Visit to the Katugastota Meteorological Department
As part of our field visit to investigate the rainfall conditions associated with the Akurana flood on October 17, we visited the Katugastota Meteorological Department to observe the meteorological instruments and understand their data recording processes.
Upon arrival, we met with the Technical Officer (TO), who introduced us to the instruments installed at the station and explained their functions. The instruments included a rain gauge for measuring rainfall, as well as equipment for recording wind direction, wind speed, atmospheric pressure and lightning activity.
Figure 1: Rain Gauge used by Met Department to measure rainfall
One of the main instruments demonstrated during the visit was the rain gauge, which records rainfall continuously using a mechanical recording system.
The recording process involves several components:
Catch: Rain falls into a funnel and flows into a narrow chamber inside the metal cylinder.
Float and pen: As water collects in the chamber, a float rises. A lever connects the float to a pen, which moves upwards as the rainfall amount increases.
Clock drum: A paper chart is wrapped around a drum operated by a wind-up clock. The drum completes one rotation every 24 hours. As the pen moves upwards with increasing rainfall, the paper moves sideways with time, producing a continuous rainfall record.
Siphon: When the pen reaches the 10 mm mark, a siphon automatically empties the chamber within a few seconds. The pen then returns to zero and begins recording again. This produces a series of saw-tooth patterns on the chart during periods of rainfall.
Check gauge: A separate standard rain gauge collects rainfall at the same location. Its readings are measured manually at 8:30 AM each day and used as a reference to check the recorded values.
Figure 2: Instruments used by Met Department to measure rainfall, wind speed, wind direction, pressure, lightning etc.
Examination of Rainfall Records
During our discussion, we explained our rainfall monitoring activities and informed the TO that we were missing one hour of rainfall data from October 17, the day of the Akurana flood.
Although the TO could not officially share the digital data files, he kindly showed us the raw data graphs generated directly by the instruments. We examined the recorded graphs and values while he explained the available information. We also requested the atmospheric pressure records for October 17, which he subsequently showed us at the office.
Figure 3: Rainfall data for 17 Oct, recorded by the rain gauge
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