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The Magdalena River basin is the most important source of water in Colombia and one of the most biologically diverse areas in the world; it spans almost every Andean ecosystem, from snow-capped mountains, cloud forests, high-altitude grasslands and wetlands, to dry forest valleys and coastal lagoons. The 274,000 km2 basin presently generates 85% of Colombia's GDP, with at least 20 million people relying on the river network as their source of drinking water and food.  The 1,528 km-long Magdalena River also provides 70% of Colombia's hydropower and 95% of the country's thermoelectric energy, and serves as a vital commercial freight artery linking the interior highlands with the coastal lowlands. However, intense agriculture, ranching, agrochemical pollution, roads, mining, and dams, reservoirs and other water infrastructure projects are changing the natural systems. Currently, 20 important dams retain water in the basin, and at least 16 more are planned for the next 15 years, that would double the current energy generation capacity. 
Since 2010, the Environmental Ministry of Colombia (MADS) and the National Authority for Licensing (ANLA) are developing an environmental flow policy to mitigate the impacts of hydrological alteration. The Nature Conservancy has supported this initiative with collaboration of important partners such as the National Institute for Hydrology, Meteorology and Environmental Studies (IDEAM), Regional Environmental Authorities (CARs), Cormagdalena, Javeriana University, Antioquia University, and other Colombian and international entities, such as the Stockholm Environment Institute. This collaborative effort is focused on building a Decision Support System based on freshwater conservation portfolio (blueprint), a hydrologic model, the precautionary environmental flows defined within ELOHA framework and included in the modeling using Indicators of Hydrologic Alteration (IHA), and key stakeholders necessities.
Former advances in ELOHA framework for the Magdalena River Basin include a 23 river type classification based on flow variables that is now under review, as we currently double the available hydrologic gauge stations; furthermore, we are including biophysical variables and species distributions in order to classify every stream in the Basin. The hydrologic modeling of the Magdalena Basin is developed in WEAP system as an integrate water management tool, and also useful for knowledge, monitoring and future conditions scenarios evaluation. There are two applications of WEAP, one for the whole Basin that runs at a monthly scale and a second one for the Upper Magdalena Basin running at a daily scale. These applications include the characteristics and operation rules of current hydropower development and future expansion projects of hydropower generation for 2014 and 2025, defined with ANLA.
In order to evaluate the effects of current and future hydropower development on flow, IHA is included in the WEAP applications for the Magdalena Basin, considering the precautionary ecologic limits of hydrologic alteration defined by the hypothesis of ecological response relationships identified with experts for each river type of the Basin during a previous workshop. Hydropower development scenarios include four flow conditions, i) "natural" flow that represents the original hydrologic response of the basin, ii) current flow that reflect the hydrologic alteration of current infrastructure, iii) the expected flow alteration under two hydropower development scenarios and iv) the expected flow of hydropower development considering operation rules defined by precautionary environmental flows.
Additionally, TNC is working with Antioquia University to define migratory fish species routes and reproduction areas, to validate and adjust some of the relations between ecological response and flow alteration hypothesis, and to generate distribution data bases for freshwater related reptiles, amphibians, waterfowls, macro-invertebrates and fishes.
ELOHA framework in the Magdalena Basin is currently under development, for more information contact:


Juliana Delgado
Freshwater specialist
Northern Andes and Southern Central America (NASCA) Program
The Nature Consevancy
Bogotá, Colombia
(57-1) 2357055

Thomas Walschburger
Science Coordinator
Northern Andes and Southern Central America (NASCA) Program
The Nature Conservancy
Bogotá, Colombia
(57-1) 2357055