Improvement of Farmland Drainage Calculation Method under Environmental Change in Huaibei Plain*

Changes and new thoughts are vital if the farmland drainage method in the Huabei Plain is to be improved. In this article, drainage flow was chosen as the research object. Based on long-series precipitation data, the spatial distribution of precipitation was analysed. The peak value relation index (m) was either adjusted or unadjusted in contrast calculations with the empirical formula and the average draining formula. The adjustment rationality and adjustment range of m were researched. Results of calculations were analysed and used to improve the applicability of the empirical formula. The spatial distribution of precipitation showed a decreasing trend from south-west to north-east. Before adjustment, the result of the empirical formula was equivalent to the flow of 1 day of draining water. After adjusting m to 0.84-0.87, the result was equivalent to the flow of 1.5 days of draining water. With the decrease of rainfall frequency, the drainage flow of the average draining formula was greater than that of the empirical formula and the ratio was 1.13 times when the runoff depth was 50 mm. m can be selected from 0.84 to 0.87 for calculating drainage flow in the Huabei Plain by using the empirical formula and has a direct ratio with precipitation.