Here is an overlay I did in MS Paint to show where I'd at least like 1 wall....but I'm not sure it's possible to just put a wall in the middle of a sloping hill like this......

I think this wall will need to be about 4ft tall to be able to make the ground level just below my deck area

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I think it's going to be hard for you to get good advice on this here unless your pictures do a good job of conveying the existing space. There's nothing (such as a house) in the pictures to indicate level. We can't perceive the slope unless the camera is held level and the view in lined up transverse to the slope. Show WIDE views first and then closer in for detail, if necessary. Where are pictures of the "pretty bad erosion issues"?

You may not need all the walls you think you need. Are the slopes like what is around your house commonly found around other houses in the area? How are others successfully handling slopes?

Some things to think about:

Can you lower the grade at the top of the slope (under a deck?) rather than trying to bring or keep the adjacent grade higher? Depth of the foundation wall footing can limit that depending on your frost depth and how deep the footing is. Deck footings are not that costly as compared to those retaining walls, if you have to do new ones at a lower depth.

Erosion is caused by volume and speed (slope = speed) of water. Eliminating water from getting to the slope will reduce volume and roof runoff is generally the biggest supply of water volume on a residential site. You mentioned gutters, so make sure that you collect the water from the downspouts and pipe it somewhere so that it does not find the slope. Obviously, flattening sections of the slope with retaining walls reduces speed of runoff as well.

Interruption of slope slows water speed as well. Surface treatment can slow water speed. An example is long shreddy bark mulch that sort of weaves itself together helps, but it can only do so much.

You can build a wall halfway up a slope, but it has to have enough structural characteristics to work in its situation and can easily be just as big or bigger under ground as what you would need by terracing.

There are more landscape contractors who know how to put together retaining walls than there are that know how to design retaining walls.

ANY WALL or combinations of walls exceeding 4' in height REQUIRE structural engineering by a licensed structural engineer. This is not as $cary as it sounds. All you need from them is usually a single cross section detail showing how the wall has to be built. Typically, someone designs the layout plan (plan view showing where the wall(s) goes and the top and bottom of wall spot grades.

There are large modular block retaining wall systems that are far more economical than either poured concrete, concrete masonry units, or smaller modular block walls (small modular blocks are the most common wall type done by landscape contractors). The big blocks are often 2' high x2'x4'. Some of the names are Econo-block or Redi-Rock. They weigh about 2,000 pounds each. The problem is that there are less people installing them, so your basic landscape contractor will steer you to something that he does rather than a cheaper solution that does not involve them. These blocks are less attractive than some others, but it will face away from you and can be mitigated with plantings.

I have reached out to landscaping companies here in town......they act like they know how to solve the erosion problems. The company that quoted me the high price told me it's possible to have just one wall down the middle of the hill.....they were going to get with me next week on options and costs. That quote was for like an Allen Block system. They have sent out their "designers" and each company I've had come out talks about the drainage as well as the wall, so I believe they are taking this all into account.

I have never seen those Redi Rock blocks before, but they look pretty awesome. 2,000 lbs each though? My goodness, I bet nothing would move those short of a major earthquake. I doubt anyone around here would do that kind of stuff.....I don't even think they could get the equipment in my backyard needed to hoise blocks that big!

I tried to get some more pictures of my hillside, but my phone battery died after one shot..

These trees closest in the shot the roots are being exposed at the bottom.....it's complete mud underneath the trees....no grass at all.....so it's just washing away more and more everytime it rains. I've been wondering if maybe I should plant some shade tolerant plants that are good for soil erosion all around underneath the base of these trees....maybe that would buy me some time too?

As you can see, we have pretty much no flat ground beyond the end of our house.....eventually my grand plans are to if we get the top section level, I will turn it into a concrete patio with a sitting wall of some sorts. It could look awesome if I let my imagination run wild.....but I'm sure the costs will run wild too!

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If you are dealing with collapsing sinkholes, you need more than a landscaping contractor. Sinkholes present very complex and potentially serious problems.

If you are dealing with collapsing sinkholes, you need more than a landscaping contractor. Sinkholes present very complex and potentially serious problems.

great.......i feel like I screwed up beyond belief in buying this house

Is there a full basement under the room with the window in that last picture? If there is, you may have a lot less problems and expense than you think.

No. Slab foundation. Hardly any houses have basements around here.

bgav, you used the term "sinkhole" but the general discussion does not indicate that a sinkhole is likely. It's probably a hole caused by surface erosion in which case solving erosion problems would take care of it.

