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Hi,

 

I've built a surface water model and am in the process of sensitivity testing. One of the parameters I am looking at is the initial moisture.

 

I have specified the Green-Ampt method with a USDR soil Type then in the 4th column of my tsoilf I have tested 0.5 and 1 (0 is the default so doesn't need to be tested).

 

Please could you help with my understanding of the following:

- Initial moisture in general - is it representative of initial saturation levels?

- What the values 0, 0.5 and 1 mean? I.e is 0 fully saturated and 1 un-saturated?

- Is this an appropriate way to test saturation levels?

 

Thanks

 

Harriet

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Hi Harriet,

The initial moisture content is the fraction of the soil that is initially wet.  The soil capacity (that is output in the TUFLOW log file) is calculated as the difference between the saturated moisture content (i.e. the soil porosity) and the initial moisture content.  The Initial moisture and the porosity are both fractions and the initial moisture should not exceed the porosity, in this case the soil capacity is set to 0.

For example, for a USDR "Sandy Loam" the porosity fraction is 0.412 and the initial soil moisture can vary between 0.0 (un-saturated) and 0.412 (saturated). It should be noted that Infiltration will still occur in the case that the soil is initially saturated (based on the saturated hydraulic conductivity).

If the groundwater depth is shallow, i.e. soil infiltration is limited by the groundwater, then setting a groundwater level or groundwater depth would be appropriate.  For example if the groundwater depth is set to 0.1m the infiltration will cause the ground water to rise (based on the cumulative infiltration and the porosity) until the groundwater level reaches the ground elevation, after this no additional infiltration will occur.  The default groundwater depth is infinite.  The can be set via the groundwater level commands (e.g. mAHD)
Set GWL == <value>
Read GIS GWL == <polygons of ground water level>
Read Grid GWL == <grid of groundwater level>


Or via the groundwater depth commands (e.g. m below surface)
Set GWD == <value>
Read GIS GWD == <polygons of ground water depth>
Read Grid GWD == <grid of groundwater depth>


Hope that helps.

Phil

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Hi Phil, all,

I'm working on a direct rainfall model, where I'm looking into the effects of groundwater and infiltration on overall flooding in the basin.
There are several soil types, all of which have initial moisture content set equal to porosity, except one soil where the initial moisture is lesser than the porosity. 

I'm running the model for two scenarios, where the groundwater depths are defined as below:

Scenario 1: The groundwater depths across the basin are defined by polygons and read in the tgc by Read GIS GWD command. The depths vary between 0.5m-1.2m below the surface.

Scenario 2: The groundwater depths across the basin is set to 0.5m with Set GWD == 0.5 command in tgc

I see from your post above that:

On 6/11/2014 at 11:21 AM, par said:

It should be noted that Infiltration will still occur in the case that the soil is initially saturated (based on the saturated hydraulic conductivity).

However, when I examine the result files (dGW and CI timeseries) I observe that:

  • Infiltration is closer to zero (<5mm) from the last timestep of CI, wherever initial moisture content was set equal to porosity
  • The groundwater depth defined is not being picked up in the model, wherever initial moisture content was set equal to porosity, in both the scenarios mentioned above

So, my questions below:

  • Does infiltration continue to occur irrespective of the initial soil moisture? 
  • Is the ground water depth (at t=0) in model modified by something else? any check files to see?

Or am I missing something?

Thanks,

Prabhanjan

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