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IDF Fitting Coefficient for Sarawak in SUStoM

Note: This post is already obsolete; we now no longer use the manually IDF fitting coefficient because we now have authoritative data, please refer New MSMA 2 data for Sabah and Sarawak based on Estimation of Design Rainstorm in Sabah and Sarawak (Revised and Updated 2018) for more information. 

The post is retained only for historical reference purpose. 

In this post, we will talk about IDF fitting coefficients as published by DID Sarawak, to be used for SUStoM in conjunction with MSMA 2. This is the approach we took and as an initiative to produce a set of data to be used in stormwater management for Sarawak only, way before we implement the rainfall data based on “Estimation of Design Rainstorm in Sabah and Sarawak (Revised and Updated 2018)” publication. 

SUStoM is the short form for  Sarawak Urban Stormwater Management, which was approved by State Cabinet on 28th January 2016 as a planning standard for development control to incorporate stormwater management into the design to minimize environmental degradation and improve aesthetic as well as recreational appeal of areas in Sarawak.

SUStoM needs to be read in conjunction with Manual Saliran Mesra Alam (MSMA) 2. A full copy of SUStoM can be found here.

the Average Rainfall Intensity is determined by the following formula, based on empirical Equation 2.2:


In MSMA 2, the fitting constants above are provided in Table 2.B1, but MSMA 2 contains only fitting constants for West Malaysia. East Malaysia, Sarawak and Sabah rainguage locations are being unfortunately left out.

For Sarawak, there is one solution: Sarawak Hydrological Yearbook, vol. 40.  The book can be purchased from Sarawak DID. This book contains the IDF curve graphs for 2, 5, 10, 20, 50, 100 years, for the following rainguage locations:

  1. Kuching, Airport
  2. Ukong
  3. Stapang
  4. Sri Aman
  5. Song
  6. Sibu JKR Water Works
  7. Serian
  8. Sarikei
  9. Saratok
  10. Nanga Lubau
  11. Nanga Lemai
  12. Mukah JKR
  13. Miri Airport
  14. Long Semado
  15. Limbang
  16. Lawas Airfield
  17. Daro
  18. Bintulu Airport
  19. Belaga
  20. Asa Jaya

Based on the graphs, we have extracted the fitting constants for each rainguage locations, so that we can calculate the Average rainfall intensity for any ARI, given any rainguage location.

Thus if you go to MiTS 2. You will be able to obtain the  IDF curve for any ARI, nicely generated for you, as shown below.


Note that even though there is no data for ARI 200, but we can interpolate the ARI 200 year curve, thanks to the fitting constants that we calculated.

Interested in how we extract the fitting coefficients from the published graphs? Do drop us an email expressing your interest, and we will make it into one of our future blog posts!

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