I think your only choice is to bury them deeper. You could do this by digging them up, removing some soil from below them, and re-laying them, or start to gradually topdress the area with topsoil (not "enriched" topsoil, you don't want much organic matter in the stuff as it will just break down) or sand.

I personally would try topdressing first, especially since you have apparently already lost a bunch of soil due to runoff (which has probably accumulated into high spots further down the slope), so I imagine this would also improve the grading there. Spread a quarter inch of soil or sand over the area by shoveling it on and sweeping it in with a broom, once every two weeks. Idea is to slowly encourage the existing grass to adapt to the new soil level each time. A quarter inch is conservative, so if it looks like your grass can take more than that without getting stressed I would try that too.

And while you're at it, do the same over every low spot in your lawn, if you have any. You'll love the results!

Good luck,
Paul

Paul,

Thanks for the advice. I was wondering if I could dig out a small drywell and put sand in the drywell where the pipe ends and then do the topdressing you suggest. Since the ground is bare can I add some fall seeding later?

Thanks again,

Bob

1) Can you extend the pipes further along, and downhill? You don't need to relay the entire thing, just the last few feet, if you can get a slope further away.

2) There are "pop up" terminators for those pipes which might help. They spread the water out more evenly and lay flat when water is not flowing. That might help the erosion.

3) Why not use gravel instead of sand? You could dig out the end of the pipe, and terminate it in a catchment basin with holes at the bottom and gravel.

I would worry, however, about terminating a pipe underground without any sort of overflow. inevitably heavy rainstorms will create problems.

What heimert says is very true. A pipe buried without an overflow is washout just waiting to happen. You can do a short term fix but you'll have the same problem over and over no matter how deep your bury it.

Do a web search on "rain gardens" and see if this fits your site. If not think about cutting the downspouts and installing rain barrells or another drain system that will redirect the flow of water out onto the surface of the yard where it wont be so concentrated.