The IQQM CropMod2 replicates the water requirements for a cropped area. This is a process-based model which allows you simulate a farmer’s decision on the area to plant in each season and evapotranspiration of the different crop types, and generates a demand based on the maintenance of a target soil moisture level. You can also simulate rice irrigation by specifying ponding behaviour and return flows.
When working with crop models, first configure crops using the Crop Parameter dialog. Then, use the water user feature editor to configure the remaining parameters.
Configuring generic crop settings
Before configuring an IQQM CropMod2 Demand model on a Water User node, you must specify crops and their associated parameters for the entire scenario using . Crop parameters defined in this way are accessible for each water user node. This dialog is used to add crops (which can be imported via a .xml file), delete crops, and specify parameters.
Figure 1. Crop Parameters
Figure 2 shows the dialog when a new crop is created. Note that Use Pattern is toggled to OFF. Table 1 describes the parameters used in this dialog.
The method for defining crop parameters is based on FAO 56 which divides the growth period of every crop into four developmental stages based generally on water requirements. These stages are:
- Initial (or establishment) stage - occurs between planting and when there is approximately 10% ground cover. Water requirements are quite low and constant;
- Crop development (or vegetative) stage - sees a rapid increase in the amount of water required by the crop until there is generally about 70% to 80% ground cover and maximum rooting depth is achieved;
- Mid-season (or flowering) stage - requires the maximum amount of water in the life of the crop; and
- Late (or yield and/or ripening) stage - there is an approximate halving of water requirement as the crop ripens, reaches maturity and is harvested.
Figure 2. Crop Parameters, Default crop, Use Pattern Off
Table 1. Crop Model - Crop parameters
Parameter | Type | Description |
|---|---|---|
Repeats | integer | The growth pattern and duration is repeated by the specified number. For example a growth season of 5 months when repeated by a factor of 3 will have a growth period of 15 months. |
| Use Pattern | When toggled to ON, | |
Is Ponded | When toggled to ON, the crop mix in the water user node for this crop type requires input for targets for minimum and maximum pond level. Levels are used as targets to irrigate and drain area as occurs for rice. | |
Coefficient | Coefficients that define the straight lines connecting the four growth stages for the crop water requirements | |
Initial | Coefficient at start of the initial phase | |
Development | Coefficient at end of the initial phase and start of development phase | |
Mid-Season | Coefficient at end of the development phase and start of Mid-Season phase | |
Late-season | Coefficient at end of the Mid-Season phase and start of Late-Season phase | |
Maturity | Coefficient at end of the Late-Season phase | |
Growing days | days | Number of days within each stage of crop growth. |
Figure 3 shows the dialog when Use Pattern is toggled to ON. In this configuration, the daily time-step values can be entered manually or imported as a .csv file.
Figure 3. Crop Parameters, Crop, Use Pattern On
Figure 4 shows the dialog for the Irrigation return that can be configured for a crop. This dialog is similar for On Farm Loss and On Farm Escape.
Figure 4. Crop Parameters, Crop, Irrigation Return
Configuring crop models
Once crops have been configured, use the water user feature editor to configure characteristics of the IQQM crop model. Figure 5 shows the parameters that can be configured for the model.
Figure 5. IQQM crop model
The main IQQM Crop model panel (shown in Figure 6) is divided into three main sections. Parameters for each of these sections is outlined in Tables 2 and 3.
Figure 6. IQQM Crop Model, main
The Planted Area section broadly defines the area to be used and the proportions between the primary and secondary crops. The parameters that must be defined are described in Table 2.
The Primary Season Decision Date refers to the day when the water user decides the area of crop(s) to plant in the primary season. This should be before the Start Date of any specified primary crop, otherwise the area initially planted will be based on the primary crop decision from the previous year. The start date of the crop is specified in the Crop mix tab. Similarly, the Secondary Season Decision Date is the day when the water user decides the area of crop(s) to plant in the secondary season. Just like the primary season, this should be before the Start Date of any specified secondary crops.
