The number that could not be true

If you read anything about the Kallada — a government page, an academic introduction, a conservation report — you will meet the same sentence. The river carries an average runoff of 76,000 million cubic metres of fresh water into the estuary every year.

It is not true, and what makes it worth a story is that anyone can prove that with a pocket calculator.

Where it comes from

The figure traces to one document: the Ramsar Information Sheet for the Ashtamudi Wetland, filed in August 2002. It appears in section 7, the site overview — which is to say, in the opening summary, the part most likely to be copied by anyone in a hurry. It is the only discharge figure in the document.

From there it went everywhere. That is what a Ramsar sheet is for: it is the citable international record for a wetland of global importance. Twenty-four years of writing about this river has rested on it.

The arithmetic

The Central Water Commission gives the Kallada a basin area of 1,699 square kilometres. That is the number you need, and it is the only other one.

Divide 76,000 million cubic metres by 1,699 square kilometres and you get a runoff depth of 44.7 metres.

That is the claim, stated plainly: every square metre of this basin sheds nearly forty-five metres of water into the river each year. And since runoff cannot exceed rainfall, the basin must first receive at least forty-five metres of rain annually.

Kerala’s wettest ground gets somewhere around 2.5 to 3.5 metres. Cherrapunji, one of the wettest inhabited places on earth, averages under twelve. The figure is not merely too large for the Kallada. It is too large for the planet.

A second check, if the first feels too neat

Kerala’s forty-four rivers together have a total average annual yield of about 70,323 million cubic metres, per the state’s own Economic Review.

So the Ramsar sheet credits one minor river, in one district, which the Central Water Commission does not even classify as medium, with about 108% of what the Periyar, the Bharathappuzha, the Pamba and forty-one others carry combined.

What the real figure is

A 2022 study of saltwater intrusion in this river, published in Water Supply, gives it: the Kallada travels 121 km with an average annual runoff of 2,152 million cubic metres of fresh water.

The Ramsar sheet is out by a factor of about thirty-five.

And the real number passes the test the printed one fails. Run the same sum: 2,152 million cubic metres over 1,699 square kilometres is 1,266 mm of runoff, against basin rainfall of roughly 2,500 to 3,000 mm. That is a runoff coefficient near 45% — exactly what a steep, forested, monsoon-fed Western Ghats catchment ought to produce. It is not just plausible; it is characteristic.

How it probably happened

This is a hypothesis and we offer it as one. Note that 76,000 sits very close to Kerala’s statewide river runoff of around 70,000 to 78,000 million cubic metres. The likeliest explanation is not fabrication but filing: somebody completing a four-page form in 2002 put a state-level aggregate into a river-level field.

What makes that reading persuasive is that it is not the only such error on the sheet. The area field, in section 6, gives the site as 61,400 hectares — 614 square kilometres — for a lagoon that the same government’s own literature puts at about 61.4 square kilometres. Two different fields, one document, each out by a clean power of ten.

That is the honest editorial point, and it is not really about the Kallada. This is not a typo. It is an unaudited form that became an authority, and stayed one for twenty-four years, because it was the kind of document nobody expects to have to check.

The numbers we do use

For the record, and because the alternatives circulating online are no better sourced: the Central Water Commission’s Integrated Hydrological Data Book for non-classified river basins, 2006, gives the Kallada a length of 121 km and a basin of 1,699 square kilometres, with its origin in the Papanasam range south of Kulathupuzha at 900 m. The gauge-and-discharge station on the river is at Pattazhy.

The 120 km on the Ramsar sheet and the 128 km and 1,614 square kilometres that appear on aggregator sites are not CWC figures, and we do not print them.