Assessing the link between environmental flow, hydropeaking operation and water quality of reservoirs
Introduction
The construction of a dam implies the creation of a new and complex human-made ecosystem with non-natural regulation depending on the purpose of the reservoir. Reservoirs enable flood control, electricity generation, and water management for human consumption and agriculture. Other purposes, such as navigation and recreation, have been added over time. Regardless of these uses, the construction and operation of a reservoir lead to environmental problems affecting the riverine vegetation, aquatic species, water quality, and river morphology, as well as social impacts on the surrounding areas (Collier et al., 1996). In this context, the construction and operation of the reservoir require awareness of the effects on both the pre-existing environment and the new human-made reservoir.
Most previous studies have focused on the downstream river, where the operational scheme of the withdrawals alters the natural flow rate and the sediment load. Downstream of the dam, erosion near structures and modifications of the channel morphology are to be expected, among other effects (Carling, 1988, Brandt, 2000, Graf, 2006). Additionally, the presence of a dam affects the aquatic ecosystem downstream of the reservoir due to alterations of the flow rate itself, changes in water depth and velocity, variations in water temperature, destruction of fish nesting sites on banks, obstruction of fish migration due to the dam barrier and increases in the concentration of fine sediment (Baxter, 1977, Collier et al., 1996, García et al., 2011, Gray and Ward, 1982). Water quality problems, as well as the anomalous growth of biological species and changes in biodiversity, are common inside the reservoir itself (George and Edwards, 1976, Baxter, 1977, Chung et al., 2009a). With respect to the nutrients, catchment management and the control of point and non-point source emissions have been useful in the mitigation of these environmental problems (Cooke et al., 2005, Peng et al., 2014). In other cases, it has been necessary to implement in-lake engineering, which includes the use of mixers, barriers, oxygenators and selective withdrawals (Morillo et al., 2006, Chung et al., 2009b, Chung et al., 2014).
In the particular case of a reservoir built for hydropower purposes, the operation of the hydropower plant alters the thermal structure of the water column and the mixing processes in the reservoir, due to the number of outlets, the location of the outlets and the withdrawal scheme (Casamitjana et al., 2003, de la Fuente and Niño, 2008, Ibarra et al., 2015). Hydropeaking operation in the hourly scale characterizes the behavior of hydropower plants. This operation policy produces energy for only a few hours each day, when the energy demand is maxima, while the rest of the time the system produces minimal energy and stores the inflow volume. The environmental flow usually defines this minimum energy produced during the day. The impacts of hydropeaking operation on the downstream river are well-understood: changes in benthic communities, habitat degradation and fish mortality, among others (Saltveit et al., 2001, Young et al., 2011). However, the influence of the hydropower operating policy on the reservoir water quality is not clear. Changes in the outflow are external perturbations of the physical environment, which have ultimately consequences on plankton dynamics (Reynolds, 1984, Reynolds, 1993, Hoyer et al., 2009).
The aim of this article was to investigate the link between hydropower plant operation, environmental flow constraints and water quality at a reservoir. The Rapel reservoir (34° S, 71.6° W) was chosen for this purpose: an old, dendritic and monomictic reservoir, located in central Chile (Vila et al., 1987, Vila et al., 2000, de la Fuente and Niño, 2008). The Rapel hydropower plant operates in the context of the Central Interconnected System (SIC), which provides energy to most of the Chilean population (CDEC-SIC, 2013). An Independent System Operator (ISO) minimizes the system's economic costs and defines which power plants will supply the energy demand. Since the construction of the Rapel Dam in 1968, no environmental restrictions have been imposed on its operation, and therefore the ISO has established a hydropeaking operation scheme. During its operation, the reservoir has received discharges of domestic, agro-industrial and mining wastewaters, which contain high rates of sediments and nutrients as well as metal compounds (Vila et al., 2000). The first eutrophication-related problems were observed in the 1970s: unnatural fish deaths and algae bloom events started to occur (Cabrera et al., 1977, Vila et al., 1987, Vila et al., 2000). Previous research has shown that hydropower operation affects the hydrodynamics of the reservoir, forces deeper stratification (de la Fuente and Niño, 2008), enhances vertical mixing and decreases horizontal dispersion (Ibarra, 2013, Ibarra et al., 2015), and alters the effluent temperature (Guzmán, 2013).
For this study, the three-dimensional ELCOM-CAEDYM model (Hipsey et al., 2010) was implemented to simulate the hydrodynamic and water quality of the reservoir, together with the interactions among sediments, nutrients and algae species. Operation of the ISO was simulated using a model called MIPUC that reproduces the economical operation of the entire SIC and consequently defines the required water volume to be released for hydropower generation. This outflow information is used as input data in ELCOM-CAEDYM simulations, which output the water quality of the reservoir, specifically, the variations in phytoplankton concentrations. The next section describes the models implemented in this study, the indicators used for analysis and comparison of the results, and the simulation scenarios proposed. The results section presents the validation of the models. Finally, the results of a total of 20 simulation scenarios are compared in terms of the indicators, as well as in terms of the factors that enhance or limit phytoplankton growth.
Section snippets
Study site
The Rapel reservoir is a dendritic and monomictic reservoir with a storage capacity of 400 Hm3, composed of 3 sub-basins with different retention times (Fig. 1a). The southern part of the system contains the Cachapoal basin, which receives inflows from the Cachapoal and Tinguiririca Rivers. In the eastern zone, the Alhué basin receives waters from Alhué Creek. Finally, the Muro basin receives contributions from the other two basins, and it is located in the northwestern zone of the reservoir.
