Green-Ampt Infiltration Parameters: Difference between revisions

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Revision as of 00:08, 16 January 2026 view source Tuflowduncan (talk \| contribs) Bureaucrats, Administrators 1,219 edits Updates plots to make a bit more professional Tag: Visual edit ← Older edit		Latest revision as of 23:36, 20 January 2026 view source RussellGardner (talk \| contribs) Bureaucrats, Administrators 456 edits →Initial Moisture
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Line 134: 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. The three initial moisture sensitivity tests have been undertaken with the Green-Ampt method using both a pre-2023 release of TUFLOW and a post-2023 release of TUFLOW. Figure 9 shows how variations in the initial moisture affect the simulated cumulative infiltration, whereas Figures 10 and 11 show the effects of varying the initial moisture on flows at the catchment outlet when using the pre-2023 and post-2023 releases of TUFLOW. As the initial moisture is increased at the beginning of your simulation, there is less infiltration (as you are closer to soil capacity) and more runoff, causing the catchment outflows to exhibit a faster response to rainfall upstream. As the event progresses, soils become more saturated and the influence of the initial moisture parameter becomes less significant. In the examples shown here, the catchment outflows, as visible in Figures 10 and 12, show a higher responsiveness to variations in initial moisture at the beginning of the simulations, and attain higher peak values, when using the post-2023 TUFLOW releases. [[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> '''Figure 9: Sensitivity of cumulative infiltration in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model.'''<br> [[File:Initial moisture.jpg\|border\|760x760px\|Figure 10: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model in pre-2023 release of TUFLOW.]]<br> '''Figure 10: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model in pre-2023 release of TUFLOW.''' [[File:Init moisture post 2023 v2.jpg.jpg\|border\|760x760px\|Figure 11: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model in post-2023 release of TUFLOW.]]<br> '''Figure 11: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the initial moisture parameter in the Green-Ampt infiltration model in post-2023 release of TUFLOW.''' === Max Ponding Depth === Line 147 ⟶ 151: == In built USDA soil type == The model was also run with the default in-build USDA soil types. Figure 1112 shows the outputs. As expected the higher the soil type, then typically the more the infiltration and the lower the produced runoff. Soils 8-11, which represent sandy soils do not show any runoff in this example as the rainfall applied directly to the mesh is all infiltrated.<br> <br> [[File:Soil Type.jpg\|border\|760x760px\|Figure 1112: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the USDA soil type parameter in the Green-Ampt infiltration model.]]<br> '''Figure 1112: Sensitivity of simulated flow at the Cefn-Brwn gauge location in the Plynlimon Gwy catchment to the USDA soil type parameter in the Green-Ampt infiltration model.''' == Summary ==