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Navigation: Main Menu and Buttons > Model > MODFLOW Dialog Boxes > MODFLOW Packages and Programs Dialog Box > FMP: Farm Process (for MODFLOW OWHM Version 2) SALINITY_FLUSH_IRRIGATION: Farm Process V4 Salinity Flush Irrigation Options |
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The SALINITY_FLUSH: Farm Process V4 Salinity Flush Irrigation Options pane is used to activate the SALINITY_FLUSH block in the Farm Process in MODFLOW-OWHM version 2 and specify options for it. It is in the Farm Process group on the MODFLOW Packages and Programs dialog box.
The pane has two collapsible tabs on it. The tabs can be opened or closed by clicking on their headers.
The two tabs are
These options write the summarized salinity irrigation flush results. For a detailed description of the data printed see the the files in doc\Output_Header_Defintion of the MODFLOW-OWHM release. PRINT BYWBS: This option causes the results to be summarized by water balance subregion with the aggregated crop data. PRINT BYWBS_BYCROP: This option causes the results to be summarized by water balance subregion with the separated crop data. PRINT ALL: This option causes the results to be summarized by cell. |
Expression Variable Near Zero: To prevent any divide by zero errors a minimum expression variable value may be set. If the absolute value of this variable is less than this value, it is set to it. If not specified then it is set to 0.0, which makes it have no effect WBS salt concentration: is used to specify the source water supply salt concentration for each water balance subregion in PPM (mg/L) ***NOT MODEL UNITS!!! If not specified, then all source water supplies use a salt concentration of 0.0 PPM (mg/L). The data are specified in the Water Balance Subregions dialog box. WBS irrigation uniformity: The irrigation uniformity represents how evenly the irrigation method is spread across the root zone. It is specified from 0.0 to 1.0, with 1 being perfect, uniform spread. If not specified, then all irrigation is assumed to be perfectly, uniform (1.0). The data are specified in the Water Balance Subregions dialog box. The data are specified by irrigation types. Irrigation types are specified in the Farm Irrigation Types dialog box. Crop salinity demand: HAS_CROP_SALINITY_DEMAND indicates if crop has a salinity irrigation demand calculated. If specified as a False, then it does not have it. If it is True then it does. If keyword is not included, then all crops are assumed to have salinity flushing. If specified as a list, the data are specified in the Farm Land Use Properties dialog box. Crop salinity tolerance: CROP_SALINITY_TOLERANCE specifies each Crop's salinity tolerance (ECe) in Electrical Conductivity (EC) in units of deciSiemens per meter (dS/m). ***NOT MODEL UNITS!!! Note 1 dS/m = 640 ppm = 640 mg/L Crop max leach: The maximum leaching requirement is 1.0, but this could result in a division by zero (RHOADES equation). It may be any value between 0.0 and 0.9999. This allows the user to specify a maximum allowed leaching requirement. If not specified then it is set to 0.99 Crop leaching requirement: The crop leaching requirement is the fraction of total irrigation (applied) water that must pass through the soil to prevent the soil salinity from reaching the tolerance of the crop. The data are specified in the Farm Land Use Properties dialog box. When the crop root zone has become too saline for the existing plants, it requires extra water to leach out the accumulated salts by increasing the leaching fraction (LF). Maintenance leaching is necessary to keep the average rootzone salinity below the plant threshold EC levels. The leaching fraction (LF) is defined as LF = Ddw/Diw = Ciw/Cdw = ECiw/ECdw and it is customary to substitute electrical conductivity (EC) for Concentration (C) because the EC is much easier to measure than concentration and EC is linearly related to the total salt concentration, where Ddw= the equivalent depth of water passing below the rootzone Diw = the equivalent depth of water applied (irrigation + rainfall) Ciw (ECiw) = Salt concentration (EC) of the applied water Cdw (ECdw) = Salt concentration (EC) of the drainage water Leaching requirement (LR) is the minimum LF that a plant can endure without salinity stress. LR = Ciw/C*dw = ECiw/EC*dw where C*dw (EC*dw) is the maximum permissible salt concentration (EC) of the drainage water. Using Rhoades equation (1974), the LR is related to ECa by LR = ECiw / (5ECt -ECa) where ECt is equal to the plant salt tolerance or threshold EC. (modified from https://ucanr.edu/sites/Salinity/Salinity_Management/Salinity_management_practices/Salinity_leaching/) Crop extra water: CROP_SALINITY_APPLIED_WATER is the extra water that must be applied to the crop in units of L3/T (model units). Its result is added to the crops "ADDED_DEMAND" to include its irrigation as a salt flush. To force all the water into the ground, you must specify the WBS Block ADDED_DEMAND_RUNOFF_SPLIT close to Zero. The data are specified in the Farm Land Use Properties dialog box. RHOADES Equation ==> (ETi/DU)/(1-LR) - ETi
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