Environmental Flows

Characterizing the Natural Flow Regime for Environmental Flows in the Chilean Cordillera de los Andes

Samuel Sandoval Solis    Belize A. Lane    Diego Rivera Salazar   Helen E. Dahlke   Rebecca L. Teasley   Marcelo Somos


The Cordillera de los Andes is the longest continental mountain range in the world, extending north to south through seven South American countries with an average height of 13,000 feet (Compagnucci 2000). In Chile, the Andes form the headwaters to the country’s major rivers, which run short, steep courses east to west towards the Pacific Ocean. These river systems are at high risk from a combination of climate change, population growth, over-allocation of water resources, and the lack of an integrative environmental water policy. Characterizing the natural flow regimes of these snowmelt-driven rivers is imperative to understanding and preserving the ecological and geomorphic functions provided by Chile’s unique riverine ecosystems.

The main drivers of streamflow variability in Chile’s rivers are runoff from winter rainfall and snowmelt sources in the upper Andes. The relative timing and contribution of both factors presents a marked latitudinal gradient. In turn, precipitation is controlled by the large-scale regional climate system. Thus, streamflow variability is directly controlled by precipitation variability (Buytaert 2006). The result is a highly variable system, showing inter-annual variability close to 40% as the standard deviation to mean ratio (Salazar, 2013). For example, during El Niño events, precipitation largely exceeds long term averages, leading to extensive flooding and groundwater recharge, and opposite conditions occur during La Niña events. Moreover, there is a decadal variability related to the Pacific decadal Oscillation and the Antarctic Annular Mode. Under such conditions, mean streamflow values are not the best option for quantifying environmentally-significant flows, since they do not incorporate ecologically-significant events like floods and droughts (Salazar 2013).

The natural flow paradigm approach has the potential to better capture the “natural” conditions of Chile’s snowmelt-driven rivers, given the high variability and data limitation of the systems. This approach considers five components of the natural flow regime critical to regulating ecological processes in river ecosystems: the magnitude, frequency, duration, timing and rate of change of hydrologic conditions (Poff and Ward, 1989). These components can be used to characterize the full range of flows and hydrologic phenomena critical to the integrity of aquatic and riparian ecosystems (Poff et al., 1997). In addition, comparisons are needed regarding different approaches to e-flows estimation in data-scarce systems.




Why is this project needed?

In Chile, the market primarily defines water allocation, as the State gives complete ownership of water rights to private companies or persons. This legal framework impedes the action of the State in issues of environmental sustainability and social equity. A clear example of this situation is that environmental flows are legally and operationally environmental externalities, as water is allocated to non-environmental sectors only. Thus, the environmental requirements must compete in the market with highly economically “efficient” sectors, but under very asymmetric conditions, because the environment is not even recognized as a water user (Bauer 2004).

As environmental considerations have become more recognized in water resources management, there has been increasing interest in the incorporation of e-flows as a conservation and restoration tool for Chile’s rivers. However, the legal framework is vague in defining e-flows, how they are estimated, and the potential implications of such an environmental policy. In addition, climate change projections for Chile involve extreme climatic variability acting over many time scales (seasonal, interannual, decadal), and with high spatial variability (latitudinal and altitudinal).

What is new about it?

The Chilean Water Authority (Dirección General de Aguas) very recently released a new directive regarding e-flows requirements (Environmental Ministry of Chile, 2013). Although minimum discharge is still defined as a percentage of long term averages, the new regulation incorporates monthly streamflow values, recognizing seasonal variability as a key driver of riverine ecosystem health. This legislation represents a huge step towards the preservation of Chile’s unique riparian and aquatic ecosystems and recognition of the value of the services they provide for humans. It provides an unprecedented opportunity for research on the hydrology, ecology and management of Chilean river systems. However, the directive does not explicitly recommend any procedure for calculating e-flows (e.g. what happens if short records are available, what is the appropriate base period for averaging, how is discharge linked to habitat requirements, etc.), and only applies to new surface water rights.  This study will quantify environmental water requirements in an ecologically-sound manner while engaging in meaningful discussion and problem solving regarding the implementation of an environmental flow policy in Chile.




  1. to assist in the estimation of the natural flow regimes of a representative sample of Chile’s rivers and to develop e-flows recommendations for regulated or planning to be regulated rivers
  2. to deploy a field campaign for “ecological calibration”; i.e. to  consult with local experts regarding the value of specific components of the natural flow regime for river conservation and to confirm that the data analysis performed matches empirical ecological, geomorphic and water quality data
  3. to document this analysis in papers, journals and reports in both English and Spanish (4) to generate a comparison between natural flow regimes in Chile and California, and use Chilean natural flows analysis to lend insight into environmental policy for California’s rivers.

Project Deliverables

  1. a policy briefing for Chilean water management policymakers
  2. a workshop designed for Chilean Water User Organizations (WUOs) and other river system stakeholders; WUOs have the mandate to manage Chile’s irrigation water, mainly sourced from river intakes.