Modelling farm dams in Source using the Onstream Farm Dam node
Create Onstream Farm Dam node(s) in
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a Source model
Modelling farm dams in Source is more commonly undertaken as part of a catchment model, where sub-catchment flows provide the inflows to each farm dam node. However, the farm dam node is available from the Node palette and can also be used in a schematic river system model. The creation of a farm dam node (1) in a river system model from the Schematic Editor and (2) in a catchment model from the Geographic Editor, is different. The methods for both models are described separately below:
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Figure 3 Bulk Change Node Models interface
Configure Onstream Farm Dam node(s) in
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a Source model
There are two ways to configure the The parameters of the an onstream farm dam . One method is for the individual node of the Onstream Farm Dam, and another method is for all nodes of modelled Onstream Farm Dams. Two methods can be used jointly.
For an individual node of the Onstream Farm Dam
The user can use Future Editor (such as Edit in Figure 2) to set up the parameters of the farm damcan be configured individually per node using the Feature Editor of each node. Since a farm dam model typically contains many farm dam nodes, this method can be time consuming. Another option is to configure multiple nodes of modelled onstream farm dams using the Source Feature Table. These two methods can be used in conjunction to facilitate model configuration.
1 Configure an individual Onstream Farm Dam node
Double click on a node or right click to access the Edit option will open the node Feature Editor. The user can then use the Feature Editor to set up the farm dam node parameters. Clicking on Edit from the selected farm dam node will open the farm dam editor (Figure 4)
Figure 4 Farm dam Dam editor – Dam Information
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a. Dam Information
The farm dam information is on the default interface of the farm dam editor (Figure 4). The parameters
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Dam Capacity, Max. Dam Surface Area and Initial Storage Percentage in Figure 4 are self-
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explanatory. Other parameters are described below.
- Diversion Fraction - decides how much the “upstream” flow, which includes both the upstream flow and interstation diverted flows are not included in the water balance calculation. This parameter indicates how much of the upstream inflow, will be involved included in the water balance calculation in for the edited farm damnode. The remaining water in the “upstream” flow will be diverted directly to the downstream flow.
- Dead Storage Volume (/Dead Storage Proportion) – is the volume of the farm dam stored below the level of the lowest outlet (the minimum supply level). The demand and release requirements cannot access this water, but the natural loss (e.g. evaporation, seepage) in this water still occurs. Dead Storage Volume can also be
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- input as
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- a percentage or proportion of Dam Capacity by ticking the Use Proportion checkbox. The parameter name will
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- change to Dead Storage Proportion when the Use Proportion checkbox is ticked. The user can click on the %/
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- proportion button to swap the type between percentage (%) and proportion.
Note that the values entered from different types (i.e., volume, percentage, and proportion) for the same farm dam
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will only be automatically converted
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once the configuration is saved by clicking on the OK button of the Editor interface.
The Dead Storage Volume can be entered
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as (a)
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a
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Value, (b)
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a Data Source
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- normally
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a time series
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, or (c)
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a Function.
The allowable range of Dead Storage Volume is between zero and max capacity.
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Percentage and proportion
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ranges are from 0 to 100 and 0 to 1 respectively. If the entered values are not within the permitted range,
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a run error will occur. The user then needs to fix this issue. The example screen of the error message (e.g. for entering -1) is shown in Figure 5. “166” in Figure 5 is the name of the associated farm dam node.
Figure 5
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Run error screen for unsuitable input of Dead Storage Volume
- Bypass Flow - defines the maximum capacity of the flow bypassed from the upstream flow directly to the downstream of the farm dam.
Now Bypass Flow can be entered by four types of data sources: (a) from a value, (b) from Data Source, normally it is a time series, (c) from the function and (d) a Monthly Pattern shown in Figure 6.
Figure 6 The Editor Screen of Select Source for ByPass Flow
The Bypass Flow is designed to be greater or equal to zero. If the entered value is negative, the running error will occur. The user then needs to fix this issue. The example screen of the error message (for entering -2 for Bypass Flow) is shown in Figure 7.
Figure 7 Running error message for unsuitable input of Bypass Flow and Release Volume
- Release Volume - defines the voluntary water release requested from the farm dam. The volume(s) can be entered by three types: (a) from a value, (b) from Data Source, which normally is a time series and (c) from the function.
The Release Volume is also greater or equal to zero. If the entered value is negative, the running error will occur (Figure 7). The user then needs to fix this issue.
