Thanks for the explanation!

I can see that at first the energy was primarily people energy, then it was supplemented by the energy of horses. Finally, mechanical energy started replacing parts of both. Using traditional EROEI calculations, the EROEI goes down, as more mechanization takes place. This is one reason why the EROEI of ethanol from Brazil sugar cane (using hand labor for harvesting) is better than from, say ethanol from US sugar cane.

Have you done any calculation of actual point-in-time numbers of EROEI using "standard" calculations, to the extent that there are such things? Energy embedded in infrastructure will have to be amortized over a suitable number of years.