Each contiguous part of the Grand Canal only flows in one direction, it would be impossible for it to work otherwise.

You do have a point though that this new river in Egypt may be the 'largest' on some other metric.

The issue isn’t direction but rather having multiple branches as a river only includes the main channel going downstream from a single point.

For example the Mississippi and Ohio river are considered different rivers even though their waters mix and both flow downstream through the same channel.

https://en.wikipedia.org/wiki/Ohio_River, https://en.wikipedia.org/wiki/Mississippi_River

According to this definition then Iraq’s man-made river (Saddam’s river) is longer at 565 km. the official role of the river was to collect irrigation water from Mesopotamia fertile land all the way to the Persian Gulf, though the real reason Saddam built it was to dry the Arab Marshes as it was difficult to contain the rebels in the marshes. https://ar.wikipedia.org/wiki/%D8%A7%D9%84%D9%85%D8%B5%D8%A8...

I thought most of that 565km distance was an existing waterway.

In English: https://en.wikipedia.org/wiki/Draining_of_the_Mesopotamian_M...

I think the distinction the authors are making - correctly or not, I’m not sure, plenty of rivers don’t flow to the sea - is this artificial river flows into the sea, not into other canals or rivers.

The grand canal connects the Yellow and Yangtze rivers, for example.