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.
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Figure 1. Irrigator demand model
Target Modifier
Irrigation modifiers are included in Source to allow a simple mechanism to reduce irrigation intensity for recurring time periods. To enable a target modifier, right click on the demand model and choose Add Target Modifier (as shown in Figure 1). This provides equivalent functionality to demand reductions in the PRIDE model. By specifying a target modifier, a new soil depletion target is calculated during the specified period that results in a reduction in irrigation demand equivalent to the modifier you specified.
District Supply Escape
The district requirement is adjusted to allow for any district delivery supply escapes and losses associated with delivering water to the district. The volume removed before getting to the crop is called the escape volume. The escape volume can either be lost from the system or returned back to the water user as a return flow. This is an optional parameter in the demand model and can be added by right clicking Irrigator, then choosing Supply Escape. It is expressed as a percentage.
District Return Efficiency
Returned water is surplus drainage water from irrigation or from rainfall runoff. This water can be redirected into the on farm storage or otherwise can be returned to the river via a confluence node. This is optional in the demand model configuration and can be added by right clicking Irrigator and choosing Add Return Efficiency. This is also expressed as a percentage.
Climate Configuration
There are four parameters that can be defined for climatic data:
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- A Regulated Target - the target at which Irrigators water and attempts to maintain soil depletion; or
- An Opportunistic Target - used to generate opportunistic requests.
Economics
Some You can configure some simple , economic considerations are provided in Irrigator. To enable economic values to be configured for a crop, right click on the crop and choose Enable Economics. A simple, linear crop water production function is used to predict the reduction in crop yield resulting from water stress. Irrigator records the relative yield as a daily time series. The following parameters must be specified as an expression:
- Yield factor - represents the Yield response factor, as expressed in equation 90 of FAO56. Note that in Irrigation, the yield response factor is entered as a percentage rather than as a fraction
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- ;
- Expected Usage - this is a depth
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- measured in mm (note that 100mm is equivalent to 1ML/ha)
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- ; and
- Productivity - allows you to multiply the relative yield by a productivity term (eg. $/ha or tonnes/ha) to calculate socio-economic outputs.
For more information consult the /wiki/spaces/SD35/pages/57872388 page of the Source Scientific Reference Guide.
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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This specifies the percentage of applied irrigation and rainfall that becomes deep percolation and drains below the rootzone. A 10% supply escape efficiency would indicate that 10% of the applied water becomes runoff. The return efficiency is not configurable for deep percolation.
Target Modifier
Irrigation modifiers are included in Source to allow a simple mechanism to reduce irrigation intensity for recurring time periods. To enable a target modifier, right click on the crop type, choose Add Target Modifier. This provides equivalent functionality to demand reductions in the PRIDE model. By specifying a target modifier, a new soil depletion target is calculated during the specified period that results in a reduction in irrigation demand equivalent to the modifier you specified.
District Supply Escape
The district requirement is adjusted to allow for any district delivery supply escapes and losses associated with delivering water to the district. The volume removed before getting to the crop is called the escape volume. The escape volume can either be lost from the system or returned back to the water user as a return flow. This is an optional parameter in the demand model and can be added by right clicking Irrigator, then choosing Supply Escape. It is expressed as a percentage.
District Return Efficiency
Returned water is surplus drainage water from irrigation or from rainfall runoff. This water can be redirected into the on farm storage or otherwise can be returned to the river via a confluence node. This is optional in the demand model configuration and can be added by right clicking Irrigator and choosing Return Efficiency. This is also expressed as a percentage.