Manual Saliran Mesra Alam Malaysia (MSMA), or in English the Urban Stormwater Management Manual for Malaysia is the stormwater drainage design standard first released by the Department of Irrigation and Drainage Malaysia (D.I.D) in 2000. It is compulsory for all engineers in Malaysia to design drainage system to comply with the requirements of MSMA. 11 years after its first publication, DID has completely revised the first edition of MSMA (MSMA1) with the release of the second edition (MSMA2). There are a lot of changes in the second edition including the following (based on case studies done for Kuala Lumpur):
ten out of the fourteen storm stations in Kuala Lumpur have its design rainfall risen by up to 126%.
For commercial and city area, the design flow using the Rational Method has gone up by up to 131%.
The Site Storage Requirement for On-Site Detention for a factory site in Kuala Lumpur has gone up by up to 235%,
The storage volume of a detention basin has gone up by up to 130%.
The rise in the magnitudes of the main design parameters as outlined above can be attributed to the changes between the first and the second editions of MSMA as follows:
135 stations in Peninsular Malaysia with longer storm data. This results in higher storm intensities for certain durations and Average Recurrence Intervals.
West Malaysia is now divided into 5 regions for the determination of the temporal pattern, compared to the first edition where it was divided into east and west coast of the Peninsula. The dissimilar hydrograph peaks and shapes due to the changes in temporal patterns.
The coefficient of runoff in the Rational Method is now set according to the types of landuse, and not affected by storm durations and intensities, and whether a catchment is urban/rural in condition. This resulted in differences in the estimated peak flow.
The Time-Area Method in MSMA2 is affected by the differences in the storm intensites, temporal patterns and the loss model used. For Kuala Lumpur it is noticed that the rainfall intensities have increased and the temporal pattern is more peaky, thus resulting in a more peaky flow hydrograph.
The Approximate Swinburne Method in MSMA2 gives higher Site Storage Requirement (SSR) than the Swinburne Method in MSMA1. MSMA2 used the approximate method based on a set of approximation tables and this has resulted in an over estimation of the Site Storage Requirements.
Compared to MSMA1, the increase in the storm intensities, temporal patterns and the selection of loss rate have caused a rise in the storage volume of a detention basin using MSMA2.
A software program Is built to assist engineers to perform the computations using both editions precisely and to allow comparison be made of their changes quickly, in view of the many changes in computational methods between the first and second editions of MSMA. The tool is a drainage design software designed for MSMA. Ir. Dr. Quek Keng Hong- a professonal engineer in Malaysia is the programmer of the software. MSMAware also covers more than a dozen storm stations and their temporal patterns in the Sarawak.