Swales: TTT

Swale element in TTT menu

Weir elements may be incorporated as check dams for detailed design

It is recommended that grass and enhanced grass swales be modelled using the 'Swale' element in the TTT. A 'swale' has to connect two existing elements within the TTT Bioswales or dry swales, which have amended filter media, should be modelled as bioretention cells. The alternative is to use the 'enhanced swale' within the LID toolbox, but this incorporates fewer design parameters (and doesn't account for infiltration).

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)
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 (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
Cross 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.
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

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%, use Check dams to create temporary ponding, increase infiltration, and slow flow to reduce erosion.
Swale side slopes (run/rise)	Suggested value of 3 or 4 if design permits.

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.

Structures constructed of a non-erosive material, such as suitably sized aggregate, wood, gabions, riprap, or concrete; used to slow runoff water. Can be employed in practices such as bioswales and enhanced grass 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.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

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.

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

Penetration of water through the ground surface.

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

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 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.

(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).