Bioretention System — Filter Bed Sizing

Ref: MSMA 2nd Edition (2012), Chapter 9 — Bioretention System; Eq. 9.1–9.2, Tables 9.6–9.7

MSMA Ch 9 requires the bioretention system to hold the Water Quality Volume (WQv) from a 40 mm (3-month ARI) storm and drain it within 24 hours through a filter media with ≥ 13 mm/hr permeability. Minimum footprint is 3 m × 6 m (18 m²) per Table 9.6.

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Af = (WQv × df) / [k × (hf + df) × tf]

Ref: MSMA 2nd Edition (2012), Chapter 9 — Bioretention System; Eq. 9.1–9.2, Tables 9.6–9.7

WQv = A_catch × C × 0.040 (runoff from 40 mm 3-month ARI storm)

Water Quality Volume (3-month ARI = 40 mm)

Eq 9.1 (underdrain): k = permeability of filter media (m/day)

Eq 9.1 — with underdrain

Contributing Catchment

Contributing Catchment Area (m²)

Area draining to the bioretention cell

Runoff Coefficient (C)

MSMA Table 2.5 — same as Rational Method

System Configuration

Impermeable (with underdrain)Permeable (no underdrain)

Filter Bed Depth (df) (m)

MSMA Table 9.6: 0.45–1.0 m planting soil depth

Average Head Above Filter (hf) (m)

Typically half of ponding depth (0.075–0.15 m)

Design Drain Time (tf) (day)

Maximum 1 day per MSMA §9.3.1

Filter Media Permeability (k) (m/day)

Table 9.7: Sand 1.0, Bioretention soil 0.312, Leaf compost 2.65

Table 9.7 — Media permeability k (m/day):

Sand: 1
Peat: 0.6
Leaf Compost: 2.65
Bioretention Soil (engineered): 0.312

Water Quality Volume (WQv)

—m³

Engineering aid only — final design must be endorsed by a registered PE under BEM.

Filter Bed Surface Area

—m²

Engineering aid only — final design must be endorsed by a registered PE under BEM.

Disclaimer: This output is an engineering calculation aid only and does not constitute a final or endorsed design. All designs submitted to Malaysian authorities must be endorsed by a registered Professional Engineer (PE) under the Board of Engineers Malaysia (BEM) in accordance with the Registration of Engineers Act 1967.