Thermal functioning of a tropical reservoir assessed through three-dimensional modelling and high-frequency monitoring

Abstract

Urban lakes and reservoirs provide important ecosystem services. However, their water quality is being affected by anthropogenic pressures. The thermal regime is a strong driver of the vertical transport of nutrients, phytoplankton and oxygen. Thermal stratification can modify biogeochemical processes. In this paper, a three-dimensional hydrodynamic model was implemented and validated with high-frequency measurement of water temperature. The simulation results were in agreement with the measurements. For all simulation period, the model performance was evaluated based on hourly values, presenting a maximum RMSE of 0.65 ºC and Relative Error of 2.08%. The results show that high-frequency measurement associated with a three-dimensional model could help to understand and identify the reasons for the changes in the thermal condition of a shallow urban lake. The impact of the stream inflow on the temperature was highlighted, showing that during higher discharge events, when the river temperature is colder than the lake water, it flows into the lake deeper layers. The inflow water sank to the deeper layers where the lake morphology changes. The model showed an impact along the entire lake, showing the importance of monitoring the inflow water temperature. This modelling tool could be further used to study specific patterns of reservoir hydrodynamics.

Two-Dimensional Modelling of the Mixing Patterns in a Tropical Semiarid Reservoir

“…Accordingly, Curtarelli et al [39] noted river inflow as a contributor to the water column's stability with higher-temperature gradients in the river-reservoir transition zone. Also, Plec et al [42] found underflow conditions in a tropical reservoir.…”

“…On this basis, the mixing patterns of a water body are mainly influenced by meteorological forcings, such as air temperature, wind speed and direction, and rainfall, along with in-lake dynamics, namely inflow, outflow, withdrawal, and its water depth [22,[36][37][38][39][40][41][42]. Plec et al [42] investigated, with a 3D model set-up in a Brazilian reservoir, the impacts of stream inflow on the lake's thermal structure and found that colder inflows might generate a density current that favours nutrient release from sediment. Also, the reservoir's morphology is significant in its hydrodynamic behaviour [22,41,43].…”

Hydrodynamic Modeling of Stratification and Mixing in a Shallow, Tropical Floodplain Lake

“…Hydrodynamic models appropriate for lakes and reservoirs include three‐dimensional (3D) (e.g., AEM3D, Hodges & Dallimore, 2019; Si3D, Smith, 2006) and one‐dimensional formulations (1D) (e.g., DYRESM, Imberger & Patterson, 1981; GLM, Hipsey et al., 2019; LAKE 2.0, Stepanenko et al., 2016). These and similar models have been applied to a variety of lakes and reservoirs (e.g., Jin et al., 2000; Plec et al., 2021; Rueda & Schladow, 2003; Vidal et al., 2013; Woodward et al., 2017). However, modeling applications have focused on seasonal variations in stratification and have rarely examined vertical and temporal changes in stratification over 24‐hr periods.…”