EVALUATION OF THE CHANGES BETWEEN THE FIRST … · 1 evaluation of the changes between the first...

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EVALUATION OF THE CHANGES BETWEEN THE FIRST AND SECOND EDITIONS OF THE

“URBAN STORMWATER MANAGEMENT MANUAL FOR MALAYSIA (MSMA)”

Ir. Dr. Quek Keng Hong B.E. (civil), M.Eng.Sc, Ph.D. (NSW), PE

Managing Director, MSMAware Sdn Bhd

Note: Condensed versions of this paper are submitted for publication in the IEM Journal and Bulletin.

(This paper may be download from http://paper.msmam.com)

Abstract

This paper investigated the changes between the first and second editions of MSMA on five key parameters as follows: (i) Design Average Recurrence Interval, (ii) Design Storm, (iii) Rational Method, (iv) On-Site Detention and (v) Total volume of sedimentation basins. The magnitudes of changes were quantified using case studies and the results are as follows:

(i) Design Average Recurrence Interval: For medium density residential and commercial and city area, the storm intensity has increased by up to 122% for minor system for an ARI increase from 5 to 10 years, and up to 133% for major system for an ARI increase from 50 year to 100 years between MSMA (2000) and (2011). It is emphasised that the changes in the storm intensity is not only due to changes in the ARI but also the higher IDF data in MSMA (2011).

(ii) Design Storm: For durations of between 15 to 700 min, the IDF estimates using MSMA (2011) were mostly higher than those estimated using MSMA (2000). In the study, out of 14 stations, 10 of them (or 71%) were higher than the MSMA (2000) curve, while the remaining 4 stations (or 29%) were lower than the first edition estimates. It is concluded that the design storms estimated based on MSMA (2011) for Kuala Lumpur can be up to about 26% higher than MSMA (2000) for duration below 700 minutes, for 71% of the stations.

(iii) Rational Method: For commercial and city area, the peak discharge from MSMA (2011) is about 31% higher than the peak discharge from MSMA (2000). The discharge has increased from 16.9 to 22.1 m3/s. The runoff coefficient C has increased from 0.905 to 0.95 while the storm intensity has increased from 224.3 mm/hr to 279.4. The increase in C for commercial and city area and storm intensity in MSMA (2011) has attributed to a significantly higher peak discharge. In conclusion, the peak discharge computed using the Rational Method in MSMA (2011) is up to 31% higher than that in MSMA (2000). This increase is caused principally by the higher storm intensity in MSMA (2011) and by the higher C for commercial and city area in MSMA (2011). In general, it is concluded that 71% of the stations in Kuala Lumpur will have up to 26% higher storm intensity and up to 31% higher peak discharges for commercial and city area.

(iv) On-Site Detention: The result shows that for Kuala Lumpur, the PSD and SSR using MSMA (2011) are about 20% and 190% of MSMA (2000). The PSD and SSR using the ESM Method for Kuala Lumpur is about 55% and 103%, respectively, of those using MSMA (2000). For Pulau Pinang, the PSD and SSR using MSMA (2011) are about 18% and 180% of MSMA (2000), while the PSD and SSR using the ESM Method is about 55% and 129%, respectively, of those using MSMA (2000). The approximate Swinburne’s Method in MSMA (2011) results in underestimate of PSD and over estimate of the SSR. The ESM Method appeared to give slightly higher estimate of SSR compared to MSMA (2000) but a lot lower estimate compare to MSMA (2011). The ESM Method may be used instead of MSMA (2011) to give a better estimate of the PSD and SSR.

http://paper.msmam.com/

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(v) Total volume of Sedimentation Basin: The dry sediment basin volume using MSMA (2011) is half of that using MSMA (2000) for 6 month ARI design (for projects taking more than two years) as MSMA (2011) does not cover 6 month ARI. The wet sediment basin volume was 65% higher using MSMA (2011) compared to MSMA (2000) because of it was based on 50 mm of rainfall for temporary BMP in MSMA (2011), compared to the 75th percentile storm of 36.75 mm in MSMA (2000) which is lower.

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1. Introduction

1.1 Evolution of Drainage Guidelines in Malaysia

Before 2001, engineers in Malaysia applied the “Planning and Design Procedure No. 1” (DID, 1975) published by the Department of Irrigation and Drainage (DID) in 1975 for their drainage design. This is a relatively simple document to use- with only 242 pages covering ten chapters.

But this has changed with the introduction of the Urban Stormwater Management Manual for Malaysia” (“Manual Saliran Mesra Alam Malaysia”) in 2000 (DID, 2000- referred to herein after as MSMA, 2000). The new Manual is much more thorough in its coverage of subject matters compared to the old procedure. It contains 48 chapters spanning more than 1,100 pages.

In 2011, the Department published an updated version of the same manual, known as MSMA 2nd Edition (DID, 2011- referred to herein after as MSMA, 2011). This document was launched by the Department in early 2012 and enforced on 1 July, 2012. The document is roughly half the thickness of the first edition. There are many significant changes in computational procedures between the two editions of MSMA (2000, 2011).

1.2 Overall Changes in MSMA (2011) from MSMA (2000)

The overall layout of MSMA (2011) has changed from MSMA (2000) as follows:

The number of chapters has reduced from 48 in the first edition to 20 in the second edition.

The number of pages has reduced by roughly half.

The topics are now more “focused” compared to the previous edition with chapters named after specific drainage elements such as detention pond and On-Site Detention.

New chapters namely, on “Rainwater Harvesting” and “Pavement Drainage” are included.

The content of the 20 chapters are as follows:

Chapter 1- Design Acceptance Criteria

Chapter 2- Quantity Design Fundamental

Chapter 3- Quality Design Fundamentals

Chapter 4- Roof and Property Drainage

Chapter 5- On-Site Detention

Chapter 6- Rainwater Harvesting

Chapter 7- Detention Pond

Chapter 8- Infiltration Facilities

Chapter 9- Bioretention System

Chapter 10- Gross Pollutant Traps

Chapter 11- Water Quality Ponds and Wetlands

Chapter 12- Erosion and Sediment Control

Chapter 13- Pavement Drainage

Chapter 14- Drains and Swales

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Chapter 15- Pipe Drain

Chapter 16- Engineered Channel

Chapter 17- Bioengineered Channel

Chapter 18- Culvert

Chapter 19- Pump and Tidal Gate

Chapter 20- Hydraulic Structures

Table 1.1 is a comparison of the various chapters in MSMA (2000, 2011) given by DID.

Table 1.1 Comparison of Chapters in MSMA (2000, 2011) (After DID Seminar Paper, 2012)

MSMA (2000) MSMA (2011)

Part A: Introduction

Chapter 1: Malaysian Perspective Chapter 1- Design Acceptance Criteria

Chapter 2: Environment Processes Chapter 1- Design Acceptance Criteria

Chapter 3: Stormwater Management Chapter 1- Design Acceptance Criteria

Part B : Administration

Chapter 4: Design Acceptance Criteria Chapter 1- Design Acceptance Criteria

Chapter 5: Institutional and Legal Framework Chapter 1- Design Acceptance Criteria

Chapter 6: Authority Requirement and Documentation

Chapter 1- Design Acceptance Criteria

Part C : Planning

Chapter 7: Planning Framework Chapter 1- Design Acceptance Criteria

Chapter 8: Strategic Planning Chapter 1- Design Acceptance Criteria

Chapter 9: Master Planning Chapter 1- Design Acceptance Criteria

Chapter 10: Choice of Management Chapter 1- Design Acceptance Criteria

Part D : Hydrology and Hydraulics

Chapter 11: Hydrologic Design Concepts Chapter 2- Quantity Design Fundamental

Chapter 12: Hydraulic Fundamentals Chapter 2- Quantity Design Fundamental

Chapter 13: Design Rainfall Chapter 2- Quantity Design Fundamental

Chapter 14: Flow Estimation and Routing Chapter 2- Quantity Design Fundamental

Chapter 15: Pollutant Estimation, Transport and Retention

Chapter 3- Quality Design Fundamentals

Chapter 16: Stormwater System Design Chapter 2- Quantity Design Fundamental

Chapter 17: Computer Models and Softwares Chapter 2- Quantity Design Fundamental

Part E : Runoff Quantity Control

Chapter 18: Principle of Quantity Control Chapter 5- On-Site Detention/Chapter 7- Detention Pond

Chapter 19: On-site Detention Chapter 5- On-Site Detention

Chapter 20: Community and Regional Detention Chapter 7- Detention Pond

Chapter 21: On-site and Community Retention Chapter 8- Infiltration Facilities

Chapter 22: Regional Retention Chapter 8- Infiltration Facilities

Nil Chapter 6- Rainwater Harvesting

Part F : Runoff Conveyance

Chapter 23: Roof and Property Drainage Chapter 4- Roof and Property Drainage

Chapter 24: Stormwater Inlets Chapter 13- Pavement Drainage

Chapter 25: Pipe Drains Chapter 15- Pipe Drain

Chapter 26: Open Drains Chapter 14- Drains and Swales

Chapter 27: Culvert Chapter 18- Culvert

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Chapter 28: Engineered Waterways Chapter 16- Engineered Channel

Chapter 29: Hydraulic Structures Chapter 20- Hydraulic Structures

Part G : Post Construction Runoff Quality Controls

Chapter 30: Stormwater Quality Monitoring Chapter 3- Quality Design Fundamentals

Chapter 31: Filtration Chapter 9- Bioretention System

Chapter 32: Infiltration Chapter 8- Infiltration Facilities

Chapter 33: Oil Separators Chapter 10- Gross Pollutant Traps

Chapter 34: Gross Pollutant Traps Chapter 10- Gross Pollutant Traps

Chapter 35: Constructed Ponds and Wetlands Chapter 11- Water Quality Ponds and Wetlands

Chapter 36: Housekeeping Practices Nil

Chapter 37: Community Education Nil

Part H : Construction Runoff Quality Controls

Chapter 38: Action to Control Erosion and Sediment


Chapter 39: Erosion and Sediment Control Measures


Chapter 40: Contractor Activity Control Measures Chapter 12- Erosion and Sediment Control

Chapter 41: Erosion and Sediment Control Plans Chapter 12- Erosion and Sediment Control

Part I : Special Application

Chapter 42: Landscaping Annex 1: Ecological Plants

Chapter 43: Riparian Vegetation and Watercourse Management

Chapter 17- Bioengineered Channel

Chapter 44: Subsoil Drainage Nil

Chapter 45: Pumped Drainage Chapter 19- Pump and Tidal Gate

Chapter 46: Lowland, Tidal and Small Island Drainage

Nil

Chapter 47: Hillside Drainage Nil

Chapter 48: Wet Weather Wastewater Overflows Nil

Nil Annex 2: Maintenance

Nil Annex 3: IDF Curves

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2. Changes in the Design ARI.

The design storm ARI is covered in Chapter 4 of the first edition and Chapter 1 of the second edition.

2.1 Major and Minor Design ARI (MSMA, 2000)

The design storm ARI’s for MSMA (2000) is covered in

Table 2.1.

2.2 Major and Minor Design ARI (MSMA, 2011)

The design storm ARI’s for MSMA (2011) is covered in Table 2.2.

2.3 Comparison

The changes in major/minor design storm ARI. for various types of development are evaluated by comparing

Table 2.1 and Table 2.2 as follows:

1. For Major System, the ARI. for most types of development is fixed at 100 year

ARI. in MSMA (2011), unlike MSMA (2000) where the ARI. is defined as “up to 100 year” for all development types- subject to cost benefit analysis by the engineer.

2. For residential development, the types of development have been combined into two types namely, bungalow/Semi-D and link houses/apartment with higher ARI. of 5 and 10 years for minor systems compared to 2, 5 and 10, respectively, for low, medium and high density residential classifications in the first edition. For major system, the ARI. has increased to mostly 100 years compared with “up to 100 years” in the first edition.

3. In the first edition, for commercial, business and industrial are grouped according to whether these are located in CBD or non-CBD areas. But in the second edition, these are divided into: commercial and business centers, industry, and institutional building/complex with ARI. of 10 for minor system compared to 5 for non-CBD in the first edition. For major system, the ARI. is fixed at 100 years in the Second edition compared to “up to 100” in the first edition.

4. The term “open space” in the first edition has been replaced by “sport fields” in the second edition. The ARI. for minor system is now 2 years compared to 1 year previously, while the ARI. for major system has reduced to 20 years from “up to 100 years” previously. Interestingly, this is the only reduction in ARI. in the second edition.

5. There is a new category called “infrastructure/utility” in the new publication with ARI. of 5 and 100 years for minor and major systems, respectively.

2.4 Evaluation

In summary, the major changes are as follows:

1. For Major Systems, the ARI. for most types of development is fixed at 100 year ARI. in MSMA (2011) from “up to 100 year” in MSMA (2000).

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2. MSMA (2011) has eliminated the subjectivity in the determination of ARI for major system via cost benefit analysis by the engineer.

3. For minor systems, the ARI has increased from 2 to 5 years to 10 years for low and medium density residential developments and commercial, business and industrial development in non-CBD areas.

4. For parks and sport fields, the ARI for major system has reduced to 20 years from “up to 100 years” previously. This reflects D.I.D’s effort in promoting the use of these amenities for storage.

5. The effect of changes in design ARI on storm intensities is covered in the following case study.

Table 2.1 Design Storm ARIs for Urban Stormwater System Adoption (MSMA, 2000)

Type of Development Average Recurrence interval (ARI) of Design Storm (Year)

Quantity Quality

Minor System Major System

Open Space, Parks and Agricultural Land in urban areas

1 Up to 100 3 month ARI. (for all types

of development)

Residential:

- Low density 2 Up to 100

- Medium density 5 Up to 100

- High density 10 Up to 100

Commercial, Business and Industrial- Other than CBD

5 Up to 100

Commercial, Business, Industrial in Central Business District (CBD) areas of Large Cities

10 Up to 100

Source: Table 4.1 of MSMA (2000)

Table 2.2 Design Storm ARI Adoption (MSMA, 2011)

Type of Development Minimum Average Recurrence interval (ARI) of Design Storm (Year)

Residential Minor System Major System

- Bungalow and Semi-D 5 50

- Link Houses/Apartment 10 100

Commercial and Business Centers

10 100

Industry 10 100

Sport Fields, Parks and Agricultural Land

2 20

Infrastructure/utility 5 100

Institutional Building/Complex 10 100

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Source: Table 1.1 of MSMA (2011)

2.5 Case Study on Design ARI

In this case study, the changes in the design ARI. on rainfall intensities is assessed. Using the design storm ARI. for the old and new procedures, the rainfall intensities for both minor and major systems are compared. The quantum of increase is assessed. The location of the study is in Sg. Batu, Kuala Lumpur.

2.5.1 Methodology

1. The ARI for three types of landuses: park, medium density residential and commercial area were determined based on MSMA (2000) and MSMA (2011) as shown in Table 2.3 and plotted in Figure 2.1 and Figure 2.2, respectively, for minor and major systems.

2. For park, the ARI have changed from 1 and <100 for minor and major systems to 2 and 20 years for minor and major systems, respectively.

3. For medium density residential and commercial area, the ARI have increased from 5 and <100 for minor and major systems to 10 and 100 years for minor and major systems, respectively.

4. The ARI for <100 year for MSMA (2000) is assumed to be 50 year. 5. The minor and major storm intensities for MSMA (2000) and MSMA (2011)

computed and summarized as shown in Table 2.3.

2.5.2 Evaluation

To compare the increase in storm intensity, a ratio R is defined as follows:

1

2

i

iR

where i2 is the storm intensity based on MSMA (2011) i1 is the storm intensity based on MSMA (2000)

The ratio R is tabulated as shown in the table.

1. The ratio R has increased by up to 110% for minor system and up to 103% for major system for the first type of landuse i.e., park. This increase in design storm intensity was due to higher IDF data in MSMA (2011), which negates the effect of the reduction of ARI in the new guideline to 20 year.

2. For the second and third types of landuses i.e., medium density residential and commercial and city area, the ratio R has increased up to 122% for minor system for an ARI increase from 5 to 10 years, and up to 133% for major system for an ARI increase from 50 year to 100 years.

3. It is emphasised that the changes in the storm intensity is not only due to changes in the ARI but also the higher IDF data in MSMA (2011). For changes in IDF data between MSMA (2000) and (2011), please refer to the case study on Design Storm.

4. Due to the linear nature of the discharge and storm intensity in the Rational Method, it is expected the same proportional increase in the design discharge is observed.

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5. This case study only serves to determine the changes in storm intensities with changes in ARI. It is not suggesting that all medium density residential and commercial and city areas are currently designed for a 50 years ARI for major system.

