Garita reservoir
In 1993 a study was carried out on the reserovir in a cooperation between the Department of Hydraulic Engineering at NTNU, SINTEF and Instituto Costarricense de Electricidad (ICE). ICE owns and operates the reservoir and the corresponding hydropower plant. The study included measurements of water velocities and sediment concentrations in the reservoir. This was compared with results from a 3D numerical model. The results were presented in the following article:
Olsen, N. R. B., Jimenez, O., Abrahamsen, L. and Løvoll, A. (1999) "3D CFD modelling of water and sediment flow in a hydropower reservoir", International Journal of Sediment Research, Vol. 14, No. 1.
Supply channel, seen in in the direction against the current.
A constant water discharge of 17 m3/s was kept during the measurements. This was controlled by point velocity measurements in the supply channel. Measurements of sediment concentrations were also taken.
Supply channel, with gates controlling the inflow dicharge
The measurements were carried out in the summer 1993.
Photos from the field work
The data was used by L. Abrahamsen in his Master thesis. He also did many of the computations in the current study, including making the grid shown below.
Computational grid seen from above
Eight cells were used in the vertical direction. The bed roughness was varied and both the first order upwind and the second order upwind method was used. This gave approximately the same velocity field.
Velocity vectors in a colour plot that shows the water depth
The scale indicates high values with red colours and low values with blue colours
Velocity vectors in a colour figure that indicates horizontal velocity
The results from the velocity compuations corresponded well with the measurements. Also relatively independent of calibration parameters and discretization schemes.
The results from the computations of the sediment concentrations were not as good as for the velocities. The inflowing sediment concentrations varied considerably from day to day and also during the day. It was therefore difficult to get point measuremetns consistent with the results from the numerical model, which only could compute steady flow. The average trap efficient on the day with least variation in inflowing sediment concentrations corresponeded fairly well.