DESIGN OF DRAINAGE SYSTEM

BASED ON MASMA

INTEGRATED DESIGN PROJECT –IDP (ECM506)

BY
IR.BASIR NOORDIN
 -COURSE OUTCOMES-
DRAINAGE DESIGN

At the end of the course, the students should be able to:-

a. undertake problem identification, formulation and solution through

analyzing and solving complex design problem.

b. Use the design standards with consideration of real world constraint

in particular the environmental responsibilities of professional
engineer and matters related to economic, legislation, lifespan, etc.

08/12/2017
 CONTENTS
1. INTRODUCTION
Guidelines to be used
2. DESIGN CONSIDERATION
Time of concentration
Inlet Time to
Manning’s roughness
Channel Flow Time tf
Minimum tc
Rainfall intensity
Return period
Short duration storm
Runoff coefficient
Calculation worksheet – example
3. DESIGN PROCEDURES
4. ANALYSIS/CALCULATION – EXAMPLES
5. DETAIL DRAWINGS
 INTRODUCTION
GUIDELINES TO BE USED :
Manual Saliran Mesra Alam Malaysia
Urban Stormwater Management Manual for M’sia
http://www.water.gov.my
MASMA
1. 40 CHAPTERS
• OPEN DRAN
• CULVERT
• DRAINAGE PIPE
• SILT TRAP
• DETENTION POND
• ETC
 DESIGN OF DRAINAGE (SCOPE OF WORK)
1. Site visit : to know the existing site condition
• existing drainage system (type, size, material), existing levels, existing slopes, existing
structures, condition on surrounding area, maximum/minimum flood level, etc
2. Information to be used during site visit :
• key plan, location plan, site plan, architectural plan, survey plan
3. Liaison with local authority/ (Basic data required from local authority for planning &
design of drainage system :
• requirements on submission or guidelines to be followed
• available master plan of the development area, history on the flood level, maximum &
minimum flood level, rainfall intensity, enquiring for existing suitable discharge point with an
appropriate level,

4. Design : use all the information from above for detail design
Refer architectural plan/site plan/location plan/survey plan :
• is there any drainage system stated around the building or outside building?
• identify the possibility of discharge point (check the level)
• identify the starting point of the drainage system, proposed the most suitable alignments of
the drainage system so that the water from the proposed building/project/surrounding area can
be discharged or connected to the proposed discharge point. (check the proposed
platform/road level)
• refer design consideration
• prepare drainage calculation
• prepare drainage layout plan
• prepare drainage detailing
DESIGN CONSIDERATIONS
 Time of Concentration
tc = t0 + tf Refer MSMA Sec.14.4
Upstream divide

t0
• t0 = overland flow time (inlet time)
• tf = channel flow time tf

• Typically small catchments (<50km2) are more

likely to have constant intensity over entire area, and
hence travel time is relatively short (tc < 20min).
 Inlet Time t0
• MSMA Eq. 14.1 (Friend’s formula)

107nL1/ 3 t0 = sheet flow time (min)

t0  L = sheet flow length (m)
S n = Manning’s coefficient
S = surface slope (%)

(MSMA Sec.14.4.2(C))
In urban drainage, inlet time is primarily roof drainage
flow time which is very small and considerably uncertain
– hence, a minimum of 5min may be adopted.
Manning’s roughness
 Channel Flow Time tf
MSMA Eq. 14.4 a & b (Manning’s eq.)

L tf = channel flow time

tf  L = channel length
V
V = assumed velocity

Generally, V > 0.6m/s to avoid water ponding.

 tc for Natural Catchment
(with mixed flow path)

MSMA Sec.14.4.3 (Bransby-Williams’ Eq.)

