农田排涝模数计算方法的比较

正确计算排涝模数,对于确定排涝工程的适宜规模具有重要现实意义。该文以湖北省四湖流域螺山排区为例,根据排区下垫面条件进行产流计算,分别采用经验公式法和平均排除法计算不同排涝标准下的排涝模数,分析2种计算方法中排涝天数、排涝模数及排涝重现期之间的关系。结果表明:经验公式法对应于平均排除法的排涝天数为3.5d。当经验公式法求得的排涝模数小于平均排除法求得的排涝模数时(本区对应排涝天数小于3.5d),选用平均排除法计算排涝模数偏于安全;而当经验公式法求得的排涝模数大于平均排除法求得的排涝模数时(本区对应排涝天数大于3.5d),则选用经验公式法计算排涝模数偏于安全。此外,在排涝模数确定的条件下(即工程的排水能力一定),采用不同的排水公式校核排水标准时存在差异。一日暴雨时,采用平均排除法(采用三日排除)10年一遇和20年一遇的设计标准分别相当于经验公式法15年一遇和33年一遇的设计标准;而在三日暴雨下,平均排除法(采用五日排除)10年一遇和20年一遇的设计标准则分别相当于经验公式法4年一遇和7年一遇的设计标准。研究成果对合理选择排涝模数计算方法具有一定参考价值。

Comparison of methods for calculating farmland drainage modulus

Abstract: The correct calculation of drainage modulus is of important practical significance for the determination of the suitable scale of water logging control projects. Taking the Luoshan drainage area in Four-lake Watershed in Hubei Province as an example, based on the runoff generation characteristics of underlying surfaces in the drainage area, the drainage area was classified into 4 kinds of underlying surfaces, i.e. the paddy field, the arid land (including wasteland), the water surface, and the building plot. Then the runoff of different underlying surfaces was calculated respectively. Drainage moduli under different water logging control standards were calculated with the empirical formula and average draining method respectively. Then the relationship between days of drainage for water logging control, drainage moduli and return periods derived from both calculation methods was analyzed. Results showed that the corresponding days of drainage for water logging control calculated by the empirical formula were 3.5 days. When drainage moduli calculated by the empirical formula were less than that by the average draining method, days of drainage for water logging control were less than 3.5 days in the drainage area. Then drainage moduli calculated by the average draining method were suggested to ensure the project safety. However, when drainage moduli calculated by the empirical formula were more than that by the average draining method, days of drainage for water logging control were more than 3.5 days in the drainage area. So drainage moduli calculated by the empirical formula were relatively safe. In addition, if drainage moduli were determined, the drainage standard checked with different methods was different. The design standards with return periods of 10 years and 20 years and the water logging discharge duration of three days derived from the average draining method were equivalent to design standards with return periods of 15 years and 33 years derived from the empirical formula under one-day rainstorm respectively. However, design standards with return periods of 10 years and 20 years and the water logging discharge duration of five days derived from the average draining method were equivalent to design standards with return periods of 4 years and 7 years derived from the empirical formula under three-day rainstorm, respectively. This research can be used as a reference for reasonable selection methods for calculating drainage modulus.