Table 2. Crop Model, Planted Area parameters
Parameter | Units | Description |
|---|---|---|
Maximum Irrigable Area | ha | Maximum area that can be planted. |
Max Area for Primary Crop | ha | This is the maximum area that can be used in a simulation for all crops nominated as primary. A primary crop is one that is grown during the primary season, where there may be more than one crop type grown. This area cannot exceed the Maximum Irrigable Area. |
Max Area for Secondary Crop | ha | This is the maximum area to be used in a simulation for all crops nominated as "winter". A secondary crop is one that is grown during the winter months, which is defined in the crop mix (winter). This area cannot exceed the Maximum Irrigable Area. |
The Soil section defines soil inputs. There are individual stores for each crop type. Areas that are not being cropped are referred to as fallow, and are simulated using two soil layers. Fallow area occurs between cropping seasons or during the irrigation season if the maximum developed area is not planted. At the end of a cropping season, the soil moisture of the crop area and fallow areas are merged. Table 3 provides a description of the parameters. Refer to the Source Scientific Reference Guide for more information.
Table 3. IQQM Crop Model, Soil parameters
Parameter
Units
Description
Max available soil moisture
mm
Depth of soil moisture available to the crop (field capacity). A soil moisture level of 0 represents the wilting point and the default settings will try to maintain a soil moisture level of half the field capacity.
Upper soil moisture depth of Fallow
mm
Depth of the upper soil moisture store for fallow areas. The lower soil store depth is equal to the Maximum available soil moisture less Upper soil moisture depth. Upper soil moisture store cannot be greater than the depth of the Maximum available soil moisture. The upper store is depleted by evaporation and the lower store, by the seepage rate. Water can move from the upper store to the lower store at the Infiltration Rate.
Infiltration rate from upper Fallow to lower Fallow
mm/d
The maximum rate of water movement from the upper soil moisture store to the lower moisture store. The actual infiltration rate is the product of this rate and the ratio of upper fallow moisture to upper fallow moisture capacity.
Seepage
mm/d
The maximum rate at which water drains from the lower soil moisture store when the area is not irrigated (fallow). Soil moisture will be depleted by the product of this rate with the ratio of actual soil moisture to maximum soil moisture.
Fallow factor
%
The IQQM Crop Model replicates the water requirements for a cropped area. This is a process-based model which allows you to simulate a farmer’s decision on the area to plant in each season (along with evapotranspiration of the different crop types) and generates a demand based on the maintenance of a target soil moisture level. You can also simulate rice irrigation by specifying ponding behaviour and return flows.
When configuring crop models, the first step is to specify the crops using the Crop Parameter dialog. Then, use the water user feature editor to configure the model.
| Anchor | ||||
|---|---|---|---|---|
|
The Crop Parameters dialog shown in Figure 1 (accessible via ) allows you to specify crops and their associated parameters for the entire scenario. Crop parameters defined in this way are accessible for each water user node. This dialog is used to add crops (which can be imported via a .xml file), delete crops, and specify various parameters.
Figure 1. Crop Parameters
To add a new crop, right click Crop Parameters and choose Add Crop from the contextual menu. Figure 2 shows the resulting dialog. Note that the default for Use Pattern is OFF. Table 1 describes the parameters used in this dialog.
The method for defining crop parameters is based on FAO 56 which divides the growth period of every crop into four developmental stages based generally on water requirements. These stages are:
- Initial (or establishment) stage - occurs between planting and when there is approximately 10% ground cover. Water requirements are quite low and constant;
- Crop development (or vegetative) stage - sees a rapid increase in the amount of water required by the crop until there is generally about 70% to 80% ground cover and maximum rooting depth is achieved;
- Mid-season (or flowering) stage - requires the maximum amount of water in the life of the crop; and
- Late (or yield and/or ripening) stage - there is an approximate halving of water requirement as the crop ripens, reaches maturity and is harvested.
