一、问题的提出经验单位线,由于它脱胎于流域的实测洪水,因而最能综合反应本流域的汇流特性。这是现有的其它任何一种带有理论性的单位线均未具有的独特优点,然而,时段内流域净雨时空分布均匀这一难于符合实际情况的基本假定,使计算成果往往产生很大的误差。严格的说,经验单位线在这样的情况下,由于与它的基本假定相差太大而不能使用。但是,为了水文计算和预报的需要又必须进行雨洪推算。为此,只好采用经验处理的办法。其常用的处理办法,是用暴雨中心位置不同的单位线来推算不同面分布情况的暴雨产生的洪水。由于暴雨中心的位置不可能合理的代表暴雨的面分布情况,中心位置相同的暴雨可能有各种不同的分布情况。再者,由于此种方法纯属经验处理,不是从成因途径来解决,因而必然难以得到满意的结果。 First, the problem proposed unit line of experience, because it is born out of floods measured in the basin, which can most comprehensively reflect the converging characteristics of the basin. This is a unique advantage not found in any existing unit line with any theory. However, the basic hypothesis that time-space distribution of net rain in a watershed is difficult to be realistic makes the calculation results often have large The error. Strictly speaking, the empirical unit line can not be used under such circumstances because it differs too much from its basic assumption. However, rainwater projections must be made for the hydrological calculations and forecasts. To do so, we have to adopt an empirical approach. The common approach is to use the unit lines with different storm centers to calculate the flood caused by heavy rains with different surface distributions. Due to the fact that the location of a rainstorm center can not reasonably represent the surface distribution of rainstorms, there may be a variety of different distributions of rainstorms with the same center location. Furthermore, since this method is purely empirical, it is not necessarily solved by the cause of formation, so it is inevitable to obtain satisfactory results.