Background

Farm dams functionality in Source is designed to simulate the impact of farm dams on streamflow at a sub-catchment scale. For each farm dam, Source conducts a water balance, including inflows, rainfall, evaporation, seepage, water usage (demand), and overflow (spill) components (Figure 1) in each time step. This means that, for each time step (e.g., a day), each water balance component is accounted for in Source for every farm dam modelled. 

Figure 1 Water balance of a farm dam

Acknowledgments

The Western Australian Department of Water would like to thank SKM for the assistance in the preparation of this document. 

Disclaimer

The Western Australian Department of Water has produced the original document. Any representation, statement, opinion or advice expressed or implied in this publication is made in good faith and on the basis that the Western Australian Department of Water and its employees are not liable for any damage or loss whatsoever which may occur as a result of action taken or not taken, as the case may be in respect of any representation, statement, opinion or advice referred to herein. Professional advice should be obtained before applying the information contained in this document to particular circumstances.

Modelling the farm dam in Source

Create node(s) for the farm data in the Source model

The creation of the farm dam node (i) in the river system model from the Schematic editor and (ii) the catchment model from the Geographic Editor is different. The methods for both models are described separately below.

From Schematic Editor:

The icon of the green triangle on the Node Palette represents the onstream farm dam. Dragging the icon from the Node Palette to the Schematic Editor interface can create a farm dam node. The accurate coordinates of farm dams’ positions are not required.

From Geographic Editor

There are two ways to add the onstream farm to the catchment model from the Geographic Editor

1. Change an existing model element to an onstream farm dam:

The first step is to select an existing model element (e.g., a Confluence node) and right-click on it, and the context menu then will be displayed. Clicking on the menu item of Change Node Model (1 in Figure 2) on the context menu will display the additional context menu, and further clicking on the Onstream Farm Dam option (2 in Figure 2) will change the node to Onstream Farm Dam that is displayed as a green triangle icon. The user can use the menu item of Add Node (3 in Figure 2) to add a Confluence node for node model change if needed. The accurate coordinates of farm dams’ positions may not be essential.

Figure 2 Modeling Onstream Farm Dam node from Geographic Editor

2. Bulk Change Node Models for onstream farm dams:

Right-clicking on any place in the model interface of Geographic Editor will display a context menu, which includes the menu item Bulk Change Node Model (4 in Figure 2). This menu item allows the user to change a group of nodes to onstream farm dams at once. The procedure is as follows:

• Prepare a location shapefile of the nodes for the fam dams - These locations should be already used during the model building and exist as nodes in the catchment model.
• Open Bulk Change Node Models editor - Clicking on the menu item Bulk Change Node Model will show the interface of the Bulk Change Node Models editor (Figure 3). Initially, the contents in the Nodes Located box and the selected item in the dropdown list of destination node types are empty.
• Configure Bulk Change Node Models editor - Clicking on the button of Load node location shape file (Figure 3) will display the Open dialogue box, which allows the user to select the prepared location shape file. After the user clicks on the OK button on the Open dialogue box, the node names (e.g. 156, 157) in the Source model will be displayed in the Nodes Located box, and those nodes have the exact locations defined in the shapefile.  The user must select Onstream Farm Dams from the dropdown list below the Nodes Located box.
• Convert the selected nodes to destination node type – Clicking on the button of Change all loaded nodes in Figure 3 will convert all nodes in the Nodes Located box to the selected node type in the dropdown list (e.g. Onstream Farm Dams in Figure 3).
• The user can repeat the above steps to convert nodes to other types. Otherwise, clicking on the Done button can close the window.

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

Figure 3 Bulk Change Node Models editor

Configure Onstream Farm Dams node(s) in the Source model

There are two ways to configure the parameters of the 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 dam. Clicking on Edit from the selected farm dam node will open the farm dam editor (Figure 4)

(1) The farm dam information

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

• Diversion Fraction - decides how much the “upstream” flow, which includes both the upstream flow and interstation inflow, will be involved in the water balance calculation in the edited farm dam. The remaining water in the “upstream” flow will be diverted directly to the downstream flow.
• Bypass Flow - defines the maximum capacity of the flow bypass from the “upstream” flow directly to the downstream of the farm dam. 
• 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.

Figure 4 Farm dam editor – Dam Information

(2) Interstation Flow:

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.

Clinking 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 5). 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 5 Farm dam editor – Interstation Flow

(3) 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.

Clinking on the Seepage in the left panel of Figure 4 will display the Seepage parameter in the right panel for configuration (Figure 6). The parameters can be configured by the constant value or time series from Data Source.

Figure 6 Farm dam editor – Seepage

(4) Demand

Clinking on the Demand in the left panel of Figure 4 will display the demand parameters in the right panel for configuration (Figure 7). 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 7 Farm dam editor – demand

(5) Rainfall

Clinking on the Rainfall in the left panel of Figure 4 will display the rainfall parameters in the right panel (Figure 8). 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 8 Farm dam editor – Rainfall

(6) Evapotranspiration

Clinking on the Evapotranspiration in the left panel of Figure 4 will display the evapotranspiration parameters in the right panel  (Figure 9). 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 9 Farm dam editor – Evapotranspiration

Clicking on the OK button in Figure 4 will save the setup of the farm dam. The Cancel button will discard the entered parameters.

For all Onstream Farm Dams nodes

Source 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 10). Clicking on the Onstream Farm Dam in the left panel (Figure 10) will display the existing values of all editable parameters for all onstream farm dams in the right panel.

The Feature Table headlines of all parameters are the same as (or similar to) those names described in the above section of For an individual node of Onstream Farm Dam except for four headlines below:

• 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 4) will be used in the water balance calculation. Variable indicates the option Allow dam surface area to vary according to dam volume (Figure 4) will be used in water balance calculation.
• Is Custom Param – shows the value of the check box Custom Equation Parameters (Figure 4). 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 4). 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 4). 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 10 Farm dam configuration for multiple farm dams through the Feature Table

Recorders of Onstream Farm Dam node

Some recorders for the onstream farm dam in Source are described below to clarify the difference between the similar recorders.

Migrate the Source model using the FarmDams plugin across to CORE

The onstream farm dam functionality in Source can be accessed from the plugin of FarmDamsplugin before Version V5.21 or CORE without the Farm Dams plugin after Version V5.21. Only Source projects using the Farm Dams plugin in Version 5.20 can be automatically mitigated to the project with farm darn functionality from CORE.  The users need to upgrade their old models ( using the Farm Dams plugin) to Source V5.20 with the farm dam plugin first and save it as the upgraded project. The user  then opens the upgraded project in later versions such as late 5.21 without the Farm Dams plugin, and the Source will autumnally migrate the farm dam functionally in the project file from plugin to CORE.