at the end of dry season
- Wet-season peak flow: Coincides with the largest storms in winter
- Wet-season baseflow: Sustained by overland and shallow subsurface flows in the periods between winter storms
- Spring recession flow: Represents the transition from the wet to dry season and is characterized by a steady decline of flows over a period of weeks to months
- Dry-season baseflow: Sustained by groundwater inputs to rivers
Managing for these functional flow components preserves ecologically essential patterns of flow variability within and across seasons, but it does not require either full restoration of natural flows or maintenance of historical ecosystem conditions. These functional flow components can be quantified by a suite of functional flow metrics—statistical measures of the flow characteristics of each of the five functional flow components—that reflect the natural diversity in flow characteristics seasonally and across years.
In the long and narrow country of Chile (mean width of 180 km and a length of 4270 km (from 18 ° to 56°S), rivers are short. Most start at the Andes flowing westward over steep slopes, across the flat lower gradient Central Valley, and finally through the Coastal Range to reach the Pacific Ocean. Agriculture, cities, and industries are mainly located in the Central Valley, accounting for 88% of the extracted water. From North to South, climate and landscapes change from arid to semi-arid Mediterranean to wet. Changes in precipitation patterns shape the streamflow regimes. Rivers in Central Chile (32-36°S) reach minimum flows from January to May, with winter peaks from rainfall and spring peaks from snow and glacier melt from June to September. The relative magnitude of the spring snowmelt decreases southward, as the Southern region (36 – 44 °S) receives more rainfall but less snow as the altitude of The Andes decreases.
In both Chile and California, the geography, climate, and landscape shape the streamflow regimes, such that an understanding of these interacting factors is necessary to determine how the river ecosystem functions. Retaining key seasonal flow signatures, both baseflows and peak flows, along with space for the river to move and create riparian habitat, is necessary to support river functioning and ecosystem health.
A Functional Flows approach does not require the high density and range of data needed to develop flow ecology relationships as in more mechanistic methods (e.g., Poff et al., 2010) but rather considers how the natural flow regime interacts with basic physical channel conditions, floodplains, sediment regimes, thermal regimes and biologic and biogeochemical processes to support critical ecosystem functions. By protecting underlying functions and variability patterns that sustain river ecosystems, this approach is likely to deliver broad benefits for freshwater biota, including threatened fish species and their supporting ecosystem, as well as valued ecosystem services, such as clean water, fisheries, and recreation.
A traditional focus on single species (even single life history stages of single species) has tended to favor static environmental flow requirements that vary little within seasons and across years. However, native freshwater biota in Mediterranean climates, such as California and Chile, are adapted to the high natural seasonal and interannual variability in river flows. A Functional Flows approach preserves particular elements of natural flow variations upon which native species depend. Natural fluctuations in flows across time and space interact with the surrounding landscape to drive ecosystem processes, such as movement of organic matter and nutrients, scour and erosion of sediment, and hydrological connectivity enabling vegetation growth or fish migration (Palmer & Ruhi, 2019; Yarnell et al., 2015). Disrupting ecological functions from stabilization of flow regimes and fragmentation of habitat in time and space, reduces long-term resiliency and biodiversity of river systems.
Using a Functional Flows approach, environmental flow allocations can be targeted to components of the flow regime that most directly support ecological functions, while allowing diversions for human uses during other times (e.g., most winter high flow periods) (Stein et al. 2022). Over longer timescales, the approach also provides flexibility to adjust environmental water allocations in different water year types, maximizing allocations in wet years to enhance ecosystem conditions and limiting allocations in drought years to those needed to avoid catastrophic ecosystem impacts. This provides the ability to ‘design’ or tailor implementation to local conditions and needs. Flexible approaches that aim to maximize ecosystem functionality, especially during wetter years, will help build the resiliency of ecosystems to future droughts. Such proactive, long-term approaches are becoming more important as global temperatures rise and the intensity and spatial extent of drought increases in much of the western hemisphere.
3. Flowing forward
Current regulation related to minimum flows in Chile relies on streamflow data provided from government agencies and should consider the local characteristics and conditions of the watercourse. Discussion often focuses on the feasibility of applying certain methods to determine a fixed minimum flow, instead of discussing a more holistic approach that considers interactions with other variables and the expected environmental outcomes of such flows. The Functional Flows approach is promising for Chile’s water management, as it requires a focus on functionality and outcomes rather than extensive detailed parametrization.
In California, technical guidance for implementing a Functional Flows approach is provided in the California Environmental Flows Framework (CEFF), developed by a broad range of academic, agency, and non-governmental researchers (ceff.ucdavis.edu). CEFF provides a way to holistically incorporate functional flows, ecosystem goals, local requirements, and regulation. It provides guidance on balancing multiple management objectives via a stakeholder or community-driven process and advocates for monitoring and adaptive management programs. In the third blog of this series, we will discuss lessons from the California Environmental Flows Framework (CEFF) that might guide development of a Chilean Environmental Flows Framework, (ChEFF).
References and Further Reading:
Alvarez-Garreton, C.; Lara, A.; Boisier, J.P.; Galleguillos, M. The Impacts of Native Forests and Forest Plantations on Water Supply in Chile. Forests 2019, 10, 473.
