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Swales: TTT

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TTT.png

Swale element in TTT menu
Outfall element in the TTT menu
Weir elements may be incorporated as checkdams

It is recommended that swales be modelled as a 'Swale', which has it's own menu button in the TTT. For detailed scenarios of enhanced swales, the weir element can be incorporated for checkdams. The alternative is to use the 'enhanced swale' within the LID toolbox, but this incorporates fewer design parameters.

A 'swale' has to connect two existing elements within the TTT. Where another element isn't specified an 'outfall' can be used.

A 'swale' as a conveyance element in the TTT (key parameters)
General Info
Upstream Node Name of node on the inlet end of the swale (higher elevation)
Downstream Node Name of node on the outlet end of the swale (lower elevation)
Length (m) Length of the swale
Manning's Roughness Lower numbers indicate less surface obstruction and result in faster flow.
Suggested range for mown grass (dependent on density) 0.03 – 0.06 [1]
Upstream Invert (m) Depth of swale invert above node invert at inlet end of the swale
Downstream Invert (m) Depth or elevation of the swale invert above the node invert at the outlet end of the swale
X Section
Maximum Depth (m) Depth of the swale
Bottom Width (m) Bottom width of the trapezoidal swale
For a triangular channel, enter 0
Left Side Slope (m/m) Left side slope (run/rise). Suggested value of 3 or 4 if design permits. Enhanced swales
Right Side Slope (m/m) Right side slope (run/rise). Suggested value of 3 or 4 if design permits.
Seepage (mm/hour) Infiltration rate of native (or amended) soil

The TTT also includes an 'enhanced swale' element within the LID toolbox. In version 1.0 this element does not incorporate checkdams and doesn't account for any infiltration capacity.

Parameters for 'enhanced swales' in the LID toolbox of the TTT
Surface
Berm height (mm) This is the height of the curb which constrains the overland sheet flow of water. Where the bottom of the slope discharges directly into another LID facility without impedance, the value is 0.
Surface roughness (Manning’s n) Lower numbers indicate less surface obstruction and result in faster flow.
Suggested range for mown grass (dependent on density) 0.03 – 0.06 [1]
Surface slope (%) If the slope > 3%, consider using small Checkdams or weirs to permit temporary ponding, increase infiltration, and slow flow to reduce erosion.
Swale side slopes (run/rise) Suggested value of 3 or 4 if design permits Enhanced swales
  1. 1.0 1.1 Oregon State Univ., Corvallis. Dept. of Civil, Construction and Environmental Engineering.; Environmental Protection Agency, Cincinnati ONRMRL. Storm Water Management Model Reference Manual Volume I Hydrology (Revised). 2016:233.https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100NYRA.txt Accessed August 23, 2017.