Data needed in the Porous Media module

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epelde.ane@gmail.com
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Posts: 172
Joined: Thu Jan 01, 1970 00:00

Data needed in the Porous Media module

Postby epelde.ane@gmail.com » Wed Jul 06, 2011 11:36

Hello to all!

Trying to enter data to the PorousMedia module, I find that I need:
-Hydraulic properties of each soil I define and,
-Impermeability values for each soil.

Both are dependent to the texture of a soil, so what I need is a texture map shape instead a land use shape, don´t do I?

Would I have to enter the data in the data file this way?:

<beginproperty>
NAME: SoilID
...
<endproperty>


<begin soiltype>
ID: 1
..properties..
<endsoiltype>


and then, the same for the permeability???

<beginimpermeablefraction>
NAME: impermeablefraction
...
<endimpermeablefraction>


<begin permeability>
ID: 1
..\"permeability value of the soil..
<endpermeability>


Thanks in advance,
ane

Jauch
Site Admin
Posts: 98
Joined: Thu Jan 01, 1970 00:00

Postby Jauch » Wed Jul 06, 2011 13:07

Hi Ane :)

For each different soil (and horizon, if the same \"soil\" have horizons with different characteristics), you must create a soil profile.
For example: if I have two different soil types in my study area and the first soil type have 2 distinct horizons (with different hydraulic properties), i will have to create 3 soil profiles like this:

Code: Select all

<begin soiltype>
  !Soil 1, horizon 1
  ID: 1
  ..properties..
<endsoiltype>

<begin soiltype>
  !Soil 1, horizon 2
  ID: 2
  ..properties..
<endsoiltype>


<begin soiltype>
  !Soil 2, only one horizon
  ID: 3
  ..properties..
<endsoiltype>


After this, I need to define each horizon. Because I have 2 diferent Horizons for the first soil And only 1 for the second, I'll have to define 2 horizon blocks in the data file.
Let's assume that the top horizon for the first soil goes from layer 7 to 10 and the bottom horizon goes from 1 to 6, and that this distribution is the same for the entire area (even if the second soil have only one horizon that fills the entire soil profile):

Code: Select all

!Horizon 1 - Top
<beginhorizon>
  KLB : 7
  KUB : 10

  <beginproperty>
    NAME                  : SoilID
    INITIALIZATION_METHOD : ASCII_FILE
    FILENAME              : GridDataSoil_1.dat
    DEFAULTVALUE          : 1
  <endproperty>

  <beginproperty>
    NAME                  : Theta
    INITIALIZATION_METHOD : CONSTANT
    DEFAULTVALUE          : 0.38
  <endproperty>
<endhorizon>

!Horizon 2 - Bottom
<beginhorizon>
  KLB : 1
  KUB : 6

  <beginproperty>
    NAME                  : SoilID
    INITIALIZATION_METHOD : ASCII_FILE
    FILENAME              : GridDataSoil_2.dat
    DEFAULTVALUE          : 1
  <endproperty>

  <beginproperty>
    NAME                  : Theta
    INITIALIZATION_METHOD : CONSTANT
    DEFAULTVALUE          : 0.38
  <endproperty>
<endhorizon>


Because we have more than one soil in the area, I need to define the soils ID in a grid data file for each horizon.

So, again, lets assume that your area have four cells, and that half are of soil 1 and half of soil 2, like this:

Soil1 Soil2
Soil1 Soil2

Then, the first grid data, (for horizon 1), must have these soil ID's:

1 3
1 3

The second grid data, (for horizon 2), must have these soil ID's:

2 3
2 3

The ID, in both horizons are the same for the soil 2, because it have only one horizon.

And that's all for the soil definition. :)

Now, the question about the impermeabilization.
The impermeabilization is 2D, because it's for the surface only. It is not linked to the oil, but more to the land use. So, lets assume that you have 2 different land uses, like urban (1) and uncovered soil (2), like this:

1 2
2 2

Now, assuming that the impermeabilization, or area that will not allow infiltration in a time step, for the urban is 0.5 (50%) and for the uncoverd soil is 0.05 (5%).
So, you need to create a grid data file (like gridimp.dat) that have these values:

0.5 0.05
0.05 0.05

And insert the impermeabilization block in the porous media data file:

Code: Select all

<beginimpermeablefraction>
  NAME                      : impermeablefraction
  INITIALIZATION_METHOD     : ASCII_FILE
  DEFAULTVALUE              : 0
  REMAIN_CONSTANT           : 1
  FILENAME                  : gridimp.dat
<endimpermeablefraction>


You must have attention to the \"format\" of the grid data files, because they are not very \"obvious\"... The best is to create and edit them using the Mohid Gis or Mohid Studio.

If you do not understand something (I know can that this can be a litle cofusing in the beggining), just ask ;)

Best regards,

Eduardo Jauch
MohidLand Developer

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Postby epelde.ane@gmail.com » Wed Jul 06, 2011 17:17

Thanks eduardo! :D
I see.. I think I undestand more or less how work soils, horizons..
So now, I have to think how I´m going to prepare this kind of data. I think it will be better, to get started, if I just define 1 horizon with different soils and I´ll create more when I have the neccessary info...

What I asked you about the texture map was because I found hydraulic properties and permeability values for each kind of texture (depending on the quantity of clay, sand.. and so on). With your explanation I understand that the impermeability must be estimated by eye?

