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TUFLOW 1D Channels and Hydraulic Structures: Difference between revisions

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== What entry/exit loss and contraction coefficients should I use for 1D culverts? ==
We don’t provide hard recommendations on the exit and entry losses to use for culverts as we have found different organisations around the world, typically government, have their own guidelines for different types of inlets configurations and require these to be used, for example, the <u>[https://www.ipwea-qnt.com/products-resources/qudm/ Queensland Urban Drainage Manual]</u> (QUDM). However, it is very important to understand how losses are applied and that different 1D solvers may treat them differently. For cross-checking your results from any hydraulic modelling software, a simple calculation applying the entry and exit losses (allowing for any automatic adjustments as discussed below) to the computed head (V2/2g), plus allowing any surface roughness losses (Manning's equation) for longer culverts, is the best practice for culverts flowing in a sub-critical flow condition (i.e. downstream controlled flow).<br>
 
For the entrance loss values, the approach should be to use values as quoted in the literature or guidelines for the inlet shape and design unless there is evidence to use another value (e.g. comparison with reliable calibration data would indicate different energy losses).
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A scruffy dome is a type of dome inlet screen installed over a drop inlet, commonly used in stormwater systems. These inlets can be modelled in TUFLOW using a 1D Q type pit with a depth–discharge curve that reflects the hydraulic performance of the dome.
 
[https://www.ipwea-qnt.com/products-resources/qudm/ <u>QUDM</u>] recommends using the lesser of the weir flow or orifice flow equations to define inlet capacity (see Section 7.5.4). A blockage factor is also recommended to account for potential debris build-up during flood events (see Table 7.5.1 Provision for blockage at kerb inlets). This factor may vary depending on local guidelines, so regional standards should be consulted.
 
Once the rating curve is calculated, it can be added to the pit inlet database and linked to the Q type pit.
<br>
 
<ol>
[[File:How do I model a scruffy dome in TUFLOW.png|frameless]]
[[File:How_do_I_model_a_scruffy_dome_in_TUFLOW.png|300x300px]]<br>
</ol>
 
== How can trash screens be represented? ==
A trash screen is a physical barrier, typically made from bars or mesh, placed at the inlet or outlet of a culvert, pipe, or channel to prevent debris from entering or exiting the structure.
 
Trash screens can be represented by applying additional head losses and blockage effects in accordance with the<u>[https://www.ipwea-qnt.com/products-resources/qudm/ QUDM]</u> guidance. The approach depends on the location of the screen and the degree of blockage, as summarised in the table below.
 
Possible use cases include:
Where the screen is attached directly to the culvert inlet or outlet, the losses are applied to the culvert itself. For screens located upstream or downstream of the culvert, a short zero length channel should be set up as an RF (rectangular culvert with fixed losses) type in the 1d_nwk GIS layer to represent the screen. In both cases, the net flow area should be reduced to account for the bars and any debris blockage, either by adjusting the flow area directly or by using the %blockage option.
 
* Where the screen is attached directly to the culvert inlet or outlet, the losses are applied to the culvert itself.
<span style="color:red">Under Construction => '''<span style="color:black">Recommended setup for representing trash screens (based on QUDM guidance).</span>'''</span>
* Where the screen is located upstream of a culvert inlet or downstream of a culvert outlet, it can be modelled as a short zero length CF, IF, or RF channel before (upstream) or after (downstream) the culvert.
{| class="wikitable"
* In all cases, the net flow area should be reduced to account for the bars and any debris blockage, either by adjusting the flow area directly or by using the pBlockage attribute.
! style="text-align:center;" | Case
! Screen
Type
! Screen Location
! Screen Type
! Flow Area (Width_or_Dia, Height)
! Form_Loss
! EntryC_or_WSa
! ExitC_or_WSb
! QUDM Reference
|-
| style="text-align:center;" | '''A'''
| rowspan="2" style="text-align:center;" | Inlet || Upstream of culvert inlet || Zero length RF channel before culvert || rowspan="5" | Set to net flow area<sup>1</sup> (or use %blockage) ||''K_t*'' || style="text-align:center;" | — || 0.0 (or 0.001)<sup>4</sup> || Sec. 12.5.6, Eq. 12.1 & 12.2
|-
| style="text-align:center;" | '''B''' || At culvert inlet || Losses/blockage applied to culvert ||''K_t'' (if ''K_t'' > ''K_e'') || 0.0 (or 0.001)<sup>4</sup> || style="text-align:center;" | — || Sec. 12.5.6, Eq. 12.3 – 12.5
|-
| style="text-align:center;" | '''C'''
| rowspan="3" style="text-align:center;" | Outlet || Clean screen at outlet || rowspan="3" | Zero length RF channel after culvert ||''C_d A_r'' (''C_d'' ≈ 1.5 round bars, 1.9 rectangular bars) || style="text-align:center;" | — || ''K_exit'' || Sec. 12.5.7, Eq. 12.8
|-
| style="text-align:center;" | '''D''' || Partially blocked screen at outlet || rowspan="2" |''K_t*''|| rowspan="2" style="text-align:center;" | — || 1.0 || Sec. 12.5.7, Eq. 12.9
|-
| style="text-align:center;" | '''E''' || Downstream of outlet ||''K_exit'' || Sec. 12.5.7, Eq. 12.10
|}
 
For example, the image below could be represented as a rectangular shaped screen located upstream or downstream of a culvert, modelled as a short zero length RF (rectangular culvert with fixed losses) channel using a 1d_nwk GIS layer.
Note:
<ol>
[[File:Trash_screen_schematic.png|alt=|300x300px]]
</ol>
 
== How can fishway baffles in a culvert be modelled? ==
# Net flow area should account for the effect of screen bars and any debris blockage.
<span style="color:red; font-weight:bold;">UNDER CONSTRUCTION</span>
# Values of ''K_t'', ''K_t*'', ''C_d'', ''A_r'', and ''K_exit'' should be obtained from the relevant QUDM equations and tables.
# ''RF'' = rectangular culvert with fixed losses. The F flag ensures specified inlet and outlet losses are applied without default adjustments (see Table 5.2 in the <u>[https://docs.tuflow.com/classic-hpc/manual/latest/ TUFLOW Manual]).</u>
# Attribute set to 0 (or 0.001 if a value of 0.0 sets this to the default value). <br><br>
 
Fishway baffles are barriers inside a culvert that slow the water and help fish swim through.
[[File:Trash screen schematic.png|frameless]]<br><br>
 
These approaches could be used to represent them inside a model:
 
* Short culvert with smaller opening.
** A short culvert section is added with its bottom and top levels set to match the fish baffle. The width is set to the total width of the fish passage gaps. This represents the reduced space for water to pass through.
 
* Two culverts in a row.
** Two culverts are connected in series. The first is the normal culvert, and the second is a very short culvert with a smaller opening sized to the fish baffle gaps.
 
For both options, sensitivity testing is recommended because at low flows the way the culvert is defined can change the results. These methods do not include turbulence or detailed 3D water movement around the baffles. If accurate fish passage flows are required, a CFD 3D model can be used to determine the flows and those flows can then be applied using a 1D Q type channel.
<ol>
[[File:Rectangular culvert baffled.png|alt=|300x300px]]
</ol>
<br>
 
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