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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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An onstream farm dam node is represented in the Node Palette as a green triangle .  Dragging Dragging the node icon from the Node Palette to the Schematic Editor interface will drop a farm dam node in an existing Source model. This node can then be manually linked to other nodes in the model as needed. Accurate coordinates of farm dams’ positions are not required , but can be entered through the Source Feature Table if required.

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The first step is to select an existing model element (e.g., a Confluence node). Right-click on the selected node to display the context menu. Click on Change Node Model (step 1 in Figure 21) on the context menu to display an additional context menu. Select the the Onstream Farm Dam option (step 2 in Figure 21) to change the node to an Onstream Farm Dam that is displayed as a green triangle. If there is no existing model element, the the Add Node option (step 3 in Figure 21) can be used to add a Confluence for subsequent node model changes.

Figure 2 1 Modeling Onstream Farm Dam node from Geographic Editor

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Right-clicking on any place in the Geographic Editor model interface will display a context menu, which includes the Bulk Change Node Model menu menu item (step 4 in Figure 21). This menu item allows the user to bulk change a group of nodes to onstream farm dams:

• Prepare a location shapefile of the nodes for the farm dams - to facilitate later conversion, these exact locations should have been used during the model building and should already exist as e.g. Confluence nodes in the catchment model
• Right-click to select the the Bulk Change Node Model menu item. This will open the Bulk Change Node Models editor interface (Figure 32). Initially, the contents in the contents of the Nodes Located box and the selected item in the dropdown list of destination node types are empty.
• Click on the button to Load node location shape file (Figure 32). This will display an Open dialogue box, which allows the user to select a prepared location shape file. After the user clicks on the OK button in the Open dialogue box, the names of the matching nodes (e.g. 156, 157) in the Source model will be displayed in the Nodes Located box. These nodes must have the exact locations as defined in the shapefile.  Select Onstream Farm Dam as the target node type from the dropdown list below the Nodes Located box.
• Select Change all loaded nodes  (as in Figure 32) to convert all nodes in the Nodes Located box to the target node type in the dropdown list (e.g. Onstream Farm Dam in Figure 32).
• The user can repeat the above steps to convert nodes to other types if needed. Otherwise, click on the Done button to close the window.

Note: The Bulk Change Node Models tool can also be used to convert the located nodes to other types, such as Supply Points, Gauges, etc. The procedure is the same as above for onstream farm dams, and the user just needs to select the expected node type (e.g. Supply Point) from the dropdown list instead of Onstream Farm Dam.

Figure 3 2 Bulk Change Node Models interface

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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 43)

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Figure 4 3 Farm Dam editor – Dam Information

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The farm dam information is on the default interface of the farm dam editor (Figure 43). The parameters Dam Capacity, Max. Dam Surface Area and Initial Storage Percentage in Figure 4 3 are self-explanatory. Other parameters are described below.

• Diversion Fraction - This parameter indicates how much of the upstream inflow is 'diverted' to pass though through the farm dam and will be included in the water balance calculation for the node. The remaining water will be re-directed (through bypass) 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 input as a percentage or proportion of Dam Capacity by ticking the Use Proportion checkbox. The parameter name will change to Dead Storage Proportion when the Use Proportion checkbox is ticked.  The user can click on the %/proportion button to swap the type between percentage (%) and proportion.

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The allowable range of Dead Storage Volume is between zero and max capacity. Percentage and proportion ranges are from 0 to 100 and 0 to 1 respectively. If the entered values are not within the permitted range, 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 54. “166” in Figure 5 4 is the name of the associated farm dam node.

Figure 5 4 Run error screen for unsuitable input of Dead Storage Volume

• Bypass Flow - defines a low flow/environmental flow bypass requirement for onstream farm dams. Flow is transferred from upstream 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 65.

Figure 6 5 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, a run 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 76.

Figure 7 6 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 issueto zero. If the entered value is negative, the running error will occur (Figure 6). The user then needs to fix this issue.

• Activation Date Enabled and Activation Date- defines whether the farm dam will be ignored in the water balance simulation and when the Source begins to use the data of this farm for water balance simulation if it is active. The setup consists of two steps: (1) ticking on the check box of Enable Active Date will allow the model to use this farm data in the water balance simulation. (2) enter a date in the text box of the Activation Date. From that date, Source will begin to use the data of this farm dam in the water balance simulation until the End Date of the simulation. The entered date will be automatically truncated by the Start Date and End Date during the simulation.