Arismendi I & B Penaluna. 2009. Peces nativos en aguas continentales del Sur de Chile / Native inland fishes of Southern Chile, funded by the Millenium Scienti!c Initiate through the FORECOS Nucleus Millenium P04-065-F of Mideplan.
Arumí, J.L.; Rivera, D.; Holzapfel, E.; Boochs, P.; Billib, M. et al,: Effect of the irrigation canal network on surface and groundwater interactions in the lower valley of the Cachapoal river, Chile. Chilean Journal of Agricultural Research 69 (2009), Nr. 1, S. 12-20. DOI: https://doi.org/10.4067/S0718-58392009000100002
Boettiger, C., K Börk, R. Ponce Oliva, D. Rivera, J. Lund, and S. Yarnell (2024), Minimum Flow Laws in California and Chile, CaliforniaWaterBlog.com, February 25, 2024
Bovee, K. D. (1982). A Guide to Stream Habitat Analysis Using the Instream Flow Incremental Methodology. Fort Collins, CO: U.S. Fish and Wildlife Service. Report no. Instream Flow Inf. Pap. 12.
Fernández-Cirelli, A.; Arumí, J.L.; Rivera, D.; Boochs, P.W.: Environmental effects of irrigation in arid and semi-arid regions. In: Chilean Journal of Agricultural Research 69 (2009), Nr. SUPPL. 1, S. 27-40. DOI: https://doi.org/10.4067/S0718-58392009000500004
Grantham, T., J. Howard, B. Lane, R. Lusardi, S. Sandoval-Solis, E. Stein, S. Yarnell and J. Zimmerman (2020), Functional Flows Can Improve Environmental Water Management in California, CaliforniaWaterBlog.com, November 29, 2020 https://californiawaterblog.com/2020/11/29/functional-flows-can-improve-environmental-water-management-in-california/
Horne, A., Webb, J. A., Stewardson, M., Richter, B., and Acreman, M. (2017). Water for the Environment: From Policy and Science to Implementation and Management. Academic Press.
Obester, A., S. Yarnell, and T. Grantham(2020), Environmental Flows in California, CaliforniaWaterBlog.com, March 18, 2020, https://californiawaterblog.com/2020/03/18/environmental-flows-in-california/
Palmer, M., and Ruhi, A. (2019). Linkages between Flow Regime, Biota, and Ecosystem Processes: Implications for River Restoration. Science 365, 1264. doi:10.1126/science.aaw2087
Poff, N. L., Richter, B. D., Arthington, A. H., Bunn, S. E., Naiman, R. J., Kendy, E., et al. (2010). The Ecological Limits of Hydrologic Alteration (ELOHA): a New Framework for Developing Regional Environmental Flow Standards. Freshw. Biol. 55, 147–170. doi:10.1111/j.1365-2427.2009.02204.x
Sangüesa, C.; Pizarro, R.; Ingram, B.; Balocchi, F.; García-Chevesich, P.; Pino, J.; Ibáñez, A.; Vallejos, C.; Mendoza, R.; Bernal, A.; et al. Streamflow Trends in Central Chile. Hydrology 2023, 10, 144. https://doi.org/10.3390/hydrology10070144
Stein, E.D., J. Zimmerman, S.M. Yarnell, B. Stanford, B. Lane, K. Taniguchi-Quan, A. Obester, T.E. Grantham, S. Sandoval-Solis, and R.A. Lusardi. 2021. The California Environmental Flows Framework: Meeting the Challenges of Developing a Large-Scale Environmental Flows Program. Frontiers in Environmental Science-Freshwater Science 9:769943. Doi: 10.3389/fenvs.2021.769943
Yarnell, S. M., Petts, G. E., Schmidt, J. C., Whipple, A. A., Beller, E. E., Dahm, C. N., et al. (2015). Functional Flows in Modified Riverscapes: Hydrographs, Habitats and Opportunities. Bioscience 65, 963–972. doi:10.1093/biosci/biv102
Yarnell, S. M., Stein, E. D., Webb, J. A., Grantham, T., Lusardi, R. A., Zimmerman, J., et al. (2020). A Functional Flows Approach to Selecting Ecologically Relevant Flow Metrics for Environmental Flow Applications. River Res. Applic 36 (2), 318–324. doi:10.1002/rra.3575
The California Environmental Flows Framework website. http://ceff.ucdavis.edu.
Sarah Yarnell is a Senior Research Hydrologist at the Center for Watershed Sciences. Diego Rivera Salazar is a Professor in the School of Engineering & Center for Resources Management, Universidad del Desarrollo, Santiago, Chile, Centro de Recursos Hídricos para la Agricultura y la Minería (ANID/FONDAP) (PI).
This blog post is the second of three posts resulting from an international collaboration on environmental flows between Chile’s Universidad del Desarrollo and Universidad de Talca, and the University of California, Davis (ANID Project FOVI 220188) law, engineering, economics, hydrology, and ecology researchers. The first post explained a bit about minimum flow regulations in California and Chile. This post provides an overview of functional flows for implementing environmental flows in Chile. The third post will look at lessons from the California Environmental Flows Framework (CEFF) that might guide development of a Chilean Environmental Flows Framework, (ChEFF). Project FOVI 220188 “Minimum flows and information of water uses in surface waters: experiences and challenges in Chile and California” is funded by Chile’s National Agency of Research and Development (ANID).
