Irrigator operates on a daily basis generating demands and extracting water to meet these demands via the water user and supply nodes. Irrigator maintains a daily water balance for each cropping area during its planting season to calculate the daily soil water deficit and an irrigation requirement. The irrigation requirements are used by the Water User to generate orders and opportunistic requests and to subsequently place orders and requests and to extract water from a water source.The model can be applied in both regulated and unregulated systems.
Configuring generic crop settings
The Irrigator model is based on FAO56 - "Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56: (http://www.fao.org/docrep/X0490E/X0490E00.htm). Before configuring an Irrigator Demand Model on a Water User node, you must specify crop factors for the entire scenario using Crop factors defined in this way are accessible for each water user node. More details regarding this can be found at IQQM CropMod2 Demand Model.
To configure an irrigator demand model in Source, right click Demand Models in the Water User node's feature editor and choose Add Irrigator (Figure 1).
District Configuration
This describes a number of parameters that can be set at an irrigation district level. The maximum following parameters must be configured:
- Maximum irrigated area - this represents the maximum area that can be irrigated within a district.
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- It is used to calculate the fallow area at each time-step, which impacts on the rainfall runoff from the fallow area.
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- The total irrigated area can exceed the maximum irrigated area if incorrectly configured, causing a warning message to be recorded
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- at run time;
- Soil moisture capacity
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- - this is assumed constant for all crops in the district. Soil moisture capacity is nominally the difference between the soils field capacity and permanent wilting point
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- ; and
- Irrigation start and end dates - if these are configured, orders and requests will only be generated within the irrigation season.
Figure 1. Irrigator demand model
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- Evapotranspiration - defined in FAO56 as the amount of transpiration that would occur from a reference crop. Procedures for calculating evapotranspiration are documented in FAO56. In addition, the BOM and SILO climate products produce daily estimates for FAO56. Alternatively, pan evapotranspiration and pan factors can be used to define evapotranspiration;
- Average evapotranspiration (Figure 3) - used when forecasting orders. Two options are provided for specifying the average evapotranspiration. You can enter a daily pattern of average evapotranspiration, or you can select to calculate an average evapotranspiration runtime, where the average is calculated as a rolling average of the number of previous model time-steps specified. A value of 14 days would be a good first estimate; and
- Rainfall and average rainfall are used to specify the actual forecast rainfall.
Figure 2. Irrigator demand model (Climatic parameters)
Figure 3. Irrigator demand model (Average evapotranspiration)
Fallow Crop
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This is used to define parameters specifically related to the crop to be planted. To add a new crop, right click Irrigator and choose Add Crop Type. Consult Figure 4 shows an example of a crop, named Wheat, that has been added to the model. Consult the Source Scientific Reference Guide for greater detail regarding parameters for the following sections.
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4. Irrigator demand model (General and Soil Configurations)
Soil Configuration
Crop specific soil factors can be defined on the same page as General Configuration - see Figure 34. Soil moisture capacity is specified at the district level and this is assumed constant for all crops in the district. The Depth of the Root Zone, Depletion Factor and Initial Depletion are specified for each crop.
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Planting decisions are represented as a trigger in the Irrigator Demand Model and include a decision type, plant date, optional harvest date , planted area definition and an under irrigation factor.The number and size of cropped areas changes over time in response to planting decision triggers and available water.
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| Note: Irrigator allows more flexible representations of crop based planting decisions than earlier crop demand models, which better align with economic modelling. If the planted area is defined using the expression editor, then other factors such as economics can be considered. In addition, planting decisions can be reviewed periodically during the season. This allows decisions to be made to cut back the irrigated area, reduce irrigation intensity or potentially trade water if there is insufficient water to finish the crop. |
Figure 4. Irrigator demand model (Planting Decision Trigger)
Soil DepletionTarget soil depletion
The amount of water in the rootzone is defined in terms of rootzone depletion. Rootzone depletion , which describes the soil water deficit of the rootzone , relative to field capacity. The target depletion is a user specified input and can be specified as either a time series, a pattern or as an expression.
Two target depletions can be specified (as shown in Figure 4):
- A Regulated Target - the target at which Irrigators water and attempts to maintain soil depletion; andor
- An Opportunistic Target - used to generate opportunistic requests.
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Figure 5 - Irrigation demand model (Crop Economics)
Runoff
The supply escape efficiency defines the amount of applied irrigation water that becomes runoff. A value of 0 results in no irrigation runoff, 10% indicates that 10% of the applied irrigation water becomes runoff. You must also specify a return efficiency, which means that the proportion of runoff that is returned to the water user can be stored in the farm storage or returned to the river. By default, both are set to 0, and do not need to be configured.
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