Figure 2. Crop Parameters, Use Pattern Off
Table 1. Crop Model - Crop parameters
Parameter | Type | Description |
|---|---|---|
Repeats | integer | The growth pattern and duration is repeated by the specified number. For example a growth season of 5 months when repeated by a factor of 3 will have a growth period of 15 months. |
| Use Pattern | Refers to the crop factor pattern used. This is NOT the format used in default of growing days. | |
Is Ponded | When toggled to ON, the crop mix in the water user node for this crop type requires input for targets for minimum and maximum pond level. Levels are used as targets to irrigate and drain area as occurs for rice. | |
Coefficient | Coefficients that define the straight lines connecting the four growth stages for the crop water requirements. | |
Initial | Coefficient at start of the initial phase. | |
Development | Coefficient at end of the initial phase and start of development phase. | |
Mid-Season | Coefficient at end of the development phase and start of Mid-Season phase. | |
Late-season | Coefficient at end of the Mid-Season phase and start of Late-Season phase. | |
Maturity | Coefficient at end of the Late-Season phase. | |
Growing days | days | Number of days within each stage of crop growth. |
Figure 3 shows the dialog when Use Pattern is toggled to ON. Daily time-step values can be entered manually or imported as a .csv file.
Figure 3. Crop Parameters, Crop, Use Pattern On
There are three parameters that can result in the water requirement being scaled up. Additional extractions are required if there is a practice of applying excess irrigation, with the excess being captured and returned to the water user storage. Additional extractions are also required if losses occur prior to delivery of extractions to the crop.
Figure 4 shows the dialog for the Irrigation return that can be configured for a crop in Crop Parameters. This dialog is similar for On Farm Loss and On Farm Escape.
Figure 4. Crop Parameters, Crop, Irrigation Return
| Info |
|---|
Irrigation return, on farm loss and on farm escape are only relevant to IQQM Crop Model, not other crop models, even though the crop factors configured in Crop Parameters are used in other crop demand models. |
Three factors may also be configured at the Return Flow tab in IQQM Crop Demand Model at a Water User to apply scaling of these parameters, allowing variation for crops from one farm to another.
These factors are:
- Irrigation return factor - Allows you to scale the irrigation return parameter defined through crop parameters configuration. This factor and parameter combined, result in an increase in the volume ordered with the additional volume being available for returning to the water user storage;
- On farm loss factor - Allows you to scale the on farm loss parameter defined through crop parameters configuration. On-farm loss represents the percentage of water that is diverted from the river and passes the irrigators meter, but doesn’t make it to the cropped area and doesn’t reappear at any other point. An on farm loss will result in the volume ordered being increased and is applied after irrigation return; and
- On farm escape factor - Allows you to scale the on farm escape parameter defined through crop parameters configuration. On-farm escape represents the percentage of diversions that is lost prior to being applied to crops however this flow returns to the river system at a confluence node. An on farm escape will result in the volume ordered being increased and is applied after the irrigation return factor and the on farm loss factor.
Configuring crop models
Once crops have been configured, use the water user feature editor to first create an IQQM Crop model, then configure its characteristics (Figure 5).
Figure 5. IQQM crop model
The main IQQM Crop model panel (shown in Figure 6) is divided into three main sections:
- The Planted Area section broadly defines the area to be used and the proportions between the primary and secondary crops. Refer to Table 2 for information on the configurable parameters;
- The decision dates refer to the date when the area to be irrigated is calculated using a risk function. In practice, this is the date when farmers decide how much area is to be irrigated. Primary Season Decision Date refers to the day when the water user decides the area of crop(s) to plant in the primary season. This should be before the Start Date of any specified primary crop, otherwise the area initially planted will be based on the primary crop decision from the previous year. Similarly, the Secondary Season Decision Date is the day when the water user decides the area of crop(s) to plant in the secondary season. Just like the primary season, this should be before the Start Date of any specified secondary crops; and
- The Soil section defines soil inputs. There are individual stores for each crop type. Areas that are not being cropped are referred to as fallow, and are simulated using two soil layers. Fallow area occurs between cropping seasons or during the irrigation season if the maximum developed area is not planted. At the end of a cropping season, the soil moisture of the crop area and fallow areas are merged. Table 3 provides a description of the parameters.
