Drainage Calculators
Stormwater hydrology, IDF curves, drain sizing, culvert design, and detention ponds per MSMA 2nd Edition and JPS guidelines.
Rational Method — Peak Flow
Peak stormwater flow using MSMA Rational Method (Q = CiA/360). Valid for catchments ≤ 80 ha.
MSMA 2nd Ed, Ch 2, Eq. 2.3
IDF Curve — Rainfall Intensity
Rainfall intensity from MSMA Eq. 2.2 with official λ/κ/θ/η constants for 13 major Malaysian stations.
MSMA 2nd Ed, Table 2.B1
Time of Concentration (Tc)
Compute tc using overland + drain flow time per MSMA Table 2.1 (QUDM, 2007). Slope in %.
MSMA 2nd Ed, Ch 2, Table 2.1
Manning's Drain Sizing
Size rectangular & trapezoidal open channel drains with MSMA velocity/freeboard checks.
MSMA 2nd Ed, Ch 14 & 16
Culvert Hydraulic Design
Preliminary box (RCBC) and pipe (RCP) culvert sizing (full-flow approximation).
MSMA 2nd Ed, Ch 18
Detention Pond Volume
Volume estimate using pre/post-development Rational Method flows over storm duration.
MSMA 2nd Ed, Ch 7
On-Site Detention (OSD)
Simplified PSD + SSR sizing using MSMA Table 5.A1 Five Regions with impervious % interpolation.
MSMA 2nd Ed, Ch 5 §5.8.3
Rainwater Harvesting Tank
Tank sizing per MSMA Eq. 6.1 plus AARY for 17 Malaysian towns (Table 6.4).
MSMA 2nd Ed, Ch 6
Bioretention System
Filter bed area sizing (Eq 9.1 / 9.2) for water quality treatment — 3-month ARI WQv.
MSMA 2nd Ed, Ch 9