Universidad Nacional de Colombia Sede Manizales1, Universidad Autonoma de Manizales2, Universidad Nacional de Colombia Sede Manizales, IDEA3, Universidad de Caldas4
Recently, the growth in demand of water for: domestic, agricultural, livestock, industrial, mining and hydropower generation, are putting pressure on water resources in Colombia, causing water stress in river basins and increasing conflicts over water use (IDEAM, 2008), especially in terms of water demand for ecosystems.
Multiple methods are used worldwide to estimate river flows needed to maintain healthy rivers ecosystems (Tharme, 2003). However, very few of these are and holistic, accounting for seasonal and inter-annual flow variation needed to support the whole range of ecosystem services that healthy rivers provide. The best method for a given situation depends on the amount of resources and data available, the most important issues, and the level of certainty required.
Colombian regulations define ecological flow as the needed for the preservation of flora and fauna along the river to maintain the natural ecosystem, without causing significant alterations. According to this regulation, the minimum ecological flow must be maintained in different reaches, in order to ensure the conservation of aquatic resources and ecosystems. The environmental flow is defined as the volume of water required in terms of quality, quantity, duration and seasonality for sustaining ecosystems and the development of socio-economic activities of users along the stream.
The estimation of hydrological regime is the basis of hydrological methods; it is usually expressed as a percentage of a statistical central tendency, as a percentile of the flow duration curve, or associated with a return period. The hydraulic methods relate hydraulic variables as wetted perimeter, depth and flow velocity with habitat availability for the target species in the ecosystem. The ecological or habitat methods use indicators and habitat integrity indices as a basis for the development of communities and indices of biotic integrity of specific communities as fish, periphyton, macroinvertebrates and riparian vegetation. Finally, holistic approaches related all these components in the river, using the hydrologic analysis, hydraulic classification, biological data, the economic, social and expert knowledge (Tharme., 2003, Castro et al, 2006; King et al., 2008). This study concludes that methods considering hydroclimatological variability and the influence of macroclimatic phenomena are most appropriate for Colombian Andean basins and should be considered during Water Resources Management studies.
MATERIALS AND METHODS
In Colombia different methodologies have been applied to the estimation of ecological and environmental flows. This article compares and discusses these methods through a case study in an Andean high mountain basin, which is characterized by a bimodal hydrological regime associated to the Intertropical Convergence Zone ITCZ and influenced by El NiÃ±o Southern Oscillation, ENSO.
The ChinchinÃ¡ river basin (1052 km2) located in the Andean region of Colombia is studied; the basin shows water stress and high vulnerability, because it has a very low rate of retention and regulation with respect to the available surface water.
Hydrological, hydraulic and holistic methods proposed by the IDEAM (2008, 2010), the MADVT (2004), MADS (2013) and UN-MADVT (2008) were evaluated.
The hydroclimatic analysis of variables was performed from daily records of stations located in the basin for the period 1981-2010, according to supplied data by IDEAM, Hydroelectric CHEC, the National Coffee Centre Research -CENICAFE- and the National University of Colombia at Manizales.
In addition to the analysis of flow records, hydrological modeling was performed to determine the regime. The TETIS model was applied in this case study (FrancÃ©s et al., 2007) and the impact of ENSO was evaluated. Finally, an analysis of uncertainty associated to the estimation of environmental flows considering various criteria was performed.
RESULTS AND DISCUSSION
The environmental and ecological flows for the ChinchinÃ¡ river basin using different methodologies -EFM- are presented in Table 1. There are significant variations between different statistics used to evaluate methodologies proposed by Colombian regulations during the estimation of ecological and environmental flows in this Andean basin.
*Qp50: Historical data, EFM_1: IDEAM, (2000), EFM_2:IDEAM, (2004), EFM_3: MAVDT, (2004), EFM_4: IDEAM, (2008), EFM_5: UN-MAVDT, (2008), EFM_6: IDEAM, (2010), EFM_7: MADS, (2013)
Each methodology used to estimate has an uncertainty which was calculated by statistical procedures. It is important to highlight those methods able to estimate environmental flow in different hydrological regimes as dry hydrological conditions due to El NiÃ±o and humid conditions during La NiÃ±a, because these macroclimatic events affect the seasonality and inter-annual variability in the basin.
This article compares and discusses different methodologies for the estimation of the environmental and ecological flows applied in an Andean basin in Colombia. Some of these methodologies estimate a single value for the whole year, therefore they can only be considered as a first approximation of the ecological minimum flow. It is necessary to consider hydrological, hydraulic and habitat criteria in the estimation of environmental flow in Andean watersheds, because the temporal variability of flows along the year affect the results, this variability is due to macroclimatic phenomena such as ENSO and ITCZ. In this sense, holistic methods are more appropriate and should be integrated into the water resources management plans in Colombian Andean basins. 1.Castro L.M., Carvajal Y. and Monsalve E. A. (2006). "Enfoques teÃ³ricos para definir el caudal ambiental". IngenierÃa y Universidad. Vol 10, Num 2. Pontificia Universidad Javeriana Colombia.
2. FrancÃ©s F., Velez J.J, Velez J.I and Lopez F. (2007). "Split parameter structure for the automatic calibration of distributed hydrological models". Journal of Hydrology, 332, p 226-240.
3. IDEAM. (2008). Estudio Nacional del Agua. Instituto de HidrologÃa, MeteorologÃa y Estudios Ambientales de Colombia. BogotÃ¡.
4. IDEAM. (2010). Estudio Nacional del Agua. Instituto de HidrologÃa, MeteorologÃa y Estudios Ambientales de Colombia. BogotÃ¡.
5. King J. M., et al. (2008). Environmental Flow Assessments for Rivers: Manual for the Building Block Methodology. 339 p.
6. MADS (2013). MetodologÃa para la estimaciÃ³n y evaluaciÃ³n del caudal ambiental en proyectos que requieren licencia ambiental. Ministerio de Ambiente y Desarrollo Sostenible. BogotÃ¡.
7. MAVDT (2004). ResoluciÃ³n 865 de 2004. Ministerio de Ambiente Vivienda y Desarrollo Territorial. BogotÃ¡, Colombia
8. Tharme, R.E. (2003). "A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers". River Research and Applications, 19, 397Â–441
9. UN-MAVDT (2008). MetodologÃa para la estimaciÃ³n del caudal ambiental en proyectos licenciados. Universidad Nacional de Colombia Sede BogotÃ¡, Ministerio de Ambiente Vivienda y Desarrollo Territorial. 135 p.