While slopes can present erosion problems, these are not unsolvable. Usually, all that's needed are groundcover-like plants whose roots form a network that holds soil in place and whose tops protect the soil surface from slamming rain and flowing water. Sometimes it can be difficult to establish such plants (if rain washes them out before they are established,) but it's not impossible if one dedicates one's self to the process. I would consider retaining walls necessary only if the grade is so steep that it cannot possibly stay in place as a slope. Do you have slopes so steep that no planting can possibly hold them? Look around the neighborhood and see if like slopes exist and if they are stabilized by plants. It such slopes exist elsewhere, they can exist on your property as well. You would only need to find plants capable of stabilizing them and working with your overall landscape goals. While the last picture you added is still too close-up, the slopes seen in it do not seem overly difficult.

It's likely that if you have plenty of places where retaining walls COULD go, but limiting them to places where they are actually NEEDED might be a better strategy. We would not be able to suggest where such places might be without seeing some overall, wide shots of the areas. If you seek advice about where retaining walls could go from contractors who sell them, it is likely you will be advised to add a lot more walls than you need. Consider hiring a landscape architect or a qualified designer to advise on where walls would make the most sense.

IâÂÂd look into the idea of cutting into that slope closer to the house. IâÂÂm not saying that this is the answer, but certainly something to explore. YouâÂÂll need to protect your slab from freeze/thaw, so youâÂÂd have to stay out about 5â away from the foundation. IâÂÂd ditch the little existing garden wall, if the idea becomes viable. A wall close to the house could be smaller and the bottom of the wall can be on more solid ground as it would be at the bottom of a 3 or 4â cut.
IâÂÂm not sure what is going on under the porch roof, but sonotube footings and new roof columns are a lot less than a huge retaining wall halfway down the slope. You could add a step or two down onto your porch area which could have a new lower patio floor supported by a new retaining wall 3â or 4â high with another wall sweeping out from the house corner (where the porch meets it in the pictures). It could go out 4 or 5 feet in front of the foundation (for frost protection) with a cut in front of it (youâÂÂll lose those plants back there). You can use the cut material to build out the flat area at the top of what will be a lower slope. Then you can put a dry laid patio on the flat area and a set of steps coming down from the porch. Make sure to have gutters with downspouts for your entire roof being piped to dry wells or a suitable discharge location.
That should be a lot less than $40k, if it works ... very hard to know from a few pictures.

@Yardvaark
They are sinkholes.....I was walking on the grass here and boom, my foot just fell through the ground.
Our ground is extremely spongey when it's wet. I've never felt ground give so much when I lived in Ohio as I do here now down south. I don't know if it's the kind of grass or what....but this bermudagrass just seems to not have very strong roots
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It's very hard to take good pictures to show you all the hill, and the entire contour of the ground around my house. I drew this picture in MS Paint to kind of describe it. The street goes downhill in front of our house....across the street the houses sit on a hill higher level than our house.....the front yard then kind of slightly slopes down before it levels out.......there is about a 8 ft wide section of grass between me and my neighbor's house......then the hill drops off fairly soon just past the end of our house......could it be that water is just flowing through this area like a river? You don't see this happening up top, but maybe below ground, thus the sinkholes on the hill?
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Can I make a suggestion that you do not call a landscape guy to come fix your homes soil and stability issues?

A landscape guy can make it look nice, but you need more than a nice lawn, you need to find out why you are having a failure. Try and contract some one who builds foundations.

They may have buried stumps when they built the subdivision or house. Maybe there is limestone under there.

There is no help like local help that knows what is going on in your area - geology, soil, varmints, ...

It would be my suggestion, too, to get local help. There is not sufficient information in the pictures to make good sense of the issues. And, sorry, I can't understand your drawing. Part of it looks like plan view and part looks like elevation.

While you might call it a "sinkhole" in concept, t looks more like buried organic matter rotted away, left a void and collapsed. The holes are very small and do not indicate a systemic problem, based on the information you are supplying.

I know this post is a little old but how did you make out here. I'm in a similar situation so it would be nice to hear how this turned out.

J Mac. Best to start your own new thread about your project/dilemma.

However, if you do, PLEASE include better pictures than were submitted for this thread. Show whole, broad scenes from a straight-on camera angle ... not snippets and not areas viewed from an angle. To get such pictures, stand in line with the center of the scene and take a series of slightly overlapping pictures that pan across the scene from left to right, while you just pivot. Or, it the scene is not too wide, you can use the panoramic feature of your camera. (If the scene is wide, the pano feature will distort too much, making it hard for us to understand the space.)

I was hoping bgaviator would follow up with what solution he went with and the outcome.