report drainage

HEROES CONSULTANT No. 3005, Tingkat Bawah, Desasiswa Lembaran, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang.

INTRODUCTION

Foreword

In professional project practice it can be divided into five chapters like earthwork design,

water reticulation design, drainage and culvert design, road design and sewerage. In this project

we conducted drainage and culvert design.

This chapter will explain how the drainage system is designed, the process involved and

the consideration taken. In geomorphology, a drainage system is the pattern formed by the

streams, rivers, and lakes in a particular watershed. They are governed by the topography of the

land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land.

A drainage system in agriculture is an intervention to control water logging aiming at soil

improvement for agricultural production. A drainage system for industrial and residential is a

facility to dispose of liquid waste. An effective drainage system must be planned, analyzed and

designed which is very essential to control the quantity, quality, timing, distribution of runoff

resulting from storm events and also to control the erosion. Besides, the capacity of storm water

that flows through the drainage structures must be analyzed to determine their ability to convey

the developed discharge to avoid flooding. Therefore, the process of designing the drainage

system should be considered to the parameter such as the depth of drain, area of developed, the

material used for the structure and other factors that can affect the performance of designed

drainage system.

In designing the drainage system, the concepts that have being used are according to

standard in MASMA. Many problems in Malaysia related to urban water management has using


MASMA (Urban Stormwater Management Manual Malaysia) which has been introduced by the

government through JPS (Jabatan Pengaliran Dan Saliran) since 2001.

Generally, these manual act as a guideline to manage and plan good stormwater and drainage

system especially in urban and develop area.

OBJECTIVE

There are several objectives that have been made to meet in designing the drainage system for

this project:

a. To provide complete calculation and design detail for an effective minor

conveyance system for residential discharge and storm water.

b. To determine appropriate size of drain for the proposed system that can cater a

maximum flow rate for ARI of 5 years.

c. To understanding the basic concept and procedure in design the size of drainage

system that can accommodate to the peak flow capacity by using MASMA.

d. To provide an effective drainage system that following the standard that is

provided in MASMA.

e. To provide for public and private property convenience and safety from flooding.


DESIGN CRITERIA AND ASSUMPTIONS

Hydrological Calculation of Catchment

For estimating the catchment runoff in urban or built up area, reference were made to the

Rational Method outlined in “DID – urban stormwater Management Manual For Malaysia”

which relate peak runoff to rainfall intensity through a proportional factor. The formula is as

follows:

Qy = C. yIt. A

360

Where; Qy = y year ARI peak flow (m3/s)

C = dimensionless runoff coefficient

yIt = y year ARI average rainfall intensity over time of concentration, tc, (mm/hr)

A = catchment area (ha)

Rainfall intensity. I

Overland flow time of concentration using equation below:

¿=107n L1 /3

S1/ 2

td=LdV

Adopted time of concentration, tc = to + td


Polynomial expressions in the form of equation 13.2 (DID-Urban Stormwater Manual for

Malaysia) have been used in determining of design rainfall intensities

Ln ( RIt ) = a + b. Ln (t) + c.(ln (t))² + d (ln (t))³

where,

( RIt ) = the average rainfall intensity (mm/hr) for ARI and duration t.

R = average return interval (years)

T = duration (minutes)

a to d are fitting constant dependent on ARI

The design rainfall depth pd for a short duration d (minutes) is given by, when t < 30minutes

Pd = P30 – FD (P60 – P30)

Where P30, P60 are the 30-minute and 60-minute duration rainfall depths respectively, obtained

from the published design curve. FD is the adjustment factor for storm duration.

Runoff Coefficient, C

Recommended runoff coefficient (C) values for rainfall intensities ( I ) of up to 200mm/hr have

been obtained from Design Chart 14.3 (urban area), (DID-Urban Stormwater manual for

Malaysia) respectively. For I > 400mm/hr, a value of C = 0.9, should be used for all types of

ground cover. For I values between 200 and 400mm/hr, interpolation between the applicable C

values I = 200mm/hr and I = 400m/hr has been used.


HYDRAULIC ANALYSIS

Design storm

Open drain has been designed to cater for flows up to and including the minor system design

ARI as specified in Table 4.1

Minor System - 5 years

Major System - 50 years

Velocity

The velocity of design should be in the range of 0.6 m/s < v < 4 m/s. if the condition is not

fulfilled, the design of the drain is assumed fail.

Drain capacity

Open and swale drain have been sized by using Manning’s formula equation.

