Research papersThe potential impact of climate variability on siltation of Andean reservoirs
Introduction
The global water storage capacity of hydroelectric reservoirs is decreasing annually while the economic activity, the hydropower industry and the world population continue to grow strongly (Palmieri et al., 2003). Therefore, sustainable management of reservoirs and water resource infrastructure is necessary to guarantee the projected usable lifespan of the hydroelectric infrastructure for future generations. About 80% of the reservoir volume in Europe will be filled up with sediments by the year 2080, and in North America by the year 2060 (Hauer et al., 2018). Likewise, in the near future, the hydropower sector will be impacted by an increase in sediment production due to global warming (Hauer et al., 2018). Large dams interrupt water flow and sediment transport, and trigger deposition of sediments in the middle or lower reaches of rivers as well as inundations of the surrounding areas. Sedimentation in the reservoirs might add compressional forces on the dam structure thereby exceeding the normal hydrostatic design, and the decrease of water storage in the reservoir and clogging of water intake also hinders the production of energy (Morris et al., 2008, Annandale et al., 2016). In this sense, the World Bank proposed a life cycle management approach for reservoir infrastructure with special emphasis on the economic evaluation of sediment management (Palmieri et al., 2003). It highlighted techniques to reduce the influx of sediments, to manage and evacuate sediments from the reservoir, and to replace lost storage of the reservoirs.
The boom in hydropower development in Andean river basins was identified as one of the top 15 global conservation issues (Sutherland et al., 2013). For this region, the electricity generation might increase by 550% from 2005 to the year 2050, thereby needing an increase in water volume from 70.5 billion m3 to 150.7 billion m3 (WEC, 2010). Of the Andean countries, Peru has the highest numbers of existing and proposed hydropower projects, because of its rapidly evolving energy demands (estimated at 8% growth per year) and regulatory framework that aims at promoting renewable energy (Tamayo et al., 2016, World Bank, 2017). Existing studies on the sustainability of its reservoirs are mainly focused on the largest ones, for example the Gallito Ciego and Poechos reservoirs in northwestern Peru. The admissible sediment's storage limit (dead storage) in Gallito Ciego reservoir was reached in 10 years, even though its designed lifespan was 50 years (Ramirez and Cisneros, 2007). The Poechos reservoir was highly affected by recent El Niño events where the average sediment fluxes exceeded those of normal years by a factor of 11 thereby shortening its life span considerably (Tote et al., 2011).
Despite these initial efforts, studies that describe the impact of changing sediment transfer due to climate change to the hydroelectric infrastructural system are still limited (Latrubesse and Restrepo, 2014). This is reason for concern as Andean countries like Peru are highly vulnerable to changes in precipitation rates and patterns as shown by the recent 2017 and 2018 El Niño Southern Oscillation (ENSO) events (Cadilhac et al., 2017). These high-intensity runoff events are associated with landsliding (Clark et al., 2016), mudflows (Tote et al., 2011), and gully erosion (Molina et al., 2008), and potentially lead to catastrophic flooding downstream (Coppus and Imeson, 2002, Roman-Gonzalez et al., 2019). During such extreme rainfall events the suspended sediment concentrations in Andean rivers may be 360 times higher when compared to normal conditions (Molina et al., 2015, Morera et al., 2013)
This paper evaluates the potential impact of climate variability on the water storage capacity of hydroelectric reservoirs in Andean countries, via a case study of the Cañete River in the Peruvian Coastal Range. By using a coupled hydrological-sediment transport model, we assessed projected changes in sediment transport rates under different scenarios of precipitation variability. The model simulations allowed us to evaluate the possible impacts of precipitation change on the life cycle of a hydroelectric plant.
Section snippets
Socioeconomic characteristics
The Cañete River is located approximately 150 km south of Lima (Peru). The basin has an extension of 6049 km2 and connects the Peruvian Andes to the Pacific Ocean (Fig. 1). The lower (Fig. 2b), arid part of the Cañete basin (0–1500 m a.s.l.) is an important agricultural area that produces fig, avocado, lúcuma, orchards, sugar cane, alfalfa crops and river shrimps (INEI, 2017). The middle basin (Fig. 2b) is predominantly sub-humid and hosts subsistence agriculture. The upper part (>4000 m
Materials and methods
A coupled hydrological and sediment transport model was built to simulate water flow and sediment transport in the Cañete River upstream of the Capillucas dam (Fig. 3). The HEC-HMS (U.S. Army Corps of Engineers, 2000) and HEC-RAS (U.S. Army Corps of Engineering, 2016) platforms were applied to simulate precipitation-runoff and sediment transport. Both models have been widely applied in the USA to describe discharge and sediment transfer in river channels (Knebl et al., 2005, Pereira et al., 2009
Hydrological model
The results for six gauging stations present a marked increase in discharge including high flow rates during the rainy season (Dec. – Apr.) followed by a sustained low rate in the dry season (May. – Nov.) (Fig. 8). During most of the model runs the modelled data followed the same discharge pattern as the observed flow data. Likewise, the high r2 and d values (r2 > 0.67 and d > 0.85), and RVB of around zero in most of the stations (Table 6) are indicative for an acceptable model performance at
Limitations of gauge-based sediment load measurements
One of the main issues to assess the impact climate change will have on fluvial systems is the scarcity of observed hydrometeorological data (Guyot et al., 2017, Lavado et al., 2012, Rau et al., 2017). Commonly, the spatial distribution of rainfall and discharge measurement stations is limited and the recorded data do not present continuous time series. This is especially true for the Andean countries (Restrepo and Syvitski, 2006, Latrubesse and Restrepo, 2014). Our hydrological model yielded
Conclusions
The amount of sediment transported in Andean rivers may increase over the next years due to climate variability and change. As a result, hydroelectric reservoirs could be silting up more rapidly than anticipated. The methodology presented in this paper coupled a hydrological and sediment transport model to model the sediment load of the 6049-km2-large Cañete River basin in the Peruvian Andes. Ten climate change scenarios were developed to evaluate the potential impact of precipitation change on
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by the Proyecto Glaciares+, implemented by CARE Peru and the University of Zurich (Switzerland) and funded by the Swiss Agency for Development and Cooperation (SDC), and by the ARES POP project on “Erosion and sediment yield in response to climate change and variability” funded by the Coopération au développement de l’Académie de Recherche et d’Enseignement supérieur (Belgium). Miluska Rosas was supported by a PhD Scholarship from the Conseil de l’Action Internationale
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