Author(s): Janusz Kazmierski; Wojciech Majewski
Linked Author(s): Wojciech Majewski
Keywords: Lake currents; Pumped-storage powerplant; Lower reservoir; Mathematical model; Field measurements
Abstract: Lakes in the natural state have usually weak hydrodynamics. Wind driven currents in natural state do not exceed 0. 1 m/s and daily water surface variations are of the order of several centimetres. The situation is quite different when the lake operates in pumpedstorage powerplant system as the lower or upper reservoir. In this situation daily water surface variations and water currents have much higher values. Sustainable development requires an earlier estimate of hydrodynamic changes, which may occur in new situation. The paper presents the description of a comprehensive study concerning hydrodynamic changes, and in particular currents, of a natural lake used as the lower reservoir of pumped-storage powerplant. They are determined by means of mathematical model verified by detailed field measurements. Lake Zarnowiec operates as the lower reservoir of the pumped-storage powerplant. It is of glacial origin and has a longitudinal shape with high hills on both sides. The volume of the lake is 120 mln m3, surface area 14, 3 km2, max. depth 19. 4 m, average depth 8. 4 m, max. length 7. 6 km, max width 2. 6 km, and the length of the shoreline 18. 7 km. Max. daily water surface variation did not exceed 5-7 cm. Wind induced currents were of the order of 0. 1 m/s. Average inflow to the lake through 2 small rivers and groundwater amounts to 2. 2 m3/s. Annual water exchange in the lake is about 60% of its volume. Upper reservoir of the pumped-storage powerplant is located on nearby hills 110 m above lake level. It has the volume of 15. 9 mln. m3 and the surface area of 1. 35 km2. Upper reservoir is connected with the powerplant by means of 4 penstocks 7 m in diameter. Powerplant is equipped with 4 reversible Francis units of the total power of716 MW. Daily exchange of water between upper and lower reservoir amounts to 13. 8 mln m3 which results in daily water surface variation in the lake of about 1m. Water discharge to the lake during turbine cycle amounts to 700 m3/s which results in max. water currents near discharge point of about 1, 0 m/s. Completely different current pattern can be observed during turbine and pump cycles. Mathematical model was used to estimate 3-D water currents in the lake based on exact bathymetry of the lake. Field measurements of the currents indicate that there is good agreement between calculated and measured values.
Year: 1999