Q = (1/n) x AR2/3 S1/2


Step to determine rainfall intensity

Determine Catchment / sub catchments

Determine drainage system

Select ARIDetermine time of concentration, tc

Intensity, I

Values a,b,c,d use Table 13.A1

Area location conveyance quantity purpose : detention & retention Quality purpose estatics biodiversityEquationTable

If t c < 30 min

If t c > 30 min

Intensity, I

If t c > 30 min

If t c > 30 minFind I for selected ARI at t=30 & t=60 using Eqn. 13.2 by substitute t=30 min & t=60 min Convert I to P using Eqn. 13.4 to get P at t=30 and t=60Use Figure 13.3 and located the dev. siteto find value of 2 P 24h Using Table 13.3 using values of 2 P 24h and t c , determine value of FD Use Eqn. 13.3, P for that t c is find by substitute at t=30 & t=60 and value FD

Convert P for that t c to I using Eqn. 13.4To get I at that t c

Direct apply Eqn. 13.2


HYDROLOGICAL CALCULATION OF CATCHMENT AND HYDRAULIC CALCULATIONS FOR

DRAINAGE SYSTEM

HYDROLOGICAL CALCULATION OF CATCHMENT

Swale drain

DRAIN 1

DESIGN OF DRAIN IN ACCORDANCE TO URBAN STORM MANAGEMENT MANUAL FOR MALAYSIA

Total pervious area of site = 0.05 haTotal impervious area of site = 0.028 ha

Determine overland flow time of concentration overland sheet flow to basin

L = 9.87 m n = 0.003

S = 2 %

to = 107nL1/3 / S1/2

to = 4.87 min

Assume velocity in the drain, V = 1 m/s

Ld = 47.2 m

td = 0.79 min

Adopted time of concentration, tc = 5.66 min

Based on volume 4-chapter 13 of the urban storm management manual on design rainfall,the polynomial approximation of the IDF curves is as followed:

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


Where:

Rlt

= the average rainfall intensity (mm/hr) for ARI and duration t

R = average return interval (years)

t = duration (min)

a - d fitting constants depending on ARI

State Location Data period ARI Coefficient of the IDF polynomial constants (Year) a b c d 2 4.1689 0.816 -0.2726 0.0149 5 4.7867 0.4919 -0.1993 0.0099Perak Bagan 1960 10 5.276 0.2436 -0.1436 0.0059 Serai - 20 5.661 0.0329 -0.0944 0.0024 1983 50 5.3431 0.3538 -0.1686 0.0078 100 5.3299 0.4357 -0.1857 0.0089

The design storm for the durations of time of concentration, Tc ;t = 30

Pervious area I(5yrs,30) = 94.04 mm/hr t = 60I(5yrs,60) = 62.75 mm/hr

P30 = 47.02 mmP60 = 62.75 mm

Impervious area I(5yrs,30) = 94.04 mm/hrI(5yrs,60) = 62.75 mm/hr

P30 = 47.02 mmP60 = 62.75 mm

Duration P24h West Coast (120mm)

5 1.8510 1.1315 0.7220 0.4230 0


The design rainfall depth for short d is given by equation 13.3 :

Pd = P30 - FD(P60 - P30)

Pervious area FD = 1.85Impervious

area FD = 1.85

Pd = 17.92 mm Pd = 17.92 mm

I(5yrs, tc) = 190.07 mm/hr I(5yrs, tc) = 190.07 mm/hr

Values of FD for equation 13.3

Duration (min) West Coast East Coast ≤ 100 120 150 ≥ 180 All5 2.08 1.85 1.62 1.40 1.39

10 1.28 1.13 0.99 0.86 1.0315 0.80 0.72 0.62 0.54 0.7420 0.47 0.42 0.36 0.32 0.4830 0.00 0.00 0.00 0.00 0.00

Pervious area C = 0.62Impervious

area C = 0.9

Q = 0.0164 cumec Q = 0.013 cumec

Determination of drain capacity :

T = B +2ZY A = Y(B + T)/2 P = B + Y{(1 + Z12)1/2 + (1 + Z2

2)1/2}

T = 3.00 m A = 0.54 m2 P = 3.07 m

R = A / P

R = 0.18

side slope (H : V) = 1 : 4 Channel area, A = 0.54 m2

channel slope, S = 0.002 Channel wetted perimeter, P = 3.074 mmanning roughness, n = 0.035 Hydraulic radius, R = 0.176


base width, B = 0.6top width = 3water depth, Y = 0.3

Q = (1/n) x A x R2/3 x So1/2 , Q = 0.2164

Q = 0.2164 cumec > Qpeak OK! , Qpeak = 0.0297

V = Q/A V = 0.401 m/s

Calculation of Qpre (before construction)


Total pervious area of site = 1 ha

Adopted time of concentration, tc

tc = Fc x L / A1/10 x S1/5

where tc = min data

L = length flow path to outlet (km) L = 0.07 km

S = slope S = 5.02

A = catchment area, (ha) A = 1 ha

Fc =92.5 (ha) , 58.5 (km2) Fc = 58.5 km2

tc = 5.672 min




Where:Rlt = the average rainfall intensity (mm/hr) for ARI and duration tR = average return interval (years)t = duration (min)


State LocationData

period ARI Coefficient of the IDF polynomial constants (Year) a b c d 2 4.1689 0.816 -0.2726 0.0149 5 4.7867 0.4919 -0.1993 0.0099Perak Bagan 1960 10 5.276 0.2436 -0.1436 0.0059 Serai - 20 5.661 0.0329 -0.0944 0.0024 1983 50 5.3431 0.3538 -0.1686 0.0078 100 5.3299 0.4357 -0.1857 0.0089

