SWMM 5 Horton Infiltration

Horton's equation

Named after the same Robert E. Horton mentioned above, Horton's equation^[2] is another viable option when measuring ground infiltration rates or volumes. It is an empirical formula that says that infiltration starts at a constant rate, $f 0$ , and is decreasing exponentially with time, $t$ . After some time when the soil saturation level reaches a certain value, the rate of infiltration will level off to the rate $f c$ .

f t = f c + (f 0 - f c) e - k t

Where

f t

is the infiltration rate at time t;

f 0

is the initial infiltration rate or maximum infiltration rate;

f c

is the constant or equilibrium infiltration rate after the soil has been saturated or minimum infiltration rate;

k

is the decay constant specific to the soil.

The other method of using Horton's equation is as below. It can be used to find the total volume of infiltration, F, after time t.

$F_t = f_ct+{(f_0 - f_c)\over k}(1-e^{-kt})$

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Comments

Sergio De Hoyos March 12, 2014 at 3:09pm

Hi Bob,

I've been performing sensitivity analysis on my SWMM watershed model by changing horton infiltration parameters but my results show no change, meaning the model is insensitive to infiltration. I get the same result when performing sensitivity for manning's n in pervious areas. Considering that my watershed is around 30% impervious, I was not expecting this result and worry I might be doing something wrong. Since this parameters are correlated and are all related to pervious areas, is there a guideline I should follow when assessing their sensitivity.

Thank you for your help!

Sergio

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