IANYLA - I Am Not Your Landscape Architect
March 29, 2009 9:27 AM
How do we stop (or slow) the erosion of soil down a slope into a stream?
We live in a condo in Shelby Township, Michigan. The soil slopes from the street level to a small stream. How do I find a landscape architect / service that will forestall the erosion?
The erosion has moved flower boxes and patio slabs, but not parts of the building yet. The stream (it is actually called a drain) is usually slow running; but when it rains heavily, it fills up. The soil is very sandy.
I put together a set of pictures and some text on a (self-linking) page here. Please be aware that the pictures have more detail than will interest just the casual observer.
We previously considered planting something that would slow the erosion, but I think that the problem is bigger than that.
I am not asking for instructions on how to fix it; I am asking for the name of a professional or service that will assess and fix the problem.
Our condo association is small, only eight families; so I don't need to say that we don't have piles of cash in the bank.
The erosion has moved flower boxes and patio slabs, but not parts of the building yet. The stream (it is actually called a drain) is usually slow running; but when it rains heavily, it fills up. The soil is very sandy.
I put together a set of pictures and some text on a (self-linking) page here. Please be aware that the pictures have more detail than will interest just the casual observer.
We previously considered planting something that would slow the erosion, but I think that the problem is bigger than that.
I am not asking for instructions on how to fix it; I am asking for the name of a professional or service that will assess and fix the problem.
Our condo association is small, only eight families; so I don't need to say that we don't have piles of cash in the bank.
I'm not quite sure what you have is erosion that can be fixed with landscaping. Soil moves over time and your soil movement is very slow and probably has more to do with the soil type rather than the vegetation on your property. The type of soil that you have is probably more important to know than the vegetation that is on your property. You can look up your soil type here: Web Soil Survey. If the depth of the top soil is very deep, you are likely going to need some retaining walls. So you need a civil engineer - which is alot more expensive than a landscaper is going to be - but those foundations are likely to move if you don't get a handle on this. While I work in a field somewhat related to this, this is not professional advice.
posted by bigmusic at 11:04 AM on March 29, 2009
posted by bigmusic at 11:04 AM on March 29, 2009
I am not a landscape architect, but I do think you need one and that you will probably end up with a containment wall or other hard stabilization rather than just vegetation given the slope of your hill.
I am a stream ecologist (IANYSE), and I can tell you that your problem is probably a change in stormwater timing and peak flows due to development upstream. A more long term solution that stabilizing that hillslope is better stormwater management for your stream. You say your condo association is small, so it is probably not runoff from your complex and parking lot that is the problem. I don't know all that much about stormwater management in the Midwest, but my understanding is that your local drain commissioner is probably the go to person for this problem.
They may be best able to recommend a local consulting firm to do the physical work, as well.
posted by hydropsyche at 11:57 AM on March 29, 2009
I am a stream ecologist (IANYSE), and I can tell you that your problem is probably a change in stormwater timing and peak flows due to development upstream. A more long term solution that stabilizing that hillslope is better stormwater management for your stream. You say your condo association is small, so it is probably not runoff from your complex and parking lot that is the problem. I don't know all that much about stormwater management in the Midwest, but my understanding is that your local drain commissioner is probably the go to person for this problem.
They may be best able to recommend a local consulting firm to do the physical work, as well.
posted by hydropsyche at 11:57 AM on March 29, 2009
Well, I'll be a civil engineer in 3 more weeks, so here's my 2 cents: first, some long term settlement is pretty normal. I also wasn't sure if you're worried about the erosion by the stream, or the slope settlement? They're generally 2 different (but related...) problems. Planting vegetation is a great way to stabilize the slope, if you do plant more though, make sure it doesn't take a lot of water. Water can be very very bad.
-I looked at your pictures, watering those planters next to the house might be making it settle faster, and you're definitely concerned about settlement/slope stability, there's no erosion going on except along the riverbank, something to keep in mind when you call around. Also, keep an eye out for any cracks in your foundation.