Table 2.3 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Major and Minor System for Sg

Batu, Kuala Lumpur

Landuse ARI (Minor)

ARI (Major)

ARI (Minor)

ARI (Major)

i (Minor)

i (Major)

i (Minor)

i (Major)

R (Minor)

R (Major)

MSMA (2000) MSMA (2011) MSMA (2000) MSMA (2011)

Park

1 <100 2 20 64.8 100.5 71.2 103.4 1.10 1.03

Medium Density Residential

5 <100 10 100 75.7 100.5 92.4 134.1 1.22 1.33

Commercial and City Area

5 <100 10 100 75.7 100.5 92.4 134.1 1.22 1.33

Note1: i in mm/hr for duration of 60 minutes Note 2: ARI for <100 year is assumed to be 50 year

Figure 2.1 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Minor System for Sg. Batu, Kuala

Lumpur

Figure 2.2 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Major System for Sg. Batu, Kuala Lumpur

0

20

40

60

80

100

Park Medium DensityResidential

Commercial andCity Area

Sto

rm In

ten

sity

(m

m/h

r)

Development Types

i (Minor) (MSMA, 2000) i (Minor) (MSMA, 2011)

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3. Changes in Design Storm, Temporal Pattern and Areal Reduction Factor

3.1 Design Storm Computation

3.1.1 Evolution of Methods of Computation for Design Storm With the publication of second edition of MSMA, Chapter 2 of MSMA (2011) now supersedes Chapter 13 of MSMA (2000).

In this section, the theories of design storm in both editions of MSMA (2000 and 2011) are covered.

3.1.2 Derivation of IDF Curves using MSMA (2000)

In the second edition, the following polynomial equation (Equation 13.2 in MSMA, 2000) has been fitted to the published IDF curves for the 35 major urban centres in Malaysia:

32))(ln())(ln()ln()ln( tdtctbaI t

R (Equation 3.1)

where

RIt is the average rainfall intensity (mm/hr) for ARI R and duration t R is the average return interval (years) t is the duration (minutes) a to d are fitting constants dependent on ARI.

The fitted coefficients for the IDF curves for all the major cities are given in Appendix 13.A of MSMA (2000). Equation 3.1 is strictly applicable to rainfall duration of 6 hours or less. For short duration of less than 30 minutes in MSMA (2000), the intensities are computed as follows:

The design rainfall depth Pd for a short duration d (min) is given by:

0

50

100

150

Park Medium DensityResidential

Commercial andCity Area

Sto

rm In

ten

sity

(mm

/hr)

Development Types

i (Major) (MSMA, 2000) i (Major) (MSMA, 2011)

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)( 306030 PPFPP Dd (Equation 3.2)

where P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from the published polynomial curves. FD is the adjustment factor for storm duration based on Table 13.3 and Figure 13.3 of MSMA (2000).

3.1.3 Derivation of IDF Curves using MSMA (2011)

In MSMA (2011) (Equation 2.2), the following empirical equation was fitted to the IDF data for 135 major urban centres in Malaysia:

d

Ti (Equation 3.3)

where

i is the Average rainfall intensity (mm/hr) T is the Average return interval (years) for ARI of between 0.5 and 12 months and 2 and 100 years. d is the Storm duration (hours) where d is between 0.0833 and 72 hours

, κ, θ and η are the fitting constants dependent on the raingauge location. Refer Table

2.B1 in Appendix 2.B of MSMA (2011).

3.1.4 Comparison The following changes were noted:

1. In the Second Edition, the formula for computing the IDF data has changed from a polynomial based formula to an empirical equation.

2. The storm intensities have changed due to the changes in the formula used.

3. In the first edition, the data used were up to about 1983 or 1990. For instance, the data used for the Federal Territory was only up to 1983 in MSMA (2000). However, in the Second Edition, the data used were more up-to-date.

4. In the first edition, the IDF data were available only for 35 major urban centers. In the second edition, however, this has been increased to 135 major urban centers in Malaysia.

5. In MSMA (2000) the IDF formula is applicable for storm duration of 30 minutes to 6 hours, whereas in MSMA (2011), the formula is applicable between 5 min and 72 hours. In MSMA (2000), for duration of less than 30 minutes, a short duration formula is required.

6. In MSMA (2000) the storm ARI is available for 2 to 100 years, whereas in MSMA (2011), it is available for 2 to 100 years, plus 0.5 to 12 months.

7. IDF curves were plotted in Annex 3 of MSMA (2011) for the 135 major urban centers for ARI. from 2 to 100 years and duration of 5 min to 72 hours. However, these were not provided for ARI of between 0.5 to 12 months. So it is necessary to compute them.

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8. In MSMA (2000) the whole of Kuala Lumpur is represented by one IDF curve. But in MSMA (2011), it involves 14 stations covering different parts of Kuala Lumpur. The same is noted for the stations in all states. For example, in Selangor there are now ten stations.

9. MSMA (2011) covers the IDF data of 12 states and federal territory in Peninsular Malaysia. Sabah and Sarawak are not covered. In MSMA (2000), the two East Malaysian states are covered.

3.1.5 Evaluation 1 Overall, the quality of the storm data in MSMA (2011) is better as the

new data is more up-to-date. 2 The IDF data in MSMA (2011) covers longer storm durations from 5

minutes to 72 hours, and the lower range ARI of 0.5 to 12 months. 3 There are now 135 stations in MSMA (2011) compared to only 35

previously. 4 IDF curves are plotted in Annex 3 of MSMA (2011) for 135 major

urban centres. 5 No IDF data is provided for East Malaysian states of Sabah and

Sarawak. 6 The changes in the IDF data is expected to change the magnitudes

of design storm. 7 The magnitude of changes in the design rainfall is covered in the

following case study.

3.2 Storm Temporal Pattern

This is covered in Chapter 13 of the first edition and Chapter 2 of the second edition.

3.2.1 Temporal Pattern in MSMA (2000) In MSMA (2000), the temporal pattern is covered in Section 13.3 of Chapter 13.

Table 3.1 (Table 13.4 of MSMA, 2000) gives the recommended time steps for

durations of up to 360 minutes. Appendix 13.B gives the design temporal patterns for East and West Coast of Peninsular Malaysia. For east Malaysia, it recommends the use of temporal patterns for East Coast of Peninsula.

Table 3.1 Standard Durations for Urban Stormwater Drainage

Standard Duration (minutes) No. of Time Intervals Time Interval (minutes)

10 2 5

15 3 5

30 6 5

60 12 5

120 8 15

180 6 30

360 6 60

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3.2.2 Temporal Pattern in MSMA (2011) In MSMA (2011), the temporal patterns to be used for a set of durations are given in Appendix 2.C for the following five regions:

Region 1- Terengganu and Kelantan

Region 2- Johor, Negeri Sembilan, Melaka, Selangor and Pahang

Region 3- Perak, Kedah, Pulau Pinang and Perlis

Region 4- Mountainous Area

Region 5- Urban Area (Kuala Lumpur)

Table 3.2 (Table 2.4 of MSMA, 2011) provides the recommended time intervals for the above design rainfall temporal pattern.

Table 3.2 Recommended Intervals for Design Rainfall Temporal Pattern (Table 2.4 in MSMA, 2011)

Storm Duration (minutes) Time Interval (minutes)

< 60 5

60-120 10

121-360 15

>360 30

3.2.3 Evaluation

1 MSMA (2011) provides the temporal pattern for storm duration of up to 72 hour compared to MSMA (2000) at only 6 hour.

2 MSMA (2000) divides the temporal pattern for east and west cost of Peninsular Malaysia. MSMA (2011), on the other hand, divides the whole peninsula into five regions as described above.

3 In MSMA (2011), no mention of temporal pattern for East Malaysia- but in MSMA (2000), it is recommended that the temporal pattern for East Coast of Peninsula be used for Sabah and Sarawak.

4 MSMA (2011) recommends smaller time intervals.

3.3 Areal Reduction Factor

Areal reduction factor (ARF) is given in Table 13.1 of MSMA (2000) but not in MSMA (2011). Literature in hydrology state that ARF should be applied to convert point intensity to catchment average and it is not correct to ignore ARF for larger catchments. Hence the following procedure as given in MSMA (2000) should be applied for MSMA (2011): The IDF curves give the rainfall intensity at a point. For larger catchment, the uneven spatial distribution of a storm is important. Areal reduction factors are applied to design point rainfall intensities to account for the fact that it is not likely that rainfall will occur at the same intensity over the entire catchment area of a storm. The point estimates of design storms are adjusted for the catchment area by following the procedure recommended in HP1 (DID, 1982), which is similar to the United States Weather Bureau's method.

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The design rainfall is calculated from the point rainfall intensity as follows (Equation 13.1 in MSMA, 2000):

pc IFI (Equation 3.4)

where

F is the areal reduction factor which is expressed as a factor less than 1.0. Ic is the average rainfall over the catchment, and Ip is the point rainfall intensity.

The values of F for catchment areas of up to 200 km2 and durations of up to 24 hours are given in Table 3.3 and Figure 3.1 below (Table 13.1 and Figure 13.1 of MSMA 2000, respectively). Note that the range of applicability is limited to catchment areas of up to 200 km2 only.

Table 3.3 Areal Reduction Factors

Figure 3.1 Plot of Areal Reduction Factors

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3.4 Case Study on Design Storm

The design storm estimates are compared using the IDF formulas from the first and second edition for a major urban center in Malaysia. The objective is to determine the changes in design rainfall due to differences in the IDF formulas. The urban center selected in the case study is Kuala Lumpur.

3.4.1 Methodology 1. The IDF curves were computed using Equation 3.1 for Kuala Lumpur for

duration of more than 30 minutes as tabulated in Table 3.4 and plotted as shown in Figure 3.2.

2. For duration of less than 30 minutes, the short duration curve of Equation 3.2 was applied. The results for 5 and 15 minutes are tabulated as shown in Table 3.5 and Table 3.6, respectively.

3. Equation 3.3 was applied to the 14 stations in Kuala Lumpur (Table 2.B1) (see Table 3.9). The results for Station No. 3116004 was tabulated as shown in Table 3.7 and plotted as shown in Figure 3.3 for ARI of 2 to 100 years and 0.5 to 12 months.

4. Table 3.8 is a summary of the storm intensities for ARI of 100 years for Kuala Lumpur based on MSMA (2000) and the 14 stations in MSMA (2011).

5. Figure 3.4 to Figure 3.9 are plots of the IDF data for MSMA (2000) and the 14 stations in MSMA (2011) for ARI of 100, 50, 20, 10, 5 and 2, respectively. It shows the scattering of values above and below the MSMA (2000) curve.

3.4.2 Evaluation The results from above are evaluated as follows: 1 Lower half of Table 3.8 summarises the ratios of the design storms for MSMA

(2011) to MSMA (2000) for ARI of 100 years. 2 It is noted the design storms estimated using MSMA (2011) scattered on both

sides of the IDF curve using MSMA (2000). 3 It can be seen that for shorter durations, the design storms for MSMA (2011)

can be 26% (Station 13) higher than the estimate based on MSMA (2000). 4 For long duration of say 72 hours, the reverse is true: the MSMA (2011)

estimates can be up to 36% (Station 6) lower than those using MSMA (2000). 5 For medium durations of between 15 to 700 min, the estimates using MSMA

(2011) were mostly higher than those estimated using MSMA (2000). In the study, out of 14 stations, 10 of them (or 71%) were higher than the MSMA (2000) curve, while the remaining 4 stations (or 29%) were lower than the first edition estimates.

6 It is concluded that the design storms estimated based on MSMA (2011) for Kuala Lumpur can be up to about 26% higher than MSMA (2000) for duration below 700 minutes, for 71% of the stations.

7 Each state has about a dozen stations with different IDF constants as shown in Appendix 2.B. There is a need to know which of the dozen or so stations to use in your design. In Kuala Lumpur, for instance, there are 14 stations- but none of the station names appeared familiar.

8 MSMA (2011) does not cover Sabah and Sarawak like in MSMA (2000).

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Table 3.4 IDF for Kuala Lumpur (MSMA 2000) ARI a b c d 30 60 90 120 150 180 200 250 300 360 480 600 720 1080 1440 2880 4320

LN(T) 3.4012 4.0943 4.4998 4.7875 5.0106 5.1930 5.2983 5.5215 5.7038 5.8861 6.1738 6.3969 6.5793 6.9847 7.2724 7.9655 8.3710

2 5.3255 0.1806 -0.1322 0.0047 99.0 64.8 48.9 39.5 33.2 28.7 26.3 21.8 18.7 15.9 12.3 10.0 8.4 5.7 4.3 2.1 1.4

5 5.1086 0.5037 -0.2155 0.0112 117.9 75.7 56.4 45.1 37.7 32.5 29.8 24.7 21.1 18.0 14.0 11.5 9.8 6.9 5.4 3.0 2.2

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 62.5 50.1 42.0 36.2 33.2 27.6 23.7 20.4 16.0 13.3 11.5 8.3 6.7 4.1 3.2

20 4.9781 0.7533 -0.2796 0.0166 142.4 91.3 68.0 54.5 45.7 39.4 36.2 30.2 26.0 22.4 17.8 14.9 12.9 9.5 7.8 5.1 4.2

50 4.8047 0.9399 -0.3218 0.0197 156.6 100.5 74.7 59.8 50.1 43.2 39.7 33.1 28.6 24.7 19.6 16.5 14.4 10.8 9.0 6.2 5.4

100 5.0064 0.8709 -0.3070 0.0186 172.2 110.2 81.8 65.4 54.7 47.2 43.3 36.1 31.1 26.8 21.3 17.9 15.6 11.6 9.6 6.5 5.4

Table 3.5 Short Duration IDF for Kuala Lumpur (Duration= 5 min) (MSMA 2000)

ARI a b c d 30 60

LN(T) 3.4012 4.0943 tc (min) P30 (mm) P60 (mm) FD Pd (mm) Id (mm/hr)

2 5.3255 0.1806 -0.1322 0.0047 99.0 64.8 5 49.51 64.8 2.08 17.7 212.5

5 5.1086 0.5037 -0.2155 0.0112 117.9 75.7 5 58.93 75.7 2.08 24.0 288.1

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 5 65.18 83.9 2.08 26.3 315.3

20 4.9781 0.7533 -0.2796 0.0166 142.4 91.3 5 71.22 91.3 2.08 29.4 352.4

50 4.8047 0.9399 -0.3218 0.0197 156.6 100.5 5 78.32 100.5 2.08 32.1 385.3

100 5.0064 0.8709 -0.3070 0.0186 172.2 110.2 5 86.12 110.2 2.08 36.0 432.3

Table 3.6 Short Duration IDF for Kuala Lumpur (Duration= 15 min) (MSMA 2000)

ARI a b c d 30 60

LN(T) 3.4012 4.0943 tc (min) P30 (mm) P60 (mm) FD Pd (mm) Id (mm/hr)

2 5.3255 0.1806 -0.1322 0.0047 99.0 64.8 15 49.51 64.8 0.8 37.3 149.1

5 5.1086 0.5037 -0.2155 0.0112 117.9 75.7 15 58.93 75.7 0.8 45.5 182.0

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 15 65.18 83.9 0.8 50.2 200.9

20 4.9781 0.7533 -0.2796 0.0166 142.4 91.3 15 71.22 91.3 0.8 55.1 220.5

50 4.8047 0.9399 -0.3218 0.0197 156.6 100.5 15 78.32 100.5 0.8 60.5 242.2

100 5.0064 0.8709 -0.3070 0.0186 172.2 110.2 15 86.12 110.2 0.8 66.9 267.4

17

Table 3.7 IDF Data for Kuala Lumpur (Station No. 3116004) (MSMA 2011)

Location:3 Ibu Pejabat JPS 1 Station No: 3116004 Duration (min): 5 15 30 60 90 120 150 180 240 300 360 480 600 720 1080 1440 2160 2880 4320

ARI (T) YR ARI (T) MTHλ (lambda) κ (kappa) θ (theta) η (eta) 0.083333 0.25 0.5 1 1.5 2 2.5 3 4 5 6 8 10 12 18 24 36 48 72

0.04 0.5 65.9923 0.2857 0.1604 0.8341 86.405 55.949 37.624 23.511 17.438 14.000 11.768 10.194 8.105 6.772 5.842 4.621 3.849 3.313 2.371 1.869 1.335 1.051 0.750

0.5 6 65.9923 0.2857 0.1604 0.8341 175.737 113.792 76.522 47.819 35.466 28.474 23.935 20.733 16.484 13.773 11.882 9.398 7.828 6.738 4.822 3.801 2.715 2.138 1.526

1 12 65.9923 0.2857 0.1604 0.8341 214.224 138.713 93.281 58.291 43.233 34.710 29.177 25.273 20.094 16.790 14.484 11.456 9.542 8.214 5.878 4.633 3.310 2.606 1.860

2 24 64.689 0.149 0.174 0.837 223.408 147.088 99.792 62.715 46.602 37.445 31.488 27.280 21.691 18.122 15.631 12.359 10.290 8.855 6.332 4.987 3.559 2.800 1.996

