My initial reaction would be probabl rushes indicate blocked or severed field drains.
Unlike most people, I guite like rushes. Quite a few Jack Snipe can be found in mine.
I like rushes too, to a certain extent! good for sheep to shelter in, pheasants to nest in, but when a third of the field is huge clumps that you can't get through, its time to reclaim some grazing!
I literally lost a sheep in one of the clogged areas, I was ill for a few days, then knew there was a ewe missing, after looking for her a few days, I could smell it.

Too late to help her, but a few days earlier...
So this year i've been making 'pathways' through the worst overgrown areas, I don't like using weedkiller, but there comes a time when my sheep are more important.
I was very proud of myself finding an old stone drain, husband decided to replace it, with a solid drain pipe! area is nearly as boggy as before .
Then he and his mate did the same with a big drain going across a field, admittedly it's confusing where all these drains come and go, but again the bottom corner is no better.
but of course they wont listen to a woman.