In 2000 the Department of Irrigation and Drainage Malaysia first printed the stormwater drainage design guideline known as the Urban Stormwater Management Manual for Malaysia or the Manual Saliran Mesra Alam Malaysia, MSMA. Fullfilment of the requirements of MSMA when designing drainage works is required legally of all engineers in Malaysia. The Department of Irrigation and Drainage has completely amended the first edition of MSMA (known as MSMA1) with the release of the second edition (known as MSMA2) about Eleven years after its first edition. With reference to the case studies carried out for Kuala Lumpur, there are many differences in the second edition include:
The design storm has gone up by up to 126% for 10 out of the 14 rainfall stations in Kuala Lumpur.
The design discharge using the Rational Method has gone up by up to 131% for commercial and city area.
The Site Storage Requirement for OSD for a factory site in Kuala Lumpur has increased by up to 235%,
Detention basin has gone up by up to 130% in the volume.
The differences between the first and the second editions of MSMA resulted the increase in the values of the main design parameters as follows:
Longer storm data covering 100 more storm stations in Peninsular Malaysia. This gives rise to in higher storm intensities for certain durations and Average Recurrence Intervals.
Compared to previously where it was divided into east and west coast of the Peninsula for the determination of the storm temporal pattern, West Malaysia is now separated into five regions. The different hydrograph peaks and shapes due to the differences in temporal patterns.
Not affected by rainfall durations and intensities, and whether a catchment is urban/rural in condition, the coefficient of runoff in the Rational Method is now determined according to the types of landuse. Differences in the estimated peak discharge is the result .
The differences in the rainfall intensites, temporal patterns and the loss model used all affected the Time-Area Method in MSMA2. The rainfall intensities for Kuala Lumpur have increased and the rainfall temporal pattern is more peaky, resulting in a more peaky flow hydrograph.
The Approximate Swinburne Method in the second editon gives higher Site Storage Requirement (SSR) than the Swinburne Method in the first edition. The approximate method in the second editon has resulted in an over estimation of the Site Storage Requirements.
Compared to the first edition, the increase in the rainfall intensities, temporal patterns and the choice of loss rate have resulted a rise in the volume of a detention basin using the second edition.
In view of the many differences in computational procedures between the first and second editions of MSMA, a tool is developed to help engineers to perform the computations using both editions precisely and to allow comparison be made of their changes quickly. The tool is a stormwater design software developed for MSMA. The software is created by Ir. Dr. Quek Keng Hong- a professonal engineer in Malaysia. MSMAware also contains more than a dozen storm stations and their temporal patterns in the Sarawak.