You need to use mathematical integration to calculate the area under the graphs (AUG). So you need to know the mathematic function that best describes infiltration and runoff, integrate, then calculate the difference :)

Dear Andrew & Monyer

Thank you for your answers. However, my question was how to calculate the sprinkler ponded infiltration rate? which is different from the continuously ponded infiltration rate, so I can do this mathematical integration and calculate the accurate runoff amount. I might ask the question in wrong way before, but now I have prepared my question correctly.

Looking for more answer for this issue.

You asked about the 'actual runoff', which is the shaded area of your graph, the value of which is obtained by integration. To calculate the RATE, you need to specify the time and then differentiate the sprinkling rate hyperbolic curve at that point to obtain the rate equation :)

Dear Andrew

Thanks again for your answer. But unfortunately that is not what I am asking for. As I know how to calculate the shaded area but the sprinkler ponded infiltration rate is missing. I have just the continuously ponded infiltration rate, and I need to know how to find the sprinkler ponded infiltration rate by using the continuously ponded infiltration rate.

I hope that my question is more clear now.

Regards,

The infiltration rate is the velocity or speed at which water enters into the soil. It is usually measured by the depth (in mm) of the water layer that can enter the soil in one hour. So you could do a trial and make your own curve of cumulative time versus cumulative infiltration for your particular substrate :)

I think that empirically is the right answer because the result depends on soil type, and existing soil moisture. The type of vegetation and depth of top soil might also influence the result. It will also change if you dig up the soil to take it to the lab or take measurements of undisturbed soil in the field.