Fc L
tc 
A1/10S 1/ 5

tc = time of concentration (min)

L = catchment length (from outlet to upstream divide) (km)
Fc = conversion factor = 58.5
S = slope of stream flow path (m/km)
A = catchment area (km2)
Minimum tc
 FREEBOARD
Clause 26.3.5 page 26-4 (MASMA)
The depth of an open lined drain shall
include a minimum freeboard of 50mm
above the design storm water level in
the drain
 VELOCITIES
Clause 26.3.6 page 26-5 (MASMA)

To prevent sedimentation and vegetative growth, the minimum

average flow velocity shall not be less than 0.6 m/s.
The maximum average flow velocity shall not exceed 4.0 m/s.
For flow velocities in excess of 2 m/s, drains shall be provided
with a 1.2 m high handrail fence or covered with solid or grated
covers for the entire length of the drain for public safety.
 Rainfall Intensity Qp = C I A

MSMA Equation 13.2

ln I = a + b ln t + c (ln t)2 + d (ln t)3

where t = tc
a,b,c,d are constants obtained from Appendix 13.A
MSMA Appendix 13.A
 Return Period
(Annual Recurrence Interval, ARI)
 Short Duration Storm
MSMA Section 13.2.7

Appendix 13.A is only valid for 30 < t < 1000min

For shorter duration,
Pt = P30 – FD (P60 – P30) 5 < t < 30min

where Pt is the rainfall depth for a duration t

P60 & P30 can be obtained from Appendix 13.A
FD can be obtained from Table 13.3
Hence I = Pt / t
 2-yr ARI Daily Rainfall Map
(Figure 13.3, MSMA)

Table 13.3
2
P24 (mm)
Duration
(min) West Coast East Coast
<100 120 150 >180 All
5 2.08 1.85 1.62 1.40 1.39
10 1.28 1.13 0.99 0.86 1.03
15 0.80 0.72 0.62 0.54 0.74
20 0.47 0.42 0.36 0.32 0.48
30 0.00 0.00 0.00 0.00 0.00
1.0

0.9
Runoff Coefficient

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

MSMA Design Chart 14.3, 14.4

0
1.0

0.9

0.8

0.7

0.6

0.5

For I > 200mm/h

0.4

interpolate linearly to C = 0.9

0.3
at I = 400mm/h
0.2

0.1

0
200 300 400
 tcritical = (tc)max Refer MSMA Sec.14.4.2

1. Estimate tc
2. Determine I
3. Determine C
4. Calculate Qp A
5. Design drain tf
t0
B tc = t 0

tf

C t0
D
tf tf
tc1 , tc2
E t0 = tcritical
tc
 Qp = C I A

Moving downstream,
tc (hence t) , I , A  A
tf = 4min
 Qp 
t0 = 5min
B
t0t=
c =9min
9min

tf = 4min
t0 = 5min
D C
tf = 6min tf = 4min
tc1 = 13min
E
tc2 = 9min
tc = 19min t0 = tcritical = 13min
 DEPTH OF OPEN DRAIN
CLAUSE 26.3.3 (MSMA)
The maximum depth for lined open drain shall be as follows:

Cover Condition Maximum Depth (m)

Without protective 0.5

covering
With solid or grated 1.0
cover
 WIDTH OF OPEN DRAIN
CLAUSE 26.3.3 (MSMA)
The width of lined open drain may vary between a minimum
width of 0.5 m and maximum width of 1.0 m

Cover Condition Minimum/maximum

width (m)
Without protective 0.5 m minimum
covering 1.0 m maximum
With solid or grated 0.5 m minimum
cover 1.0 m maximum
 Drain Section

[1]

m
Length

[2]
Location
Return Period

yr
[3]
Sub-area

Area [4] [5]

ha
Catchment

Overland flow
[6]

min
Drain time
[7]

min
Time of
Flow time
[8]

min
concentration

Critical Time of
[9]

min

Concentration

Intensity
[10]

mm/h

Runoff Coefficient
[11]

Equivalent Runoff
[12]

Coefficient

Total Equivalent
Rational Method

ha
[13]

Area

Discharge
[14]

m 3/s

Drain Section
MSMA Appendix 16.A.2

[15]
Calculation Worksheet (I)

Gradient
[16]

1 in

Capacity
[17]

m 3/s

Actual Velocity
[18]

m/s
Drain Design

Flow Time
[19]

min
m

Invert Level
[20]
DESIGN PROCEDURES
 DESIGN PROCEDURES
The processes generally involve the following steps:

