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When designing for flood mitigation techniques, there are a few parameters that are needed, such as Rainfall Intensity, Average Recurrence Interval (ARI), and rainfall Temporal Pattern. We have encountered Rainfall Intensity and Average Recurrence Interval for Sarawak in the previous post. In this post, we will talk about the temporal pattern for Sarawak.

A temporal pattern is used to represent the typical variation of rainfall intensities during a typical storm duration, it gives the proportion of total rainfall over a certain time interval within a given rainfall duration. In MSMA 2, temporal pattern is needed for Time Area Method pond design ( which is required if the development area is more than 80 ha). Like the case for Rainfall Intensity, MSMA 2 doesn’t contain data for East Malaysia. Thus we are required to find the data from elsewhere.

One of the ways that we can do is to use the temporal pattern of the East Coast of Peninsular Malaysia to approximate the Sarawak temporal pattern, due to the geography proximity.

Another, better way is to collect and analyze the temporal pattern in Sarawak, and this task has been done by a group of researchers in UNIMAS, for Southern Region of Sarawak. Their findings have been published in an article named Development of Temporal Rainfall Pattern for Southern Region of Sarawak ( UNIMAS E-Journal of Civil Engineering, Vol. 3 Special Issue 2012). In the journal paper the authors compare and contrast the temporal pattern for east coast West Malaysia and Southern region of Sarawak:

temporarl pattern

The authors conclude that the temporal pattern is “quite similar for 10 and 15-minutes duration, due to the nature of the short period of rainfall, but deviates as it reaches the 30,60, and 120 minutes rainfall, as much as 23.2% of the total rainfall“.

In MiTS 2, we have implemented this table of temporal pattern into our Detention Pond Time Area Method design, so that our users in Sarawak can use the more recent and more accurate data when doing the time area method design.