- Dam Surface Area Options - provides three options for the dam surface area during the water balance calculation:
- Constant dam surfaces area using ‘Max. Dam Surface Area’ parameter – The entered constant value of Dam Surface Area is used in water balance calculation such as converting rainfall and evaporation from the depth to volume in the farm dam storage.
- Allow dam surface area to vary according to dam volume - The area will be calculated on the basis of the storage volume, default equations and parameters. The storage volume is from the beginning of the time step. The calculated dam surface area at each time step will be used in water balance calculation. Custom Equation Parameters check box is unticked.
- Custom Equation Parameters – This function works only when the option Allow dam surface area to vary according to dam volume is selected and the Custom Equation Parameters check box is ticked. The dam surface area will be calculated based on the storage volume at the beginning of the time step, and the equation of Volume =A*Area^B. Where A and B are input parameters from the Interface. The calculated area at each time step will be used in water balance calculation.
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b. Interstation Flow
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Inflows into a farm dam in this farm dam model come from two alternative sources: (i) overflows from the upstream dam(s) and (ii) the local flow generated by the interstation area between the upstream dams and this dam.
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Clicking on the Interstation Flow in the left panel of Figure 4 will display the Interstation flow parameters in the right panel for the configuration (Figure 8). The parameters include Scaling Factor and Reference Timeseries Values/Data Source. The user can select the option Values for the constant value or Data Source for a timeseries defined in Source Data Sources.
The interstation inflow is calculated based on a reference value or time series (i.e., at a flow gauge) that has been scaled down/up. If the scaling factor is 0.8 and the reference timeseries value is 0.25 ML/d, the Actual Interstation Flow (ML) is 0.2 ML/d. The scaling factor reflects (a) the interstation catchment area relative to the reference catchment area; and (b) the nonlinear relationship between the catchment area and flow.
Figure 8 Farm dam editor – Interstation Flow
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c. Seepage
Seepage from the farm dam into the underlying soil can be modelled by defining an exfiltration rate (e.g., mm/d). The water that seeps from the farm dam is lost from the catchment and does not re-enter the system downstream.
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Clicking on the Seepage in the left panel of Figure 4 will display the Seepage parameter in the right panel for configuration (Figure 9). The parameters can be configured by the constant value or time series from Data Source.
Figure 9 Farm dam editor – Seepage
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d. Demand
Clinking on the Demand in the left panel of Figure 4 will display the demand parameters in the right panel for configuration (Figure 10). The demand parameters include Demand Factor and Demand Timeseries Values/Data Source. The demand factor can be estimated from the ratio of the average annual demand of the farm dam volume.
In this farm dam model, the demand is not directly using Demand Timeseries. The demand volume is determined by the demand factor and farm dam volume, and its temporal distribution is determined by the Demand Timeseries Values/Data Source.
Figure 10 Farm dam editor – demand
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e. Rainfall
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Clicking on the Rainfall in the left panel of Figure 4 will display the rainfall parameters in the right panel (Figure 11). The parameter is the rainfall to the edited farm dam, and it can be configured by constant Values or timeseries data in Data Sources. Its unit is depth such as mm, and Source will convert it to volume by the dam area calculated as the description in section (1) The farm dam information.
Figure 11 Farm dam editor – Rainfall
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f. Evapotranspiration
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Clicking on
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Evapotranspiration in the left panel of Figure 4 will display the evapotranspiration parameters in the right panel (Figure 12). The parameter is the evapotranspiration from the edited farm dam, and it can be configured by constant Values to timeseries in Data Source. Its unit is depth such as (mm/day) and Source will convert it to volume using the calculated dam area as the description in section (1) The farm dam information.
Figure 12 Farm dam editor – Evapotranspiration
Clicking on the The OK button in (Figure 4) will save the setup of the farm dam setup. The Cancel button will discard the entered parameters.
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2 Configure multiple Onstream Farm Dam nodes
The Source Feature Table allows inputting, editing, checking, and outputting all parameters of all farm dams together. Tool menu item Edit » Feature Table... can access Feature Table for this functionality (Figure 13). Clicking on the Onstream Farm Dam in the left panel (Figure 13) will display the existing values of all editable parameters for all onstream farm dams in the right panel.
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- open Source version 5.20 with the FarmDam plugin (and ObservationPointNodeModel plugin, if needed) installed
- load the existing model in Source version 5.20
- save the now upgraded project in Source version 5.20
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