HYD_scs_ia(): Initial abstraction according to SCS

About:

Calculate the Initial abstraction (Ia) according to Soil Conservation Soil (SCS).

\begin{equation} S = \frac{25400}{CN} -254 \end{equation} \begin{equation} S_{20} = 0.2 \times S \end{equation} \begin{equation} Ia = S_{0.05} = 1.33 \times S_{20}^{1.15}\end{equation}

 Where,

• $S$, potential storage, mm;
• $S_{20}$, potential storage for $\frac{Ia}{S}=0.2$, mm;
• $S_{0.05}$, potential storage for $\frac{Ia}{S}=0.05$, mm;
• $CN$, Curve number;

Further studies concluded that $S_{20}$ is too high, with $S_{0.05}$ are obtained values with better correlation.

More information about soil Conservation Service methodology please see Wikipedia.

Module: Hydrology

Function: HYD_scs_ia(cn2,amc)

Definition of variables:

• cn, curve number.
• amc, antecedent moisture condition: 1, 2 or 3;

Sample code:

from Hydrology import *

cn2 = 90

amc = 1 
ia = HYD_scs_ia(cn2,amc)
print("Ia (AMC I):",ia)

amc = 2
ia = HYD_scs_ia(cn2,amc)
print("Ia (AMC II):",ia)

amc = 3
ia = HYD_scs_ia(cn2,amc)
print("Ia (AMC III):",ia)

Result:

Ia (AMC I): 114.582222222
Ia (AMC II): 107.244444444
Ia (AMC III): 104.027111111