Colin Gleason had been attempting to measure the runoff from Greenland’s melting ice sheets when he developed the new technique, which relies on measurements of a river’s width over time.
Field measurements of river depth and flow are often difficult to obtain. ‘Our new method doesn’t require access to the country or getting in the river to safely take measurements,’ said Gleason. ‘As long as we can get multiple pictures of a river, we can tell you how much water was flowing in the river at the time the images were taken.’
Gleason and his co-author, Laurence Smith, tested the technique on the Mississippi, Athabasca and Yangtze rivers using images from the US Landsat programme and field calculations carried out by government agencies. Their estimates were within 20 to 30 per cent of the actual flows. ‘That might sound like a big error, but right now, we have no idea about the flow rates of most rivers around the world,’ said Smith. ‘To get a number that’s within even 30 per cent of accurate is incredibly helpful.’
Since submitting their research for publication, Gleason and Smith have tested their method on 19 other rivers, with similar results.
This story was published in the May 2014 edition of Geographical Magazine