Modelling drought impacts on the hydrodynamics of a tropical water supply reservoir

ABSTRACT

Changes in meteorological patterns to drier conditions alter the hydrodynamic processes of reservoirs and can affect their thermal structure. The aim of this study was to assess the impacts of a severe drought period on the hydrodynamics of a tropical reservoir. One-dimensional hydrodynamic modelling was applied from 2009 to 2016 to simulate the thermal dynamics of the highly drought-impacted Serra Azul reservoir, a drinking water supply reservoir located in southeast Brazil. After calibration (r = 0.91, root mean square error [RMSE] = 1.33 °C) and validation of the model (r = 0.87, RMSE = 2.06 °C), physical indicators were calculated to evaluate the stratification and mixing processes in the water column. Results showed that the reservoir hydrodynamics were affected by the drought period through an increase in mixing frequency and duration. Negative implications for water quality are expected, such as higher concentration of dissolved substances and nutrients and increased turbidity, salinity, and electrical conductivity, as observed in most lakes and reservoirs subjected to drought. Different water withdrawal scenarios were simulated, and a critical water withdrawal volume that could prevent drought impacts on the Serra Azul reservoir thermal regime was identified. This study indicates the need for managers to understand potential impacts of extreme meteorological events in reservoir dynamics, particularly when the reservoirs are part of drinking water systems.

KEYWORDS:

• General Lake Model (GLM)
• lentic water bodies
• physical indicators
• thermal dynamics
• water column mixing

Acknowledgements

The authors are grateful to the Agência Nacional de Águas (ANA: National Water Agency – Brazil) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the financial support to this research. The first author was supported by a CAPES MSc research grant. The last author is a CNPq PQ fellow. Additionally, we are grateful to the Minas Gerais State Water Utility Company (COPASA) for providing data and for collaboration. The authors also thank the National Institute of Meteorology (INMET) and the Geological Survey of Brazil for providing data.

Disclosure statement

No potential conflict of interest was reported by the authors.