Difference between revisions of "Permeable pavements: Sizing"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
Line 28: Line 28:


----
----
Where the storage reservoir depth is fixed or constrained the footprint area of the water storage reservoir, A<sub>r</sub> can be calculated:
Where the storage reservoir depth is fixed or constrained the footprint area of the water storage reservoir, A<sub>r</sub> can be calculated:<br>
<math>A_{r}=\frac{i \times D \times Ai}{(n\times d_{r})+f'D}</math>
<math>A_{r}=\frac{i \times D \times Ai}{(n\times d_{r})+f'D}</math>


When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used:
When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used:

Revision as of 18:09, 10 December 2021

The following calculation is used to size the stone storage bed (reservoir) used as a base course. It is assumed that the footprint of the stone bed will be equal to the footprint of the pavement. The following equations are derived from the ICPI Manual [1]

For full infiltration design, to calculate the total depth of clear stone aggregate layers needed for the water storage reservoir[edit]

The equation for the maximum depth of the stone reservoir (dr, max, mm) is as follows:

Where:



  • D = Duration of the design storm event event (hr)
  • i = Intensity of the design storm event (m/hr)
  • R = Ai/Ap; the ratio of impervious contributing drainage area (Ai) to permeable pavement area (Ap). Note that the contributing drainage area should not contain pervious areas. R should not normally exceed 2.
  • f' = Design infiltration rate of underlying native soil (mm/hr)
  • n = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. clear stone)

On highly permeable soils (e.g., infiltration rate of 45 mm/hr or greater), a maximum stone reservoir depth of 2 metres is recommended to prevent soil compaction and loss of permeability from the mass of overlying stone and stored water.

For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe[edit]

For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (dr) can be calculated as follows:

Where:

  • f' = Design infiltration rate (mm/hr), and
  • t = Drainage time (hrs), e.g. 72 hours, check local regulations for drainage time requirements.
  • n = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. clear stone)

Where the storage reservoir depth is fixed or constrained the footprint area of the water storage reservoir, Ar can be calculated:


When sizing the area of permeable paving based on the contributing drainage area, the following equation may be used: Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle A_p=\frac{Q_c\times A_c}{V_R\times (d_p – P + (q'\times t))}}

Back to Permeable pavements

  1. Smith, D. 2006. Permeable Interlocking Concrete Pavements; Selection, Design, Construction, Maintenance. 3rd Edition. Interlocking Concrete Pavement Institute. Burlington, ON.