Rational Method Ph 6012-7102620

Rational Method Ph 6012-7102620

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Call 6012-710-2620





Manual Saliran Mesra Alam Malaysia (MSMA), or the Urban Stormwater Management Manual for Malaysia is the urban drainage design procedure first distributed by the Department of Irrigation and Drainage Malaysia (D.I.D) in 2000. It is compulsory for all engineers in Malaysia to build drainage works to comply with the requirements of MSMA. 11 years after its first publication, DID has completely updated the first edition of MSMA (MSMA1) with the release of the second edition (MSMA2). There are many changes in the second edition include (taken from case studies completed for Kuala Lumpur):





1. The design storm has risen by up to 126% for 10 out of the 14 storm stations in Kuala Lumpur.





2. The design flow using the Rational Method has gone up by up to 131% for commercial and city area.





3. The Site Storage Requirement for On-Site Detention for a factory lot in Kuala Lumpur has risen by up to 235%,





4. 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 due to the differences between the first and the second editions of MSMA as follows:





1. Longer precipitation data covering 100 more rainfall stations in Peninsular Malaysia. This gives rise to in higher storm intensities for certain durations and ARI's.





2. West Malaysia is now grouped into 5 regions for the determination of the storm temporal pattern, compared to previously where it was divided into east and west coast of the Peninsula. The differences in temporal patterns give rise to dissimilar hydrograph peaks and shapes.





3. The coefficient of runoff in the Rational Method is now fixed according to the types of landuse, and not dependent on storm durations and intensities, and whether a catchment is urban/rural in condition. This resulted in differences in the estimated peak flow.





4. 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 noted that the storm intensities have increased and the storm temporal pattern is more peaky, thus giving rise to a more peaky flow hydrograph.





5. The Site Storage Requirement (SSR) based on the Approximate Swinburne Method in MSMA2 is higher than that using 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.





6. The storage volume of a detention basin has risen using MSMA2 compared to MSMA1 because of the increase in the storm intensities, temporal patterns and the choice of loss rate.





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 differences quickly. The tool is a drainage design software created for MSMA- which is known as the MSMAware. The software is developed by Ir. Dr. Quek Keng Hong who is a practising professional engineer in Malaysia. MSMAware also covers the East Malaysian state of Sarawak where more than a dozen storm stations in the state and their temporal patterns are included into the software.

















Rational Method Ph 6012-7102620










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