Dr. Quek's tips on MSMA (Part 27)- MSMA Workshop A- Day 2 (20-9-2022)

DESIGN STORM

Design Storm ARI

All stormwater drainage design in MSMA (2011) must comply with the design storm ARI’s (Average Recurrence Intervals) as given in Table 2.1.?

TABLE 2.1 DESIGN STORM ARI (MSMA, 2011)

Type of Development Minimum Average Recurrence interval (ARI)?

of Design Storm (Year)

Minor System Major System

Residential 5 50

-Bungalow and Semi-D

-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

Source: Table 1.1 of MSMA (2011)

Design Storm Computation

Below are DID’s current guidelines and procedures for the computation of design storms:

MSMA (2011)- the second edition of MSMA (MSMAware Data Type: W1).

HP 1 (DID, 2021)- for Peninsular Malaysia (W2).

HP 26 (DID, 2018)- for East Malaysia (E1).

Sarawak Hydrological Year Book (2020)- for East Malaysian state of Sarawak (E2).

Note that the first edition of MSMA (2000) has been superceded by the Second Edition (MSMA, 2011), hence is not included in the list above.

Table 2.2 is a summary of the types and sources of storm data for West Malaysia.?

Table 2.3 is a summary of the types and sources of storm data for East Malaysia.?

Figure 2.1 is a flow chart showing the computation of design storm with the applications of Areal Reduction Factor and storm temporal pattern.

TABLE 2.2 DESIGN STORM DATA FOR WEST MALAYSIA

Data Type Description Guideline Details Type References Appendix

W1A IDF Data for Gauged Stations in West Malaysia (MSMA, 2011) MSMA (2011) IDF data for 135 stations for West Malaysia- High ARIs between 2 and 100 Year Gauged Stations Table 2.B1 in MSMA2011 2.6.1

W1B IDF Data for Gauged Stations in West Malaysia (MSMA, 2011) MSMA (2011) IDF data for 127 stations for West Malaysia- Low ARIs between 0.5 and 12 Month. Gauged Stations Table 2.B2 in MSMA2011 2.6.2

W2A IDF Data for Gauged Stations in West Malaysia by DID (HP1) HP1 (2021) 158 stations by DID Gauged Stations Table 4.1 in HP1 2.1.1

W2B IDF Data for Gauged Stations in West Malaysia by Met Malaysia (HP1) HP1 (2021) 22 stations by Met Malaysia (MMS) Gauged Stations Table 4.2 in HP1 2.1.2

W3 IDF Data for Ungauged Stations in West Malaysia (10 km Grid) (HP1) HP1 (2021) 10 km grid. No of grids= 1426 Ungauged Stations Appendix IV in HP1 2.2.1

W4 IDF Data for Ungauged Stations in West Malaysia (20 km Grid) (HP1) HP1 (2021) 20 km grid. No of grids= 382 Ungauged Stations Appendix V in HP1 2.2.2

W5 ARF (Areal Reduction Factor) in HP1 HP1 (2021) ARF for West Malaysia Ungauged Stations Table 7.1-4 of HP1 (2021) 2.8.1-4

W6 CCF (Climate Change Factor) in HP1 HP1 (2021) CCF for West Malaysia Ungauged Stations Table 8.1-5 for West Malaysia 2.13.1-5

W7 ARF (Areal Reduction Factor) in MSMA (2000) MSMA (2000) ARF for any location in Malaysia Ungauged Stations Table 13.1 of MSMA (2000) 2.7

W8A Temporal Pattern in MSMA (2011) MSMA (2011) Temporal Pattern for West Malaysia Ungauged Stations App 2.C of MSMA (2011) 2.10

W8B Temporal Pattern (HP1) HP1 (2021) Temporal Pattern for West Malaysia Ungauged Stations Table 6.2-5 of HP1 2.11

Table 2.3 is a summary of the types and sources of storm data for East Malaysia.?