I know the engineering consulting firm I worked for did stuff like this, it would probably be expensive though.
posted by piper4 at 3:35 PM on March 29, 2009
-I looked at your pictures, watering those planters next to the house might be making it settle faster, and you're definitely concerned about settlement/slope stability, there's no erosion going on except along the riverbank, something to keep in mind when you call around. Also, keep an eye out for any cracks in your foundation.
I know the engineering consulting firm I worked for did stuff like this, it would probably be expensive though.
posted by piper4 at 3:35 PM on March 29, 2009
It looks like you have two separate issues: movement of the slope and erosion along the banks of the stream. The stream erosion doesn't look like a big problem and wouldn't be too difficult to fix if desired. The movement of the slope could be more significant.
It is hard to tell from a set of pictures where the movement is happening. If the movement is relatively shallow, then you can probably fix the problem quite easily. If the movement is quite deep, then the problem becomes more difficult.
The first thing to do is to try to fix the problem by redirecting the flow of water. Observe the flow of water during a heavy rain and see where the water runs down the slope, from the street and from your roof. Are the areas that are causing problems getting very wet? They probably are and if you can divert the water you might be able to solve the problem that way. For water coming from the roof, you can make changes pretty easily (you might want to consider some sort of gravel drain), but for water coming from the road, you'll need to talk to your municipality.
If the water angle doesn't solve the problem, you can consider retaining walls and other civil engineering tricks (look for a geotechnical engineer). If those trees haven't stopped the movement of the slope, nothing you plant is going to do much good.
If you want to slow erosion on the stream bank, look into soil bioengineering, which uses terraces and fences made out of natural materials along with vegetation to stabilize these kinds of areas. I won't go into detail here, so ask if you want more information on that issue.
posted by ssg at 4:41 PM on March 29, 2009
It is hard to tell from a set of pictures where the movement is happening. If the movement is relatively shallow, then you can probably fix the problem quite easily. If the movement is quite deep, then the problem becomes more difficult.
The first thing to do is to try to fix the problem by redirecting the flow of water. Observe the flow of water during a heavy rain and see where the water runs down the slope, from the street and from your roof. Are the areas that are causing problems getting very wet? They probably are and if you can divert the water you might be able to solve the problem that way. For water coming from the roof, you can make changes pretty easily (you might want to consider some sort of gravel drain), but for water coming from the road, you'll need to talk to your municipality.
If the water angle doesn't solve the problem, you can consider retaining walls and other civil engineering tricks (look for a geotechnical engineer). If those trees haven't stopped the movement of the slope, nothing you plant is going to do much good.
If you want to slow erosion on the stream bank, look into soil bioengineering, which uses terraces and fences made out of natural materials along with vegetation to stabilize these kinds of areas. I won't go into detail here, so ask if you want more information on that issue.
posted by ssg at 4:41 PM on March 29, 2009
That stream isn't eroding for starters and it certainly isn't eroding the top of your hill. The stream banks look quite stable and the vegetation is older and no tree roots are exposed, nor are you activley losing trees or experiencing lateral channel migration that I can see. What is happening is that your hill is sliding down into the stream.
Your problem is most likely related to one of two things or both of them.
1) your condo is built on fill and they didn't compact it properly or build necessary retaining walls and drains. The road is definitely built on fill and it was built too close to the stream for sure. The fill is sliding downhill due to it's inherently unstable nature.
2) The hill is inherently stable but is getting wet and slumping or experiencing rilling and erosion due to becoming saturated. Basically water is running down the hill, saturating the ground and the hill is slumping or is simply being washed away by the flowing water. This is most likely due to poor drainage from the road collecting run off and directing it own the hill but septic systems are notorious for causing this kind of problem too. Downspouts from your gutters, leaking water mains, old French drains, badly sloped parking lots, vegetation removal, footpaths etc can all funnel water into new paths where it washes away formerly stable material. A "small" condo building is certainly enough to create impacts to drainage that will cause slow slumping of a steep hill.
In summary: you don't have a bank erosion problem you have a falling-down-hill problem. Top down not bottom up. Call whoever owns the road and tell them it's de-stabilizng your property and see what they say. Ultimatly you probably need to get a civil engineer who is very, very good at hillslope drainage out there. Some combination of improved runoff patterns and possibly a retention wall will most likely be the fix. Shouldn't be too expensive unless you have to do a lot of work to fix the damage that has already happened.
posted by fshgrl at 6:45 PM on March 29, 2009
Your problem is most likely related to one of two things or both of them.