Best regards,
ane

Jauch
Site Admin
Posts: 98
Joined: Thu Jan 01, 1970 00:00

Postby Jauch » Wed Jul 06, 2011 18:06

Hi Ane :)

About the soils, the best \"first\" step is to use only one \"soil\" with one \"horizon\", for a first aproximation.
Doing this way, you do not need to prepare a \"grid data\" file, using, for the horizon (that you will have only one), a defualt value for SoilID property, like this:

Code: Select all

<begin soiltype>
  !Soil
  ID: 1
  ..properties..
<endsoiltype>

<beginhorizon>
  KLB : 1
  KUB : 10

  <beginproperty>
    NAME                  : SoilID
    INITIALIZATION_METHOD : CONSTANT
    DEFAULTVALUE          : 1
  <endproperty>

  <beginproperty>
    NAME                  : Theta
    INITIALIZATION_METHOD : CONSTANT
    DEFAULTVALUE          : 0.38
  <endproperty>
<endhorizon>


I'll try to put a better description of this point (soils) in our WIKI in the next days.

The \"impermeable fraction\" (see http://www.mohid.com/wiki/index.php?tit ... rmeability) is a parameter that try to simulate the fact that the soil surface, spatially, have diferent permeablity values, due to existence of rocks, buildings, streets, vegetation etc, that prevents the water from precipitation from infiltrating in a percentage of the area. In a car park, for example, you will have probably a very high impermeabilization (almost 100%).

This \"impermeabilization\" is not due to the soil itself (most of time), but exists because of what is above it.

The values I usually use are 0.5 for urban area and 0.1 for agricultural areas, but you can change this according to the area you are modelling.

davidbrito
MOHID Advanced user
Posts: 187
Joined: Thu Jan 01, 1970 00:00

Postby davidbrito » Thu Jul 07, 2011 01:53

Hello,

I think that you are talking about soil permeability (1) that is different from soil surface area available for infiltration (2).

The first one may be obtained from soil texture and for MOHID each soil that exists in the watershed has to be defined in terms of hydraulic properties to know how water will flow in soil with van Genuchten parameters (can be obtained from texture or from soil lab):

Example:

Code: Select all

<beginsoiltype>
ID                    : 1
THETA_S               : 0.43                !This is saturation water content
THETA_R               : 0.089               !This is residual water content             
N_FIT                 : 1.23                !Some van Genuchten parameter
SAT_K                 : 2.7777e-6           !Saturated conductivity in m/s
ALPHA                 : 0.010               !Some van Genuchten parameter
L_FIT                 : 0.50                !Some van Genuchten parameter
<endsoiltype>


The second one - cell area fraction available for infiltration is defined in the <beginimpermeablefraction> <endimpermeablefraction> and is given a value between zero (completely permeable) to one (completely impermeable) - given by a constant value or a grid to have spatial distribution. In the case of total impermeability (cemented ground in urban areas) there is no infiltration in that cell and all water will be routed in runoff. If value is zero all the cell area will be available for infiltration.


With this said with the soil type block you define every unique soil parameters but then you need to give the soil distribution in the watershed. This can be done using a constant value or a grid (spatial distribution) in the horizon block.


Hope it helped,
All the best,
David

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Postby epelde.ane@gmail.com » Thu Jul 07, 2011 08:10

Hi!
Ok.. I see. I didn´t understand that because I saw that it wasn´t the same a texture and a cemented area... So, now it´s understood. :)
Thanks for the explanations!
ane

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Postby epelde.ane@gmail.com » Thu Jul 14, 2011 16:19

Hello all,
I´m doing the impermeability map, and I wonder how can I know which value belong to each land use type. I think that deciding it can be very subjective. Have you make an estimate for different land uses when using MOHID? I have artificial areas (I guess they are cemented areas), water-wetland, forestal areas, agricultural areas, pastures..

Thanks,
ane

davidbrito
MOHID Advanced user
Posts: 187
Joined: Thu Jan 01, 1970 00:00

Postby davidbrito » Fri Jul 15, 2011 18:48

Hello Ane,

What we usually do is for urban areas use 0.5 (meaning that half of the area is not available for infiltration - cemented area) and that in every other landuse value is 0.0 meaning that are not covered areas and all area is available for infiltration.

Remind that if water will infiltrate or not is not dependent on this impermeability matrix. Infiltration depends on infiltration velocity that depends on i) the hidraulic gradient between surface water that is trying to infiltrate and water content in soil surface and ii) the soil conductivity. Basically is the same equation that is solved for water movement in soil - Darcy Law.

All the best.

David

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Postby epelde.ane@gmail.com » Wed Jul 20, 2011 14:08

Thanks David, made the impermeability map!

Now, it comes a problem when I try to decide the geometry of the catchment. I´ve defined a cartesian top system, and as I have 2 main stratigraphical units, I guess I have to define 2 horizons.
So, the question is, how many layers do I have to create for each horizon? Is there any way of stimating it? Sorry but I can´t see which is the difference between layer and horizon..

Can you give me a hand with this, please?

Best regards,
ane

davidbrito
MOHID Advanced user
Posts: 187
Joined: Thu Jan 01, 1970 00:00

Re: Data needed in the Porous Media module

Postby davidbrito » Wed Aug 31, 2011 08:41

Hello,

Check the answer to this in topic:
viewtopic.php?f=3&t=1276

David


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