TABLE 2.3 DESIGN STORM DATA FOR EAST MALAYSIA

Data Type Description Guideline Details Type References Appendix

E1A IDF Data for Gauged Stations in East Malaysia (HP26) HP26 (2018) 54 stations in Sabah Gauged Stations Table 4.1 of HP26 2.3.1

E1B IDF Data for Gauged Stations in East Malaysia (HP26) HP26 (2018) 120 stations in Sarawak Gauged Stations Table 4.2 of HP26 2.3.2

E2 IDF Data from SHYB (Sarawak Hydrological Yearbook) Data SHYB (2020) 12 stations in Sarawak Gauged Stations SHYB (Sarawak Hydrological Yearbook) 2.5

E3 IDF Data for Ungauged Stations in East Malaysia (10 km Grid) (HP26) HP26 (2018) 10 km grid. No of grids=2346 Ungauged Stations From CD-ROM 2.4.1

E4 IDF Data for Ungauged Stations in East Malaysia (20 km Grid) (HP26) HP26 (2018) 20 km grid. No of grids= 646 Ungauged Stations From CD-ROM or Figure 5.1-5.4 of HP26 2.4.2

E5A ARF (Areal Reduction Factor) in HP26 HP26 (2018) ARF for Sabah in East Malaysia Ungauged Stations Table 6.12 of HP26 2.9.1

E5B ARF (Areal Reduction Factor) in HP26 HP26 (2018) ARF for Sarawak in East Malaysia Ungauged Stations Table 6.13 of HP26 2.9.2

E6A CCF (Climate Change Factor) for East Malaysia (HP26) HP26 (2018) CCF (Climate Change Factor) for Ungauged Stations in East Malaysia (10 km2 Grid) Ungauged Stations CD-ROM 2.14.1

E6B CCF (Climate Change Factor) for East Malaysia (HP26) HP26 (2018) CCF (Climate Change Factor) for Ungauged Stations in East Malaysia (20 km2 Grid) Ungauged Stations CD-ROM 2.14.2

E6C CCF (Climate Change Factor) for Sabah, East Malaysia (HP26) HP26 (2018) 49 stations in Sabah Gauged Stations Table 7.1 of HP26 2.14.3

E6D CCF (Climate Change Factor) for Sarawak, East Malaysia (HP26) HP26 (2018) 116 stations in Sarawak Gauged Stations Table 7.2 of HP26 2.14.4

E7 Temporal Pattern (HP26) HP26 (2018) Temporal Pattern for East Malaysia Ungauged Stations - 2.12

TABLE 2.4 STORM DATA PERIOD OF VARIOUS PROCEDURES

PROCEDURE DATA PERIOD

MSMA (2000) 1990

MSMA (2011) 2000-2010

HP1 (2021) 2019

HP26 (2018) 2016

SHYB 2020

MSMA (2011) (W1)

In Equation 2.2 of Chapter 2 in MSMA (2011), the following empirical equation was fitted to the IDF data for 135 major urban centres in West Malaysia:?

i=(λ?T^κ)/(d+θ)^η?(2.1)

where

i = Average rainfall intensity (mm/hr)

T??= Average return interval (years) for high ARI of between 2 and 100 years for MSMA (2011), HP1 (2021) and HP26 (2018). For MSMA (2011) it also includes low ARI of between 0.5 and 12 months.

d??= Storm duration (hours) where d is between 0.0833 and 72 hours

λ, κ, θ and η= Fitting constants dependent on the raingauge location. Refer Table 2.B1 for high ARI and Table 2.B2 for low ARI in Appendix 2.B (MSMA, 2011).?

These data are presented in Table 2.B1 and 2.B2 in MSMA (2011) as follows:

High ARI’s in Table 2.B1 of MSMA (2011) (Appendix 2.6.1) (W1A).

Low ARI’s in Table 2.B2 of MSMA (2011) (Appendix 2.6.2) (W1B).

HP1 (2021) (W2, W3, W4)

DID published an update to the HP 1 (1982) in August 2021. This publication adopts the similar approach as MSMA (2011) but included later data up to 2019 and more stations in Peninsular Malaysia.

Gauged Stations (W2)

Gauged stations data are included in the following tables in HP1:

Table 4.1 of HP1 (Appendix 2.1.1) by DID (W2A).

Table 4.2 of HP1 (Appendix 2.1.2) by MMS (W2B).

These data are different from those in Table 2.B1 and 2.B2 in MSMA (2011) and include more up to date data.

Ungauged Stations (W3, W4)

The figures for determining the four IDF parameters (λ, κ, θ and η) for ungauged stations are presented in HP1 (2021) as follows:

10 km grids in Appendix IV of HP1 (Appendix 2.2.1) (W3).

