Search found 46 matches

by rvang
Mon Nov 19, 2012 3:07 pm
Forum: STANMOD
Topic: Flux Averaged Concentration
Replies: 7
Views: 11803

Dear dburnell,

No, there is no change in the sign of the concentration. The flux-averaged concentration simply corrects the volume-averaged concentration for the diffusion/dispersion contribution Cf=Cr-D/v dCr/dx.

All the best. --Rien van G.
by rvang
Mon Jun 14, 2010 5:25 pm
Forum: RETC
Topic: Calculation of hydraulic capacity
Replies: 2
Views: 7126

Yes, it is dtheta/dh.

Rien van G.
by rvang
Mon Jun 07, 2010 4:14 pm
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: Transpiration calculation
Replies: 4
Views: 8524

I think you need to revisit your numbers. Precipitation appears less than your root water uptake, so perhaps you should not expect much if any drainage from the column. What are the units in space and time? Having leaching of 60 cm (per day?) when precipitaiton is only 0.274 cm (per day?) during all...
by rvang
Thu Feb 18, 2010 11:00 am
Forum: STANMOD
Topic: Direct and indirect CDE equlibrium
Replies: 2
Views: 6492

Jourak: Something simple must have gone wrong. Send me the effluent data data and I will have a look at it (email to rvangenuchten@yahoo.com). Did you use CFITIM within STANMOD the analyze the data (easiest)? Yes, you should use flux-averaged concentration data for the break-through curve. Regards. ...
by rvang
Wed Feb 10, 2010 12:51 pm
Forum: RETC
Topic: textural classes
Replies: 1
Views: 6486

Saska: There have been a number of studies suggesting that you can make a simple linear correction to the water retention curve (e.g., as predicted with pedotransfer functions, or measured) to account for the gravel content (i.e., by assuming that gravel contains no water); just correct the saturate...
by rvang
Wed Dec 23, 2009 12:19 am
Forum: STANMOD
Topic: about single region model
Replies: 5
Views: 8618

Wuhayong:

Assume one-site kinetic partioning from the gas phase into the liquid phase. Use f=0 (no sorptio in gas phase), and interpret k (or Kd) as the partionining coefficient between the gas and liquid phases.

Good luck. --Rien van G.
by rvang
Wed Aug 05, 2009 9:45 pm
Forum: STANMOD
Topic: cxtfit
Replies: 2
Views: 6498

Yes, Lola, You can use the dirac delta function, as long as you specify the mass correctly. You can use dimensionless concentrations if sorption is linear. That is something you need to investigate (batch sorption experiments?), i.e., if the isotherm is linear or not. Use a numerical solution (HYDRU...
by rvang
Tue Dec 04, 2007 2:40 am
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: Brook-Corey in RETC
Replies: 1
Views: 3362

Srilert:

When using the BC option in RETC, alpha in the output is 1/ha, where ha is the air entry value. n in the output the pore-size distribution index in the BC model. Please see the manual.

Regards. --Rien van G.
by rvang
Tue Dec 04, 2007 2:27 am
Forum: RETC
Topic: Output of Brook-Corey
Replies: 1
Views: 7432

Srilert:

alpha equals 1/(air entry value), and n is the pore-size distribution index in the BC equation.

Regards. --Rien van G.
by rvang
Tue Feb 13, 2007 1:55 am
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: Other hydraulic models
Replies: 2
Views: 3295

Franta:

You can use the "Modified VG" model (see soil hydraulic model), and do an inverse with that model. The modified VG adds a linear extension to the K(h) model to account for macroporosity. This is discussed on page 17 and 18 of the older HYDRUS2D manual (Fig. 2.3).

Rien van G.
by rvang
Sat Sep 02, 2006 4:00 pm
Forum: STANMOD
Topic: CXTFIT PVP problem
Replies: 5
Views: 6216

Nobuo, and others: The CXTFIT manual and other manuals/programs can be downloaded from http://www.ars.usda.gov/Services/docs.htm?docid=8910 which is the new dedicated USDA-ARS site. For STANMOD and HYDRUS, users are routed also to the hydrus site (www.hydrus2d.com) for the latest versions. If needed...
by rvang
Wed Aug 16, 2006 11:52 am
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: representing the capillary fringe
Replies: 2
Views: 4770

Jon Paul: Jirka probably has to do that for you. But be forewarned that changing it to -30 cm has nothing to do with accounting for the capillary fringe as such. Alpha controls the always poorly defined extent of the capillary fringe (especially for clay soils). See also recent VZJ paper by Marcel S...
by rvang
Wed Jun 14, 2006 12:07 am
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: Prediction of the k-function, revisited
Replies: 3
Views: 4622

Hector:

You may want to look also at a recent paper (Feb 2006) with Marcel Schaap in Vadose Zone Journal:

http://vzj.scijournals.org/cgi/reprint/5/1/27

Rien van G.
by rvang
Sun Nov 13, 2005 5:52 pm
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: SWC
Replies: 1
Views: 2896

Mizo, If you do not select the hysteresis option, the program uses whatever hydraulic properties you specify in "Water Flow - Soil Hydraulic Parameters", which can be drying, wetting, or whatever you want. Only when you select hysteresis will alpha be for drying and you need an additional parameter ...
by rvang
Thu Nov 10, 2005 11:47 pm
Forum: Hydrus 2D (old version 1996 - 2005)
Topic: van Genuchten
Replies: 1
Views: 2999

Sparks: Se is effective saturation, as given by Eq. (2.17) in the HYDRUS-2D manual, or Eq. (6) in the RETC manual. We used Cap Greek Theta for Se in the original 1980 paper, while S was indeed used for the slope of Theta (or Se) versus (log h). S or Sw is often used for relative saturation (or somet...