I was actually kind of surprised how many showed up around the valley in general, but Griffith Park, not so much (yet).

I'm not suggesting going nuts on street gutters or anything... it's just that OSM wants *some* descriptive tag at any crossing of those ways, or it will complain. In this case, the "ford" tag just means the (intermittent, shallow) water and the highway are on the same layer, no culvert or bridge. The wiki page even suggests using a depth=0 tag for particularly insignificant cases. Again, it's just a kind of mental gymnastics of decoupling the meaning a word has in your mind for purposes of tag names, I struggled a little with "driveway", myself.

Anyway, that's my best attempt at an understanding of the situation. If you find a more elegant solution, let me know! You could always ask here:

https://community.openstreetmap.org/c/communities/us/78

This is the most relevant thing I found in the older Q&A forums:

https://help.openstreetmap.org/questions/72108/stream-running-along-and-over-a-road

If you *really* don't want to add the ford tags, you could add an explanatory "note" tag and ignore the warnings that come up, I suppose.