## alpha equals to inverse of AEP?

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qingdu
Posts: 3
Joined: Tue Jul 07, 2020 8:56 pm
Location: USA

### alpha equals to inverse of AEP?

Hello,

I am using a V-G model that simulates the West central Florida sand, I put alpha=0.03 for having a 30cm AEP, n=1.7, l=0.5, but from profile information it only got 2cm AEP, I changed alpha to 0.025 and 0.3 the AEP still remain 2cm, if change n=3 it has 4cm AEP, but I cannot use very high number for n because that would be unrealistic. How can I change the parameter? Thank you in advance!
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Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: alpha equals to inverse of AEP?

I assume that AEP refers to the Air-Entry Point, right? The standard van Genuchten (VG) model does not have an air-entry point. In the VG model, the water content increases all the way till the pressure head reaches a zero value. Hydrus offers you an option to use the VG model with the air-entry value of – 2 cm (based on some work Rien did and published with Marcell Schaap in early 2000). If you want to have a larger air-entry value, you need to use the modified VG model. Then by manipulating the Theta_m value, you can get different values of AEP. J.

qingdu
Posts: 3
Joined: Tue Jul 07, 2020 8:56 pm
Location: USA

### Re: alpha equals to inverse of AEP?

Thank you Jirka for explaining,

I meant capillary zone for AEP, I was hoping to have 15cm capillary zone, from the parameters I have it only shows of a 2cm capillary zone, if I want a 15cm capillary zone model I will need to set an unrealistic high n value, how I can change it? And the other question is how can set rootzone thickness? Thank you.