Can I slow the storm water flow? A culvert/erosion/dam question.

In 1872, a railway spur was built through the timber. A 3 foot corrugated culvert carries storm water under the railroad grade on my property. Evidence suggests the downstream end of the culvert was originally at ground level, but now through erosion it's 12 FEET OVERHEAD! Over the years, every major rain has poured through the culvert and scoured out a hole down to the limestone bedrock and continued downstream. In many places along the "canyon" bottom you can see a layer of clay.

What I'm wondering is if I can slow this flow down. Why? Because I'm working on developing the scour hole as a swimming hole and I'd like to prevent big gushes during large rain events from disturbing any work I do down there. The pool stays full, clear, and flowing year-round, filled by springs along the edges even in the deepest freeze and driest conditions. It's 6 feet deep and I've pumped it out to confirm there are no dangerous surprises inside and it's also let me confirm where the spring water flows in.  

I have about 300 feet of dry wash before the culvert entrance to slow things down. So the question is, how would you slow the flow and buffer the power of water before it spills out of the culvert? Brush dams across the wash? Hay bales? Logs? At the very least, I'm putting a large grate in front of the culvert mouth to keep large objects out (like the rusty metal bucket I pulled out of the pool!) No worries about downstream in this case, just backwoods before flowing into a larger creek. Thanks in advance for the suggestions.

There is a video on youtube about Viktor Schauberger. He was a genius when it came to water, because he payed attention to nature and emulated it. I highly recommend it. Short summary: water wants to zig-zag. If you let it, it will slow down considerably.

I'm having decent success slowing water in our creeks with brush dams  https://permies.com/t/51421/Creek-repair-brush-dams

You'll want to start your dams well upstream of the culvert.  We only use rock dams close to our culvert because we don't want rogue sticks from the brush dams to jam it.  One-rock dams work well over time to raise the soil level in the creek bed.  https://permies.com/t/53556/Creek-repair-rock-dams

> zig zag

Sounds right.

Wondering. What is the percolation rate in/around the dry wash?

If you "slow things down", will the water just  rise until it's over the highest dam or will it sink into the soil if  you give it another, say, 1/2 to 1 hour to do so? The volume of water entering the channel you show (dry wash) will still enter it regardless of what you do if I understand your situation right. That means that while you can provide "catchment" by various means, once that catchment is full the water will continue on its way just as fast as ever. Unless before the catchment(s) is full the water actively seeps into the ground before it over-tops your system and continues on fast as before. Various dams, etc can spread the water and  (potentially) create a pretty large catchment but it _will_ fill up unless the water percolates into the ground.

Even if there is no percolation, simply creating a very large catchment which drains relatively slowly will provide the benies you look for until it gets full. Once full, it will run as fast as the water entering your system, whatever rate that is. If it's late in the storm and precip is tapering off, that might not be very fast and you have total success. If it's a long storm and you're still getting major runoff when you catchment system fills up, it will drain at the full rate of the downpour over your watershed that feeds the dry wash  you show, just like it does now.

So the perc rate could indicate how effective "slow down" the water would be for you.


Regards,
Rufus

There are a few solutions, much depends on a few factors.
- How often does the flow occur ?
- what volume of water are you looking at being involved?
1000gallons, 4000 gallons.
- Is there room for a series of dams?
- Is money an issue ?
Water will over time seek a path whereby it is not travelling fast enough to erode the soil.
Thats why they meander. In your case it has been through a hard surfaced tunnel and fallen on errodable soil.
So if you can reduce the flow rate of any water that comes to enter your culvert, you will have achieved an outcome that you want.
So starting near the top, up above the culvert a small leaking rock dam to hold the initial flush of water.
Then a series of similar dams down to the culvert. Each dam to have is top level in line roughly with the bottom level of the higher dam.

say you have 1000gallons of water per rain event, if you have a volume stored between all the small dams of 1000gallons you will
dramatically slow the water down and have it pass through the culvert over say, 1 hour instead of 5 minutes.

Rufus Laggren wrote: Various dams, etc can spread the water and  (potentially) create a pretty large catchment but it _will_ fill up unless the water percolates into the ground...

Once full, it will run as fast as the water entering your system, whatever rate that is.

Not necessarily.  Various structures can "de-energize" water so that no matter how fast it enters the system, it will be slower as it leaves the system.

> slower as it leaves the system...

I don't think that is true once the system is full and the water is running over the tops of all dams. If it's coming in at a certain rate and all storage has been filled, it will leave the system at the rate it enters. Except if some percolates into the soil enroute, thus reducing the amount of water leaving the system. The system ideally acts as a buffer, a balloon bag, a temporary holding tank, each stage releasing water slowly - until all stages get filled up. The highest stage would fill first and then pass on all water at full volume to the next lower and when that filled, it again would pass on water at full volume to the next lower and so on.

If the storage is large enough to contain the whole "event" then water will always be able to flow out of the system at the regulated rate. But if the whole system fills up, water _must_ flow through it at full volume. By the "system filling up" I mean that all the (perhaps multiple) catchments fill to the point where the water just flows over the top down to the next catchment - it can't hold any more. When this happens to all the catchments, the water is leaving the system as fast as it is entering because the system has no more storage and cannot hold or delay any of the water.

Regards,
Rufus

Rufus Laggren wrote:> slower as it leaves the system...

If the storage is large enough to contain the whole "event" then water will always be able to flow out of the system at the regulated rate. But if the whole system fills up, water _must_ flow through it at full volume. By the "system filling up" I mean that all the (perhaps multiple) catchments fill to the point where the water just flows over the top down to the next catchment - it can't hold any more. When this happens to all the catchments, the water is leaving the system as fast as it is entering because the system has no more storage and cannot hold or delay any of the water.

