Swales: TTT

Swale element in TTT menu

thumb|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)

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
Upstream Invert Offset (m)	Depth of swale invert above node invert at inlet end of the swale
Downstream Invert Offset (m)	Depth or elevation of the swale invert above the node invert at the outlet end of the swale
Depth (m)	Depth of the swale
Bottom Width (m)	Bottom width of the trapezoidal swale (i.e., open channel) 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
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

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated open channel, with check dams; designed to convey, treat and attenuate stormwater runoff.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

The point, location, or structure where wastewater or drainage discharges from a sewer pipe, ditch or other conveyance to a receiving body of water.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

A compacted earthen wall that diverts runoff or creates shallow ponding of runoff. In some cases, runoff ponds behind the berm and gradually flows through it or is infiltrated.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).