Numerical modeling of stratified dam reservoirs and lakes

Due to drought in most of the countries in recent years, the protection and control of water resources have particular importance. These water resources have two forms included man made water resources structures such as dams, and natural water resources like lakes. The complexity of real fluid flow makes it impossible to solve the governing equations without making some form of simplifying approximation, even with the use of complex models and fast computers. This dissertation models and studied on the stratification of reservoirs or lakes with different conditions by changing some important parameters that can affect the temperature and suspended sediment distrubution patterns in reservoir/lake, numerically. Several models and simulations were performed for this goal. The commercial software package Flow 3D was selected as the numerical model for simulations of this dissertation. Near this code, the CE-qual-W2 was used to achieving the purpose of this thesis. Therefore, this program is used to analyse the thermal stratification of case study. The Koycegiz lake was selected as the case study, because of the importance of this lake as a water resource. Before simulating the Koycegiz lake, a series of model scenarios and sensitivity simulations were done to understand and quantify the formation of the stratification and propagation of suspended sediments in reservoirs and lakes with several changes in some important parameters included as discharge, temperature of water, suspended sediment concentrations and outlet type. Comparison of these results of scenarios shows that the changing in selected parameters could affect the position and thickness of the suspended sediment and temperature layers in reservoir. It was found changes in position and location of plunging point in most of the simulation results with a denser inflow current than reservoir. It was also concluded that the bottom outlet could be very effective on water quality of reservoir, when density/turbidity currents occurred. In the case study simulations, in first step, the hydrodynamic of Koycegiz lake was studied. In defined conditions, the approximate velocity vectors and directions were determined in different depths. Then, the salinity and temperature variations during time in defined conditions were investigated. In this part of simulations, the environment temperature was not definable to the FLOW3D program. Therefore, the temperature variations in depths and surface of the lake were under the influence of heat transfer between different layers. There was another parameter affected these temperature. This parameter was temperature of the inflow rivers. After that, three scenarios were done for the aim of evaluating and investigating the suspended sediment distribution pattern in the lake, in an unexpected flood event. According to these simulations, the flood was happened in only Namnam river, only Kargicak river and filnally, in both of Namnam and Kargicak rivers, simultaneously. In the next part of the simulations of Lake Koycegiz, the thermal stratification modeling of this lake was considered. In these models, which were done using CE-qual-W2 two-dimensional program, the output results of temperature of model in different depths were compared with observed data. The model results were harmonious with the measurements conducted in Lake Koycegiz. Modeled values of temperature in epilimnion and thermocline layers had a good concordance with the observed data. In other part of this thesis, effect of a possible dam construction on Namnam river is studied, briefly. Totally, it could conclude that the construction of dam on Namnam river will affect the Lake koycegiz. These effects will be in the case of the salinity, temperature, suspended sediment concentration, sediment particles type and diameter, dissolved oxygen and other parameters.