Lookup table for hydraulic parameters

[AquaPore]

Hi,

Thanks for providing support to parameterize Wflow model.
Similar to the lookup table lulc

I am writing to determine if there are available lookup tables which could provide feasible ranges of Wflow hydrological parameters for different classes (e.g. Excessively drained, Imperfectly drained, Moderately drained, Poorly drained etc…).

For example for the following soil hydraulic parameters:
• soil_layer_water__brooks_corey_exponent
• soil_water__air_entry_pressure_head
• soil_water__residual_volume_fraction
• soil_water__saturated_volume_fraction
• soil_layer_water__vertical_saturated_hydraulic_conductivity
• soil_wet_root__sigmoid_function_shape_parameter

Many thanks for any help you may provide,
Joseph A.P. Pollacco

[shartgring]

Hi Joseph,

The Wflow parameter documentation lists some default values. See also https://deltares.github.io/Wflow.jl/dev/model_docs/parameters_landhydrology_sbm.html

Additionally, some comments per parameter (note: there are hydrologists more experienced than me, so this comment mainly reflects my thoughts):
• soil_layer_water__brooks_corey_exponent --> not sure, the calculation inside hydromt_wflow happens in the code block I list below. It might be worth to check https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0169748 and https://soil.copernicus.org/articles/7/217/2021/soil-7-217-2021-discussion.html and https://bsssjournals.onlinelibrary.wiley.com/doi/full/10.1111/ejss.12192 . Code block:

hydromt_wflow/hydromt_wflow/workflows/soilgrids.py

Line 213 in b41e608

def brooks_corey_layers(

• soil_water__air_entry_pressure_head --> -10.0 cm is the default Wflow value, I think we always use that value as I cannot find it in hydromt_wflow
• soil_water__residual_volume_fraction: is is theta_r in literature, see https://deltares.github.io/Wflow.jl/dev/model_docs/land/landhydrology_sbm.html#soil-processes . By definition this is a value between 0 and 1. Typical value can be 0.1 or lower.
• soil_water__saturated_volume_fraction: this is theta_s in literature, see https://deltares.github.io/Wflow.jl/dev/model_docs/land/landhydrology_sbm.html#soil-processes . By definition this is a value between 0 and 1. Typical value can be up to 0.5.
• soil_layer_water__vertical_saturated_hydraulic_conductivity --> can often be found in geological maps or soil maps, this is the vertical conductivity in mm/day. Can vary logarithmically, so from order 10 mm/day to 10,000 mm/day
• soil_wet_root__sigmoid_function_shape_parameter --> It seems that we always set this to -500 mm by default, see for example the example config of hydromt_wflow https://deltares.github.io/hydromt_wflow/stable/user_guide/wflow_build.html#

[shartgring]

I see now that we indeed do not have a function for the air pressure entry but we are working on it, see for example #411

[AquaPore]

Dear @shartgring ,

A great thanks for your useful information. I may help in the near future to helpn to derive pedotransfer functions, but from my understanding, it will be good if the following issue is resolved:

(SBM model: soil hydraulic parameters per soil layer)[https://github.com/Deltares/Wflow.jl/issues/761]

With kindness,
Joseph A.P. Pollacco

[shartgring]

Dear @AquaPore,

The current approach is to derive parameter maps inside HydroMT Wflow which is the model builder for Wflow. So I actually think that it would be a good fit to include in HydroMT Wflow. But we would have to take a closer at the papers for that

[vers-w]

Please note that we do already make use of pedotransfer functions, see also /main/hydromt_wflow/workflows/ptf.py. References to these PTFs are included in ptf.py. This is done for the following (hydromt_wflow) internal parameters:

• kv (saturated hydraulic conductivity)
• poresizeindex (Brooks-Corey pore size distribution index)
• thetas (saturated water content)
• thetar (residual water content)

These parameters are computed using SoilGrids data (per SoilGrids layer). From these parameters the maps mentioned in function soilgrids are derived. Output maps theta_s and theta_r are indeed average values. For vertical saturated hydraulic conductivity an exponential decline with depth is assumed resulting in two output maps: ksat_vertical and f. Output map soil_brooks_corey_c_ is available per SBM soil layer (based on poresizeindex).

For Wflow parameter soil_water__air_entry_pressure_head a default value of -10.0 cm is used, and as @shartgring indicated we are indeed working on estimating this parameters based on a PTF. For the soil_wet_root__sigmoid_function_shape_parameter a default value is used.

For supporting other PTFs in hydromt_wflow, I agree with @shartgring, we would have to take a closer look at the mentioned papers, independent of supporting soil hydraulic parameters per soil layer in the Wflow kernel.

[AquaPore]

Dear @shartgring and @vers-w ,

A great thanks for taking the time to respond to my query. As a soil scientist and developper of Richards' equation, I have been working with the soil moisture release curve and unsaturated hydraulic conductivity of Kosugi, which is far more accurate than Brooks and Corey and the beauty is that it has the same number of parameters. Since Kosugi is physically based, describing pore distribution as lognormal enables reducing the feasible space and identifying relationships between equivalent soil_water__air_entry_pressure_head and soil_brooks_corey_c. There is also a relationship between soil hydraulic parameters and saturated hydraulic conductivity, which can also be implemented when saturated hydraulic conductivity decreases with depth. It is worth noting that these models were developed for the Richards' equation.

Will be delighted to discuss further and you will be more than welcome to join the talk/discussion

Looking further for discussion,
Joseph A.P. Pollacco