Investigation of Temperature Dynamics in Small and Shallow Reservoirs, Case Study: Lake Binaba, Upper East Region of Ghana

Abstract

An unsteady fully three-dimensional model of Lake Binaba (a shallow small reservoir) in semi-arid Upper East Region of Ghana has been developed to simulate its temperature dynamics. The model developed is built on the Reynolds Averaged Navier-Stokes (RANS) equations, utilizing the Boussinesq approach. As the results of the model are significantly affected by the physical conditions on the boundaries, allocating appropriate boundary conditions, particularly over a water surface, is essential in simulating the lake's thermal structure. The thermal effects of incoming short-wave radiation implemented as a heat source term in the temperature equation, while the heat fluxes at the free water surface, which depend on wind speed, air temperature, and atmospheric stability conditions are considered as temperature boundary condition. The model equations were solved using OpenFOAM CFD toolbox. As the flow is completely turbulent, which is affected by the complex boundary conditions, a new heat transfer solver and turbulence model were developed to investigate the spatial and temporal distribution of temperature in small and shallow inland water bodies using improved time-dependent boundary conditions. The computed temperature values were compared with four days of observed field data. Simulated and observed temperature profiles show reasonable agreement where the root mean square error (RMSE) over the simulation period ranges from 0.11 to 0.44˝C in temporal temperature profiles with an average value of 0.33˝C. Results indicate that the model is able to simulate the flow variables and the temperature distribution in small inland water bodies with complex bathymetry.

Three-Dimensional Modeling of Wind- and Temperature-Induced Flows in the Icó-Mandantes Bay, Itaparica Reservoir, NE Brazil

“…For the density-induced flow, a velocity increase took place to a lower extend in some specific zones, e.g., on the bottom and superficial layers next to the lateral boundaries, while there was a general decrease at the intermediate water depths. According to Abbasi et al [19], higher wind leads to higher return flows and shallow parts respond faster to air heating; the occurrence of these two phenomena are observable in our results, respectively in Figures 5c, 8 and 9. Moreover, during the heating phase, temperatures increase especially in the top layers near the water surface [19], as noticed as well in Figures 10 and 11.…”

“…Only a limited number of CFD simulations for temperature distribution in shallow and small inland water bodies in semi-arid areas can be generally found [19]. As addressed by numerous experts [6,12,15,19], weather conditions (wind, temperature) influence currents and stratification in reservoirs, whose hydrodynamic processes and thermal state are the main drivers of their ecosystem. The classification of lakes according to their circulation patterns has proven to be very useful for limnology assessments [12,30].…”

“…In the region, further ecosystem impacts are generally attributed to the intensive and increasing aquaculture production, by the insufficient treatment of sewage from agricultural villages and by the untreated drainage water from irrigation [5]. Due to the decreasing inflows and the warming climate, the number of reservoirs rarely valid, hence the application of 3D hydrodynamic models is required for proper calculations, as pointed out by many researchers even for very shallow depths (e.g., [14,19]). …”

“…The classification of lakes according to their circulation patterns has proven to be very useful for limnology assessments [12,30]. Moreover, the vertical resolutions of the measured temperature profiles are often not sufficient for assessing small-scale turbulence effects or investigating variations of water temperature induced by wind velocity and heating in shallow waters [19]. Therefore, research is needed to deepen the knowledge of such complex processes in areas already challenged by climate change, water multiple uses and lack of advanced modeling techniques.…”

“…How do the flow velocities change and to which extent? • Density differences are known to drive currents [6,12,19,21]: how does heating of the water surface due to warmer air temperature alter the hydraulics in the bay and how (e.g., velocity profiles, intensities)? Which are the consequent three-dimensional effects (e.g., stratification, flow circulation)?…”