Page - 1040 - in Book of Full Papers - Symposium Hydro Engineering

Comparing the range of the pressure coefficients for NT1 plunge pool case with those available in the literature shows that the NT1 proposed pre-excavated plunge pool shall be deep enough to not be eroded in an extensive area deeper than the proposed invert level of 105.0 m asl by its design flood jet. Also, the calculations show that the spillway jets for all range of floods shall be fully developed before impacting the plunge pool surface which will reduce the erosive power of the plunging jets. Provision of the dents on flip buckets, which are not embedded in the disintegration length relationships, shall further improve the jets disintegration and aeration. 9. REFERENCES [1] BOLLAERT, E., DUARTE, R., PFISTER, M., SCHLEISS, A., MAZVIDZA, D. Physical & numerical model study investigating plunge pool scour at Kariba Dam, 24th Congress of CIGB – ICOLD, kyoto, Japan, 2012, pp. 241-248. [2] ERVINE D.A. Falvey H. R. and Withers W. Pressure fluctuations on plunge pool floors. J. of Hydraulic Res., IAHR, 1997, Vol. 35, Nº2, pp. 227-279. [3] CASTILLO L.G. Pressure characterization of undeveloped and developed jets in shallow and deep pool. Proceedings of the 32nd IAHR Congress, Venice, 2007, 2, 645–655. [4] CASTILLO L.G. Aerated jets and pressure fluctuation in plunge pools. Proc.7th International Conference on Hydroscience and Engineering, Philadelphia, 2006, 1–23. [5] BOLLAERT, E., SCHLEISS, A. Scour of rock due to the impact of plunging high velocity jets 1: Experimental results of dynamic pressures at pool bottoms and in one and two dimensional closed end rock joints. J. Hydraulic Res., 2003, 41(5), 465–480. 10. SUMMARY & KEYWORDS Nam Theun 1 is a hydropower plant under construction in Lao PDR, located about 170 km east of Vientiane. The scheme comprises a 177 m high RCC curved gravity dam. The flood release structures including the plunge pool at the dam toe need to be designed to withstand the high dynamic loads and is one of the major hydraulic design issues. In order to reduce the scour depth, the spillway flip buckets will end at different elevations and will be equipped with baffle blocks that will spread the jet and improve its aeration. In addition, the presumable scour depth and the required pre-excavation are important design parameters both with regard to the powerhouse tailwater conditions, the serviceability of the powerhouse itself and the dam safety. Several 1040