5 60 64.689 0.149 0.174 0.837 256.090 168.606 114.390 71.889 53.419 42.923 36.095 31.270 24.864 20.773 17.917 14.167 11.795 10.150 7.258 5.716 4.079 3.210 2.288

10 120 64.689 0.149 0.174 0.837 283.952 186.950 126.836 79.711 59.231 47.593 40.022 34.673 27.569 23.033 19.867 15.708 13.079 11.254 8.048 6.338 4.523 3.559 2.537

20 240 64.689 0.149 0.174 0.837 314.846 207.290 140.636 88.384 65.675 52.771 44.376 38.445 30.569 25.539 22.028 17.417 14.502 12.479 8.923 7.028 5.015 3.946 2.813

50 600 64.689 0.149 0.174 0.837 360.904 237.614 161.209 101.313 75.282 60.491 50.868 44.069 35.041 29.275 25.251 19.965 16.623 14.304 10.229 8.056 5.749 4.523 3.225

100 1200 64.689 0.149 0.174 0.837 400.171 263.466 178.748 112.336 83.473 67.072 56.402 48.864 38.853 32.461 27.998 22.137 18.431 15.861 11.341 8.932 6.375 5.016 3.576

Table 3.8 Summary of IDF Data for Kuala Lumpur (MSMA, 2000) and 14 Stations in Kuala Lumpur (MSMA 2011) for ARI of 100 YR

KL 5 15 30 60 90 120 150 180 240 300 360 480 600 720 1080 1440 2160 2880 4320 Duration (min)

ARI (T) YR 0.083333 0.25 0.5 1 1.5 2 2.5 3 4 5 6 8 10 12 18 24 36 48 72 Duration (hr)

Stn 0 432.310 267.416 172.244 110.206 81.759 65.388 54.726 47.221 36.112 31.112 26.825 21.297 17.880 15.556 11.590 9.558 7.493 6.457 5.444 I (mm/hr) (MSMA, 2000) (A)

Stn 1 395.431 269.801 185.729 116.946 86.495 69.122 57.820 49.848 39.298 32.595 27.938 21.862 18.051 15.424 10.854 8.449 5.929 4.610 3.231 I (mm/hr) (MSMA, 2011) (B)

Stn 2 441.196 271.343 178.198 109.984 81.358 65.305 54.927 47.619 37.937 31.762 27.450 21.783 18.193 15.699 11.298 8.941 6.426 5.082 3.650 I (mm/hr) (MSMA, 2011) (B)

Stn 3 400.171 263.466 178.748 112.336 83.473 67.072 56.402 48.864 38.853 32.461 27.998 22.137 18.431 15.861 11.341 8.932 6.375 5.016 3.576 I (mm/hr) (MSMA, 2011) (B)

Stn 4 384.224 245.872 164.731 103.009 76.565 61.605 51.887 45.024 35.907 30.078 26.002 20.640 17.239 14.875 10.703 8.468 6.083 4.809 3.451 I (mm/hr) (MSMA, 2011) (B)

Stn 5 344.150 236.902 165.239 106.156 79.666 64.389 54.362 47.234 37.714 31.600 27.314 21.665 18.079 15.584 11.184 8.830 6.322 4.985 3.565 I (mm/hr) (MSMA, 2011) (B)

Stn 6 326.773 232.073 164.818 107.094 80.618 65.210 55.050 47.811 38.124 31.896 27.532 21.781 18.134 15.602 11.144 8.767 6.245 4.906 3.489 I (mm/hr) (MSMA, 2011) (B)

Stn 7 339.034 252.147 184.338 122.080 92.365 74.786 63.100 54.736 43.511 36.285 31.222 24.561 20.350 17.434 12.328 9.625 6.780 5.283 3.714 I (mm/hr) (MSMA, 2011) (B)

Stn 8 348.841 241.830 168.695 107.763 80.392 64.640 54.329 47.021 37.297 31.082 26.744 21.056 17.467 14.983 10.634 8.328 5.895 4.610 3.259 I (mm/hr) (MSMA, 2011) (B)

Stn 9 348.150 254.023 183.554 120.752 91.285 73.967 62.487 54.281 43.273 36.183 31.210 24.654 20.499 17.614 12.543 9.844 6.987 5.474 3.879 I (mm/hr) (MSMA, 2011) (B)

Stn 10 328.113 230.955 164.005 107.379 81.483 66.376 56.379 49.228 39.610 33.386 28.998 23.176 19.454 16.850 12.222 9.722 7.034 5.589 4.039 I (mm/hr) (MSMA, 2011) (B)

Stn 11 353.107 235.097 160.538 101.368 75.467 60.702 51.078 44.270 35.221 29.436 25.395 20.085 16.726 14.395 10.296 8.109 5.788 4.554 3.247 I (mm/hr) (MSMA, 2011) (B)

Stn 12 486.768 300.551 196.180 119.472 87.453 69.612 58.147 50.117 39.547 32.857 28.217 22.164 18.363 15.740 11.160 8.738 6.186 4.839 3.423 I (mm/hr) (MSMA, 2011) (B)

Stn 13 507.188 326.983 217.871 134.141 98.415 78.351 65.410 56.329 44.366 36.792 31.541 24.699 20.411 17.456 12.313 9.603 6.760 5.267 3.704 I (mm/hr) (MSMA, 2011) (B)

Stn 14 295.879 215.078 154.744 101.189 76.175 61.524 51.839 44.932 35.691 29.758 25.607 20.152 16.705 14.319 10.141 7.927 5.595 4.366 3.076 I (mm/hr) (MSMA, 2011) (B)

Stn 1 0.91 1.01 1.08 1.06 1.06 1.06 1.06 1.06 1.09 1.05 1.04 1.03 1.01 0.99 0.94 0.88 0.79 0.71 0.59 B/A

Stn 2 1.02 1.01 1.03 1.00 1.00 1.00 1.00 1.01 1.05 1.02 1.02 1.02 1.02 1.01 0.97 0.94 0.86 0.79 0.67 B/A

Stn 3 0.93 0.99 1.04 1.02 1.02 1.03 1.03 1.03 1.08 1.04 1.04 1.04 1.03 1.02 0.98 0.93 0.85 0.78 0.66 B/A

Stn 4 0.89 0.92 0.96 0.93 0.94 0.94 0.95 0.95 0.99 0.97 0.97 0.97 0.96 0.96 0.92 0.89 0.81 0.74 0.63 B/A

Stn 5 0.80 0.89 0.96 0.96 0.97 0.98 0.99 1.00 1.04 1.02 1.02 1.02 1.01 1.00 0.97 0.92 0.84 0.77 0.65 B/A

Stn 6 0.76 0.87 0.96 0.97 0.99 1.00 1.01 1.01 1.06 1.03 1.03 1.02 1.01 1.00 0.96 0.92 0.83 0.76 0.64 B/A

Stn 7 0.78 0.94 1.07 1.11 1.13 1.14 1.15 1.16 1.20 1.17 1.16 1.15 1.14 1.12 1.06 1.01 0.90 0.82 0.68 B/A

Stn 8 0.81 0.90 0.98 0.98 0.98 0.99 0.99 1.00 1.03 1.00 1.00 0.99 0.98 0.96 0.92 0.87 0.79 0.71 0.60 B/A

Stn 9 0.81 0.95 1.07 1.10 1.12 1.13 1.14 1.15 1.20 1.16 1.16 1.16 1.15 1.13 1.08 1.03 0.93 0.85 0.71 B/A

Stn 10 0.76 0.86 0.95 0.97 1.00 1.02 1.03 1.04 1.10 1.07 1.08 1.09 1.09 1.08 1.05 1.02 0.94 0.87 0.74 B/A

Stn 11 0.82 0.88 0.93 0.92 0.92 0.93 0.93 0.94 0.98 0.95 0.95 0.94 0.94 0.93 0.89 0.85 0.77 0.71 0.60 B/A

Stn 12 1.13 1.12 1.14 1.08 1.07 1.06 1.06 1.06 1.10 1.06 1.05 1.04 1.03 1.01 0.96 0.91 0.83 0.75 0.63 B/A

Stn 13 1.17 1.22 1.26 1.22 1.20 1.20 1.20 1.19 1.23 1.18 1.18 1.16 1.14 1.12 1.06 1.00 0.90 0.82 0.68 B/A

Stn 14 0.68 0.80 0.90 0.92 0.93 0.94 0.95 0.95 0.99 0.96 0.95 0.95 0.93 0.92 0.87 0.83 0.75 0.68 0.57 B/A

0.876 0.955 1.023 1.017 1.023 1.030 1.035 1.040 1.081 1.047 1.047 1.041 1.031 1.019 0.975 0.929 0.843 0.768 0.647

NB. Station 0 denotes the Kuala Lumpur station used in MSMA (2011). For Stations 1 to 14, refer to Table 3.9 for Station ID and Name

18

.

Table 3.9 Summary of Stations in Kuala Lumpur (After Table 2.B1 in MSMA, 2011)

Station No. Station ID Station Name

1 3015001 Puchong Drop, Kuala Lumpur

2 3116003 Ibu Pejabat JPS

3 3116004 Ibu Pejabat JPS1

4 3116005 SK Taman Maluri

5 3116006 Ladang Edinburgh

6 3216001 Kg. Sg. Tua

7 3216004 SK Jenis Keb, Kepong

8 3217001 Ibu Bek. KM16, Gombak

9 3217002 Emp Genting Kelang

10 3217003 Ibu Bek. KM11, Gombak

11 3217004 Kg. Kuala Seleh, H. Klg

12 3217005 Kg. Kerdas, Gombak

13 3317001 Air Terjun, Sg Batu

14 3317004 Genting Sempah

19

Figure 3.2 IDF for Kuala Lumpur (MSMA 2000)

Figure 3.3 IDF For Kuala Lumpur (MSMA 2011) (Station No. 3116004)

1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)

Storm Duation (min)

Rainfall Intensity Frequency Duration Curve for KL

(Station No: 3116004) (MSMA, 2011

0.05 YR (0.5 MTH) 0.5 YR (6 MTH) 1 YR (12 MTH) 2 YR 5 YR 10 YR 20 YR 50 YR 100 YR

1

10

100

1000

10 100 1000 10000

INT

EN

SIT

Y (

MM

/HR

)

DURATION (MINUTES

IFD CURVE FOR KUALA LUMPUR (1951-1990) (MSMA 2000)

2 5 10 20 50 100

20

Figure 3.4 Comparison of Estimated Rainfall Intensity Frequency Duration Curves for Kuala Lumpur between MSMA 2000 & 2011 (ARI. =100 YR)

1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)

Storm Duration (min)

Comparison of Estimated Rainfall Intensity Frequency Duration Curves for Kuala Lumpur between MSMA 2000 & 2011 (A.R.I. =100 YR)

0 (MSMA 2000) 1 (MSMA 2011) 2 (MSMA 2011) 3 (MSMA 2011) 4 (MSMA 2011)




1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)


Comparison of Estimated Rainfall Intensity Frequency Duration Curves for Kuala Lumpur Between MSMA 2000 & 2011 (A.R.I. =50 YR)




21


1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)







1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)






22


1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)







1

10

100

1000

1 10 100 1000 10000

Rai

nfa

ll In

ten

sity

(m

m/h

r)






23

4. Changes in the Rational Method

Rational Method is covered in Chapter 14 of the first edition and Chapter 2 of the second edition.

4.1 Rational Method in MSMA (2000) MSMA relates the peak discharge to the rainfall intensity and catchment area via the Rational Method:

360

AICQ

t

y

y

(Equation 4.1)

where Qy is the y year ARI peak discharge (m3/s) C is the dimensionless runoff coefficient yIt is the average intensity of the design rainstorm of duration equal to

the time of concentration tc and of ARI of y year (mm/hr) A is the drainage area (ha)

Recommended values of C may be obtained from Design Chart 14.3 for urban areas and Design Chart 14.4 of MSMA (2000) for rural areas. The steps of computation are shown in Figure 4.1.

24

Figure 4.1 Steps of Computation in the Rational Method in MSMA (2000)

25

4.2 Rational Method in MSMA (2011) In MSMA (2011), the peak discharge is related to the rainfall intensity and catchment area via the Rational Method:

360

AiCQ

(Equation 4.2)

where Q is the peak flow (m3/s) C is the runoff coefficient given in Table 4.1 (Table 2.5 of MSMA, 2011). I is the average rainfall intensity (mm/hr) A is the drainage area (ha)

The steps of computation are shown in Figure 4.2.

4.3 Evaluation The changes in design discharge using the Rational Method are as follows: 1. The major change in the Rational Method is the coefficient of runoff. In the

second edition, it is read from a design chart and varies according to the types of landuse, the rainfall intensities and whether it is urban or rural catchments. But in the second edition, it is fixed according to the landuse- like in the P&DP No. 1 (DID, 1975), as shown in Table 4.1 (Table 2.5 of MSMA, 2011).

2. There is no change in the size of catchment area where the Rational Method can be applied. Both editions specify that the Rational Method should not be used for catchment area greater than 80 ha.

3. The magnitude of changes in the design discharge is covered in the following case study.

26

Figure 4.2 Steps of Computation in the Rational Method in MSMA (2011)

Calculate Tc

Calculate I

Calculate Qp

Calculate C

Table 2.5 (MSMA, 2011)

27

Table 4.1 Recommended Runoff Coefficients for Various Landuses (DID, 1980; Chow et al., 1988; QUDM, 2007 and Darwin Harbour, 2009) (After Table 2.5 of MSMA, 2011)

Landuse Runoff Coefficient (C)

For Minor System (≤10 year ARI)

For Major System (>10 year ARI)

Residential

Bungalow

Semi-detached Bungalow

Link and Terrance House

Flat and Apartment

Condominium

0.65 0.70 0.80 0.80 0.75

0.70 0.75 0.90 0.85 0.80

Commercial and Business Centres 0.90 0.95

Industrial 0.90 0.95

Sport Fields, Park and Agriculture 0.30 0.40

Open Spaces

Bare Soil (No Cover)

Grass Cover

Bush Cover

Forest Cover

0.50 0.40 0.35 0.30

0.60 0.50 0.45 0.40

Roads and Highways 0.95 0.95

Water Body (Pond)

Detention Pond (with outlet)

Retention Pond (no outlet)

0.95 0.00

0.95 0.00

Note: The runoff coefficients in this table are given as a guide for designers. The near-field runoff coefficient for any single or mixed landuse should be determined based on the imperviousness of the area.

4.4 Case Study on Rational Method The Rational Method for the second edition has changed from the first edition. For comparison, the method is applied to a typical catchment and the results compared. The changes in the design discharge due to changes in the runoff coefficient C are assessed. In this case study, the Rational Methods in both editions of MSMA are applied to compute the peak discharge for a major system in the study area. Figure 4.3 shows a map of the catchment area. The study area is located in Sg. Batu, Kuala Lumpur. The catchment data are as follows:

Area= 30 hectares.

Length of Overland flow= 300 m

Slope= 0.3%, paved surface.

Length of Open Drain= 600 m Three types of landuses were studied:

Park

28

Semi-D Houses

Commercial and city area

4.4.1 Rational Method (MSMA, 2000)

The three types of landuses were studied according to Table 2.1 (Table 4.1 of MSMA, 2000):

Park, ARI= 20 years

Semi-D Houses, ARI= 50 years

Commercial and city area, ARI= 100 years

Step 1- Calculate Tc Overland flow time (To) is estimated using Friend’s Formula:

2.0

3/1107

S

Lnto

where

n= 0.011 from (Table 14.2 of MSMA, 2000) for paved surface

S= 0.3%

L (Overland sheet flow path length in m) = 300 m. Applying the Friend’s Formula, To= 10 min. Average velocity in the open drain is assessed using Manning’s Equation where V is found to be 1 m/s. Td=L/V= 600/1= 600 s= 10 min. Hence, Tc= To + Td = 10+10 = 20 min Step 2- Calculate I The values of the coefficients for a, b, c and d in (Table 13.A1 of MSMA, 2000) for ARI of 100 years for Kuala Lumpur are as follows: a= 5.0064, b= 0.8709, c= -0.3070, d= 0.0186 Substituting the above coefficients into:


R

For t= 30 min, 5I30= 172.2 mm/hr For t= 60 min, 5I60= 110.2 mm/hr Convert to rainfall depths, 100P30= 172.2/2 = 86.12 mm 100P60= 110.2/1 = 110.2 mm

29

Step 3- Calculate C

According to MSMA (2000), the design rainfall depth Pd for a short duration d (min) is given by:

)( 306030 PPFPP Dd

where P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from the published polynomial curves. FD is the adjustment factor for storm duration based on Table 13.3 of MSMA (2000).

