The Geographic Wizard is the first in a series of steps required to create a catchments scenario. It consists of a structured sequence of windows (described below) that guides you through the process of defining the catchment area. On completion of the wizard, you will be presented with a node-link network.
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| Note: After a scenario has been created using the wizard, you cannot change the network, ie. you cannot merge or remove sub-catchcments. |
On completion of a step, you can move to the next step by clicking Next and backwards by selecting Back. Note that you cannot go back to the network definition step once you have completed it and moved on to the next step. Cancel allows you to quit the wizard at any time. Note that you will lose all the data entered so far. Once you have completed all steps, click Finish to close the wizard and view the catchment in the Geographic Editor. This figure also shows the action buttons that are visible at the bottom of every screen in the wizard.
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Note: In a catchments scenario, the default node type in Source is a confluence node, where the inputs to the node are the upstream sub-catchment outlets, and the output from the node is the current sub-catchment outlet. Similarly, straight through routing is the default link type in Source. On completion of the wizard, if you wish to change the node model or link type, right click on the confluence node in the Geographic Editor, then choose Change Node Model or the link type respectively, from the contextual menu. For nodes, this lists all the model types available. Choose the required model. |
Welcome screen (Step 1)
The Welcome screen gives some information about the steps within the wizard. These include:
Specifying the catchment network;
Specifying the functional units (FUs) that will be used in the scenario; and
Assigning FU areas.
Name the scenario (Step 2)
Enter a scenario name and an appropriate description, or accept the defaults.
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You must define the sub-catchments and stream network within the catchment, using either a catchment map or Digital Elevation Model (DEM).
The DEM based network generation method requires a DEM, and divides the entire node-link network into sub-catchments based on a user-specified measure of upstream area (sometimes called stream threshold), usually for first-order streams. You can define points on the stream network where confluences between sub-catchment will be formed. The minimum sub-catchment area can also be modified. For example, in a node-link network spanning 1000 km2, entering a stream threshold of 10 km2 will produce approximately 100 sub-catchments.
The minimum sub-catchment area defines the drainage area at which headwater catchments can be formed (also known as drainage threshold or stream threshold). As a result, any link in the generated network will have a total upstream catchment area of at least this amount. Individual sub-catchment sizes will vary and some will be significantly smaller. Notably, where two connected nodes are very close together, the link between them will be short and the corresponding catchment can be very small.
DEMs that have been derived only from contour maps or from other remote sensing technologies such as light detection and ranging (LIDAR) or shuttle terrain radar mapping (STRM) are usually not hydrologically correct. Such DEMs need to be adjusted to represent the flow of streams in the right direction. This is because they create a sense that there are spurious pits in the landscape when actually, none are present. |
The Draw Network method allows you to define the networks manually, by loading a sub-catchment map (a raster with cell values set according to sub-catchment number) and then connecting sub-catchments by clicking and dragging using the mouse. This specifies how those sub-catchments are linked together by the node-link. You should use this method when you have previously defined the boundaries of your sub-catchments, either by using Source or an external program.
You can create a draft of your sub-catchment boundaries using the DEM based network generation method, export those boundaries from Source, edit them in an external GIS program (for example combining or splitting sub-catchments), and then import your edited sub-catchment boundaries back into Source to create a revised sub-catchment node-link network using the Draw Network method. |
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| Note: Any spatial layers displayed in the Geographic Editor must have the same projection as the sub-catchment map or DEM that was used to create the node-link network. |
To use the DEM-based Network Generation method (shown in Figure 1):
- Choose DEM based network generation from the Available Methods drop-down menu;
- Click Load DEM;
- Navigate to the catchment DEM and open it. Source generates a default network based on a minimum sub-catchment area of 50 km2. It is recommended that you specify the minimum sub-catchment area prior to loading a high resolution DEM to reduce computational time;
- Specify a different minimum sub-catchment area in km2, if necessary, and click Recompute Streams. The drainage density depends on the minimum sub-catchment area; and
- Select a desired catchment outlet (a point in the network where all streams in the desired area converge) for investigation by clicking inside the map. This generates a network area broken into sub-catchments (shaded blue), where two sub-catchments converge at a confluence.
Once a DEM has been loaded, you can alter it by right-clicking and choosing the various options available in the contextual menu:
- To add a new catchment outlet, choose Select Cell from the contextual menu, and select another point on the catchment map;
- Pan allows you to move the map up, down, left or right;
- To zoom in, right-click, and choose Zoom In. Drag the mouse to form a zoom box (top right to lower left). To zoom out, double-click anywhere on the map or click Undo Zoom;
- To remove a catchment outlet point, choose Remove Cell;
- Choose Properties to change the attributes of various elements, such as the colour or symbol of nodes; or
- Save allows you to save the map as a .asc file.
