Analysis of down-regulation of multi-time scale inflow runoff encountering wet and dry conditions in the wet supply reservoir of Menghai Irrigation District

Abstract

Copula function is used to model, and five kinds of edge functions commonly used in hydrology are used to fit the edge distribution of the inflow runoff of three important reservoirs in Menghai Irrigation area at different time scales. The Copula function is used to construct the optimal edge distribution of the three reservoirs at different time scales. The optimal Copula function is used to solve the probability of the inflow runoff of the two reservoirs at different time scales. Finally, the runoff calculated by the minimum monthly average flow method is evaluated by the Tennant method and used as the standard for reservoir water transfer in the irrigation area. It is mainly concluded that the best Copula function of the three reservoirs at the same time scale is Clayton Copula function. Under the same time scale, the probability of abundance and dryness synchronization is greater than the probability of abundance and dryness asynchronous in the combination of abundance and dryness encounter probability of three reservoirs. In all the probability combinations of wet and dry encounters, the probability of the three reservoirs being dry in all time scales is the largest, indicating that the three reservoirs in the irrigation area are the most likely to be dry years in the combination of wet and dry encounters. The runoff of the three reservoirs calculated by the minimum monthly average flow method in the non-flood season and the flood season basically meets the ecological needs in the Tennant method evaluation criteria, and the result can be used as the standard for reservoir water transfer in irrigation areas. Under this standard, Manman Reservoir can't supply a large amount of water to the irrigation area in December of last year and January of 2010, and can only supply water to the irrigation area through Mangui and Nadameng Reservoirs. In the non-flood season of 2011, the three reservoirs can be dispatched to the irrigation area. In July and August of the flood season in 2010 and 2011, the three reservoirs were all wet and abundant, and a large amount of water supply could be dispatched to the irrigation area. Except for July and August in 2010 and 2011, the three reservoirs are all dry encounters. Under the condition of satisfying the river ecosystem of the inflow river, the three reservoirs can properly regulate the water supply in the irrigation area. The research result can provide reference for water diversion of water supply reservoirs in Menghai Irrigation area.

Keywords

edge function / Copula function / dry encounter / ecological flow / analysis of water diversion