Green-Ampt Infiltration Parameters: Difference between revisions
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=== Initial Moisture ===
The initial moisture value represents the fraction of the soil that is initially wet. As both initial moisture and porosity are expressed as fractions, the soil capacity is defined as the difference between them both. As such, the initial moisture should not exceed the porosity otherwise soil capacity will be set to zero with no infiltration occurring for that soil type. A [[TUFLOW Message 2508 |2508 WARNING]] is issued if this is the case.<br>
In pre-2023 releases of TUFLOW, a single variable storage capacity was calculated by subtracting the initial moisture fraction from the porosity, in order to reduce memory requirements. However, in TUFLOW releases 2023 and onwards, the soil porosity and initial moisture must be stored separately to allow the soil to drain correctly when using the interflow functionality. This updated approach requires that a soil thickness be specified to calculate the soil depth. If a soil thickness is not specified when using the updated approach, an infinite soil depth is assumed for each layer and therefore different initial moisture fractions no longer have an effect on modelled results. These two approaches can generate different results when using the Green-Ampt method.
As you increase initial moisture at the beginning of your simulation, you experience less infiltration (as you are closer to the soil capacity), therefore have more run-off and a quicker response. Figure 9 shows the degree of change to cumulative infiltration with varying initial moisture and the effect on the catchment can be seen in Figure 10. As the event progresses, soils become more saturated and the influence of the initial moisture parameter becomes less significant.
[[File:Init moisture F10.png|600px|Figure 9: Sensitivity of cumulative infiltration in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model.|border]]<br>
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