Project Review and Mapping
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Set up culverts using Rating Tables and Culvert Equations using QGIS and the FLO-2D Plugin.
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Set the video playback speed to 2x to complete the lessons faster.
Load Results and Maps
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.. note:: Place holder video. Final version not ready.
.. raw:: html
This lesson introduces the setup of hydraulic structures in FLO-2D using QGIS. It includes visual styling, elevation considerations, and labeling, preparing the dataset for modeling.
Step 1: Load Hydraulic Structures
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- Load the **hydraulic_structures.shp** shapefile into your QGIS project.
- Modify the layer style:
- Change the symbol to an **arrow line** for visualizing flow direction.
- Adjust the **color** to make structures more visible.
.. note::
Arrows indicate the direction of flow: inlet is the first vertex, outlet is the last.
Step 2: Understand Elevation Requirements
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- Each hydraulic structure must move flow from an **inlet** to an **outlet** grid element.
- Elevations must match the **invert elevations** of culverts and connected features.
.. tip::
Use the **Identify Features** tool on your elevation raster and grid layers to find elevation mismatches.
Common adjustments:
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- **Move** the inlet/outlet point to the nearest correct elevation cell.
- Use **elevation correction polygons** where necessary to model invert slopes and street flow paths.
- Consider **stilling basins** or **weirs** where sediment control is necessary.
Step 3: Examples of Flow Adjustments
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- Evaluate upstream/downstream cells:
- Example: Move from a 1428 ft grid cell to a 1425 ft cell to match invert.
- Ensure continuity along **trapezoidal channels** feeding culverts.
Step 4: Assign Structures to Cross-Sections
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- For culverts connecting to channels:
- Always assign outlet to the **left bank** of the cross-section.
- FLO-2D exchanges discharge to cross-sections, not grid elements.
.. note::
Right bank assignments can cause ambiguity. Use left bank consistently.
Step 5: Label the Hydraulic Structures
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- Open **Layer Properties > Labels** tab.
- Label each structure with the **structure_name** field.
- Recommended settings:
- Font size: **12 pt**
- Font color: **white** or a visible contrast color
Step 6: Check Attribute Table Fields
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- Ensure the attribute table contains:
- ``structure_name``
- ``structure_type`` (floodplain-to-floodplain, floodplain-to-channel, etc.)
- ``tailwater_switch`` (default = 0)
- ``head_reference_elevation``
- Additional culvert parameters (used in the advanced setup)
Structure Types:
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- **Floodplain to Floodplain**: Flow between two grid cells
- **Floodplain to Channel**: Connect to left bank of a cross-section
- **Channel to Channel**: Set up previously in the Channel lesson
Next Step
---------
In the next lesson, you'll learn how to define hydraulic structure parameters in the layer attribute table and export your model data.
Review a Project Run
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.. note:: Place holder video. Final version not ready.
.. raw:: html
In this lesson, we begin working with **hydraulic structures** in FLO-2D. This is the first part of a two-part lesson focusing on how to display and prepare culvert data for modeling using rating tables. The second, more advanced lesson will cover converting culverts to use the **Generalized Culvert Equation (CT)**.
Step 1: Add the Hydraulic Structures Layer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Drag and drop the hydraulic structure shapefile onto your QGIS map canvas.
- The default symbology may be muted. You should:
- Change the line style to **arrow** to indicate flow direction.
- Apply a brighter fill color for better visibility.
.. note::
Arrow symbology in QGIS applies an arrowhead at the last vertex of the polyline. This means:
- **First vertex** = Inlet
- **Second vertex** = Outlet
Step 2: Understand Flow Direction
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- FLO-2D hydraulic structures move water **from inlet to outlet**.
- Even when reverse flow (e.g. tailwater conditions) is possible, always define flow in the expected direction.
Step 3: Elevation Considerations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Grid cell elevations are averages of underlying raster pixels.
- Culverts often require **invert elevations**, not average elevations.
- Use the **Identify Features** tool on the elevation raster to get correct values.
- You may need to modify grid cell elevations at the **inlet**, **outlet**, and along small channels leading to the structures.
.. tip::
Use elevation correction polygons to modify grid cell elevations to match actual invert elevations.
Examples:
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- One culvert shows 1409 (grid cell average) while the actual invert is 1405.
- Another structure has a weir at elevation 1396.5 to separate trash from flow before it enters a stilling basin.
Step 4: Label Hydraulic Structures
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- Open the attribute table and confirm each structure has a valid name.
- Use the `structure_name` field to label structures on the map.
- Adjust label font size and color for clarity.
Step 5: Classify Structure Types
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Hydraulic structures can connect:
- Floodplain to floodplain
- Floodplain to channel (assign to **Left Bank** only)
- Channel to channel
Make sure structure types and flow paths are clearly identified.
.. important::
FLO-2D links structures to **cross-sections**, not banks. Always connect to the **Left Bank** when targeting channels.
Step 6: Next Steps
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- All structures are initially set up with **rating tables**.
- The tailwater switch is typically left at `0` (inlet-controlled flow).
- More parameters (head reference, n-value, etc.) will be discussed before data export.
.. note::
The second part of this lesson will cover converting culverts to **CT structures** using the Generalized Culvert Equation.