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

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