The Urban Stormwater Management Manual for Malaysia or the Manual Saliran Mesra Alam Malaysia (MSMA) is the urban drainage design standard first printed by the Department of Irrigation and Drainage Malaysia in early 2000. It is compulsory for all engineers in Malaysia to build drainage system to comply with the requirements of MSMA. 11 years after its first publication, DID has completely amended the first edition of MSMA (MSMA1) with the publishing of the second edition (MSMA2). There are numerous differences in the second edition include (based on case studies carried out for Kuala Lumpur):
10 out of the 14 storm stations in Kuala Lumpur have its design storm gone up by up to 126%.
For commercial and city area, the design discharge using the Rational Method has risen by up to 131%.
The Site Storage Requirement for OSD for a factory lot in Kuala Lumpur has gone up by up to 235%,
Detention basin has risen by up to 130% in the storage.
The differences between the first and the second editions of MSMA give rise to the hike in the values of the main design parameters below:
135 storm stations in Peninsular Malaysia with longer precipitation data. The storm intensities for most ARI’s are higher.
Compared to previously where it was divided into east and west coast of the Peninsula for the derivation of the rainfall temporal pattern, West Malaysia is now divided into 5 regions. The differences in temporal patterns give rise to dissimilar hydrograph peaks and shapes.
The coefficient of runoff in the Rational Method is now set according to the types of landuse, and not influenced by rainfall durations and intensities, and whether a catchment is urban/rural in condition. Changes in the estimated peak flow is the result .
The changes in the storm intensites, temporal patterns and the loss model used all affected the Time-Area Method in MSMA2. The storm intensities for Kuala Lumpur have increased and the storm temporal pattern is more peaky, resulting in a more peaky flow hydrograph.
The Approximate Swinburne Method in MSMA2 resulted in higher Site Storage Requirement (SSR) than the Swinburne Method in the first edition. The approximate method in MSMA2 has given rise to an over estimation of the Site Storage Requirements.
Compared to MSMA1, the increase in the storm intensities, temporal patterns and the choice of loss rate have given rise to a rise in the storage volume of a detention basin using MSMA2.
A software program Is built to help engineers to carry out the computations using both editions precisely and to allow comparison be made of their changes quickly, in view of the many changes in computational procedures between the first and second editions of MSMA. A drainage design software has been created for MSMA. Ir. Dr. Quek Keng Hong- a professonal engineer in Malaysia is the creator of the software. MSMAware also covers more than a dozen storm stations and their temporal patterns in the Sarawak.