2-Layer UZ soil properties


2-Layer UZ Soil Properties
Conditions:	when Unsaturated Flow selected in the Simulation Specification dialogue and the Two-Layer Water Balance method selected for the numeric engine
dialogue Type:	Integer Grid Codes with sub-dialogue data
EUM Data Units	Grid Code

The first part of the soil definition is to define the areas with the same soil profiles. This can be done using either a uniform value or distributed using a dfs2 integer grid code file or a polygon .shp file. For each unique grid code or polygon in the distribution file, a separate sub-item will appear in the data tree, in which you can define the soil profile data.

Definition of soil properties

Profile ID - This is the editable name displayed in the data tree for this profile.

Grid code value - This is the current integer grid code or polygon value read from the soil distribution.

Water content at saturation - This is the maximum water content of the soil, which is usually approximately equal to the porosity,

Water content at field capacity - This is the water content at which vertical flow becomes negligible. It practice, this is the water content that is reached when the soil can freely drain. Although, it is usually higher than the residual saturation, which is usually defined as the minimum saturation that can be achieved in a laboratory test.

Water content at wilting point - This is the lowest water content that plants can extract water from the soil.

Saturated hydraulic conductivity - The saturated hydraulic conductivity of the soil is equal to the maximum infiltration rate of the soil.

Soil suction at wetting front - The soil suction at the wetting front is used in the Green and Ampt infiltration model to increase the infiltration rate beyond the saturated hydraulic conductivity when the soil is dry. This is a soil specific value that accounts for the capillarity of the soil.

Bypass Constants The bypass constants are editable when Simple Bypass flow is checked on in the main Unsaturated Zone (V1 p. 282) dialogue. The availabe bypass parameters include:

Maximum bypass fraction - This is the maximum fraction of net rainfall that will infiltrate via simple macropore flow. Valid values are between 0 and 1.0.

Water content for reduced bypass flow - This is the threshold water content below which the bypass fraction is reduced. If the water content 10cm or 50cm below the ground surface is less than this water content, then the soil is dry and the bypass flow will be reduced.

Limit on water content for bypass flow - This is the minimum water content for bypass flow. If the water content 10cm or 50cm below the ground surface is less than this limit, then the soil is very dry and the bypass flow will be zero.

The actual relationship between the bypass constants and the calculation of the bypass flow is described in Simplified Macropore Flow (bypass flow) (V1 p. 564).