Select the design ARI for minor and major drainage system
Divide sub-catchments into segments of homogeneous land use or
surface slope.
Estimate overland flow time
Estimate flow times for all other flow components within the sub-
catchments such as Kerb gutters, pipe and channels, etc
Calculate yIt, for design ARI of y years and duration t equal to the time
of concentration, from IDF data for area of interest, by using this
equation:-
Ln (yIt) = a + bln t + c(lnt)2 + d (ln t)3
 DESIGN PROCEDURES
Calculate yIt, for design ARI of y years and duration t equal to the time
of concentration, from IDF data for area of interest, by using this
equation:-
Ln (yIt) = a + bln t + c(lnt)2 + d (ln t)3

Where yIt = average rainfall intensity (mm/hour) for y ARI and t duration
y = average return interval (ARI)
t = duration (min)
a to d = IDF fitting constant dependent on ARI

Estimate C values for each segment if there are different land covers
by from the design chart 14.3
 DESIGN PROCEDURES
Derive design rainfall intensities down to limit 30 minutes. The design rainfall depth
Pd for a storm duration d minute is given:
Pd = P30 –Fd (P60 –P30)

Where, P30 and P60 are rainfall depth for storm duration 30 min and 60 min,
respectively. Fd is the adjustment factor for the storm duration.

Calculate peak flow rate, Qy for the catchment:

Qy = (Cx yIt x A) /360

Where ;
Qy = peak flow for`y’ year ARI (m3/s)
C = Dimensionless runoff coefficient
yIt = rainfall intensity for `y’ year ARI over time of concentration, tc (mm/hr)
A = Drainage system area (ha)
 DESIGN PROCEDURES
Calculate the design of flowrate of drain by using manning formula:-
Q design = (1.49 x A x R 2/3 x S1/2)/n
Where ; Qdesign = design flow (ft3/s)
A = area (ft2)
n = Manning roughness coefficient
R = hydraulic Radius (ft)
S = Slope
 STORMWATER DRAINAGE DESIGN TO MASMA

-ESTIMATION OF PEAK DISCHARGE USING FRIEND’S FORMULA-

(EXAMPLE CALCULATION)
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE MANUAL CALCULATION-

Project : Proposed Condominium At Section R10

Wangsa Maju Kuala Lumpur
Density : Low density residential area.
STORMWATER DRAINAGE DESIGN CALCULATION TO MASMA
DESIGN RAINFALL INTENSITIES
Catchment Area
Catchment Area = 2,000 meter² = 0.200 hectare or 0.4942 acre

To calculate rainfall intensities for 2 years Design ARI (minor system)

Coefficients of the IDF Polynomial Equations

a= 5.3255 b= 0.1806 c= -0.1322 d= 0.0047 (table 13.A1)

Eqn. MSMA 13.2

ln I = a + b ln t + c (ln t)2 + d (ln t)3

tc a b c d In (I) Rainfall Pd
(min) I,(mm/hr) (mm)

30 5.3255 0.186 -0.132 0.0047 4.595 98.988 49.494

60 5.3255 0.186 -01.32 0.0047 4.171 64.780 64.780
FOR tC = 30 MINUTES
I= Pd
d

Pd = I x d

P30 = I30 x 30/60

= 49.494 mm/hr

For tc = 60 minutes
P60 = I60 x 60/60
= 64.780 x 1.0
= 64.780 mm/hr
TIME OF CONCENTRATION, tc = to (overland) + tch (drain)

FROM SURVEY PLAN:

Time of concentration, to (overland) – clause 14.4.3
to = overland sheet flow travel time (minutes) }
Lo = overland sheet flow path length = 150 m } from survey plan
n = manning’s roughness value for the surface = 0.015 } Table 14.2
S = slope of overland surface (%) = 2.50 % } assume

107 nL1/ 3 Equation 14.1

t0 
S

= 107 x 0.015 x (150)¹∕³

(2.5)½

= 5.393 minutes
From proposed section;

H = 0.5 m H
B = 0.45 m
S = 1: 250
P = wetted perimeter B
R = Hydraulic Radius =A/P
A = 0.5 x 0.45
= 0.225 m²
P = 0.5 m + 0.5 m + 0.45 m
= 1.45 m
R = A/P
= 0.225/1.45
= 0.155 m
TIME OF CONCENTRATION, tc = to (overland) + tch (drain)

