#rainfall temporal pattern

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rainfall temporal pattern Call 6012-7102620

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Manual Saliran Mesra Alam Malaysia (MSMA), commonly known as the Urban Stormwater Management Manual for Malaysia is the urban stormwater drainage design standard first published 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 revised the first edition of MSMA (MSMA1) with the publishing of the second edition (MSMA2). There are a lot of differences in the second edition include (based on case studies done for Kuala Lumpur):

1. The design storm has risen by up to 126% for ten 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 of a detention basin has gone up by up to 130%.

The hike 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 rainfall data covering 100 more stations in Peninsular Malaysia. This gives rise to in higher storm intensities for certain durations and ARI’s.

2. Peninsular Malaysia is now grouped into 5 regions for the determination of the rainfall 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 different hydrograph peaks and shapes.

3. The coefficient of runoff in the Rational Method is now established 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.

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 rainfall 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 the first edition. 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 of a detention basin has risen using MSMA2 compared to the first edition because of the increase in the storm intensities, temporal patterns and the choice of loss rate.

In view of the many differences in computational methods between the first and second editions of MSMA, a tool is developed to help engineers to carry out the computations using both editions precisely and to allow comparison be made of their differences quickly. The tool is a stormwater design software created for MSMA- which is known as the MSMAware. The software is written by Ir. Dr. Quek Keng Hong who is a professonal 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 programmed into the software.

RAINFALL TEMPORAL PATTERN : 00:00:05 rainfall temporal pattern 00:00:06 storm temporal pattern 00:00:07 Rational Method 00:00:08 Time-Area Method 00:00:09 culvert design