From Figure 13.3 (MSMA, 2000) 2P24h= 100 for Kuala Lumpur. From Table 13.3 (MSMA, 2000) for a duration of 20 min, the FD=0.47. Hence 100P20= 86.12-0.47*(110.2-86.12)= 74.8 mm Therefore 100I20= 224.3 mm/hr 50I20= 203.6 mm/hr 20I20= 185.2 mm/hr The C is determined from Design Chart 14.3 (MSMA, 2000), for the following landuses:

Park (Curve No. 7), C=0.61

Semi-D Houses (Curve No. 3), C=0.9

Commercial and city area (Curve No. 2), C=0.905 Step 4- Calculate Qp

The peak discharge for ARI=100 years is computed using the Rational Method:

360

AICQ

t

y

y

The peak discharges are determined for the three types of landuses: Park (Curve No. 7), ARI= 20 years Qp= 0.61*185.2*30/360 = 9.4 m3/s Semi-D Houses (Curve No. 3), ARI= 50 years Qp= 0.9*203.6*30/360 = 15.3 m3/s Commercial and city area (Curve No. 2), ARI= 100 years Qp= 0.905*224.3*30/360 = 16.9 m3/s

The computations were carried out on a spreadsheet and tabulated as shown in Table 4.2.

30

4.4.2 Rational Method (MSMA, 2011)

The three types of landuses were studied according to Table 1.1 of MSMA (2011):

Park, ARI= 20 years

Semi-D Houses, ARI= 50 years

Commercial and city area, ARI= 100 years

The catchment data are the same as the previous case study using MSMA (2000). Step 1- Calculate Tc The storm duration is the same as the time of concentration of 20 min as determined earlier. Step 2- Calculate I For the study area of Sg. Batu, the following fitting constants were taken from Table 2.B1 of MSMA (2011):

, κ, θ and η= 72.992, 0.162, 0.171 and 0.871.

Substituting the above into the following equation:

hrmm

d

Ti /4.279

171.060/20

100992.72871.0

162.0

For ARI= 50 years, i= 249.7 mm/hr For ARI= 20 years, i= 215.3 mm/hr Step 3- Calculate C The C is determined from Table 3.2 of MSMA (2011) for the following landuses:

Park, C=0.4

Semi-D Houses, C=0.75

Commercial and city area, C=0.95 Step 4- Calculate Qp The peak discharges are determined for the following three types of landuses: For Park, ARI= 20 years Qp= 0.4*215.3*30/360 =7.2 m3/s For Semi-D Houses, ARI= 50 years Qp= 0.75*249.7*30/360 = 15.6 m3/s For Commercial and city area, ARI= 100 years Qp= 0.95*279.4*30/360 = 22.1 m3/s

The computations were carried out on a spreadsheet and tabulated as shown in Table 4.3.

31

4.5 Evaluation

Table 4.3 is a summary of the peak discharges computed using MSMA (2000) and (2011). To find out the magnitude of increase in discharge, we define a ratio R:

1

2

p

p

Q

Q

B

AR

where A= Qp2 which is the peak discharge based on MSMA (2011) B= Qp1 which is the peak discharge based on MSMA (2000)

The ratio R is tabulated as shown in the last column of the table. It can be seen that: 1. For park, the ratio R is 0.76 indicating that the peak discharge from MSMA

(2011) is lower than the peak discharge from MSMA (2000). This is due principally to the lower C of 0.4 in MSMA (2011) compared to a higher C of 0.61 in MSMA (2000). The lower C in MSMA (2011) reflects DID’s effort in promoting more storage in parks.

2. For Semi-D houses, the ratio R is 1.02 indicating that the peak discharge from MSMA (2011) is about 2% higher than the peak discharge from MSMA (2000). The Q has increased from 15.3 to 15.6 m3/s.The C has reduced from 0.9 to 0.75 but the i has increased from 203.6 mm/hr to 249.7. The reduction in C is only for Semi-D houses, while the increase in storm intensity is generally associated with MSMA (2011). In this case, the effect of the increasing storm intensity is more prominent, thus giving a higher peak discharge.

3. For commercial and city area, the ratio R is 1.31 indicating that the peak discharge from MSMA (2011) is about 31% higher than the peak discharge from MSMA (2000). The Q has increased from 16.9 to 22.1 m3/s. The C has increased from 0.905 to 0.95 while the storm intensity has increased from 224.3 mm/hr to 279.4. The increase in C for commercial and city area and storm intensity in MSMA (2011) has attributed to a significantly higher peak discharge.

4. In conclusion, the peak discharge computed using the Rational Method in MSMA (2011) is up to 31% higher than that in MSMA (2000). This increase is caused principally by the higher storm intensity in MSMA (2011), and by the higher C for commercial and city area in MSMA (2011).

5. The magnitude of increase in peak discharge associated with the Rational Method in MSMA (2011) varies depending on the station used for the IDF computation. MSMA (2011) has provided 14 stations with different IDF data for Kuala Lumpur. In the case study for storm, it was found that 71% of these stations have higher storm intensities under MSMA (2011).

6. In general, it is concluded that 71% of the stations in Kuala Lumpur will have up to 26% higher storm intensity and up to 31% higher peak discharges for commercial and city area.

32

Figure 4.3 Catchment Map

Ld

Rive

r

Catchment Area= 30 hectares

Lo

33

Table 4.2 Computation of Peak Discharges using the Rational Method in MSMA (2000)

ARI 30 60 Calculate Tc Using Friends Formula>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Design Chart 14.3

LN(T) a b c d 3.4012 4.0943 n Lo (m) S (%) to (min) Ld (m) Vd (m/s) td (min) tc (min) P30 (mm) P60 (mm) FD Pd (mm) Id (mm/hr) C A (ha) Qp (m3/s) Type Curve No.

20 4.9781 0.7533 -0.2796 0.0166 142.4 91.3 0.011 300 0.3 10.01 600 1 10.00 20 71.22 91.3 0.47 61.8 185.2 0.61 30 9.4 Park 7

50 4.8047 0.9399 -0.3218 0.0197 156.6 100.5 0.011 300 0.3 10.01 600 1 10.00 20 78.32 100.5 0.47 67.9 203.6 0.9 30 15.3 Semi-D 3

100 5.0064 0.8709 -0.3070 0.0186 172.2 110.2 0.011 300 0.3 10.01 600 1 10.00 20 86.12 110.2 0.47 74.8 224.3 0.905 30 16.9 Commercial 2

Table 4.3 Computation of Peak Discharges using the Rational Method in MSMA (2011)

Location:13 3317001 Station Name: Air Terjun, Sg Batu Duration (min): 20 A (ha) C (Table 2.5) Landuse Q (m3/s) (A)

ARI (T) YR λ (lambda) κ (kappa) θ (theta) η (eta) 0.3 MSMA (2011)

20 72.992 0.162 0.171 0.871 215.3 30 0.4 park 7.2

50 72.992 0.162 0.171 0.871 249.7 30 0.75 Semi-D 15.6

100 72.992 0.162 0.171 0.871 279.4 30 0.95 Commercial 22.1

Table 4.4 Comparison of Peak Discharges using the Rational Method in MSMA (2000, 2011)

Landuse Q (m3/s) (A) Q (m3/s) (B) A/B

MSMA (2011) MSMA (2000)

park 7.2 9.4 0.76

Semi-D 15.6 15.3 1.02

Commercial 22.1 16.9 1.31

msma_drquek7.docx 34

5. Changes in On-Site Detention 5.1 OSD Sizing using MSMA (2000) 5.1.1 Theory

In MSMA (2000), the method of estimating Permissible Site Discharge (PSD) and Site Storage Requirement (SSR) is the Swinburne Method developed at the Swinburne University of Technology in Melbourne, Australia. The method is basically site-based, but considers the position of a site within the catchment. Refer to Figure 5.1, the peak flow time of concentration from the top of the catchment to the development site, tcs, is compared to the total time of concentration for the catchment, tc. The PSD varies with this ratio and may be less than or greater than the peak pre-development site discharge depending on the position of the site within the catchment. The method uses the Rational Method to calculate site flows, and utilizes a non-dimensional triangular site hydrograph based on the triangular design storm method as shown in Figure 5.2. The site discharges are calculated using the total catchment time of concentration tc (not the time of concentration to the development site) for the design storm ARI under consideration as shown in Figure 5.1.

Figure 5.1 Relationship Between tc and tcs for the Swinburne Method


Figure 5.2 Swinburne Method Assumptions tf= Time for Storage to Fill

5.1.2 Permissible Site Discharge (PSD) The PSD is the maximum allowable post-development discharge from a site for the selected discharge design storm and is estimated on the basis that flows within the downstream stormwater drainage system will not be increased. PSD is dependent on the following criteria:

The time of concentration of the catchment to its outlet, or a point of concern either within or downstream of the catchment.

The position of the site, time-wise from the uppermost reach of the catchment.

The original or adopted ARI of the public drainage system within the catchment and rainfall data.

The area of the development site.

The proportion of impervious area of the development site.

The type of OSD storage facility.

The extent of development or redevelopment within the catchment.

Local and/or regional drainage policies. The Permissible Site Discharge (PSD) for the site in l/s is given by (Equation 19.1 of MSMA, 2000):

2

42

baaPSD

(Equation 5.1)

The factors a and b are different for above-ground and below-ground storages due to differences in storage geometry and outflow characteristics. For above-ground storage:

csc

a

p

c

c

a ttQ

Qt

t

Qa 25.075.0333.04 (Equation 5.2)


paQQb 4 (Equation 5.3)

For below-ground storage:

csc

a

p

c

c

a ttQ

Qt

t

Qa 65.035.0333.0548.8 (Equation 5.4)

paQQb 548.8 (Equation 5.5)

where

tc is Peak flow time of concentration from the top of the catchment to a designated outlet or point of concern (min) tcs is peak flow time of concentration from the top of the catchment to the development site (min) Qa is the peak post-development flow from the site for the discharge design storm with a duration equal to tc (l/s) Qp is the peak pre-development flow from the site for the discharge design storm with a duration equal to tc (l/s).

5.1.3 Site Storage Requirement (SSR) The SSR is the total amount of storage required to ensure that the required PSD is not exceeded and the OSD facility does not overflow during the storage design storm ARI. As stated earlier, the storage design storm for estimating the SSR is 10 year ARI. In sizing the volume of the storage facility, the method assumes a triangular inflow hydrograph and an outflow hydrograph shape related to the type of storage adopted. These simplifications are acceptable providing the site catchment is small. Typically, the critical storm duration that produces the largest required storage volume is different from the time of concentration used for peak flow estimation. Therefore, storage volumes must be determined for a range of storm durations to find the maximum storage required as shown in Figure 5.3.


Figure 5.3 Typical Relationship of Storage Volume to Storm Duration

The Site Storage Requirement (SSR) for the site in m3 is calculated using the formula:

dcQtSSR dd 06.0 (Equation 5.6)

The factors c and d are different for above-ground and below-ground storages due to differences in storage geometry and outflow characteristics. For above-ground storage:

dQ

PSDPSDc 459.01875.0 (Equation 5.7)

dQ

PSDd

2

214.0 (Equation 5.8)


dQ

PSDPSDc 392.01675.0 (Equation 5.9)

dQ

PSDd

2

117.0 (Equation 5.10)

where


td= selected storm duration (min) Qd= the peak post-development flow from the site for a storm duration equal to td (l/s)

5.1.4 OSD Sizing Procedure A simplified design procedure for determining the required volume of detention storage is as follows (see Figure 5.4): 1. Select storage type(s) to be used within the site, i.e. separate above and/or

below-ground storage(s), or a composite above and below-ground storage. 2. Determine the area of the site that will be drained to the OSD storage system.

As much of the site as possible should drain to the storage system. 3. Determine the amount of impervious and pervious areas draining to the OSD

storage system. 4. Determine the times of concentration, tc and tcs. 5. Calculate the pre and post-development flows, Qp and Qa, for the area

draining to the storage for the discharge design storm with time of concentration tc.

6. Determine the required PSD for the site using Equation 5.1 for the discharge design storm.

7. Determine the required SSR for the site using Equation 5.6 for the storage design storm over a range of durations to determine the maximum value.


Figure 5.4 Steps of Computation in OSD Design in MSMA (2000)

Determination of PSD

Discharge/Storage

Design Storm

Determination of SSR

Design OSD

Determination of Pre & Post Development Flows

Determination of tc and tcs

Determination of

Impervious & Pervious Areas


5.2 OSD Sizing using MSMA (2011) 5.2.1 Limiting Catchment Areas for OSD in MSMA (2011)

Table 5.1 lists the limiting catchment areas for OSD in MSMA (2011). OSD is to be used for areas less than 5 ha. For areas above 5 ha, the use of detention pond is required.

Table 5.1 Limiting Catchment Areas for OSD or Dry/Wet Detention Pond in MSMA (2011)

Type of Storage Facility

Limiting Area (ha)

Individual OSD ≤ 0.1

Community OSD >0.1, ≤5

Dry Detention Pond 5 to 10

Wet Detention Pond >10

5.2.2 Method for OSD Design in MSMA (2011)

Below are the steps involved in OSD design based on MSMA (2011). 1. Figure 5.A1 (MSMA, 2011) divides peninsula into 5 design regions. 2. Determine project area, terrain steepness, and percentage imperviousness. 3. Table 5.A1 gives the maximum permissible site discharge (PSD) and minimum

Site Storage Requirement (SSR) values in accordance with the five regions in Peninsular Malaysia.

4. Table 5.A2 gives the maximum permissible site discharge (PSD), minimum Site Storage Requirement (SSR) and inlet values in accordance with the major towns in Peninsular Malaysia.

5. Adopt smaller PSD value from Table 5.A1 and 5.A2 for subsequent sizing of outlet pipe.

6. Table 5.A3 gives the OSD volume, inlet size and outlet size for 5 different regions in Peninsular Malaysia.

7. Table 5.A4 gives the discharge and pipe diameter relationship for low lying, mild and steep slopes.

8. Adopt the SSR is the larger from Table 5.A1 and 5.A2. 9. Sizing of OSD tank based on the SSR. 10. Adopt inlet pipe: Inlet pipe is the smaller of Table 5.A3 and 5.A4. 11. Adopt outlet pipe: Outlet pipe is the smaller of Table 5.A3 and 5.A4.


5.3 Case Study on On-Site Detention for Kuala Lumpur The case study looks at the design of a below-ground, on-site detention (OSD) facility using the guidelines described in MSMA (2000) and MSMA (2011) for a proposed factory site in SK Taman Maluri, Kuala Lumpur as shown in Figure 5.5.

Figure 5.5 Location of OSD in the Project Site

5.3.1 OSD in MSMA (2000)

5.3.1.1 Design Criteria

The proposed single storey factory can be classified as low density development. According to Chapter 11 of the Manual, on-site facilities are minor drainage structures provided on individual housing, industrial and infrastructure sites. For quantity design they are based on peak inflow estimates using the Rational Method with design storms between 2 and 10 year ARI. The design rainfall is based on Chapter 13 of the Manual. The design storm for Kuala Lumpur is used in the calculation.

River

OSD

Factory Site


5.3.1.2 Determination of Impervious and Pervious Areas

For the purpose of hydrological calculation, the area is shown in Table 5.2. It is estimated that 70% of the areas may be considered as impervious. Hence the impervious area is computed by multiplying the total area by 70% as shown in the table. The remaining 30% of the areas is assumed pervious. Hence the pervious area is computed by multiplying the total area by 30% as shown in the table.

Table 5.2 Pervious and Impervious Areas

Total area (m2) Pervious Area (m2) Impervious Area (m2)

30162 9048.6 21113.4

5.3.1.3 Determination of Time of Concentration, tc and tcs

For small catchments of up to 0.4 hectare in area, it is acceptable to use the minimum times of concentration given in Table 14.3 of MSMA (2000) instead of performing detailed calculation. The times of concentration adopted are as follows:

tc= 10 min (factory site outlet)

tcs= 5 min (roof and property drainage)

5.3.1.4 Determination of Pre and Post Development Flows

Calculate I The values of the coefficients for a, b, c and d in Table 13.A1 (MSMA, 2000) for ARI of 2 years for Kuala Lumpur are as follows: a=5.3255, b=0.1806, c=-0.1322, d=0.0047 Substituting the above coefficients into:


R

where RIt is the average rainfall intensity (mm/hr) for ARI R and duration t R is average return interval (years) t is duration (minutes) a to d are fitting constants dependent on ARI.

For t= 30 min, 2I30= 99.0 mm/hr For t= 60 min, 2I60= 64.8 mm/hr Convert to rainfall depths, 2P30= 99/2 = 49.51 mm 2P60= 64.8/1 = 64.8 mm


Calculate C According to DID (2000), the design rainfall depth Pd for a short duration d (min) is given by:

)( 306030 PPFPP Dd

where P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from the published polynomial curves. FD is the adjustment factor for storm duration from Table 13.3 (MSMA, 2000).