1) your condo is built on fill and they didn't compact it properly or build necessary retaining walls and drains. The road is definitely built on fill and it was built too close to the stream for sure. The fill is sliding downhill due to it's inherently unstable nature.
2) The hill is inherently stable but is getting wet and slumping or experiencing rilling and erosion due to becoming saturated. Basically water is running down the hill, saturating the ground and the hill is slumping or is simply being washed away by the flowing water. This is most likely due to poor drainage from the road collecting run off and directing it own the hill but septic systems are notorious for causing this kind of problem too. Downspouts from your gutters, leaking water mains, old French drains, badly sloped parking lots, vegetation removal, footpaths etc can all funnel water into new paths where it washes away formerly stable material. A "small" condo building is certainly enough to create impacts to drainage that will cause slow slumping of a steep hill.
In summary: you don't have a bank erosion problem you have a falling-down-hill problem. Top down not bottom up. Call whoever owns the road and tell them it's de-stabilizng your property and see what they say. Ultimatly you probably need to get a civil engineer who is very, very good at hillslope drainage out there. Some combination of improved runoff patterns and possibly a retention wall will most likely be the fix. Shouldn't be too expensive unless you have to do a lot of work to fix the damage that has already happened.
posted by fshgrl at 6:45 PM on March 29, 2009
btw planting stuff to slow the erosion is a great idea, Terracing and planting is even better- basically you will catch the material as it rolls downhill. The gently sloping lawn with no roughness and compacted soils that you have now is basically about the worst thing you can have Any watershed group or university extension service can tell you how to fix that. Or go to Borders and buy a book on stream restoration and follow the instructions. Or ask your local fish and game or what have you. Very easy fix.
posted by fshgrl at 6:47 PM on March 29, 2009
posted by fshgrl at 6:47 PM on March 29, 2009
ssg - I can see no water runoff down the slope even during the heaviest rains. (When the condos were built it was said that the soil had some of the best percolation numbers in the area. Many Michigan basements are wet and ours is bone dry.) There is a storm sewer drain at the end of that street and I have never seen it overflow. The runoff from the roof: In the front it goes into french drains (which are already clogged, so it flows into the street), the backside downspouts just end at ground level into pebbles, it drains right into the soil. (I wouldn't mind learning more about how to stop the stream erosion; if you have more info, please me-mail me for my email address.)
fshgrl - That sounds like an extensive explanation also... I believe the condo association across the street owns the road. It will be tough getting them to pony up cash to fix this.
posted by Drasher at 6:37 AM on March 30, 2009
fshgrl - That sounds like an extensive explanation also... I believe the condo association across the street owns the road. It will be tough getting them to pony up cash to fix this.
posted by Drasher at 6:37 AM on March 30, 2009
Reading other people's comments, it looks like we interpreted the pictures and your questions differently, and now from your follow-up question, I'm thinking I misunderstood. Does the stream flood substantially with each rain?
The pictures looked to me like you're getting a lot of flow out of the channel across the steep grassy slope. That was the erosion I was worried about, because grass cannot stand up to that, so I assumed it was new flooding. If that's not what's happening, I remove my recommendation for a containment wall.
posted by hydropsyche at 6:40 AM on March 31, 2009
The pictures looked to me like you're getting a lot of flow out of the channel across the steep grassy slope. That was the erosion I was worried about, because grass cannot stand up to that, so I assumed it was new flooding. If that's not what's happening, I remove my recommendation for a containment wall.
posted by hydropsyche at 6:40 AM on March 31, 2009
Just for the record, I have only once in ten years seen the stream fill to the point of having water on the grass itself. Even during a heavy rain, it fills to the banks only.
posted by Drasher at 5:05 AM on May 1, 2009
posted by Drasher at 5:05 AM on May 1, 2009
This thread is closed to new comments.
posted by watercarrier at 9:56 AM on March 29, 2009