Abstract
Numerical models are an important tool for simulating temperature, hydrodynamics and water quality in lakes and reservoirs. Existing models differ in dimensionality by considering spatial variations of simulated parameters (e.g., flow velocity and water temperature) in one (1D), two (2D) or three (3D) spatial dimensions. The different approaches are based on different levels of simplification in the description of hydrodynamic processes and result in different demands in computational power. The aim of this study is to compare three models with different dimensionality and to analyze differences between model results in relation to model simplifications. We analyze simulations of thermal stratification, flow velocity, and substance transport by density currents in a medium-sized drinking water reservoir in the subtropical zone, using three widely used open-source models: GLM (1D), CE-QUAL-W2 (2D) and Delft3D (3D). The models were operated with identical initial and boundary conditions over a one-year period. Their performance was assessed by comparing model results with measurements of temperature, flow velocity and turbulence. Results show that all models were capable of simulating the seasonal changes in water temperature and stratification. Flow velocities, only available for the 2D and 3D approaches, were more challenging to reproduce, but 3D simulations showed closer agreement with observations. With increasing dimensionality, the quality of the simulations also increased in terms of error, correlation and variance. None of the models provided good agreement with observations in terms of mixed layer depth, which also affects the spreading of inflowing water as density currents, and the results of water quality models that build on outputs of the hydrodynamic models.
Highlights
A large variety of different numerical models have been used for simulating temperature and hydrodynamics in lakes and reservoirs, as well as the biogeochemical and ecological processes that depend on it (e.g. Dissanayake et al, 2019; Guseva et al, 2020; Wang et al, 2020; Xu et al, 2021)
None of the models provided good agreement with observations in terms of mixed layer depth, which affects the spreading of inflowing water as density currents, and the results of water quality models 25 that build on outputs of the hydrodynamic models
Total spillway discharge had its largest volume in CE-QUAL-W2: 2.93 × 107 m3, General Lake Model (GLM) had a spillway volume as the 2D model 2.87 × 107 m3, and Delft3D simulated 3.7 % less spillway discharge than CE-QUALW2 (2.83 × 107 m3) (Fig. SI 1b)
Summary
A large variety of different numerical models have been used for simulating temperature and hydrodynamics in lakes and reservoirs, as well as the biogeochemical and ecological processes that depend on it (e.g. Dissanayake et al, 2019; Guseva et al, 2020; Wang et al, 2020; Xu et al, 2021). While the mechanistic description of underlying physical processes is identical or at 30 least similar in all models, they differ in their dimensionality, i.e. the number of spatial dimensions considered in the model. One-dimensional (1D) models usually resolve the vertical direction only (water depth), while considering homogeneity of all relevant quantities along horizontal directions. They are attractive due to their easy connection to ecological and biogeochemical modules.
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