20 km grids in Appendix V of HP1 (Appendix 2.2.2) (W4).

HP26 (2018) (E1, E3, E4)

DID published an update to HP26 in 2018. This publication adopts quite similar approach to HP1 (2021) for East Malaysia.

Gauged Stations (E1)

The values of the four IDF parameters (λ, κ, θ and η) are presented in HP26 as follows:

Table 4.1 of HP26 for Sabah (Appendix 2.3.1) (E1A).

Table 4.2 of HP26 for Sarawak (Appendix 2.3.2) (E1B).

Ungauged Stations (E3, E4)

The figures for determining the four IDF parameters (λ, κ, θ and η) are presented in HP26 for 10 and 20 km grids as follows:

10 km grids- CD-ROM of HP26 (Appendix 2.4.1) (E3).

20 km grids - Figures 5.1 to 5.4 of HP26 (Appendix 2.4.2) (E4).

Sarawak Hydrological Year Book (2020) (E2)

SHYB (2020) provides complete IDF graphs for 12 stations in Sarawak as follows in Appendix 2.5:

Appendix 2.5.1- Kuching Airport (1403001)

Appendix 2.5.2- Asa Jaya (1506034)

Appendix 2.5.3- Daro (2514004)

Appendix 2.5.4- Bintulu Airport (3130002)

Appendix 2.5.5- Sibu JKR Water Works (2218017)

Appendix 2.5.6- Ukong (4548004)

Appendix 2.5.7- Sarikei DID (2115008)

Appendix 2.5.8- Limbang DID (4749001)

Appendix 2.5.9- Song (2025012)

Appendix 2.5.10- Saratok DID (1713005)

Appendix 2.5.11- Miri Airport (4339005)

Appendix 2.5.12- Sri Aman (1412401)

Data Periods for Various Procedures

Table 2.4 is the data period for the following procedures:

MSMA (2000)

MSMA (2011)

HP1 (2021)

HP26 (2018)

SHYB (2020)

It is important to adopt up-to-date data in storm computation. By comparing the data periods for all the procedures, it can be seen for West Malaysia, HP1 has the latest data up to 2019, while SHYB has its data up to 2020.?

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FIGURE 2.1 DESIGN RAINFALL COMPUTATION

AN ILLUSTRATION OF DESIGN RAINFALL COMPUTATION (MSMA, 2011)

Areal Reduction Factor

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 based on the United States Weather Bureau's method.?

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

I_c=F?I_p (2.2)

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.?

MSMA (2000) (W7)

Areal reduction factor (ARF) is given in Table 13.1 of MSMA (2000) but not in MSMA (2011). Hence, the procedure from MSMA (2000) can also be applied to MSMA (2011).

According to MSMA (2000), ARF is necessary only for catchment above 50 km2.

The values of F for catchment areas of up to 200 km2 and durations of up to 24 hours are given in Table 13.1 and plotted in Figure 13.1 of MSMA (2000) and included in Appendix 2.7.

HP1 (2021) (W5)

The tables for ARF computation are given in HP1 for Peninsular Malaysia which is divided into four regions as follows:

ARF for Region 1 in Table 7.1 of HP1 (Appendix 2.8.1)

ARF for Region 2 in Table 7.2 of HP1 (Appendix 2.8.2)

ARF for Region 3 in Table 7.3 of HP1 (Appendix 2.8.3)

ARF for Region 4 in Table 7.4 of HP1 (Appendix 2.8.4)

HP26 (2018) (E5)

The tables for ARF computation are given in HP26 as follows:

ARF for Sabah in Table 6.12 of HP26 (Appendix 2.9.1) (E5A).

ARF for Sarawak in Table 6.13 of HP26 (Appendix 2.9.2) (E5B).

Storm Temporal Pattern

MSMA (2011) (W8A)

In MSMA (2011), the temporal patterns to be used for a set of durations are given in Appendix 2.C of MSMA (2011) 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)

The temporal patterns for MSMA (2011) are included in Appendix 2.10.

HP1 (2021) (W8B)

In HP1 (2010), the temporal patterns are given for a set of durations similar to MSMA (2011) for the following four regions as shown in Figure 2.2 (Figure 6.1 of HP1):

Region 1- Eastern

Region 2- Southern

Region 3- West Central

Region 4- Northern

The temporal patterns for HP1 are included in Appendix 2.11.

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