|
Trash screens can be represented by applying additional head losses and blockage effects in accordance with the QUDM 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 example, a rectangular shaped screen located upstream or downstream of a culvert can be represented as a short zero length RF (rectangular culvert with fixed losses) type channel in the 1d_nwk GIS layer. 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 %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 attachedlocated directly to the culvert inletupstream or outlet,downstream theof losses are applied to thea culvert itself. For example, a rectangular shaped screen located upstream or downstream of a culvert can be represented as a short zero length RF (rectangular culvert with fixed losses) type channel in the 1d_nwk GIS layer. 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 %blockage option.
{| class="wikitable"
*
! style="text-align:center;" | Case
* 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 %blockage option.<br>
! 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 CF, IF or RF<sup>3</sup> 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 CF, IF or RF<sup>3</sup> 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
|}
Note:
# Net flow area should account for the effect of screen bars and any debris blockage.
# Values of ''K_t'', ''K_t*'', ''C_d'', ''A_r'', and ''K_exit'' should be obtained from the relevant QUDM equations and tables.
# 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>
[[File:Trash screen schematic.png|frameless]]<br><br>
|