| Info | ||
|---|---|---|
| ||
| Note: In practice, the decision dates occur when farmers decide how much area is to be irrigated, and is usually earlier than the start of planting. |
Figure 6. IQQM Crop Model, main
Table 2. IQQM Crop Model, Planted Area parameters
Parameter | Units | Description | |||||
|---|---|---|---|---|---|---|---|
Maximum Irrigable Area | ha | Maximum area that can be planted. This value limits the total of primary and secondary crops, in case both crops are planted at the same time.
| |||||
Max Area for Primary Crop | ha | This is the maximum area that can be used in a simulation for all crops nominated as primary. A primary crop is one that is grown during the primary season, where there may be more than one crop type grown. This area cannot exceed the Maximum Irrigable Area. | |||||
Max Area for Secondary Crop | ha | This is the maximum area to be used in a simulation for all crops nominated as "winter". A secondary crop is one that is grown during the winter months, which is defined in the crop mix (winter). This area cannot exceed the Maximum Irrigable Area. |
Table 3. IQQM Crop Model, Soil parameters
Parameter | Units | Description |
|---|---|---|
Max available soil moisture | mm | Depth of soil moisture available to the crop (field capacity). A soil moisture level of 0 represents the wilting point and the default settings will try to maintain a soil moisture level of half the field capacity. |
Upper soil moisture depth of Fallow | mm | Depth of the upper soil moisture store for fallow areas. The lower soil store depth is equal to the Maximum available soil moisture less Upper soil moisture depth. Upper soil moisture store cannot be greater than the depth of the Maximum available soil moisture. The upper store is depleted by evaporation and the lower store, by the seepage rate. Water can move from the upper store to the lower store at the Infiltration Rate. |
Infiltration rate from upper Fallow to lower Fallow | mm/d | The maximum rate of water movement from the upper soil moisture store to the lower moisture store. The actual infiltration rate is the product of this rate and the ratio of upper fallow moisture to upper fallow moisture capacity. |
Seepage | mm/d | The maximum rate at which water drains from the lower soil moisture store when the area is not irrigated (fallow). Soil moisture will be depleted by the product of this rate with the ratio of actual soil moisture to maximum soil moisture. |
Fallow factor | % | Crop factor for fallow ground. One value is used throughout the year. This factor is applied to the evaporation rate to determine the loss rate from the upper fallow area. |
When there is a significant deficiency in the moisture store, the irrigation demand generated to refill the store is limited by the pump capacity. When the Use demand limiting factor of 2x E.T checkbox is enabled, the irrigation demand will be further limited by twice the evapotranspiration if it is less than the pump capacity.
Defining crops
To define a crop, choose the crop type from the drop-down menu (resulting in the dialog shown in Figure 7) and specify the parameters as shown in Table 4.
Figure 7. IQQM Crop model, Crop
Table 4. IQQMCrop Model, Crop general configuration
| Parameter | Description |
|---|---|
| Proportion | Area of the crop divided by the total crop area (primary + secondary). |
| Start date | Start date of crop parameters as specified in Crop parameters. |
| Tolerance | This affects regulated target moisture and opportunistic target moisture; the regulated target being half the soil moisture depth – tolerance, and the opportunistic target being half the soil moisture depth + tolerance – for non-ponded crops. It should be disabled for ponded crops. |
| Efficiency | If less than 1, crop factors increased by (1/efficiency) in the crop demand calculation. |
| Season | The season (either primary or secondary) must be chosen to specify the risk function to use. |
| Info | ||
|---|---|---|
| ||
| Note: The Start Date is the start date for the pattern of crop factors and does not represent the date the crop is planted. The date the crop is planted is the first date there is a non-zero crop factor, and this should be configured to occur after the Planting Decision Date for the season. |
Targets
By default, IQQM Crop Model will target half of the Maximum Available Soil Moisture (configured in the IQQM Crop Model main panel Soil section as shown in Figure 6) for non-ponded crops and the full Maximum Available Soil Moisture plus the Minimum Ponding Level for ponded crops. Crop targets may be added via right-clicking the crop name, as shown in Figure 8.