Hence 2P10= 49.51-1.28*(64.8-49.51)= 29.94 mm Therefore 2I10= 179.63 mm/hr From Design Chart 14.3, for category 7 (park lawns and meadows) the runoff coefficient is 0.59. For category 1 (impervious roof and concrete), the runoff coefficient is 0.91. Calculate Qp The peak discharge for ARI=2 years is computed using the Rational Method:

360

AICQ

t

y

y



For pre-development, Qp= 1.7796*179.63/360 *1000= 888.0 l/s (Qp) For post-development, Qp= 2.4552*179.63*/360 *1000= 1225.1 l/s (Qa) The results are tabulated in Table 5.3.

5.3.1.5 Determination of Permissible Site Discharge (PSD)

As stated in Section 19.3.1 of the Manual, the discharge design storm for estimating the PSD is the minor system design ARI of the municipal stormwater system to which the site is or will be connected. In this case, it is the 2 year ARI storm. The Permissible Site Discharge (PSD) for the site in l/s is given by (from Equation 19.1 of MSMA, 2000):


2

42

baaPSD

The factors a and b are different for above-ground and below-ground storages due to differences in storage geometry and outflow characteristics. For below-ground storage:

csc

a

p

c

c

a ttQ

Qt

t

Qa 65.035.0333.0548.8

paQQb 548.8

where tc= Peak flow time of concentration from the top of the catchment to a designated outlet or point of concern (min) tcs= peak flow time of concentration from the top of the catchment to the development site (min) Qa= the peak post-development flow from the site for the discharge design storm with a duration equal to tc (l/s) Qp= the peak pre-development flow from the site for the discharge design storm with a duration equal to tc (l/s)


2.9596565.01035.01.1225

0.88810333.0

10

1.1225548.8

a

1.92988240.8881.1225548.8 b

6.10932

1.929882442.95962.95962

PSD

The results are tabulated in Table 5.4.

5.3.1.6 Determination of Site Storage Requirement (SSR)

As stated in Section 19.3.1 of MSMA (2000), the storage design storm for estimating the SSR is 10 year ARI. In sizing the volume of the storage facility, the method assumes a triangular inflow hydrograph and an outflow hydrograph shape related to the type of storage adopted. These simplifications are acceptable providing the site catchment is small. Typically, the critical storm duration that produces the largest required storage volume is different from the time of concentration used for peak flow estimation. Therefore storage volumes must be determined for a range of storm durations to


find the maximum storage required. The Site Storage Requirement (SSR) for the site in m3 is calculated using the formula:

dcQtSSR dd 06.0

The factors c and d are different for above-ground and below-ground storages due to differences in storage geometry and outflow characteristics. For below-ground storage:

dQ

PSDPSDc 392.01675.0

dQ

PSDd

2

117.0

where td= selected storm duration (min) Qd= the peak post-development flow from the site for a storm duration equal to td (l/s)

The values of the coefficients for a, b, c and d in Table 13.A1 for ARI of 10 years for Kuala Lumpur are as follows: a=4.9696, b=0.6796, c=-0.2584, d=0.0147 The magnitudes of 5, 10, 15 and 20 minutes short duration design storms are computed as shown in Table 5.5 to be 315.3, 247.4, 200.9 and 169.2 mm/hr, respectively. The C values are read from Design Chart 14.3 of the Manual. For impervious area, the C values are based on Category 1 (Impervious roof and concrete) catchment for the range of rainfall intensities corresponding to tc of 5, 10, 15 and 20 min. For pervious area, the C values are based on Category 7 (park lawns and meadows) catchment for the range of rainfall intensities corresponding to tc of 5, 10, 15 and 20 min. For the area, for tc= 5 min, the peak post-development flow: Qp= 2.6452*315.3/360 *1000= 2317.0 l/s (Qd) The results and those for tc =10, 15 and 20 min are tabulated in Table 5.5. The corresponding SSR are computed using the above formula for below-ground storage.


6.6010.2317

6.1093392.016.1093675.0

c

4.602317

6.1093117.0

2

d

5.4964.606.6010.2317506.0 SSR

The results for tc =5, 10, 15 and 20 min are tabulated in Table 5.6 and plotted as shown in Figure 5.6. It can be seen that the maximum SSR is 700.9 m3 for a storm duration of 15 min. The SSR is therefore 700.9 m3.

Figure 5.6 Plot of SSR Versus Storm Duration

400 450 500 550 600 650 700 750 800

0 5 10 15 20 25


SS

R (

M3

)


Table 5.3 Computation of Pre/Post Development Peaks Develop ment

ARI a b C D 30 60 Impervious Area

Pervious Area Sum Pre/Post Dev

LN(T) LN(T) 3.4012 4.0943 tcs (min)

tc (min)

P30 (mm)

P60 (mm)

FD Pd (mm)

Id (mm/hr)

C A (ha) C A (ha) CA Qp (l/s)

Pre 2 5.3255 0.1806 -0.1322 0.0047 99.0 64.8 5 10 49.51 64.8 1.28 29.94 179.63 0 0 0.59 3.0162 1.7796 887.9

Post 2 5.3255 0.1806 -0.1322 0.0047 99.0 64.8 5 10 49.51 64.8 1.28 29.94 179.63 0.91 2.1113 0.59 0.9049 2.4552 1225.0

Table 5.4 Computation of Permissible Site Discharge (PSD)

Development Pre/Post Dev Below Ground Storage

Tcs (min) tc (min) Qp (l/s) a b PSD (l/s)

Pre-Development

5 10 887.964

Post-Development

5 10 1225.090 9596.223 9298824.1 1093.6

Table 5.5 Computation of Peak Post-Development Flow (QD) ARI a b C D 30 60 Impervious

Area Pervious Area Sum Pre/Post

Dev

LN(T) 3.4012 4.0943 tcs (min)

tc (min)

P30 (mm)

P60 (mm)

FD Pd (mm)

Id (mm/hr)

C A (ha) C A (ha) CA Qp (l/s)

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 5 65.18 83.9 2.08 26.28 315.33 0.91 2.1113 0.8 0.9049 2.6452 2317.0

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 10 65.18 83.9 1.28 41.24 247.43 0.91 2.1113 0.7 0.9049 2.5547 1755.9

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 15 65.18 83.9 0.80 50.21 200.86 0.91 2.1113 0.63 0.9049 2.4914 1390.0

10 4.9696 0.6796 -0.2584 0.0147 130.4 83.9 20 65.18 83.9 0.47 56.39 169.16 0.91 2.1113 0.58 0.9049 2.4461 1149.4


Table 5.6 Computation of Site Storage Requirements (SSR)

Pre/Post Dev Below Ground Storage

tc (min) Qp (l/s) PSD (l/s) C d SSR (m3)

5 2317.0 1093.6 601.6201 60.3980 496.5

10 1755.9 1093.6 557.9707 79.6987 670.9

15 1390.0 1093.6 510.5355 100.6735 700.9

20 1149.4 1093.6 462.868 121.7509 677.7

5.3.2 OSD in MSMA (2011)

In this section, an OSD is designed based on MSMA (2011) for the same site as in the previous section. The design is presented below and tabulated in a spreadsheet as shown in Figure 5.7.

Project Data The project area is located in Kuala Lumpur. So from Figure 5.A1 which divides peninsula into 5 design regions, the project area is located in Region 1- West Coast. The Project area is 3.0162 ha. The Terrain is mild. The % imperviousness is 70 per cent. Table 5.A1 Table 5.A1 gives the maximum permissible site discharge (PSD) and minimum Site Storage Requirement (SSR) values in accordance with the five regions in Peninsular Malaysia. From Table 5.A1, the Permissible Site Discharge (PSD)/ha= 78.54 l/s/ha. For the project area, PSD= 3.0162 x 78.54=236.9 l/s=0.237m3/s. From Table 5.A1, the Site Storage Requirement (SSR)/ha= 432.24 m3/ha. For the project area, SSR= 3.0162 x 432.24= 1303.7 m3. Table 5.A2 Table 5.A2 gives the maximum permissible site discharge (PSD), minimum Site Storage Requirement (SSR) and inlet values in accordance with the major towns in Peninsular Malaysia. From Table 5.A2, the inlet flow/ha is 214 l/s/ha. For the project area, inlet flow=3.0162 x 214= 645.5 l/s= 0.645 m3/s.


From Table 5.A2, PSD/ha= 72.96 l/s/ha. For the project area, PSD= 2.0162 x 72.96 = 220.1 l/s = 0.220 m3/s. From Table 5.A2, SSR/ha= 423.28 m3/ha. For the project area, SSR= 3.0162 x 423.28 = 1276.7 m3. Adopt smaller PSD value from Table 5.A1 and 5.A2 for subsequent sizing of outlet pipe= 0.220 m3/s. Table 5.A3: Table 5.A3 gives the OSD volume, inlet size and outlet size for 5 different regions in Peninsular Malaysia. From Table 5.A3, the inlet pipe= 714 mm diameter. From Table 5.A3, the outlet pipe= 380 mm diameter. Table 5.A4: Table 5.A4 gives the discharge and pipe diameter relationship for low lying, mild and steep slopes. From Table 5.A4, the inlet pipe for the inlet flow of 0.645 m3/s computed in Table 5.A2= 920 mm diameter. From Table 5.A4, the outlet pipe for the adopted PSD of 0.220 m3/s= 474 mm diameter Adopt PSD and SSR: Adopt the PSD value which is the lower from Table 5.A1 and 5.A2= 0.220 m3/s. Adopt the SSR is the larger from Table 5.A1 and 5.A2= 1303.7 m3. Sizing of OSD tank: The required storage is 1303.7 m3. Adopt depth= 1.2 m. Adopt width= 25 m. Length= 43.46 m. Adopt length= 45 m. Tank Storage= 1.2 x 25 x 45= 1350.0 m3 > 1303.7 OK Adopt inlet pipe: Inlet pipe is the smaller of Table 5.A3 and 5.A4= 714 mm, adopted= 750 mm. Adopt outlet pipe: Outlet pipe is the smaller of Table 5.A3 and 5.A4= 380 mm, adopted= 350 mm.


Figure 5.7 Summary of OSD Computation using MSMA (2011) for Kuala Lumpur

Location= Kuala Lumpur

Figure 5.A1 Region 1- West Coast

Project area (ha) 3.0162

Terrain= mild

% imperviousness= 70

Table 5.A1 Permissible Site Discharge (PSD)/ha= 78.54 l/s/ha

For the project area, PSD= 236.9 l/s 0.237 m3/s

Table 5.A1 Site Storage Requirement (SSR)/ha= 432.24 m3/ha

For the project area, SSR= 1303.7 m3

Table 5.A2 Inlet Flow/ha= 214 l/s/ha

For the project area, Inlet Flow= 645.5 l/s 0.645 m3/s

Table 5.A2 PSD/ha= 72.96 l/s/ha


Table 5.A2 SSR/ha= 423.28 m3/ha


Adopt smaller PSD value for subsequent sizing of outlet pipe= 0.220 m3/s

Table 5.A3 Inlet pipe= 714 mm dia

Table 5.A3 Outlet pipe= 380 mm dia

Table 5.A4 Inlet pipe for the inlet flow (Table 5.A2)= 920 mm dia

Table 5.A4 Outlet pipe for the adopted PSD= 474 mm dia

Adopt PSD is the lower from Table 5.A1 and 5.A2= 0.220 m3/s

Adopt SSR is the larger from Table 5.A1 and 5.A2= 1303.7 m3

Sizing of OSD tank:

Required storage 1303.7 m3

Adopt depth= 1.2 m

Adopt width= 25 m

Length= 43.46 m

Adopt length= 45 m

Tank Storage= 1350.0 m3 > 1303.7 OK

Adopt inlet pipe Inlet pipe is the smaller of Table 5.A3 and 5.A4= 714 Adopted= 750 mm

Adopt outlet pipe Outlet pipe is the smaller of Table 5.A3 and 5.A4= 380 Adopted= 350 mm


5.3.3 Exact Swinburne Method (ESM) Applied to MSMA2 Data

5.3.3.1 Design Criteria The design rainfall is based on MSMA (2011) for Station 4 (SK Taman Maluri). The OSD design is based on peak inflow estimates using the Rational Method with design storms between 2 and 10 year ARI.


The pervious and impervious areas are shown in Table 5.2.





5.3.3.4 Determination of Pre and Post Development Flows Calculate I

In MSMA (2011), the storm intensity for SK Taman Maluri for 2 years ARI is as follows:

d

Ti

where


, κ, θ and η are the fitting constants= 62.765, 0.132, 0.147 and 0.820,

respectively.

The rainfall intensities are summarised as shown in Table 5.7.

Table 5.7 IDF Data for SK Taman Maluri Kuala Lumpur

(ARI of 2 and 10 Year and Durations of 5, 10, 15, 20, 25, 30 and 35 minutes) (MSMA, 2011)

ARI YR λ κ θ η 5 min 10 min 15 min 20 min 25 min 30 min 35 min

2 62.765 0.132 0.147 0.82 229.256 177.971 146.705 125.484 110.056 98.291 88.995

10 62.765 0.132 0.147 0.82 283.521 220.097 181.430 155.186 136.107 121.556 110.060


Calculate C

From Table 4.1, the runoff coefficients for minor system for ARI of 10 years or less are: Sport fields= 0.3 Commercial and business centres= 0.9

Calculate Qp In MSMA (2011), the peak discharge is related to the rainfall intensity and catchment area via the Rational Method:

360

AiCQ


The pre and post development peaks for ARI of 2 years are shown in Table 5.8.

Table 5.8 Computation of Pre/Post Development Peaks

ARI tcs tc Id Impervious Area Pervious Area Sum Pre/Post Dev

LN(T) (min) (min) (mm/hr) C A (ha) C A (ha) CA Q (l/s)

2 5 10 177.97 0 0 0.3 3.0162 0.9049 447.33

2 5 10 177.97 0.9 2.1113 0.3 0.9049 2.1717 1073.59

5.3.3.5 Determination of Permissible Site Discharge (PSD) As stated in Section 19.3.1 of the Manual, the discharge design storm for estimating the PSD is the minor system design ARI of the municipal stormwater system to which the site is or will be connected. In this case, it is the 2 year ARI storm. The Permissible Site Discharge (PSD) for the site in l/s is given by (from Equation 19.1 of MSMA, 2000):

2

42

baaPSD

The factors a and b are different for above-ground and below-ground storages due to differences in storage geometry and outflow characteristics.



csc

a

p

c

c

a ttQ

Qt

t

Qa 65.035.0333.0548.8

paQQb 548.8




ARI Development tcs (min) tc (min) Qp (l/s) a b PSD (l/s)

2 Pre-Development

5 10 447.33

2 Post-Development

5 10 1073.59 7467.841 4105181.8 597.5

5.3.3.6 Determination of Site Storage Requirement (SSR) As stated in Section 19.3.1 of MSMA (2000), the storage design storm for estimating the SSR is 10 year ARI. In sizing the volume of the storage facility, the method assumes a triangular inflow hydrograph and an outflow hydrograph shape related to the type of storage adopted. These simplifications are acceptable providing the site catchment is small. Typically, the critical storm duration that produces the largest required storage volume is different from the time of concentration used for peak flow estimation. Therefore storage volumes must be determined for a range of storm durations to find the maximum storage required. The Site Storage Requirement (SSR) for the site in m3 is calculated using the formula:

dcQtSSR dd 06.0



dQ

PSDPSDc 392.01675.0

dQ

PSDd

2

117.0


The results for tc = 5, 10, 15, 20, 25, 30 and 35 min are tabulated in Table 5.10 and plotted as shown Table 5.8. It can be seen that the maximum SSR is 723.3 m3 for a storm duration of 30 min.

Table 5.10 Computation of Post Development Peaks and Site Storage Requirements (SSR)

ARI tc Id Impervious Area

Pervious Area

Sum Pre/Post Dev

Below Ground Storage

(YR) (min) (mm/hr) C A (ha) C A (ha) CA Q (l/s) PSD (l/s)

c d SSR (m3)

10 5 283.52 0.9 2.1113 0.3 0.9049 2.1717 1710.3 597.5 348.0925 24.4243 401.3

10 10 220.10 0.9 2.1113 0.3 0.9049 2.1717 1327.7 597.5 332.1753 31.4625 578.4

10 15 181.43 0.9 2.1113 0.3 0.9049 2.1717 1094.5 597.5 317.0109 38.1678 665.4

10 20 155.19 0.9 2.1113 0.3 0.9049 2.1717 936.1 597.5 302.4133 44.6226 706.9

10 25 136.11 0.9 2.1113 0.3 0.9049 2.1717 821.0 597.5 288.267 50.8777 722.9

10 30 121.56 0.9 2.1113 0.3 0.9049 2.1717 733.3 597.5 274.4936 56.9680 723.3

10 35 110.06 0.9 2.1113 0.3 0.9049 2.1717 663.9 597.5 261.0369 62.9183 713.9

Figure 5.8 Plot of SSR versus Storm Duration

400

450

500

550

600

650

700

750

800

0 5 10 15 20 25 30 35 40

SS

R (

M3)



5.4 Case Study on On-Site Detention for Pulau Pinang The case study looks at the design of a below-ground, on-site detention (OSD) facility using the guidelines described in MSMA (2000) and MSMA (2011) for a proposed factory site in Pulau Pinang at Klinik Bukit Bendera as shown in Figure 5.9.

