Appropriate Method to Estimate Farmland Drainage Coefficient in the Wanyan River Surface Waterlogged Area in Suibin County of the Sanjiang Plain, China

Abstract

Drainage coefficient has an important influence on the determination of the scale of drainage engineering and agricultural production. This paper calculated the drainage coefficient based on the calculation results of theoretical runoff using the empirical formula (QE) and the average draining method (QA), and discussed the drainage duration (TE) corresponding to the empirical formula and the area range (FA) corresponding to the average draining formula. The results showed that the observed runoff was less than the theoretical runoff. The design flow of the Wanyan River pumping station does not meet the drainage demand of the 5-year rainfall return period. For the 1-day rainfall with 3-year return period and 3-day rainfall, QE was higher than QA, and the design drainage duration was higher than TE, so it was safer to calculate the drainage coefficient using the empirical formula in the drainage engineering design. For 1-day rainfall greater than the 3-year return period, QA was higher than QE, and the design drainage duration was less than TE, and the results of the average draining formula were safer in the drainage engineering design. FA increased with the increase in rainfall duration and decreased with the increase in return period. When the rainfall duration and the drainage duration were long, the calculation results of the average draining formula were much smaller.