Figure 1. Geographic Wizard, Network definition via a DEM
Adding nodes
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Welcome screen (Step 1)
The Welcome screen gives some information about the steps within the wizard. These include:
Specifying the catchment network;
Specifying the functional units (FUs) that will be used in the scenario; and
Assigning FU areas.
Name the scenario (Step 2)
Enter a scenario name and an appropriate description, or accept the defaults.
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You must define the sub-catchments and stream network within the catchment, using either a catchment map or Digital Elevation Model (DEM).
The DEM based network generation method requires a DEM, and divides the entire node-link network into sub-catchments based on a user-specified measure of upstream area (sometimes called stream threshold), usually for first-order streams. You can define points on the stream network where confluences between sub-catchment will be formed. The minimum sub-catchment area can also be modified. For example, in a node-link network spanning 1000 km2, entering a stream threshold of 10 km2 will produce approximately 100 sub-catchments.
The minimum sub-catchment area defines the drainage area at which headwater catchments can be formed (also known as drainage threshold or stream threshold). As a result, any link in the generated network will have a total upstream catchment area of at least this amount. Individual sub-catchment sizes will vary and some will be significantly smaller. Notably, where two connected nodes are very close together, the link between them will be short and the corresponding catchment can be very small.
DEMs that have been derived only from contour maps or from other remote sensing technologies such as light detection and ranging (LIDAR) or shuttle terrain radar mapping (STRM) are usually not hydrologically correct. Such DEMs need to be adjusted to represent the flow of streams in the right direction. This is because they create a sense that there are spurious pits in the landscape when actually, none are present. |
The Draw Network method allows you to define the networks manually, by loading a sub-catchment map (a raster with cell values set according to sub-catchment number) and then connecting sub-catchments by clicking and dragging using the mouse. This specifies how those sub-catchments are linked together by the node-link. You should use this method when you have previously defined the boundaries of your sub-catchments, either by using Source or an external program.
You can create a draft of your sub-catchment boundaries using the DEM based network generation method, export those boundaries from Source, edit them in an external GIS program (for example combining or splitting sub-catchments), and then import your edited sub-catchment boundaries back into Source to create a revised sub-catchment node-link network using the Draw Network method. |
| Info | ||
|---|---|---|
| ||
| Note: Any spatial layers displayed in the Geographic Editor must have the same projection as the sub-catchment map or DEM that was used to create the node-link network. |
To use the DEM-based Network Generation method (shown in Figure 1):
- Choose DEM based network generation from the Available Methods drop-down menu;
- Click Load DEM;
- Navigate to the catchment DEM and open it. Source generates a default network based on a minimum sub-catchment area of 50 km2. It is recommended that you specify the minimum sub-catchment area prior to loading a high resolution DEM to reduce computational time;
- Specify a different minimum sub-catchment area in km2, if necessary, and click Recompute Streams. The drainage density depends on the minimum sub-catchment area; and
- Select a desired catchment outlet (a point in the network where all streams in the desired area converge) for investigation by clicking inside the map. This generates a network area broken into sub-catchments (shaded blue), where two sub-catchments converge at a confluence.
Once a DEM has been loaded, you can alter it by right-clicking and choosing the various options available in the contextual menu:
- To add a new catchment outlet, choose Select Cell from the contextual menu, and select another point on the catchment map;
- Pan allows you to move the map up, down, left or right;
- To zoom in, right-click, and choose Zoom In. Drag the mouse to form a zoom box (top right to lower left). To zoom out, double-click anywhere on the map or click Undo Zoom;
- To remove a catchment outlet point, choose Remove Cell;
- Choose Properties to change the attributes of various elements, such as the colour or symbol of nodes; or
- Save allows you to save the map as a .asc file.
Figure 1. Geographic Wizard, Network definition via a DEM
Adding nodes
Ordinarily, nodes are placed at stream confluences identified in a DEM analysis. It is possible to supplement these nodes and place additional nodes at different locations, typically to identify some point of interest, such as a gauging station of a dam wall. This will also cause additional sub-catchments to be created.
| Info | ||
|---|---|---|
| ||
| Note: In a catchments scenario, the default node type in Source is a confluence node, where the inputs to the node are the upstream sub-catchment outlets, and the output from the node is the current sub-catchment outlet. Similarly, straight through routing is the default link type in Source. On completion of the wizard, if you wish to change the node model or link type, right click on the confluence node in the Geographic Editor, then choose Change Node Model or the link type respectively, from the contextual menu. For nodes, this lists all the model types available. Choose the required model. |
Additional nodes are added from a file of geographic points (eg .MIF, .SHP, .tsd). The points are automatically added to the streams and become nodes and catchment boundaries in the network. There is the potential for this automated process to give erroneous results, so it is important to understand the process used to ‘snap’ to the stream.
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