Figure 5.9 Location of OSD in the Project Site

5.4.1 OSD in MSMA (2000)

5.4.1.1 Design Criteria

The proposed single storey factory can be classified as low density development. According to Chapter 11 of the Manual, on-site facilities are minor drainage structures provided on individual housing, industrial and infrastructure sites. For quantity design they are based on peak inflow estimates using the Rational Method with design storms between 2 and 10 year ARI. The design rainfall is based on Chapter 13 of the Manual. The design storm for Pulau Pinang at Klinik Bukit Bendera is used in the calculation.

River

OSD

Factory Site



For the purpose of hydrological calculation, the area is shown in Table 5.11 . It is estimated that 70% of the areas may be considered as impervious. Hence the impervious area is computed by multiplying the total area by 70% as shown in the table. The remaining 30% of the areas is assumed pervious. Hence the pervious area is computed by multiplying the total area by 30% as shown in the table.

Table 5.11 Pervious and Impervious Areas

Total area (m2) Pervious Area (m2) Impervious Area (m2)

30162 9048.6 21113.4





5.4.1.4 Determination of Pre and Post Development Flows

Calculate I The values of the coefficients for a, b, c and d in Table 13.A1 (MSMA, 2000) for ARI of 2 years for Pulau Pinang are as follows: a=4.5140, b=0.6729, c=-0.2311, d=0.0118 Substituting the above coefficients into:


R

where RIt is the average rainfall intensity (mm/hr) for ARI R and duration t R is average return interval (years) t is duration (minutes) a to d are fitting constants dependent on ARI.

For t= 30 min, 2I30= 98.8 mm/hr For t= 60 min, 2I60= 67.0 mm/hr Convert to rainfall depths,


2P30= 98.8/2 = 49.4 mm 2P60= 67/1 = 67.0 mm

Calculate C According to DID (2000), the design rainfall depth Pd for a short duration d (min) is given by:

)( 306030 PPFPP Dd

where P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from the published polynomial curves. FD is the adjustment factor for storm duration from Table 13.3 (MSMA, 2000).

Hence 2P10= 49.4-1.04*(67-49.4)= 31.1 mm Therefore 2I10= 186.8 mm/hr From Design Chart 14.3, for category 7 (park lawns and meadows) the runoff coefficient is 0.61. For category 1 (impervious roof and concrete), the runoff coefficient is 0.91. Calculate Qp The peak discharge for ARI=2 years is computed using the Rational Method:

360

AICQ

t

y

y



For pre-development, Qp= 954.5 l/s (Qp) For post-development, Qp= 1283 l/s (Qa) The results are tabulated in Table 5.12.

5.4.1.5 Determination of Permissible Site Discharge (PSD)

As stated in Section 19.3.1 of the Manual, the discharge design storm for estimating the PSD is the minor system design ARI of the municipal stormwater system to


which the site is or will be connected. In this case, it is the 2 year ARI storm. The Permissible Site Discharge (PSD) for the site in l/s is given by (from Equation 19.1 of MSMA, 2000):

2

42

baaPSD


csc

a

p

c

c

a ttQ

Qt

t

Qa 65.035.0333.0548.8

paQQb 548.8



97.10119565.01035.01.1225

0.88810333.0

10

1.1225548.8

a

10468173b

6.1169PSD


5.4.1.6 Determination of Site Storage Requirement (SSR)

As stated in Section 19.3.1 of MSMA (2000), the storage design storm for estimating the SSR is 10 year ARI. In sizing the volume of the storage facility, the method assumes a triangular inflow hydrograph and an outflow hydrograph shape related to the type of storage adopted. These simplifications are acceptable providing the site catchment is small. Typically, the critical storm duration that produces the largest required storage


volume is different from the time of concentration used for peak flow estimation. Therefore storage volumes must be determined for a range of storm durations to find the maximum storage required. The Site Storage Requirement (SSR) for the site in m3 is calculated using the formula:

dcQtSSR dd 06.0


dQ

PSDPSDc 392.01675.0

dQ

PSDd

2

117.0


The values of the coefficients for a, b, c and d in Table 13.A1 for ARI of 10 years for Pulau Pinang are as follows: a=3.7277, b=1.4393, c=-0.4023, d=0.0241 The magnitudes of 5, 10, 15 and 20 minutes short duration design storms are computed as shown in Table 5.14 to be 319.9, 257.0, 209.6 and 177.0 mm/hr, respectively. The C values are read from Design Chart 14.3 of the Manual. For impervious area, the C values are based on Category 1 (Impervious roof and concrete) catchment for the range of rainfall intensities corresponding to tc of 5, 10, 15 and 20 min. For pervious area, the C values are based on Category 7 (park lawns and meadows) catchment for the range of rainfall intensities corresponding to tc of 5, 10, 15 and 20 min. For the area, for tc= 5 min, the peak post-development flow: Qp= 2366.6 l/s (Qd) The results and those for tc =10, 15 and 20 min are tabulated in Table 5.14. The corresponding SSR are computed using the above formula for below-ground


storage.

5.636c

6.67d

7.498SSR

The results for tc =5, 10, 15 and 20 min are tabulated in Table 5.15 and plotted as shown in Figure 5.10. It can be seen that the maximum SSR is 728.7 m3 for a storm duration of 15 min. The SSR is therefore 728.7 m3.

Figure 5.10 Plot of SSR Versus Storm Duration

400

450

500

550

600

650

700

750

800

0 5 10 15 20 25

SS

R (

M3)


Plot of SSR Vs Storm Duration



Develop ment

ARI a b c d 30 60 Impervious Area


3.4012 4.0943 tcs (min)

tc (min)

P30 (mm)

P60 (mm)

FD Pd (mm)

Id (mm/hr)

C A (ha) C A (ha) CA Q (l/s)

Pre 2 4.5140 0.6729 -0.2311

0.0118 98.8 67.0 5 10 49.42 67.0 1.04 31.13 186.76 0 0 0.61 3.0162 1.8399 954.4

Post 2 4.5140 0.6729 -0.2311

0.0118 98.8 67.0 5 10 49.42 67.0 1.04 31.13 186.76 0.91 2.1113 0.61 0.9049 2.4733 1283.0


Development Pre/Post Dev Below Ground Storage

tcs (min) tc (min) Q (l/s) a b PSD (l/s) Pre 5 10 954.468 Post 5 10 1283.055 10119.97 10468173 1169.6

Table 5.14 Computation of Peak Post-Development Flow (QD)

ARI a b c d 30 60 Impervious Area


LN(T) 3.4012 4.0943 tc (min)

P30 (mm)

P60 (mm)

FD Pd (mm)

Id (mm/hr)

C A (ha) C A (ha) CA Q (l/s)

10 3.7277 1.4393 -0.4023 0.0241 136.6 92.8 5 68.32 92.8 1.70 26.66 319.90 0.91 2.1113 0.82 0.9049 2.6633 2366.6

10 3.7277 1.4393 -0.4023 0.0241 136.6 92.8 10 68.32 92.8 1.04 42.83 257.01 0.91 2.1113 0.71 0.9049 2.5638 1830.3

10 3.7277 1.4393 -0.4023 0.0241 136.6 92.8 15 68.32 92.8 0.65 52.39 209.57 0.91 2.1113 0.65 0.9049 2.5095 1460.9

10 3.7277 1.4393 -0.4023 0.0241 136.6 92.8 20 68.32 92.8 0.38 59.01 177.03 0.91 2.1113 0.59 0.9049 2.4552 1207.3


Table 5.15 Computation of Site Storage Requirements (SSR)

tc (min) Q (l/s) PSD (l/s) c d SSR (m3)

5 2366.6 1169.6 636.5261 67.6256 498.7

10 1830.3 1169.6 591.7092 87.4426 690.7

15 1460.9 1169.6 541.7028 109.5543 728.7

20 1207.3 1169.6 489.6754 132.5596 702.1

5.4.2 OSD in MSMA (2011)

In this section, an OSD is designed based on MSMA (2011) for the same site as in the previous section. The design is presented below and tabulated in a spreadsheet as shown in Figure 5.11 Project Data The project area is located in Kuala Lumpur. So from Figure 5.A1 which divides peninsula into 5 design regions, the project area is located in Region 3- Nothern Region. The Project area is 3.0162 ha. The Terrain is mild. The % imperviousness is 70 per cent. Table 5.A1 Table 5.A1 gives the maximum permissible site discharge (PSD) and minimum Site Storage Requirement (SSR) values in accordance with the five regions in Peninsular Malaysia. From Table 5.A1, the Permissible Site Discharge (PSD)/ha= 69.76 l/s/ha. For the project area, PSD= 3.0162 x 69.76=210.4 l/s=0.210 m3/s. From Table 5.A1, the Site Storage Requirement (SSR)/ha= 435.26 m3/ha. For the project area, SSR= 3.0162 x 435.26= 1312.8 m3. Table 5.A2 Table 5.A2 gives the maximum permissible site discharge (PSD), minimum Site Storage Requirement (SSR) and inlet values in accordance with the major towns in Peninsular Malaysia. For Alor Setar, from Table 5.A2, the inlet flow/ha is 214 l/s/ha. For the project area, inlet flow=3.0162 x 214= 645.5 l/s= 0.645 m3/s. From Table 5.A2, PSD/ha= 69.76 l/s/ha. For the project area, PSD= 2.0162 x 69.76 = 210.4 l/s = 0.210 m3/s.


From Table 5.A2, SSR/ha= 435.26 m3/ha. For the project area, SSR= 3.0162 x 425.26 = 1312.8 m3. Adopt smaller PSD value from Table 5.A1 and 5.A2 for subsequent sizing of outlet pipe= 0.210 m3/s. Table 5.A3: Table 5.A3 gives the OSD volume, inlet size and outlet size for 5 different regions in Peninsular Malaysia. From Table 5.A3, the inlet pipe= 714 mm diameter. From Table 5.A3, the outlet pipe= 355 mm diameter. Table 5.A4: Table 5.A4 gives the discharge and pipe diameter relationship for low lying, mild and steep slopes. From Table 5.A4, the inlet pipe for the inlet flow of 0.645 m3/s computed in Table 5.A2= 927 mm diameter. From Table 5.A4, the outlet pipe for the adopted PSD of 0.210 m3/s= 474 mm diameter Adopt PSD and SSR: Adopt the PSD value which is the lower from Table 5.A1 and 5.A2= 0.210 m3/s. Adopt the SSR is the larger from Table 5.A1 and 5.A2= 1312.8 m3. Sizing of OSD tank: The required storage is 1312.8 m3. Adopt depth= 1.2 m. Adopt width= 25 m. Length= 43.76 m. Adopt length= 45 m. Tank Storage= 1.2 x 25 x 45= 1350.0 m3 > 1312.8 OK Adopt inlet pipe: Inlet pipe is the smaller of Table 5.A3 and 5.A4= 714 mm, adopted= 750 mm. Adopt outlet pipe: Outlet pipe is the smaller of Table 5.A3 and 5.A4= 355 mm, adopted= 350 mm.


Figure 5.11 Summary of OSD Computation using MSMA (2011) for Pulau Pinang

Location= Penang

Figure 5.A1 Region 3- West Coast

Project area (ha) 3.0162

Terrain= mild

% imperviousness= 70

Table 5.A1 Permissible Site Discharge (PSD)/ha= 69.76 l/s/ha


Table 5.A1 Site Storage Requirement (SSR)/ha= 435.26 m3/ha


Alor Setar

Table 5.A2 Inlet Flow/ha= 214 l/s/ha

For the project area, Inlet Flow= 645.5 l/s 0.645 m3/s

Table 5.A2 PSD/ha= 69.76 l/s/ha


Table 5.A2 SSR/ha= 435.26 m3/ha


Adopt smaller PSD value for subsequent sizing of outlet pipe= 0.210 m3/s

Table 5.A3 for 3 Inlet pipe= 714 mm dia

Table 5.A3 Outlet pipe= 355 mm dia

Table 5.A4 Inlet pipe for the inlet flow (Table 5.A2)= 927 mm dia

Table 5.A4 Outlet pipe for the adopted PSD= 474 mm dia

Adopt PSD is the lower from Table 5.A1 and 5.A2= 0.210 m3/s

Adopt SSR is the larger from Table 5.A1 and 5.A2= 1312.8 m3

Sizing of OSD tank:

Required storage 1312.8 m3

Adopt depth= 1.2 m

Adopt width= 25 m

Length= 43.76 m

Adopt length= 45 m

Tank Storage= 1350.0 m3 > 1312.8 OK

Adopt inlet pipe Inlet pipe is the smaller of Table 5.A3 and 5.A4= 714 Adopted= 750 mm

Adopt outlet pipe Outlet pipe is the smaller of Table 5.A3 and 5.A4= 355 Adopted= 350 mm


5.4.3 Exact Swinburne Method (ESM) Applied to MSMA2 Data

5.4.3.1 Design Criteria The design rainfall is based on MSMA (2011) for Pulau Pinang at Klinik Bukit Bendera. The OSD design is based on peak inflow estimates using the Rational Method with design storms between 2 and 10 year ARI.

5.4.3.2 Determination of Impervious and Pervious Areas The pervious and impervious areas are shown in Table 5.11.





5.4.3.4 Determination of Pre and Post Development Flows Calculate I

In MSMA (2011), the storm intensity for Pulau Pinang for 2 years ARI is as follows:

d

Ti

where


, κ, θ and η are the fitting constants= 62.765, 0.132, 0.147 and 0.820,

respectively.

The rainfall intensities are summarised as shown in Table 5.16.

Table 5.16 IDF Data for Pulau Pinang (ARI of 2 and 10 Year and Durations of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 minutes) (MSMA, 2011)

ARI (T) YR

λ κ θ η 5 10 15 20 25 30 35 40 45 50 55 60

2 64.504 0.196 0.149 0.723 212.2 170.0 143.5 125.1 111.5 101.0 92.55 85.61 79.80 74.84 70.5 66.8

10 64.504 0.196 0.149 0.723 290.9 233.1 196.8 171.6 152.9 138.4 126.8 117.3 109.4 102.6 96.7 91.6


Calculate C From Table 4.1, the runoff coefficients for minor system for ARI of 10 years or less are: Sport fields= 0.3 Commercial and business centres= 0.9

Calculate Qp In MSMA (2011), the peak discharge is related to the rainfall intensity and catchment area via the Rational Method:

360

AiCQ


The pre and post development peaks for ARI of 2 years are shown in Table 5.17.


ARI tcs tc Id Impervious Area Pervious Area Sum Pre/Post Dev

LN(T) (min) (min) (mm/hr) C A (ha) C A (ha) CA Q (l/s)

2 5 10 170.08 0 0 0.3 3.0162 0.9049 427.489

2 5 10 170.08 0.9 2.1113 0.3 0.9049 2.1717 1025.974

5.4.3.5 Determination of Permissible Site Discharge (PSD) As stated in Section 19.3.1 of the Manual, the discharge design storm for estimating the PSD is the minor system design ARI of the municipal stormwater system to which the site is or will be connected. In this case, it is the 2 year ARI storm. The Permissible Site Discharge (PSD) for the site in l/s is given by (from Equation 19.1 of MSMA, 2000):

2

42

baaPSD


csc

a

p

c

c

a ttQ

Qt

t

Qa 65.035.0333.0548.8

paQQb 548.8





ARI Development tcs (min) tc (min) Q (l/s) a b PSD (l/s)

2 Pre 5 10 427.489

2 Post 5 10 1025.974 7136.607 3749089.9 571.0

5.4.3.6 Determination of Site Storage Requirement (SSR) As stated in Section 19.3.1 of MSMA (2000), the storage design storm for estimating the SSR is 10 year ARI. In sizing the volume of the storage facility, the method assumes a triangular inflow hydrograph and an outflow hydrograph shape related to the type of storage adopted. These simplifications are acceptable providing the site catchment is small. Typically, the critical storm duration that produces the largest required storage volume is different from the time of concentration used for peak flow estimation. Therefore storage volumes must be determined for a range of storm durations to find the maximum storage required. The Site Storage Requirement (SSR) for the site in m3 is calculated using the formula:

dcQtSSR dd 06.0


dQ

PSDPSDc 392.01675.0

dQ

PSDd

2

117.0


The results for tc = 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 min are tabulated in


Table 5.19 and plotted as shown Figure 5.12. It can be seen that the maximum SSR is 938.1 m3 for a storm duration of 45 min.