If the crop is ponded, both the Minimum and Maximum Ponding Level MUST be added here. If the Minimum Ponded Level is not added and greater than zero, the crop will target half of the soil moisture depth by default as if the crop was not ponded. The Maximum Ponded Level represents the ponding depth at which there is runoff from the crop which can join return flow, and if there is a Minimum Ponded Level configured, the Maximum Ponded Level must also be configured with value greater than or equal to the Minimum Ponded Level to work correctly.
If the crop is non-ponded, a Crop Target may be added to override the default target of half the Maximum Soil Moisture Depth. This way, different target moistures may be set for different crops within the same farm. Otherwise all crops within the same farm (or demand model) will have the same default moisture target.
Crop Target and Minimum and Maximum Ponding Level are added as either a daily or monthly pattern and the units are millimetres.
Figure 8. IQQM Crop model, Crop Targets
OFS Reserve volume
OFS Reserve volume may also be added by right-clicking the crop name as shown in Figure 6. The OFS Reserve volume is used to satisfy crop demands during dry periods and long travel times for ordered water. Just like Crop Target and Minimum and Maximum Ponding Level, it can be specified as either daily or monthly patterns and is defined in millimeters. The specified depth is multiplied by planted area for each crop type to determine the reserve volume required for the crop.
OFS Reserve volume configured in IQQM Crop Model will only be used if Maintain Target Reserve Volume is checked and the Water User Determined radio button is selected at the On Farm Storage.
Climate
The IQQM Crop Model defines three parameters for climatic data:
- Rainfall - The model uses rainfall data to replenish soil moisture. Excess runoff can be re-used by the water user node. Rainfall may be input as monthly averages or daily data entered as a constant value, a time series, or as a function. Refer to Figure
- 9 for the dialog and Table
- 5 for parameter details
- ;
- Evaporation - The model uses pan evaporation with crop factors to calculate evapotranspiration volumes. Pan evaporation is input as a time series. Refer to Figure
- 10 for the dialog; and
- Average daily evaporation - Enter average daily pattern for reference crop evapotranspiration. The daily average is used to forecast crop demand. If no average evap data is added then an average for each day of the year (ie. 365 day pattern) is derived from the time series data.
Figure
79. IQQM Crop Model, Rainfall
Table
45. IQQM Crop Model, Rainfall parameters
Parameter | Units | Description |
|---|---|---|
Crop interception loss | mm | The depth of rainfall intercepted by the vegetative cover of the crop. Effective rainfall onto crops is the actual rainfall less this interception loss. |
Fallow interception loss | mm | The depth of rainfall intercepted in fallow area. |
Expected usable rainfall in primary growing season | mm | Depth of usable rainfall available for use by a crop during the primary growing season. Usable rainfall is actual rainfall less allowance for runoff and interception losses. This value is used when calculating the area to be planted at the primary growing season decision date if the volume risk function method is used. |
Expected usable rainfall in secondary growing season | mm | Depth of usable rainfall available for use by a crop during the secondary growing |
Figure 8. IQQM Crop Model, Evaporation
Risk functions
At the start of an irrigation season, each water user node decides on how much area is to be planted (and thus irrigated). This is determined by the Decision Date for the primary and secondary season. This calculation uses a relationship referred to as the farmer’s risk function. In the IQQM crop model, farmer’s risk is modelled in two different ways: an area-based approach and a volume-based one. For the former, the function relates available resource to planted area. For the latter, the function relates current the available resource to expected available resource. The expected available resource is then divided by the calculated average crop requirement to determine the planted area. Refer to the Source Scientific Reference Guide for more information.
