Wetness-dryness encountering analysis of runoff in water source area and water receiving area for the water diversion project

Abstract

[Objective] Analyzing the runoff wetness-dryness encountering characteristics between water source and water receiving areas is essential for optimizing water diversion schemes and implementing engineering operational strategies in a timely manner. [Methods] Taking the Yangtze River to Huaihe River Diversion Project as an example, according to the monthly measured runoff data of Datong Station and Lutaizi Station from 1956 to 2022, the correlation coefficient, the standardized runoff index, as well as marginal distribution functions and joint probability distribution models based on two-dimensional Copula functions were employed, to describe the characteristics of runoff wetness-dryness for a single station and reveal the complementary patterns of two-dimensional runoff. [Results] The result indicated that weak correlations between these two stations across annual, high-flow and low-flow time scales, with Kendall correlation coefficients of 0. 216, 0. 273 and 0. 227,respectively. Datong Station experienced high-flow months from April to June, with corresponding probabilities of 0. 313, 0. 328and 0. 373; while Lutaizi Station encountered low-flow months in June and August, with probabilities of 0. 209 and 0. 179,respectively. It could also be shown that the sum of synchronous probabilities for runoff combinations were 54. 5%, 52. 5% and 52. 2% across annual, high-flow and low-flow time scales, respectively; and the probabilities of being favorable for transferring water from the source area to the receiving area were 72. 7%, 73. 7% and 73. 9% during these three time scales. [Conclusion] The conclusion were that the Gamma distribution could well fit the distribution characteristics of runoff under different time scales, and the optimal Copula functions for runoff combinations between these two stations were Frank Copula, Frank Copula and Clayton Copula across annual, high-flow and low-flow time scales. The sum of asynchronous probabilities for runoff combinations were all greater than the sum of synchronous probabilities under these time scales.

Keywords

runoff / water diversion project / wetness-dryness encountering / standardized runoff index / marginal distribution / Copula function / influencing factors