Time of concentration, tch (drain) -from proposed section

to = travel time in the channel (minutes) }

Lch = length of reach (drain) = 120 m } from survey plan
n = manning’s roughness value for the surface = 0.015 } Table 14.2
S = friction slope (m/m) = 0.004 (1:250) } assume
R = hydraulic radius = 0.155 m
V = Average velocity (m/s)

V = R⅔ S½ Equation 14.4a
n
= (0.155)⅔ (0.004)½
0.015
= 1.218 m/s
tch = n Lch
60 R⅔ S½
= 0.015 x 120
60 x (0.155)⅔ (0.004)½
= 1.643 minutes
TIME OF CONCENTRATION, tc = to (overland) + tch (drain)

tc = to (overland) + tch (drain)

= 5.393 minutes + 1.643 minutes
= 7.04 minutes

t
Say c = 7 minutes

Runoff Estimation for Storm Duration Less Than 30 minutes

For shorter duration,
Pt = P30 – FD (P60 – P30) 5 < t < 30min

where Pt is the rainfall depth for a duration t

P60 & P30 can be obtained from Appendix 13.A
FD can be obtained from Table 13.3

I = Pt / t
Using tc = 7 minutes, from Table 13.3,by interpolating,
Fd = 1.76

1.28

2.08 x

5 7 10
x = 1.28 – 2.08
7-5 10-5
X = - 0.320
Fd = 2.08 -0.32
= 1.76
Pt = P30 – FD (P60 – P30)

For t = 5 minutes

P5 = 49.464 – 2.08(64.78 – 49.464)

= 17.607 mm
I5 = P5/d d = 5min/60 min
= 17.607 = 0.0833 hour
5/60
= 211.284 mm/hour
Pt = P30 – FD (P60 – P30)

For t = 7 minutes

P7 = 49.464 – 1.76(64.78 – 49.464)

= 22.508 mm
I7 = P7/d d = 7 min/60 min
= 22.508 = 0.117 hour
7/60
= 192.93 mm/hour
Using Design chart 14.3,
Runoff coefficient, C for urban catchments are as
follows:
Pre Development :
C = 0.62 (Group 7)
C = 0.48 (Group 8)
Post Development:
C = 0.95 (Group 1)
C = 0.85 (group 4)

Use C = 0.95 for design of drain size

Using Rational Method where catchments area less than 80 hectares.
Equation 14.7

Q=CIA
360
= 0.95 X 192.93 X 0.2
360
= 0.102 m³/s
 Proposed drain section

Freeboard = 150 mm

H = 0.55 m

B = 0.5 m S = drain longitudinal slope

Qn
= 1: 250
(So)½ (B)ª∕ ³
= 0.102
= 0.004
(0.004)½ (0.5) ª/³
= 0.133 n = 0.013 (Manning’s
roughness coefficient)
From Design chart 26.4, Z = 0
Y/B = 0.35
Y = 0.35 x 0.5
= 0.175 m
Allowing the minimum freeboard of 150 mm (0.15 m), depth of drain :
H = 0.175 + 0.15 m
= 0.325 m
Say, H = 0.65 m, wide B = 0.5 m (based on clause 26.3.3)
Check velocity, v of drain;
V = Q/A
= 0.102
0.65 x 0.5
= 0.32 m/s ( 0.6 m/s < V < 4.0 m/s)
The average velocity shall be between 0.6 m/s and 4.0 m/s
Therefore try to change the gradient of the drain
 STORMWATER DRAINAGE DESIGN TO MASMA

-ESTIMATION OF PEAK DISCHARGE USING RATIONAL METHOD-

(EXAMPLE CALCULATION)
 MSMA Section 14.5.3
Assumptions of Rational Method:
• Peak flow occurs when entire catchment is contributing to flow
• Rainfall intensity is the same over the entire catchment
• Rainfall intensity is uniform over a time duration equals to tc
• ARI of the computed flow is the same as ARI of the rainfall intensity
• Catchment area less than 80 Hectares

Rational method is NOT recommended where:

• ponding in catchment is significant

• design & operation of large/ major drainage facilities (esp. storage)

 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

Project : Proposed Condominium At Section R10

Wangsa Maju Kuala Lumpur
Density : Medium density residential area.