Table 5.19 Computation of Post Development Peaks and Site Storage Requirements (SSR)

ARI tc Id Impervious Area Pervious Area Sum Pre/Post Dev PSD Below Ground Storage

LN(T) (min) (mm/hr) C A (ha) C A (ha) CA Q (l/s) (l/s) c d SSR (m3)

10 5 291.00 0.9 2.1113 0.3 0.9049 2.1717 1755.4 571.0 336.2902 21.7326 419.2

10 10 233.15 0.9 2.1113 0.3 0.9049 2.1717 1406.5 571.0 324.0971 27.1242 633.2

10 15 196.83 0.9 2.1113 0.3 0.9049 2.1717 1187.3 571.0 312.7751 32.1305 758.2

10 20 171.60 0.9 2.1113 0.3 0.9049 2.1717 1035.2 571.0 302.0947 36.8531 835.5

10 25 152.93 0.9 2.1113 0.3 0.9049 2.1717 922.5 571.0 291.9163 41.3538 883.9

10 30 138.46 0.9 2.1113 0.3 0.9049 2.1717 835.3 571.0 282.1465 45.6738 913.4

10 35 126.88 0.9 2.1113 0.3 0.9049 2.1717 765.4 571.0 272.7191 49.8423 930.0

10 40 117.37 0.9 2.1113 0.3 0.9049 2.1717 708.0 571.0 263.5849 53.8812 937.4

10 45 109.40 0.9 2.1113 0.3 0.9049 2.1717 659.9 571.0 254.7062 57.8072 938.1

10 50 102.61 0.9 2.1113 0.3 0.9049 2.1717 619.0 571.0 246.0528 61.6335 933.9

10 55 96.74 0.9 2.1113 0.3 0.9049 2.1717 583.6 571.0 237.6008 65.3708 926.0

10 60 91.62 0.9 2.1113 0.3 0.9049 2.1717 552.7 571.0 229.33 69.0280 915.5

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70

SS

R (

M3

)


Figure 5.12 Plot of SSR versus Storm Duration


5.5 Evaluation The following changes in the design procedure for On-Site Detention between MSMA (2000) and (2011) are noted:

1. The new method is based on nomograph and not based on formulas as in the first

edition. 2. The result in Table 5.20 shows that for Kuala Lumpur, MSMA (2011) gives PSD of

about 20% of MSMA (2000) and SSR of about 190% of MSMA (2000). 3. The result in Table 5.20 shows that for Kuala Lumpur, the PSD using ESM Method

gives PSD of about 55% of MSMA (2000) and SSR of about 103% of MSMA (2000) using MSMA (2011) storm and discharge data.

4. The result in Table 5.21 shows that for Pulau Pinang, MSMA (2011) gives PSD of 18% of MSMA (2000) and SSR of about 180% of MSMA (2000).

5. The result in Table 5.21 shows that for Pulau Pinang, the PSD using ESM Method gives PSD of about 49% of MSMA (2000) and SSR of about 129% of MSMA (2000) using MSMA (2011) storm and discharge data.

6. Problems using Table 5.A2 outside the 17 major towns in Peninsular Malaysia listed in the table which gives the maximum permissible site discharge (PSD), minimum Site Storage Requirement (SSR) and inlet values.

7. Method is suitable only for Peninsula. No guidance for towns in East Malaysia e.g., Figure 5.A.1 and Table 5.A2 are for Peninsula.

8. For East Malaysia, it may be necessary to apply the OSD method in MSMA (2000) since MSMA (2011) provides no guidance on this.

Table 5.20 Comparison of OSD Requirements using MSMA (2000, 2011) for Kuala Lumpur

MSMA 2000 (A) MSMA 2011 (B) ESM (C) R=B/A R=C/A

PSD (L/S) 1093.6 220 597.5 0.2 0.55

SSR (M3) 700.9 1303.7 723.3 1.9 1.03

Table 5.21 Comparison of OSD Requirements using MSMA (2000, 2011) for Pulau Pinang

MSMA 2000 (A) MSMA 2011 (B) ESM (C) R=B/A R=C/A

PSD 1169.6 210 571.0 0.18 0.49

SSR 728.7 1312.8 938.1 1.80 1.29


6. Changes in Sediment Basins

6.1 Criteria for Sizing of Wet and Dry Sediment Basins Table 6.1 (Table 39.4 of MSMA, 2000) summarises the sizing criteria for wet/dry sediment basins. Listed in the table are the three different soil types and the design considerations which apply to sediment basin design and operation for each soil type.

Table 6.1 Sediment Basin Types and Design Considerations

Soil Description Soil Type

Basin Type

Design Considerations

Coarse-grained sand, sandy loam: less than 33%<0.02 mm

C Dry Settling velocity, sediment storage.

Fine-grained loam, clay: more than 33%<0.02 mm

F Wet Storm impoundment, sediment storage.

Dispersible fine-grained clays as per type F, more than 10% of dispersible material.

D Wet Storm impoundment, sediment storage, assisted flocculation.

6.2 Sediment Basins in MSMA (2000) 6.2.1 Dry Sediment Basin

Dry Sediment basins should be used on Type C soil- which is characterized by a high percentage of coarse particles, where less than one-third of particles are less than 0.02 mm in size. Table 6.2 (Table 39.5 of MSMA, 2000) summarises the dry sediment basin sizing guidelines. For construction projects lasting two years or less to complete, a three month design ARI is required, and for those taking two years or more, a six month design ARI is required.

Table 6.2 Dry Sediment Basin Sizing Guidelines in MSMA (2000) (After Table 39.5 of MSMA, 2000)

Parameter Design Storm

(mth ARI)

Time of Concentration of Basin Catchment (min)

10 20 30 45 60

Surface Area

(m2/ha)

3 333 250 200 158 121

6 n/a 500 400 300 250

Total Volume

(m3/ha)

3 400 300 240 190 145

6 n/a 600 480 360 300

6.2.2 Wet Sediment Basin Wet sediment basins should be used on Type F or Type D soils. The duration of the design event should be 5 days- time needed to achieve effective flocculation, settling and pumpout of the stormwater. The 75th percentile 5-day rainfall event should be used as the design event. The 80th percentile 5-day event should be used if the construction site is upstream of an environmentally sensitive area, or if the construction period is more than 2 years. Sizing guidelines for wet sediment basins for normal situations are given in Table 6.3 (Table 39.6 of MSMA, 2000).


Table 6.3 Wet Sediment Basin Sizing Guidelines in MSMA (2000) (Table 39.6 of MSMA, 2000)

Parameter Site Runoff Potential Magnitude of Design Storm Event in mm

20 30 40 50 60

Settling Zone Volume (m

3/ha)

Moderate-high runoff 70 127 200 290 380

Very high runoff 100 167 260 340 440

Total Volume (m

3/ha)


Very high runoff 150 250 390 510 660

6.3 Sediment Basin Theory in MSMA (2011) 6.3.1 Criteria for Sizing of Sediment Basins

Table 6.4 (Table 1.3 in MSMA, 2011) requires temporary or permanent BMPs to be designed based on 50 and 40 mm, respectively, of rainfall applied to the catchments draining to the BMPs.

Table 6.4 Quality Control Design Criteria (Table 1.3 in MSMA, 2011)

Variables Criteria

Water Quality Volume Temporary BMPs- 50 mm of rainfall applied to catchments draining to the BMPs.

Permanent BMPs- 40 mm of rainfall applied to catchments draining to the BMPs.

Primary Outlet Sizing Based on the peak flow calculated from the 3 month ARI event.

Secondary Outlet (Spillway) Sizing As per the ARIs recommended in the respective chapters of the individual BMPs.

There is a change of approach in MSMA (2011) where temporary or permanent BMPs are designed based on 50 or 40 mm of rainfall on the catchment, compared to MSMA (2000) where these were based on the 75th or 80th percentile 5 day storm for wet ponds. Overall, the approach is MSMA (2011) is a lot simpler than MSMA (2000) as it does away with the need to compute the 75th and 80th percentile 5 day storm, and adopt 50 or 40 mm for temporary or permanent BMPs. The changes in between design requirements for MSMA (2000 and 2011) are summarised in Table 6.5.

Table 6.5 Comparison of Design Requirements for Sediment Basins between MSMA (2000 and 2011)

DURATION

MSMA (2000) MSMA (2011)

Construction Period

Dry Sedimentation Basin

Wet Sedimentation Basin

Construction Period

Dry Sedimentation Basin

Wet Sedimentation Basin

<2 YEARS 3 Month ARI 75th Percentile

5 Day Rain Temporary <18 mths

3 Month ARI 50 mm

>2 YEARS 6 Month ARI 80th Percentile

5 Day Rain Permanent >18 mths

3 Month ARI 40 mm


6.3.2 Design of Dry Sediment Basins In MSMA (2011), Table 6.6 (Table 12.18) summarises the dry sediment basin sizing guidelines. Note this is the same as Table 6.2 for 3 month ARI.

Table 6.6 Dry Sediment Basin Sizing Criteria in MSMA (2011) (Table 12.18 in MSMA, 2011)

Parameter Time of Concentration of Basin Catchment (min)

10 20 30 45 60

Surface Area (m2/ha) 333 250 200 158 121

Total Volume (m3/ha) 400 300 240 190 145

6.3.3 Design of Wet Sediment Basins In MSMA (2011), Table 6.7 (Table 12.19) summarises the wet sediment basin sizing guidelines. Note this is the same as Table 6.3. Instead of using the 75th or 80th percentile 5-day rainfall event for the magnitude of design storm in the above table, we can use the 50 and 40 mm rainfall depths for temporary and permanent BMPs according to Table 6.4.

Table 6.7 Wet Sediment Basin Sizing Volume (m3/ha) in MSMA (2011) (TABLE 12.19)

Parameter Site Runoff Potential Magnitude of Design Storm Event in mm

20 30 40 50 60

Settling Zone Volume (m

3/ha)


Very high runoff 100 167 260 340 440

Total Volume (m

3/ha)


Very high runoff 150 250 390 510 660

6.4 Case Study on Design of a Dry Sediment Basin

This worked example uses a spreadsheet to size a dry sediment basin. Problem: To design a dry sediment basin and outlet structures required for a construction site in Kuala Lumpur.

Relevant data are as follows:

Basin type= earth embankment and perforated outlet.

Soil type= sandy loam. Type C.

Construction period more than 2 years.

Area= 7.8 ha.

Compute overland flow time using Friend’s Formula where n=0.011, Lo= 50 m, S=0.3%.

Compute drain flow time for Ld= 870 m and V=1 m/s.

6.4.1 MSMA (2000) The construction period is more than 2 years, hence the design storm= 6 month ARI. 1. Determine Tc

Overland flow time (To) is estimated using Friend’s Formula:

2.0

3/1107

S

Lnto

where

n= 0.011 from Table 14.2 (MSMA, 2000) for paved surface


S= 0.3%

L (Overland sheet flow path length) = 50 m. Applying the Friend’s Formula, To= 5.5 min. Td=L/V= 870/1= 870 s= 14.5 min. Hence, Tc = To + Td = 5.5+14.5 = 20 min

2. Sizing of Sediment Basin

From Table 6.1 (Table 39.4 of MSMA, 2000), Soil Type= C Construction time > 2 years Design storm= 6 mth ARI From Table 6.2 (Table 39.5 of MSMA, 2000), for the above Tc, Required surface area= 500 m2/ha Required total volume = 600 m3/ha Catchment area= 7.8 ha Surface area required= 500 x 7.8= 3900 m2 Total volume required= 600 x 7.8= 4680 m3

6.4.2 MSMA (2011) 1. Determine Tc

Applying the same method of computation, Tc = To + Td = 5.5+14.5 = 20 min

2. Sizing of Sediment Basin From Table 6.6 (Table 12.18 of MSMA, 2011), for the above Tc,

Required surface area= 250 m2/ha Required total volume = 300 m3/ha Catchment area= 7.8 ha Surface area required= 250 x 7.8= 1950 m2 Total volume required= 300 x 7.8= 2340 m3

6.5 Case Study on Design of a Wet Sediment Basin

This worked example uses a spreadsheet to size a wet sediment basin in Ipoh.

Problem: To design a wet sediment basin and outlet structures required for a construction site in Ipoh. Relevant data are as follows:

Basin type= earth embankment and perforated outlet.

Soil type= sandy loam. Type F.

Construction period less than 2 years.

Area= 8 ha.

6.5.1 MSMA (2000) 1. Sizing of Sediment Basin

From Table 6.3 (Table 39.6 of MSMA, 2011), Soil Type= F


Construction time < 2 years The 75th percentile 5-day storm for Ipoh is 36.75 mm from analysis. From Table 6.3, for the 75th percentile 5-day storm with moderate-high runoff, Required settling zone volume= 176 m3/ha Required total volume = 264 m3/ha Catchment area= 8 ha Settling zone volume required= 176 x 8= 1408 m3 Total volume required= 264 x 8= 2112 m3

6.5.2 MSMA (2011) 1. Sizing of Sediment Basin

From Table 6.7 (Table 12.19 of MSMA, 2011), Soil Type= F Construction time < 2 years Temporary BMP- 50 mm of Rainfall applied to catchment area. From Table 6.7, for the 50 mm storm, with moderate-high runoff, Required settling zone volume= 290 m3/ha Required total volume = 435 m3/ha Catchment area= 8 ha Settling zone volume required= 290 x 8= 2320 m3 Total volume required= 435 x 8= 3480 m3

6.6 Evaluation

The results are summarized in Table 6.8. Below is an evaluation: 1. The dry basin is to be used for more than 2 years, so it should be designed for 6

month ARI. In Table 6.2, there is data for 6 month ARI but not in Table 6.6 where the data is based on 3 month ARI.

2. The results showed that the dry sediment basin volume using MSMA (2011) is half of that using MSMA (2000) for 6 month ARI design (for projects taking more than two years).

3. The 75th percentile 5-day storm for Ipoh is 36.75 mm. This was used to determine the volumes in Table 6.3. But for temporary BMP- 50 mm of rainfall applied to catchment area and was used to read the volumes in Table 6.7. Hence the volumes are about 1.65 times higher using MSMA (2011).

4. The wet sediment basin volume was 65% higher using MSMA (2011) compared to MSMA (2000) because of it was based on 50 mm of rainfall for temporary BMP in MSMA (2011), compared to the 75th percentile storm of 36.75 mm in MSMA (2000) which is lower.

5. For locations where the 75th percentile 5-day storms are lower than 50 mm, it is expected the wet sedimentation basin volume will decrease compared to MSMA (2000) using MSMA (2011).

Table 6.8 Summary of Dry and Wet Sediment Basin Volumes based on MSMA (2000 and 2011)

Dry Sediment Basin Wet Sediment Basin

Total Volume (m3) Settling Volume (m

3) Total Volume (m

3)

MSMA (2000) (A) 4680 1408 2112

MSMA (2011) (B) 2340 2320 3480

B/A 0.5 1.65 1.65


7. Conclusions

Below are the results of investigation:

Case Study 1- Design ARI: 1. For medium density residential and commercial and city area, the storm intensity has

increased by up to 122% for minor system for an ARI increase from 5 to 10 years, and up to 133% for major system for an ARI increase from 50 year to 100 years between MSMA (2000) and (2011).

2. It is emphasised that the changes in the storm intensity is not only due to changes in the ARI but also the higher IDF data in MSMA (2011).

3. Due to the linear nature of the discharge and storm intensity in the Rational Method, it is expected the same proportional increase in the design discharge is observed.

Case Study 2- Design Storm:

1. For durations of between 15 to 700 min, the IDF estimates using MSMA (2011) were mostly higher than those estimated using MSMA (2000). In the study, out of 14 stations, 10 of them (or 71%) were higher than the MSMA (2000) curve, while the remaining 4 stations (or 29%) were lower than the first edition estimates.

2. It is concluded that the design storms estimated based on MSMA (2011) for Kuala Lumpur can be up to about 26% higher than MSMA (2000) for duration below 700 minutes, for 71% of the stations.

Case Study 3- Design Discharge using Rational Method:

1. For commercial and city area, the peak discharge from MSMA (2011) is about 31% higher than the peak discharge from MSMA (2000). The Q has increased from 16.9 to 22.1 m3/s. The C has increased from 0.905 to 0.95 while the storm intensity has increased from 224.3 mm/hr to 279.4. The increase in C for commercial and city area and storm intensity in MSMA (2011) has attributed to a significantly higher peak discharge.

2. In conclusion, the peak discharge computed using the Rational Method in MSMA (2011) is up to 31% higher than that in MSMA (2000). This increase is caused principally by the higher storm intensity in MSMA (2011) and by the higher C for commercial and city area in MSMA (2011).

3. In general, it is concluded that 71% of the stations in Kuala Lumpur will have up to 26% higher storm intensity and up to 31% higher peak discharges for commercial and city area.