For both area and volume based risk functions, you must specify the wet, average and dry periods. The model interpolates between these values based on an index of current conditions. For the area based method, the model automatically calculates the index based on soil moisture. For the volume based method, the index is calculated based on the defined inflow data as follows:
- Inflow time series - If the Risk Function type is volume, specify inflow as a constant value, a time series data or as a function (Figure 9); or
- Median prior 6-Monthly Inflow - Long term average inflows are entered as a monthly pattern. The volume based risk function uses an inflow index based on the supplied time series data. The index compares the total inflow from the time series file in the preceding 183 day period to the long term average for the same period.
Figure 9. IQQM Crop Model, Risk functions
Figure 7. Farmers' risk functions
Efficiency tab
This describes a number of parameters that can result in the water requirement being scaled up (Figure 8). Additional extractions are required if there is a practice of applying excess irrigation, with the excess being captured and returned to the water user storage. Additional extractions are also required if losses occur prior to delivery of extractions to the crop. The water user efficiency tab then allows these values to be scaled down. The default crop configuration values are zero, and hence if not defined, changing the water user efficiency parameters will have no effect.
Figure 8. Water User node (IQQM CropMod2, Efficiency)
The parameters are:
- Irrigation return factor - Allows you to scale the on farm return factor defined through crop configuration. These two parameters combined, result in an increase in the volume ordered with the additional volume being available for returning to the water user storage;
- On farm loss factor - Allows you to scale the on farm loss factor defined through crop configuration. On-farm loss represents the percentage of water that is diverted from the river and passes the irrigators meter, but doesn’t make it to the cropped area and doesn’t reappear at any other point. An on farm loss will result in the volume ordered being increased and is applied after the irrigation return factor; and
- On farm escape factor - Allows you to scale the on farm escape factor defined through crop configuration. On-farm escape represents the percentage of diversions that is lost prior to being applied to crops however this flow returns to the river system at a confluence node. An on farm escape will result in the volume ordered being increased and is applied after the irrigation return factor and the on farm loss factor.
Return flow tab
Return drainage 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 shown in Figure 9. The various parameters are shown in Table 6.
Figure 9. Water User node (IQQM CropMod2, Return flow)
Table 6. Crop Model - Return Flow parameters
Parameter | Units | Description |
|---|---|---|
Rainfall runoff scaling factor | % | The IQQM crop model includes a default rainfall runoff model and the scaling factor can be used to scale the runoff up or down. This factor should only be changed from 1.0 after careful thought, as it can impact irrigation demand calculations. If a factor greater than 1.0 is used runoff increases and infiltration is reduced. Similarly, if a factor less than 1.0 is used, runoff decreases and infiltration is increased. |
Irrigation return water recycling efficiency | % | This defines the percentage of irrigation return water that can be either pumped into the water user storage for re-use (subject to storage and pumping constraints) or directed back to the river. You determine the proportion that is diverted to the storage through the ‘harvestable return flow’ parameter for the storage. |
Rainfall runoff recycling efficiency | % | Percentage of rainfall runoff that can either be pumped into the water user storage for re-use or directed back to the river. As per irrigation recycling, the proportion that is directed to the storage is dependent on the ‘harvestable return flow’ parameter for the storage. |
Tile Drainage (TD) parameters | The tile drainage function allows drainage to be defined in terms of a regression relationship with rainfall and irrigation. The amount of tile drainage is estimated as |
Crop mix tab
This tab (Figure 10) defines the proportions and timings of different crops planted in the defined area.
Figure 10. Water User node (IQQM CropMod2, Crop mix)
season. Usable rainfall is actual rainfall less allowance for runoff and interception losses. This value is used when calculating the area to be planted at the secondary growing season decision date if the volume risk function method is used. |
Figure 10. IQQM Crop Model, Evaporation
Return flow
Return drainage 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. Figure 11 shows the dialog for Return flow and Table 6 describes the configurable parameters.
