rainfall temporal pattern Call 6012-7102620

rainfall temporal pattern Call 6012-7102620

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Ph 6012-7102620





Manual Saliran Mesra Alam Malaysia (MSMA), which is also known as the Urban Stormwater Management Manual for Malaysia is the urban drainage design guideline first issued by the Department of Irrigation and Drainage Malaysia (D.I.D) in 2000. It is mandatory for all engineers in Malaysia to plan drainage structures to fullfil the requirements of MSMA. 11 years after its first publication, DID has completely updated the first edition of MSMA (MSMA1) with the publishing of the second edition (MSMA2). There are numerous differences in the second edition include (taken from case studies carried out for Kuala Lumpur):





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





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





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





4. The storage volume of a detention pond has risen by up to 130%.





The increase in the values 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:





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





2. Peninsular Malaysia is now divided into five regions for the determination of the 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 rainfall durations and intensities, and whether a catchment is urban/rural in condition. This resulted in changes in the estimated peak discharge.





4. The Time-Area Method in the second editon is affected by the changes in the rainfall intensites, temporal patterns and the loss model used. For Kuala Lumpur it is noted that the rainfall intensities have increased and the temporal pattern is more peaky, thus resulting in a more peaky discharge hydrograph.





5. The Site Storage Requirement (SSR) based on the Approximate Swinburne Method in the second editon 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 SSR's.





6. The storage volume of a detention pond has risen using the second editon compared to MSMA1 because of the increase in the rainfall intensities, temporal patterns and the choice of loss rate.





In view of the many changes 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 accurately and to allow comparison be made of their changes speedily. The tool is a drainage design software designed for MSMA- known as the MSMAware. The software is programmed 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 rainfall stations in the state and their temporal patterns are included into the software.

















rainfall temporal pattern Call 6012-7102620










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