Case Study 4- On-Site Detention: 1. The result shows that for Kuala Lumpur, the PSD and SSR using MSMA (2011) are about

20% and 190% of MSMA (2000). 2. The PSD and SSR using the ESM Method for Kuala Lumpur is about 55% and 103%,

respectively, of those using MSMA (2000). 3. For Pulau Pinang, the PSD and SSR using MSMA (2011) are about 20% and 180% of

MSMA (2000). 4. The PSD and SSR using the ESM Method for Pulau Pinang is about 55% and 129%,

respectively, of those using MSMA (2000). 5. The approximate Swinburne’s Method in MSMA (2011) results in underestimate of PSD

and over estimate of the SSR. 6. The ESM Method appeared to give slightly higher estimate of SSR compared to MSMA


(2000) but a lot lower estimate compare to MSMA (2011). 7. The ESM Method uses more up-to-date storm data in MSMA (2012) to compute the

discharges and applied the exact Swinburne’s Method to compute the SSR. 8. This suggestS the ESM Method may be used instead of MSMA (2011) to give a better

estimate of PSD and SSR.

Case Study 5- Sedimentation Basins:

1. The dry sediment basin volume using MSMA (2011) is half of that using MSMA (2000) for 6 month ARI design (for projects taking more than two years) as MSMA (2011) does not cover 6 month ARI.

2. The wet sediment basin volume was 65% higher using MSMA (2011) compared to MSMA (2000) because of it was based on 50 mm of rainfall for temporary BMP in MSMA (2011), compared to the 75th percentile storm of 36.75 mm in MSMA (2000) which is lower.

3. For locations where the 75th percentile 5-day storms are lower than 50 mm, it is expected the wet sedimentation basin volume will decrease compared to MSMA (2000) using MSMA (2011).


8. References

Drainage and Irrigation Department (1974) Rational Method of Flood Estimation for Rural Catchments in Peninsular Malaysia. Hydrological Procedure No. 5. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1975) Urban Drainage Design Standards and Procedures for Peninsular Malaysia. Planning and Design Procedure No. 1. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1976) Flood Estimation for Urban Areas in Peninsular Malaysia. Hydrological Procedure No. 16. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1980) Design Flood Hydrograph Estimation for Rural Catchments in Peninsular Malaysia. Hydrological Procedure No. 11. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1982) Estimation of the Design Rainstorm in Peninsular Malaysia (Revised and Updated). Hydrological Procedure No. 1. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1987) Magnitude and Frequency of Floods in Peninsular Malaysia. Hydrological Procedure No. 4. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1988) Mean Monthly, Mean Seasonal and Mean Annual Rainfall Maps for Peninsular Malaysia. Water Resources Publication No. 19. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1989) Rational Method of Flood Estimation for Rural Catchments in Peninsular Malaysia (Revised and Updated). Hydrological Procedure No. 5. Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1991) “Hydrological Data- Rainfall and Evaporation Records for Malaysia 1986-1990” Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (1995) “Hydrological Data- Streamflow and River Suspended Sediment Records 1986-1990” Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (2000) “Urban Stormwater Management Manual for Malaysia” Ministry of Agriculture, Malaysia. Drainage and Irrigation Department (2010) “Review and Updated the Hydrological Procedure NO. 1- Estimation of Design Rainstorm in Peninsular Malaysia” December, Prepared by NAHRIM.

Drainage and Irrigation Department (2011) “Urban Stormwater Management Manual for Malaysia” (Manual Saliran Mesra Alam Malaysia), Second edition. Quek, K.H. (1993) "Assessment of flood Estimation Techniques for Urbanizing Areas using DID Hydrological Procedures" Seminar on Drainage and Flood Issues in Urban Development, organised by Water Resources Technical Division, the Institution of Engineers Malaysia, Regent Hotel, Kuala Lumpur, 18th January.


Quek K. H. (1999) “Water Quality Modelling of Wetlands and Lake” Journal of the Institution of Engineers Malaysia, Vol. 60, No. 3, September 1999, pp 11-19. Quek K. H. and Carroll D. (1999) “Flood Hydrology Study of Multi-Cell Multi-Stage Wetlands and Lake in Putrajaya” Journal of the Institution of Engineers Malaysia, Vol 60, No. 1, March.


Contents Abstract ................................................................................................................................................... 1

1. Introduction .................................................................................................................................... 3

1.1 Evolution of Drainage Guidelines in Malaysia ........................................................................... 3

1.2 Overall Changes in MSMA (2011) from MSMA (2000) .............................................................. 3

2. Changes in the Design ARI. ............................................................................................................. 6

2.1 Major and Minor Design ARI (MSMA, 2000) ............................................................................. 6

2.2 Major and Minor Design ARI (MSMA, 2011) ............................................................................. 6

2.3 Comparison ................................................................................................................................ 6

2.4 Evaluation .................................................................................................................................. 6

2.5 Case Study on Design ARI........................................................................................................... 8

2.5.1 Methodology ..................................................................................................................... 8

2.5.2 Evaluation .......................................................................................................................... 8

3. Changes in Design Storm, Temporal Pattern and Areal Reduction Factor ................................... 10

3.1 Design Storm Computation ...................................................................................................... 10

3.1.1 Evolution of Methods of Computation for Design Storm ............................................... 10

3.1.2 Derivation of IDF Curves using MSMA (2000) ................................................................. 10

3.1.3 Derivation of IDF Curves using MSMA (2011) ................................................................. 11

3.1.4 Comparison ..................................................................................................................... 11

3.1.5 Evaluation ........................................................................................................................ 12

3.2 Storm Temporal Pattern .......................................................................................................... 12

3.2.1 Temporal Pattern in MSMA (2000) ................................................................................. 12

3.2.2 Temporal Pattern in MSMA (2011) ................................................................................. 13

3.2.3 Evaluation ........................................................................................................................ 13

3.3 Areal Reduction Factor ............................................................................................................ 13

3.4 Case Study on Design Storm .................................................................................................... 15

3.4.1 Methodology ................................................................................................................... 15

3.4.2 Evaluation ........................................................................................................................ 15

4. Changes in the Rational Method .................................................................................................. 23

4.1 Rational Method in MSMA (2000) ....................................................................................... 23

4.2 Rational Method in MSMA (2011) ....................................................................................... 25

4.3 Evaluation ............................................................................................................................ 25


4.4 Case Study on Rational Method .......................................................................................... 27

4.4.1 Rational Method (MSMA, 2000) ..................................................................................... 28

4.4.2 Rational Method (MSMA, 2011) ..................................................................................... 30

4.5 Evaluation ................................................................................................................................ 31

5. Changes in On-Site Detention ....................................................................................................... 34

5.1 OSD Sizing using MSMA (2000) ................................................................................................ 34

5.1.1 Theory ............................................................................................................................. 34

5.1.2 Permissible Site Discharge (PSD) ..................................................................................... 35

5.1.3 Site Storage Requirement (SSR) ...................................................................................... 36

5.1.4 OSD Sizing Procedure ...................................................................................................... 38

5.2 OSD Sizing using MSMA (2011) ................................................................................................ 40

5.2.1 Limiting Catchment Areas for OSD in MSMA (2011) ...................................................... 40

5.2.2 Method for OSD Design in MSMA (2011) ....................................................................... 40

5.3 Case Study on On-Site Detention for Kuala Lumpur ................................................................ 50

5.3.1 OSD in MSMA (2000) ....................................................................................................... 50

5.3.2 OSD in MSMA (2011) ....................................................................................................... 57

5.3.3 Exact Swinburne Method (ESM) Applied to MSMA2 Data ............................................. 60

5.4 Case Study on On-Site Detention for Pulau Pinang ................................................................. 64

5.4.1 OSD in MSMA (2000) ....................................................................................................... 64

5.4.2 OSD in MSMA (2011) ....................................................................................................... 71

5.4.3 Exact Swinburne Method (ESM) Applied to MSMA2 Data ............................................. 74

5.5 Evaluation ................................................................................................................................ 78

6. Changes in Sediment Basins ......................................................................................................... 79

6.1 Criteria for Sizing of Wet and Dry Sediment Basins ................................................................. 79

6.2 Sediment Basins in MSMA (2000) ............................................................................................ 79

6.2.1 Dry Sediment Basin ......................................................................................................... 79

6.2.2 Wet Sediment Basin ........................................................................................................ 79

6.3 Sediment Basin Theory in MSMA (2011) ................................................................................. 80

6.3.1 Criteria for Sizing of Sediment Basins ............................................................................. 80

6.3.2 Design of Dry Sediment Basins ........................................................................................ 81

6.3.3 Design of Wet Sediment Basins ...................................................................................... 81

6.4 Case Study on Design of a Dry Sediment Basin ....................................................................... 81

6.4.1 MSMA (2000) .................................................................................................................. 81

6.4.2 MSMA (2011) .................................................................................................................. 82


6.5 Case Study on Design of a Wet Sediment Basin ...................................................................... 82

6.5.1 MSMA (2000) .................................................................................................................. 82

6.5.2 MSMA (2011) .................................................................................................................. 83

6.6 Evaluation ................................................................................................................................ 83

7. Conclusions ................................................................................................................................... 84

8. References .................................................................................................................................... 86


Table 1.1 Comparison of Chapters in MSMA (2000, 2011) (After DID Seminar Paper, 2012) ................ 4

Table 2.1 Design Storm ARIs for Urban Stormwater System Adoption (MSMA, 2000) .......................... 7

Table 2.2 Design Storm ARI Adoption (MSMA, 2011) ............................................................................. 7

Table 2.3 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Major and Minor

System for Sg Batu, Kuala Lumpur .......................................................................................................... 9

Table 3.1 Standard Durations for Urban Stormwater Drainage ........................................................... 12

Table 3.2 Recommended Intervals for Design Rainfall Temporal Pattern (Table 2.4 in MSMA, 2011) 13

Table 3.3 Areal Reduction Factors ........................................................................................................ 14

Table 3.4 IDF for Kuala Lumpur (MSMA 2000) .................................................................................... 16

Table 3.5 Short Duration IDF for Kuala Lumpur (Duration= 5 min) (MSMA 2000) ............................... 16

Table 3.6 Short Duration IDF for Kuala Lumpur (Duration= 15 min) (MSMA 2000) ............................. 16

Table 3.7 IDF Data for Kuala Lumpur (Station No. 3116004) (MSMA 2011) ........................................ 17

Table 3.8 Summary of IDF Data for Kuala Lumpur (MSMA, 2000) and 14 Stations in Kuala Lumpur

(MSMA 2011) for ARI of 100 YR ............................................................................................................ 17

Table 3.9 Summary of Stations in Kuala Lumpur (After Table 2.B1 in MSMA, 2011) ........................... 18

Table 4.1 Recommended Runoff Coefficients for Various Landuses (DID, 1980; Chow et al., 1988;

QUDM, 2007 and Darwin Harbour, 2009) (After Table 2.5 of MSMA, 2011) ....................................... 27

Table 4.2 Computation of Peak Discharges using the Rational Method in MSMA (2000) ................... 33

Table 4.3 Computation of Peak Discharges using the Rational Method in MSMA (2011) ................... 33

Table 4.4 Comparison of Peak Discharges using the Rational Method in MSMA (2000, 2011) .......... 33

Table 5.1 Limiting Catchment Areas for OSD or Dry/Wet Detention Pond in MSMA (2011) ............... 40

Table 5.2 Pervious and Impervious Areas ............................................................................................. 51

Table 5.3 Computation of Pre/Post Development Peaks ..................................................................... 56

Table 5.4 Computation of Permissible Site Discharge (PSD) ................................................................ 56

Table 5.5 Computation of Peak Post-Development Flow (QD) ............................................................ 56

Table 5.6 Computation of Site Storage Requirements (SSR) ................................................................ 57

Table 5.7 IDF Data for SK Taman Maluri Kuala Lumpur (ARI of 2 and 10 Year and Durations of 5, 10,

15, 20, 25, 30 and 35 minutes) (MSMA, 2011) ..................................................................................... 60

Table 5.8 Computation of Pre/Post Development Peaks ..................................................................... 61

Table 5.9 Computation of Permissible Site Discharge (PSD) ................................................................ 62

Table 5.10 Computation of Post Development Peaks and Site Storage Requirements (SSR) .............. 63

Table 5.11 Pervious and Impervious Areas ........................................................................................... 65

Table 5.12 Computation of Pre/Post Development Peaks ................................................................... 70

Table 5.13 Computation of Permissible Site Discharge (PSD) .............................................................. 70

Table 5.14 Computation of Peak Post-Development Flow (QD) .......................................................... 70

Table 5.15 Computation of Site Storage Requirements (SSR) .............................................................. 71

Table 5.16 IDF Data for Pulau Pinang (ARI of 2 and 10 Year and Durations of 5, 10, 15, 20, 25, 30, 35,

40, 45, 50, 55 and 60 minutes) (MSMA, 2011) ..................................................................................... 74

Table 5.17 Computation of Pre/Post Development Peaks ................................................................... 75

Table 5.18 Computation of Permissible Site Discharge (PSD) .............................................................. 76

Table 5.19 Computation of Post Development Peaks and Site Storage Requirements (SSR) .............. 77

Table 5.20 Comparison of OSD Requirements using MSMA (2000, 2011) for Kuala Lumpur .............. 78

Table 5.21 Comparison of OSD Requirements using MSMA (2000, 2011) for Pulau Pinang ............... 78

Table 6.1 Sediment Basin Types and Design Considerations ................................................................ 79

Table 6.2 Dry Sediment Basin Sizing Guidelines in MSMA (2000) (After Table 39.5 of MSMA, 2000) . 79


Table 6.3 Wet Sediment Basin Sizing Guidelines in MSMA (2000) (Table 39.6 of MSMA, 2000) ......... 80

Table 6.4 Quality Control Design Criteria (Table 1.3 in MSMA, 2011) .................................................. 80

Table 6.5 Comparison of Design Requirements for Sediment Basins between MSMA (2000 and 2011)

.............................................................................................................................................................. 80

Table 6.6 Dry Sediment Basin Sizing Criteria in MSMA (2011) (Table 12.18 in MSMA, 2011) ............. 81

Table 6.7 Wet Sediment Basin Sizing Volume (m3/ha) in MSMA (2011) (TABLE 12.19) ...................... 81

Table 6.8 Summary of Dry and Wet Sediment Basin Volumes based on MSMA (2000 and 2011) ...... 83


Figure 2.1 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Minor System for

Sg. Batu, Kuala Lumpur ........................................................................................................................... 9

Figure 2.2 Effect of Changes in ARI for Various Landuses on the Storm Intensity for Major System for

Sg. Batu, Kuala Lumpur ........................................................................................................................... 9

Figure 3.1 Plot of Areal Reduction Factors ........................................................................................... 14

Figure 3.2 IDF for Kuala Lumpur (MSMA 2000) .................................................................................... 19

Figure 3.3 IDF For Kuala Lumpur (MSMA 2011) (Station No. 3116004) ............................................... 19

Figure 3.4 Comparison of Estimated Rainfall Intensity Frequency Duration Curves for Kuala Lumpur

between MSMA 2000 & 2011 (ARI. =100 YR) ....................................................................................... 20


between MSMA 2000 & 2011 (ARI. =50 YR) ......................................................................................... 20






between MSMA 2000 & 2011 (ARI. =5 YR) ........................................................................................... 22


between MSMA 2000 & 2011 (ARI. =2 YR) ........................................................................................... 22

Figure 4.1 Steps of Computation in the Rational Method in MSMA (2000) ......................................... 24

Figure 4.2 Steps of Computation in the Rational Method in MSMA (2011) ......................................... 26

Figure 4.3 Catchment Map ................................................................................................................... 32

Figure 5.1 Relationship Between tc and tcs for the Swinburne Method .............................................. 34

Figure 5.2 Swinburne Method Assumptions tf= Time for Storage to Fill ............................................. 35

Figure 5.3 Typical Relationship of Storage Volume to Storm Duration ................................................ 37

Figure 5.4 Steps of Computation in OSD Design in MSMA (2000) ........................................................ 39

Figure 5.5 Location of OSD in the Project Site ...................................................................................... 50

Figure 5.6 Plot of SSR Versus Storm Duration ...................................................................................... 55

Figure 5.7 Summary of OSD Computation using MSMA (2011) for Kuala Lumpur .............................. 59

Figure 5.8 Plot of SSR versus Storm Duration ....................................................................................... 63

Figure 5.9 Location of OSD in the Project Site ...................................................................................... 64

Figure 5.10 Plot of SSR Versus Storm Duration .................................................................................... 69

Figure 5.12 Summary of OSD Computation using MSMA (2011) for Pulau Pinang .............................. 73

Figure 5.13 Plot of SSR versus Storm Duration ..................................................................................... 77

EVALUATION OF THE CHANGES BETWEEN THE FIRST … · 1 evaluation of the changes between the first...

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