Soil Profiles Wizard

This screen is used in conjunction with the MABIA Method for catchment hydrology and crop water requirements.

Because direct measurement of a soil's water holding capacity, including saturation, field capacity and wilt point, can be costly and time consuming, pedotransfer functions were developed to translate more easily obtainable data into these water holding capacity values.  The SoilProfiles function estimates average soil water capacity (saturation, field capacity and wilt point) using one of seven available pedotransfer functions (PTF), in order to determine the Soil Water Capacity for catchment land use branches in the Data View, under Land Use.  This function can average over several soil profiles (sampling sites) and soil horizons (layers).  Use the Soil Profiles Wizard, available on the drop-down menu in the data grid, to build this function.  (As an alternative to using SoilProfiles, you can enter soil properties directly, or choose a texture class from the Soil Library.  These two options are also available on the drop-down menu in the data grid.)

A description of the seven pedotransfer functions and their parameters can be found in the description of the SoilProfiles function.  Once you have entered the appropriate data into the Soil Profiles Wizard, click the Save button and WEAP will create the corresponding SoilProfiles expression that embodies this data.  The following will describe how to enter this data into the wizard.

If you have soil profile data in a CSV file or Excel spreadsheet, you can read those in without having to retype the data.  For a CSV file, click the Import button and browse to find the CSV file.  To bring in the data from the Excel spreadsheet, copy the data from Excel onto the Windows clipboard and click the "Paste Special" button.  In both of these cases, WEAP will read in the rows and columns of data (from CSV file or Windows clipboard), and display it in a new window, along with its best guess as to which variable each column represents.  The data should be arranged so that each horizon of each layer is on its own row, and each column represents a different variable (e.g., profile number, horizon number, texture class, thickness, etc.).  (If you are having problems getting the correct format for import, click the "Copy to Excel" button to see what a suitable structure would look like.)

Here is an example of the import structure for soil profile data if using the Particle Size pedotransfer function.  (The columns for sand, saturation, field capacity, wilt point, and available water capacity are not required for import because they will be calculated by WEAP.)

If you do not have soil profile data already entered into a file, you can enter it into the wizard.  First, choose the pedotransfer function to use in estimating soil water capacity.  Next, indicate how many profiles (sampling sites) you have, and for each profile, how many horizons (layers) you have data for.  Horizons should be ordered from shallow to deep.  The pedotransfer function you chose will determine which other data variables are required.  Note that the Total Soil Thickness is shown, and can be edited here.

For each profile and horizon, WEAP will calculate and display the saturation, field capacity, wilt point, and available water capacity, and the weighted average across all profiles and horizons will be shown at the bottom on the row labeled "Average."  These average values are what will be used for calculating soil moisture by the MABIA Method only if you are not using two buckets for the MABIA water balance calculation. If using two buckets, WEAP will calculate the soil water capacity separately for the top and bottom bucket, based on the horizons that fall within each bucket.  The size of the buckets changes as the rooting depth changes.

Some data values will lead to numerical instability and will result in "error" being shown instead of calculated values.  For example, each of the particle sizes (clay, silt and sand) cannot be too close to 0%.  The average total thickness for all profiles entered into the Soil Profiles Wizard must be greater than or equal to the Total Soil Thickness.  Because water cannot penetrate a layer of consolidated rock, if you choose Consolidate Rock as the texture class for a horizon, WEAP will assume that the Total Soil Thickness stops at the top of that horizon.

After all the data is entered, you can click the Export button to save to a CSV file, or the "Copy to Excel" button to save it to an Excel file.

See also: Soil Water Capacity Calculation

Entered on: Data View, Branch: Catchments, Category: Land Use, Tab: Soil Water Capacity.