Hydrological situation in ancient water conservancy project

The average natural runoff of Guxian dam site for many years is 38.434 billion cubic meters, of which the runoff from July to October in flood season is 22.814 billion cubic meters, accounting for 59.36% of the annual runoff; The non-flood season runoff is 15.62 billion cubic meters, accounting for 4.64% of the annual runoff. The designed average inflow runoff of Guxian Reservoir is 22.77 billion cubic meters, including 12.55 billion cubic meters in flood season from July to October, accounting for 55.7% of the annual runoff, and 1.22 billion cubic meters in non-flood season from November to June, accounting for 44.93% of the annual runoff. The designed dry year (P=9%) runoff is 14.98 billion cubic meters, which is 65.6% of the multi-year average. The multi-year average measured sediment discharge is 919 million tons, and the multi-year average sediment discharge at the design level is 616 million tons.

The design flood of Guxian dam site is calculated indirectly by frequency analysis method and basin area difference method. The maximum difference between the calculated results of the two methods and the peak and flood magnitude of Longmen design flood is only 1.6%. The peak and flood magnitude of this design flood of Guxian dam site directly adopt the design flood results of Longmen Station, with the peak flow of the Millennium design flood of 38,5 cubic meters per second and the flood volume of 9.13 billion cubic meters on the 12th. The checked flood peak flow in ten thousand years is 49,4 cubic meters per second, and the flood volume on the 12th is 11.9 billion cubic meters. The design flood results of Guxian flood season: the flood peak flow in 2 years is 3,8 cubic meters per second, and the flood volume on the 12th is 7.72 billion cubic meters; The once-in-a-century flood peak flow is 27,4 cubic meters per second, and the flood volume on the 12th is 7.9 billion cubic meters. The 5-year flood peak flow is 24,1 cubic meters per second, and the flood volume on the 12th is 6.45 billion cubic meters. 2-year flood peak flow is 19,6 cubic meters per second; The once-in-1-year flood peak flow is 16,1 cubic meters per second, and the flood volume on the 12th is 4.85 billion cubic meters. In the non-flood season, the flood is the largest in October, with a 5-year flood peak of 5,81 cubic meters per second, followed by March, and a 5-year flood peak of 4,52 cubic meters per second.