Does the author write the word "off" instead of "of"?

Question

Water enters a lake from overland flow off the surrounding land.

It's a preposition. The way I interpret that sentence is that there is water on the surrounding land, and some of it flows off into the lake. Just as water spilled on a table might flow off the table and onto the floor. (That overland flow likely wouldn't be the main source of water in the lake, but rainwater that falls on the land near the lake has to go somewhere - some will be absorbed into the ground, some will evaporate, and some runs off into the lake.) — nnnnnn, Commented Jun 5, 2016 at 8:36
Yes, I consider overland flow a phrasal noun too, where off is a preposition that indicates where the overland flow came from. — nnnnnn, Commented Jun 5, 2016 at 10:11
Yes @Alireza but see also merriam-webster.com/dictionary/off%20of Off of is used by native speakers. Those who say it's redundant or bad English are countered by those who say it's an idiom and natural. I would probably not use it in formal contexts. — Alan Carmack, Commented Jun 6, 2016 at 4:42

Alan Carmack · Accepted Answer · 2016-06-05 12:49:41Z

Off is a preposition:

moving away and often down from

Flow refers to something in motion, and many times takes the preposition of after it:

the flow of the river
the flow of water
the flow of electricity
the flow of words

Overland flow is a compound noun. It refers to water that flows over land down towards a body of water.

It's natural to think that of is the intended word in your sentence, giving:

Water enters a lake from overland flow of the surrounding land

However, due to context and, in particular, the lack of the definite article before overland flow, we can correctly read off as a preposition.

Water enters a lake from overland flow off the surrounding land

overland flow is running or flowing off the surrounding land into the lake.

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