Water losses on paddy field due to storage below the sill height of notch for drainage may be estimated, if the probability density function (pdf) of H_l, which varies with difference between the sill height of notch and the initial water level before rainfall, is known.
The author has tried to apply the method mentioned above to the paddy field on Amba river basin with use of data obtained in the several field investigations from Jun. to Sept,, 1968. As a result of this trial, it has become evident that the pdf of H_l = x is given by the following equation

f(x) = 1/√<2^<πσ>> exp {-((<(x-μ)>^2)/(2σ＾2))}

in which μ is mean value and σ is standard deviation.
With the further analysises of the data dealt with the pdf, the relations between ∑ R and ∑ F are summarized as follows, in which ∑ R is the accumulated rainfall and ∑ F is the accumulated water losses.
(1) ∑ F～__～130 mm (∑R ＞__― 180 mm) : end of Jun. - beginning of Jul.
(2) ∑ F～__～ 70 mm (∑R ＞__― 120 mm) : middle of Jul. - end of Aug.
(3) ∑ F～__～ 40 mm (∑R ＞__― 100 mm) : beginning of Sept. - middle of Sept.
Although it was not enough to discuss in detail, some interesting problems to be taken up in the successive studies were presented.