Figure 11. IQQM Crop Model, Return flow
Table 6. IQQM Crop Model, Return flow parameters
| Parameter | Units | Description |
|---|---|---|
| Irrigation return factor | % | Allows you to scale the on farm return factor defined through crop configuration. These two parameters combined, result in an increase in the volume ordered with the additional volume being available for returning |
| On farm loss factor | % | Allows you to scale the on farm loss factor defined through crop configuration. On-farm loss represents the percentage of water that is diverted from the river and passes the irrigators meter, but doesn’t make it to the cropped area and doesn’t reappear at any other point. An on farm loss will result in the volume ordered being |
| On farm escape factor | % | Allows you to scale the on farm escape factor defined through crop configuration. On-farm escape represents the percentage of diversions that is lost prior to being applied to crops however this flow returns to the river system at a confluence node. An on farm escape will result in the volume ordered being increased and is applied after the irrigation return factor and the on farm loss factor. |
| Rainfall runoff scaling factor | % | The IQQM crop model includes a default rainfall runoff model and the scaling factor can be used to scale the runoff up or down. This factor should only be changed from 100% after careful thought, as it can impact irrigation demand calculations. If a factor greater than 100% is used runoff increases and infiltration is reduced. Similarly, if a factor less than 100% is used, runoff decreases and infiltration is increased. |
| Irrigation return efficiency | % | This defines the percentage of irrigation efficiency return water that can be either pumped into the water user storage for re-use (subject to storage and pumping constraints) or directed back to the river. You determine the proportion that is diverted to the storage through the ‘harvestable return flow’ parameter for the storage. |
| Rainfall runoff recycling efficiency | % | Percentage of rainfall runoff that can either be pumped into the water user storage for re-use or directed back to the river. As per irrigation recycling, the proportion that is directed to the storage is dependent on the ‘harvestable return flow’ parameter for the storage. |
| Tile drainage irrigation factor | % | The irrigation factor, scales the sum of the available water for the previous 30-day period. |
| Tile drainage coefficient | % | Percent of the crop area that provides tile drainage |
| Tile drainage rainfall factor | % | The rainfall factor, scales the sum of the rainfall over the previous 30-day period. |
Risk functions
At the start of an irrigation season, each water user node decides on how much area is to be planted (and thus irrigated). This is determined by the Decision Date for the primary and secondary season. This calculation uses a relationship referred to as the farmer’s risk function. In the IQQM crop model, farmer’s risk is modelled in two different ways: an area-based approach and a volume-based one. For the former, the function relates available resource to planted area. For the latter, the function relates current the available resource to expected available resource. The expected available resource is then divided by the calculated average crop requirement to determine the planted area. Refer to the Source Scientific Reference Guide for more information.
For both area and volume based risk functions, you must specify the wet, average and dry periods (using the Primary and Secondary crop dialog shown in Figure 14). The model interpolates between these values based on an index of current conditions. For the area based method, the model automatically calculates the index based on soil moisture. For the volume based method, the index is calculated based on the defined inflow data as follows:
- Inflow time series - If the Risk Function type is volume, specify inflow as a constant value, a time series data or as a function (Figure 12); and
- Median prior 6-Monthly Inflow - Long term median 6-monthly inflows are entered as a monthly pattern (Figure 13). Note that the value for each month represents median sum of 6 months of flows for the prior 6 months in megalitres. The index uses the value for the prior month up until day 14 of the month and then uses the current month for days after that, therefore the values entered here should be the sum for 6 months inflows inclusive of the current month.
The volume based risk function uses an inflow index based on the supplied time series data and monthly pattern. The index compares the total inflow from the time series file in the preceding 183 day period, to the long term median prior 6-monthly inflow from the supplied pattern for the preceding month for the first 14 days of each month, and the current month for the remainder of the month.