Validation of water quality simulation
The base simulation for the Qhyd scenario was built only on field measurements, as detailed in the previous section. Two different approaches were followed to validate the performance of the ELCOM-CAEDYM simulation. First, simulated water temperatures at the same location as the thermistor chain were compared with observations. The measured and simulated temperature time series of vertical profiles are shown in Fig. 4a and b, respectively. Both figures show similar temperatures in the entire
Discussion
The present study aims to contribute to the understanding of possibilities and limits for hydropower plant operation regarding the water quality inside the Rapel reservoir; an old, dendritic and monomictic reservoir of central Chile. Previous studies showed that the thermal structure is characterized by a sharp thermocline, whose location is defined by the elevation of the outlets for the hydropower generation (de la Fuente and Niño, 2008, Ibarra, 2013, Ibarra et al., 2015). Regarded to the
Acknowledgments
We would like to thank Andrea Castelletti for his cooperation on this research; Jannik Haas, Cristián Godoy, Carolina Meruane and Marcelo Olivares for their helpful comments on an early version of this manuscript. We thank the Centre for Water Research, University of West-ern Australia, for providing the 2010 version of ELCOM-CAEDYM model under for non-commercial purposes, and to Centro de Energía of Universidad de Chile, for providing MIPUC model. The second author acknowledges financial
References (49)
- et al.
Understanding the influence of suspended solids on water quality and aquatic biota
Water Res.
(2008) - et al.
Developing environment-specific water quality guidelines for suspended particulate matter
Water Res.
(2012) Classification of geomorphological effects downstream of dams
Catena
(2000)- et al.
A numerical simulation of the role of zooplankton in C, N and P cycling in Lake Kinneret, Israel
Ecol. Modell.
(2006) - et al.
Modeling linkages between sediment resuspension and water quality in a shallow, eutrophic, wind-exposed lake
Ecol. Modell.
(2009) - et al.
Modelling the propagation of turbid density inflows into a stratified lake: Daecheong Reservoir, Korea
Environ. Modell. Softw.
(2009) - et al.
The influence of physical and physiological processes on the spatial heterogeneity of a Microcystis bloom in a stratified reservoir
Ecol. Modell.
(2014) - et al.
Pseudo 2D ecosystem model for a dendritic reservoir
Ecolog. Modell.
(2008) Downstream hydrologic and geomorphic effects of large dams on American rivers
Geomorphology
(2006)- et al.
Revegetation in the water level fluctuation zone of a reservoir: an ideal measure to reduce the input of nutrients and sediment
Ecol. Eng.
(2014)
Hydraulic control of short-term successional changes in the phytoplankton assemblage in stratified reservoirs
Ecol. Eng.
Changes in phytoplankton biomass due to diversion of an inflow into the Urayama Reservoir
Ecol. Eng.
A new flashiness index: characteristics and applications to Midwestern rivers and streams
JAWRA: J. Am. Water Resour. Assoc.
Environmental effects of dams and impoundments
Annu. Rev. Ecol. Syst.
Herramienta Computacional para modelo de pre-despacho económico de carga
Limnological characteristics of the Rapel reservoir, central Chile
Channel change and sediment transport in regulated UK rivers
Regul. Rivers Res. Manage.
Effects of the water withdrawal in the stratification patterns of a reservoir
Hydrobiologia
A multiobjective response surface approach for improved water quality planning in lakes and reservoirs
Water Resour. Res.
Estadísticas de operación 2003–2012
Restoration and Management of Lakes and Reservoirs
Strong vertical mixing of deep water of a stratified reservoir during the Maule earthquake, central Chile (Mw 8.8)
Geophys. Res. Lett.
Diagnosis and management plan for Rapel reservoir water quality
Cited by (33)
Basin scale sources of siltation in a contaminated hydropower reservoir
2024, Science of the Total EnvironmentImpacts of hydropeaking: A systematic review
2024, Science of the Total EnvironmentTransboundary river basins: Scenarios of hydropower development and operation under extreme climate conditions
2022, Science of the Total EnvironmentCitation Excerpt :While not at the same levels of contribution, S2 (tributary only scenario) was also predicted to help increase flow during dry seasons with levels at FNP, PPS, and PST increasing from 1.7 to 6.4%, 2.2 to 7.8%, 5.3 to 11.5%, respectively. The increased dry season flow could be considered an added benefit and consistent with known benefits associated with hydropower operation which include increased water availability for irrigation of dry season crops and drought management (Rossel and de la Fuente, 2015; Branche, 2017; Hecht et al., 2019; Intralawan et al., 2019). Table 3.2 provides a summary of changes in the Mekong River flow as predicted by LMB-Source at FNP, FPS, and FST stations.
Hazardous chemical accident prediction for drinking water sources in Three Gorges Reservoir
2021, Journal of Cleaner ProductionCitation Excerpt :Hu et al. (2014) applied a self-adaptive GA-aided multi-objective ecological reservoir operation model to water quality management and the results showed that the ecological operation have a better benefit. Rossel and Alberto (2015) analyzed the effects of operation schemes on the water quality of reservoir and proved the feasibility of using operating schemes to control and prevent water quality problems. Overall, reservoir optimal operation can mitigate the adverse effects of pollution rapidly when a pollution incident occurs.
Seasonal variation in water quality parameters of Gudlavalleru Engineering College pond
2021, Current Research in Green and Sustainable ChemistryFloating photovoltaic plants: Ecological impacts versus hydropower operation flexibility
2020, Energy Conversion and ManagementCitation Excerpt :In general, any software that is able to couple the hydrodynamics of the reservoir with the water quality would be suitable for the here intended simulations. The selection of ELCOM-CAEDYM for the purposes of this study is based on previous knowledge of the Rapel Reservoir with this particular model [22–24]. Fig. 1 illustrates the conceptual scheme of the ELCOM-CAEDYM model and the full technical detail can be found in reference [19].