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== Introduction ==
This page details the method for using SAGA to create the GIS based boundary layer files. Once the GIS layers are setup (detailed in this page), these are linked to data using a boundary database, (the boundary database is described in ???parthe link<u>[[Tutorial_Module01_Archive#TUFLOW_Boundary_Condition_Database_.28bc_dbase.29 | Module 1 main page]]</u>). We will create three different boundaries:
* Upstream flow boundary
* Downstream water level - flow (stage-discharge) boundary
* Internal flow boundary
 
The first two boundaries are inputtedinput into a 2d_bc type layer. The third boundary (internal flow boundary) will be applied as a source-area boundary in a 2d_SA boundary type layer.<br>
 
== Method ==
===2d_bc typeType boundariesBoundaries===▼
 
We will create the 2d_bc boundaries first. These boundaries are external and will "snap" to the edge of our active model area. Both of these boundaries have been aligned perpendicular to flow direction. <br>
▲===2d_bc type boundaries===
We''Note: willThis createline theorientation 2d_bcis boundariesrecommended first.for These2d_bc boundaries areQT, externalHQ and willHT "snap"boundary to the edge of our active model area. Both of these boundaries should be aligned perpendicular to flow directioninputs. Care should be taken to digitise these boundariesboundary types perpendicular to flow direction (i.e. across the waterwayswaterway). WeIf willthey revieware digitised oblique to the flow patterns(i.e. innot theperpendicular) vicinitymodel of theinstabilities boundariescan laterresult in thissome tutorialcases.''
▲<ol>
<li>Load the DEM '''Module_Data\DEMs\SAGA\DEM_M01.sgrd'''</li>
<li>Load the code polygon '''TUFLOW\model\sagagis\2d_code_M01_003_R2d_code_M01_002_R.shp'''</li>
<li>Create a new map containing these layers, select both of these in the data tab of the workspace window, right click and select "Show".</li>
<li>Load the template 2d bc type layer (2d_bc_empty_L.shp) from '''TUFLOW\model\sagagis\empty\'''.</li>
<li>Save a copy of the template under the '''TUFLOW\model\sagagis''' folder as '''2d_bc_M01_003_L2d_bc_M01_002_L.shp'''. Note that we save the file into the \model\sagagis\ directory not the \model\sagagis\empty\ directory.</li>
<li>Open the newly saved, '''2d_bc_M01_003_L2d_bc_M01_002_L.shp''' add it to the map window and close the template.</li>
The SAGA window should now look something like this:<br>
[[File:Tute M01 Saga 2d bc 1.png|frame|none]]
<br>
<li>The first step is to change the style of the code region to make it a bit easier to work with. Select the '''2d_code_m01_003_R2d_code_m01_002_R''' in the data tab, and then in the settings tab of the object properties window change the following:<br>
* Set the Fill Style to "Transparent", this allows us to see the DEM behind the polygon;
* Set the Outline Size to 2, to make the object more visible;
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Select Apply.</li>
[[File:Tute M01 Saga 2d bc 2.png|frame|none|Modifications above highlighted in bold]]
<li>Before we begin modifying the 2d_bc layer, we need to enable snapping to the 2d_code region. To do this select the '''2d_bc_M01_003_L2d_bc_M01_002_L.shp''' in the data tab, in the settings tab, select the "..." button next to the "Snap to.." text.</li>
[[File:Tute M01 Saga SnapTo1.png|frame|none]]
<br>
<li>In the snap to dialogue, select the 2d_code_M01_003_R2d_code_M01_002_R in the left hand pane and move it to the right. Then select Okay. This layer is ready for input into TUFLOW.</li>
[[File:Tute M01 Saga SnapTo2.png|frame|none]]
<br>
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The type "HQ" designates this as a Water Level ("H") versus Flow ("Q") boundary. This is a stage-discharge boundary condition. If a Name is specified, the user must define this stage-discharge relationship in the boundary database. In this case a water surface slope value is specified via the "b" attribute, this value of 0.01 is in metres per metre and corresponds to a 1% water surface slope. TUFLOW will automatically create a stage-discharge curve flow this location, based on the underlying topography, roughness and specified water surface slope.</li>
[[File:Tute M01 Saga 2d bc 6.png|frame|none]]
<li>In the data tab, right click on the 2d_bc_M01_003_L2d_bc_M01_002_L layer and select "Save".</li>
[[File:Tute M01 Saga 2d bc 7.png|frame|none]]
</ol>▼
 
===2d_sa typeType boundaryBoundary===
The next step is to create an internal inflow boundary using a source-area inflow this is done with a 2d_sa type layer.
<ol>
<li>Load the '''2d_sa_empty_R.shp''' template file from the '''TUFLOW\model\sagagis\empty\'''. Save a copy of the layer in the ''''TUFLOW\model\sagagis\''' directory as '''2d_sa_M01_003_R2d_sa_M01_002_R.shp'''.</li>
<li>Load the newly created 2d_sa_M01_003_R2d_sa_M01_002_R file and close the template file.</li>
<li>Add the layer to a map window with the DEM.</li>
<li>Add a new shape and digitise a polygon around the dam in the lower right (south-east) of the screen.</li>
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<br>
<li>Save the file, by right clicking on it in the data tab and selecting save.</li>
</ol>
 
== Conclusion ==
SAGA has been used to create the a 2d_bc layer that contains an upstream "QT" type inflow boundary and a downstream "HQ" stage-discharge type boundary. A second SAGA layer created from the (2d_sa template) defines an internal source-area boundary. Please return to the tutorial model page [[Module1_test#Define_Boundary_Conditions|here]], where theOur next step is to assign hydrographs to the inflow boundary locations created in this page. Please return to the tutorial model page [[Tutorial_Module01_Archive#TUFLOW_Boundary_Control_File_.28TBC.29_Updates|here]].
▲</ol>
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