Abstract
With the implementation of the Official Mexican Standard NOM-011-CONAGUA-2000 [1], the water balance of 730 basins has been calculated and its water availability agreement is published. This rule points out to allocate water for the environment only as an annual volume since methods for estimating environmental flows were not standardized in the country. For this reason, The Water Agency (CONAGUA) issued the standard NMX-AA-159-SCFI-2012 [2], to assess environmental flows needed both, at the strategic level in Integrated Water Resources Management (IWRM), or as part of the Environmental Impact Assessment (EIA) of large hydraulic projects. For over ten years, this standard was developed and finally published in September 2012 [3]. It explains different methods from hydrological to holistic approaches, with examples for the country. Its application will cover the urgent need to preserve water for ecosystems in watersheds with high ecological importance and low stress for water use. In this paper, an analysis of the environmental flow standard and examples of the suggested hydrological methods are presented. For its implementation, some steps are taking place, mainly establishing environmental water reserves and building capacities. In addition, environmental allocations are becoming a common practice for all water projects, as well as setting limits to hydrological alterations by hydroelectric dams. The standard promotes the use of technical integration tools to analyze the responses of ecosystems to changes in the flow regime and adaptive management under different scenarios of water use. Although the main steps have been taken, its implementation as mandatory rule will take time.
Highlights
Environmental, ecological or in stream flow (EF) is the amount of water that is kept flowing down in order to maintain the river in a desired environmental condition in terms of its spatial and timing distribution required to maintain the components, functions and aquatic ecosystems processes from which people obtain benefits
Generalized flow standards can be used to allocate water for the environment [12] but, every river can have an environmental flow regime according to what people want from a river in terms of conservation and use [13]
For seasonal environmental flow estimation, the Total Ordinary Volume Regime (TOVR) and the Total Volume for Flood Regime (TVFR) were obtained using the procedure proposed by World Wildlife Fund Mexico at the study basin level
Summary
Environmental, ecological or in stream flow (EF) is the amount of water that is kept flowing down in order to maintain the river in a desired environmental condition in terms of its spatial and timing distribution required to maintain the components, functions and aquatic ecosystems processes from which people obtain benefits Environmental flow assessment (EFA) is based on a scientific process to deal with basin features, probabilistic variability of natural flows and cross section hydromorphology models. These issues determine habitat connectivity and availability to be used by species at several stages of their life cycle. The EF implementation is on progress and overcoming several drags, since hydrological records are sometimes the only available data for many regions, whereas hydraulic studies are really scarce and its development is time and cost consuming [9] These methods need to broaden their scope towards habitat availability for species, as hydraulics research. Changes can be followed by hydrological parameters, habitat availability, species presence—absence, condition factor, weight—length relationship and food webs, among others [23]
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