The design storm for the durations of time of concentration, Tc ;

t = 30

Pervious areaI(5yrs,30) = 107.28 mm/hr t = 60I(5yrs,60) = 71.60 mm/hr

P30 = 53.64 mmP60 = 71.60 mm

Duration P24h

West Coast (120mm)

5 1.8510 1.1315 0.7220 0.4230 0



Pd = P30 - FD(P60 - P30)

Pervious area FD = 1.85

Pd = 20.42 mm

I(5yrs, tc) =216.0

5 mm/hr


Duration (min) West Coast East Coast

≤ 100 120 150 ≥ 180 All5 2.08 1.85 1.62 1.40 1.39

10 1.28 1.13 0.99 0.86 1.0315 0.80 0.72 0.62 0.54 0.7420 0.47 0.42 0.36 0.32 0.4830 0.00 0.00 0.00 0.00 0.00

Pervious area C = 0.64

Qpre = 0.384 cumec

Calculation of result

Drain Qpervious Qimpervious Qtotal Qpost = 0.2331 0.016 0.013 0.0302 0.011 0.005 0.0163 0.010 0.006 0.0164 0.016 0.013 0.0295 0.016 0.000 0.0166 0.010 0.000 0.0107 0.011 0.016 0.0278 0.008 0.010 0.0189 0.027 0.042 0.069


10 0.022 0.000 0.02211 0.022 0.000 0.02212 0.016 0.011 0.02713 0.011 0.012 0.023C1 0.000 0.014 0.014C2 0.000 0.014 0.014

Qpost total 0.233

= 0.384 > Qpost OK

Concrete drain


Total impervious area of site = 0.07 ha

Determine overland flow time of concentration overland sheet flow to basin

L = 2.5 m n = 0.013

S = 2 %

to = 107nL1/3 / S1/2

to = 13.35 min

Assume velocity in the drain, V = 1 m/s

Ld = 27 m

td = 0.45 min

Adopted time of concentration, tc = 13.80 min



Where:Rlt = the average rainfall intensity (mm/hr) for ARI and duration tR = average return interval (years)t = duration (min)



State Location Data period ARI Coefficient of the IDF polynomial constants (Year) a b c d 2 4.1689 0.816 -0.2726 0.0149 5 4.7867 0.4919 -0.1993 0.0099Perak Bagan 1960 10 5.276 0.2436 -0.1436 0.0059 Serai - 20 5.661 0.0329 -0.0944 0.0024 1983 50 5.3431 0.3538 -0.1686 0.0078

100 5.3299 0.4357 -0.1857 0.0089

The design storm for the durations of time of concentration, Tc ;t = 30

Pervious area I(5yrs,30) = 94.04 mm/hr t = 60I(5yrs,60) = 62.75 mm/hr

P30 = 47.02 mm

P60 = 62.75 mm

Impervious area I(5yrs,30) = 94.04 mm/hrI(5yrs,60) = 62.75 mm/hr

P30 = 47.02 mm

P60 = 62.75 mm

Duration P24h West Coast (120mm)

5 1.8510 1.1315 0.7220 0.4230 0


Pd = P30 - FD(P60 - P30)

Impervious area FD = 1.85

Pd = 17.92 mm

I(5yrs, tc) = 77.9 mm/hr



Duration (min) West Coast East Coast ≤ 100 120 150 ≥ 180 All5 2.08 1.85 1.62 1.40 1.39

10 1.28 1.13 0.99 0.86 1.0315 0.80 0.72 0.62 0.54 0.7420 0.47 0.42 0.36 0.32 0.4830 0.00 0.00 0.00 0.00 0.00

Impervious area C = 0.9

Q = 0.014 cumec

Drainage design

design discharge, Qpost = 0.014 m3/s

try U drain size b = 300 mm

Manning equation

Q = AR2/3So1/2/n b = 2y

y = b/2y = 150 mm

area of cross section, A = by = 0.045 m2 S = 0.002

Wetted perimeter, P = b +2y = 0.6 m n = 0.013

Hydraulic radius, R = A/P = 0.075

Capacity, Q = 0.029 m3/s > 0.003 m3/s OK

Velocity, V = Q/A


V = 0.645 m/s < 4 m/s OK

use size 300 mm x 300 mm

Example of calculation of invert level

Ground level, GL = 3.2 m IL = invert level

Depth =1.2 m fall = length x gradient

Gradient = 1 : 500 IL2 = IL1 - fall

Drain 1

Length = 47 m

IL1 = GL - depth

= 2 m

IL2 = 2 - 0.094

= 1.906 m

Drain 2

Length = 22 m

IL3 = 1.906 - 0.044

= 1.862 m

drain slope invert level(m)1 0.002 1.906


2 0.002 1.8623 0.002 1.8224 0.002 1.7425 0.002 1.9726 0.002 1.9027 0.002 1.8268 0.002 1.7769 0.002 1.804

10 0.002 1.94611 0.002 1.94612 0.002 1.94013 0.002 1.884


CATCHMENT AREA




report drainage

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design criteria

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