Catchment area = 10 hectares

Overland flow = 80 m (assume)

Length of drain = 400 m

Catchment area average slope = 0.5 % (assume)

 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE ALCULATION-

Solution:
From Table 4.1, minor system (medium density) design ARI = 5
years

Step 1 : Determine, tc
From Design Chart 14.1 for paved surface,
to = 8 minutes

Average velocity in the open drain should be assessed

using Manning’s equation. Assume V = 1.0 m/s (from
proposed section).
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

td = L/V
= 400/1.0
= 400 second
= 6.7 minutes (say 7 minutes)

Therefore tc = to + td
= 8 minutes + 7 minutes
= 15 minutes.
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-
Step 2 : Determine I and C
For ARI of 5 years, from Table 13.A1, using equation 13.1
for t = 30 minutes;
a = 5.1068, b = 0.5037, c = -0.2155, d = 0.0112

Pd = P30 – F (P60 – P30)

D Intensity = Depth / Duration

ln I(t) = a + b ln t + c (ln t)2 + d (ln t)3 -Equation 13.1

 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

ln I(30) = 5.1086 + 0.5037 ln (30) – 0.2155 (ln 30)2 + 0.0112 (ln 30)3

ln I(30) = 4.7698
I(30) = 117.9 mm/hr

For t = 60 minutes;

ln I(60) = 5.1086 + 0.5037 ln (60) – 0.2155 (ln 60)² + 0.0112 (ln 60)³

ln I(60) = 4. 3271
I(60) = 75.7 mm/hr
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-
Intensity = Depth / Duration
I = Pd/d (Equation 13.4)

Pd = P30 – FD (P60 – P30) Equation 13.3

Convert to rainfall depths;
P30 = I30 X d
= 117.9 mm/hr x 0.5 hr (30 minutes = 0.5 hr)
= 58.95 mm
P60 = I60 x d
= 75.7 mm/hr x 1.0 hr (60 minutes = 1.0 hr)
= 75.7 mm
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

For tc = 15 minutes, from Equation 13.3;

Pd = P30 – FD (P60 – P30) Equation 13.3
Fd = 0.8 (from Table 13.3, duration = 15 min, West Coast ≤ 100 mm)

P15 = 58.95 – 0.8(75.7 – 58.95)

= 45.5 mm
15 min = 0.25 hr
Therefore,
I15 = P15/d
= 45.5 mm/0.25hr
= 182 mm/hr
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

Step 3 : Determine Peak Flow;

From Design Chart 14.3, C = 0.87 (category 3)

For 5 years ARI, I15 = 182 mm/hr

From equation 14.7; Q = CIA

360
Q5 = 0.87 x 182 x 10
360
= 4.4 m³/s
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-
Step 4 : Proposed Drain Section
GL/RL
Assume : Free board

Gradient, S = 1: 250 (1/250 = 0.004)

Width, b = 450 mm, P = 0.55 + 0.55 + 0.45
Depth, d = 550 mm, = 1.55 mm
Free board = 150 mm, R = A/P
Area = 0.45 x 0.55 = 0.2475/1.55
= 0.2475 mm² = 0.16 m
 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-
Step 5 : Calculate capacity of proposed drain;
Using Manning’s Equation

1
Q AR 2/3
S 1/ 2

n
Use n = 0.015 (Design Chart 26.1)
V = (R)⅔ (S)¹/² EQUATION 14.4a
0.015

= (0.16)⅔ (0.004)¹/²
0.015
= 1.3 m/s (0.6 m/s < V < 4.0 m/s)

Therefore, Velocity, V is acceptable

 STORMWATER DRAINAGE DESIGN TO MASMA
-EXAMPLE CALCULATION-

Q = VxA
= 1.3 m/s x 0.2475 m²
= 0.3 m³/s (< Q5 = 4.4 m³/s)

Therefore the proposed drain section is not sufficient. Try new drain
section.
DRAINAGE LAYOUT PLAN
EARTHWORK
EARTHWORK LAYOUT PLAN
PROPOSED CONSTRUCTION OF KOLEJ SAINS KESIHATAN AT TANJUNG
RAMBUTAN MUKIM ULU KINTA IPOH PERAK

DRAINAGE LAYOUT PLAN

DETAILING
PRECAST CONCRTE DRAIN
TYPICAL DRAIN DETAILS WITH PRECAST CONCRETE COVER
DETAIL OF CASCADE DRAIN