Hello Kovalevskis,
So sorry for the delayed response on your question. Somehow my automatic notification of comments is broken on this post so just now saw your question. Apologies.
In answer to your question about why I calculated something the way I calculated it...I was following the procedure outlined by Hurst himself nearly 100 years ago.
Hurst's input for the Nile, if I remember correctly, was the annual level of flooding, probably measured in meters. If I remember correctly he was trying to help build a dam for the river and he needed to know how high to make the dam in order to ensure there was no downstream flooding caused by having too short a dam height.
Cheers!
Jason