Geography of Sri Lanka

Top 10 “Biggest” Rivers in Sri Lanka

It depends on what “biggest” means…

Do you know what the Top 10 “Biggest” Rivers in Sri Lanka?

1D

We’ve all learnt that the Mahaweli Ganga is the longest river in Sri Lanka. Some of us might also know that the next longest is the Aruvi Aru (a.k.a. Malwathu Oya). Kala Oya comes next. Kelani Ganga and so on.

However this definition of “biggest” (i.e. “longest”) is literally one-dimentional. There are more dimensions we can look at.

2D

If we rank rivers according to their catchment areas (i.e. the land area from where they get water), we get a different Top 10.

As in the 1D case, the length of the bars in the chart, are proportional to the length of the river. The area is proportional to the catchment area.

The Top 3 remain the same. Kalu Ganga (an unsually wide river with a dense system of branches) jumps from 10th to 4th place. Maha Oya leaves the Top 10, making way for Gal Oya.

3D

We can also look at the volume of water collected by the river. Or in other words, the volume of rain precipitated into the river. Leading to another Top 10.

As in the 1D case, the length of the bars in the chart, are proportional to the length of the river. As in the 2D case, the bottom area is proportional to the catchment area. The volume of the bar is proportional to the precipitation volume.

Wet zone rivers go up in the ranking, at the expense of Dry zone rivers. Mahaweli is still 1st. But Kalu and Walawe take 2nd and 3rd place.

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Data and Code: https://observablehq.com/@nuuuwan/sl-rivers