•  If the Activation Date Enabled is not ticked, or it is in the period before the Activate Date (e.g. before 01/01/2000 in Figure 3), the farm dam merely passes on the inflows straight to the outflow without any water balance calculations. The recorders will still be active and record the values during the inactive period, but any calculation-related recorders will be set as zero, and the outflow will equal the inflow. On the date of activation, the node will start functioning as normal.

  Note that two parameters (i.e., Activation Date Enabled and Activation Date) are used instead of one parameter because this feature is only required by the farm dam node. Using two parameters in software development can avoid affecting other parts of Source but only affect the fam dam node.

• 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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Clicking on the Interstation Flow in the left panel of Figure 4 3 will display the Interstation flow parameters in the right panel for the configuration (Figure 87). 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 7 Farm dam editor – Interstation Flow

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Clicking on the Seepage in the left panel of Figure 4 3 will display the Seepage parameter in the right panel for configuration (Figure 98). The parameters can be configured by the constant value or time series from the Data Source.

Figure 9 8 Farm dam editor – Seepage

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Clinking on the Demand in the left panel of Figure 4 3 will display the demand parameters in the right panel for configuration (Figure 109). 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 9 Farm dam editor – demand

e. Rainfall

Clicking on the Rainfall in the left panel of Figure 4 3 will display the rainfall parameters in the right panel (Figure 1110). 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 the Source will convert it to volume by the dam area calculated as the description in section (1) The farm dam information.

Figure 11 10 Farm dam editor – Rainfall

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Clicking on Evapotranspiration in the left panel of Figure 4 3 will display the evapotranspiration parameters in the right panel (Figure 1211). 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 the Source will convert it to volume using the calculated dam area as the description in section (1) The farm dam information.

Figure 12 11 Farm dam editor – Evapotranspiration

The OK button (Figure 43) will save the farm dam setup. The Cancel button will discard the entered parameters.

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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 1312). Clicking on the Onstream Farm Dam in the left panel (Figure 1312) will display the existing values of all editable parameters for all onstream farm dams in the right panel.

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• Dead Storage Set Using Proportion – This is related to the value of Use Proportion checkbox on the Interface (Figure 43). Its change in the Feature Table will decide which one, Dead Storage Volume or Dead Storage Proportion, will be editable in the Feature Table.
• Dead Storage Volume and Dead Storage Proportion - The definitions of both columns are the same as those in Figure 43. However, although both columns are listed in the Feature Table, only one column in each row can be saved. The edited values in cells of column Dead Storage Proportion will be saved if Dead Storage Set Using Proportion(s) in the same rows are selected. Otherwise, the edited values in the cells of column Dead Storage Volume will be saved. After the Feature Table is saved, the remaining cells in another column (either Dead Storage Volume or Dead Storage Proportion) will be automatically converted from the saved cells by Source.
• Dam Surface Area Calculation – which only has two values for selection: Constant or Variable. The value of Constant indicates the option of Constant dam surfaces area using ‘Max. Dam Surface Area’ parameter (Figure 43) will be used in the water balance calculation. Variable indicates the option Allow dam surface area to vary according to dam volume (Figure 43) will be used in water balance calculation.
• Is Custom Param – shows the value of the check box Custom Equation Parameters (Figure 43). Its value only works when Variable is selected in the column Dam Surface Area Calculation.
• SA-Volume EQN A Factor - the value for A Factor (Figure 43). Its value will be used only when Dam Surface Area Calculation column is Variable and Is Custom Param is ticked.
• SA-Volume EQN B Factor - the value for B Factor (Figure 43). Its value will be used only when Dam Surface Area Calculation column is Variable and Is Custom Param is ticked.

The user can directly edit all parameters from Feature Table.

Figure 13 12 Farm dam configuration for multiple farm dams through the Feature Table

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To migrate older Source farm dam projects requires first u pgrading upgrading pre-Source version 5.30 models (those using the Farm Dams plugin) to Source version 5.20:

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The upgraded project can then be opened in later versions of Source without the Farm Dams plugin installed, and Source will automatically migrate the required functionality.