Regards,
Rufus

I'm kinda in the middle here. I agree that if the whole system is full, then naturally all additional rain will spill out just as fast as it comes in. But currently with no dams, the water just roars down the wash.  So the action of rain and surface drainage hitting pools of dammed water would slow it slightly by taking some energy from the momentum.

The additional benefit of "check dams" would be straining out sediment so I think as a whole, it's worth doing something. I probably just won't invest a ton of energy in the project. Maybe just a few sessions of dragging downed timber into the wash and cutting to fit. Perhaps a few t-posts to keep things in place.

Here's some more pics to define what I'm looking at. The dotted line is the path of the wash, and I believe I'll used whatever downed timber is available to make little dams or weirs really. There are a lot of old T posts on the property so I believe I can use those to keep a couple big logs in place and build around those with smaller material like brush.

And pivoting to the more permaculture side of this, what would you do with these moisture retaining areas? I'm not thinking any of them will HOLD water for long but they will create pockets of increased moisture. Especially as they age, collect sediment, and become more dense. The downside of being in heavy timber though... not enough sun to take advantage and grow much!  

I think that the presence of regular leaky rock dams would cause localised turbulence in high-flow events as ground-level water meets a dam and is forced to go 90 degrees perpendicular, increasing the disruptive effect of each dam and directing more of the energy upward. I like this idea, but I think that in addition to check dams and nutrient/sediment traps placed where water is already causing erosion, that arranging sediment traps on-contour across the whole of the landscape uphill of the problem area would make any effort in the direct path of storm water flow more effective.

I would do whatever type of blockage could be put on-contour in the path of the storm water, but preferably debris that are already naturally occuring could be reorganised. Similarly, if there are plants in the area that you notice to be impervious to those storm events, I would do what was possible to seed those dams with said plant species. They will assist in the trapping and deposition of sediment behind the dams, and might also act as a vegetative anchor on the terrain, or to decompact soil so as to increase water infiltration.

I would literally place logs on-contour, butting them up against each other and rocks and stumps. They will catch sediment, organics, and seeds, and will begin to rot, leaving behind a slight ridge and strip of rich soil and deep root systems that will continue the work of the original sediment barrier.

You mentioned clay. It might be worthwhile to look at it in the dry season, or to have some of the soil tested. If there were some water permeability issues having to do with a mineral imbalance, such as occurs with some calcium-deficient clays, it might be fixed in key areas of pooling by adding said calcium, perhaps as gypsum. Increasing the soil's potential to infiltrate the water could do wonders, keeping water nearest where it falls for long enough that much less reaches the flow upstream of the culvert. I might be wary of trying this anywhere erosion is already a problem, though.

I would love to see more, and to hear how you make out. Good luck, and keep us posted.

-CK

If you had a source of large boulders and some heavy equipment, you could move large boulders under where the water exits the culvert to disrupt the flow/make it less erosive. Then you could place large boulders along the stream bed to further baffle and slow the flow down. Piles of cobbles would work similarly (or concrete debris, or bricks, etc) Below this slowed water, you could pile rocks one course high, across the stream bed, to further slow it.

If you were going to use logs, I would stake the logs into the ground at an angle not quite covering the entire stream bed. One set of logs one way, the other set of logs downstream pointing the other way... That would slow the flow and make it travel a larger distance/have more time to percolate.

If you wanted, you could also do some willow staking behind the log dams, again, to further hold the soil down and trap water.

Rufus Laggren wrote:> slower as it leaves the system...

I don't think that is true once the system is full and the water is running over the tops of all dams.

I think it is true because if all the dams and catchments are full then the water is flowing in a much wider stream, rather than jetting through in a small narrow canyon.  It seems to me that flood waters slow as they spread out.

> much wider flow

Yup. You got me! <g>  I agree.

However, in my defense - I was thinking that culvert was going to remain the final drain for the dry wash (when it got wet).


Cheers,
Rufus

Update: I experimented a bit with partially blocking the culvert with a wooden dam. My hope was that water would pool and then seep through the imperfect blockage at a slower rate. It worked that way through the first rain. Then we got a HISTORIC rain event that overwhelmed the dam. I donned my rain gear to check it out and was horrified to see (or not see) the culvert completely underwater. And worse, there is a limestone "shelf" under the culvert that some enterprising critter had dug under allll the way through, then up out of the ground on the receiving side. So water was spilling into this hole and pouring out the far side under the limestone!

So clearly those late 1800's engineers knew what they were doing installing an over sized culvert and perhaps I am foolish to have tried to alter it. Now I am somewhat afraid to try damming it farther upstream for fear of another giant rain blasting my dam materials down to the culvert and potentially plugging it. I am thankful for nature giving me this worst case scenario before I invest much more time/energy. If anything, I'll start small and far upstream.  

For now, I've pulled the dam and replaced with a trash strainer. I have an air bubbler in the spring pond that's keeping the water clear and have enjoyed a few floats and cold swims this summer at least.

Matt Todd wrote:Update: I experimented a bit with partially blocking the culvert with a wooden dam. My hope was that water would pool and then seep through the imperfect blockage at a slower rate. It worked that way through the first rain. Then we got a HISTORIC rain event that overwhelmed the dam. I donned my rain gear to check it out and was horrified to see (or not see) the culvert completely underwater. And worse, there is a limestone "shelf" under the culvert that some enterprising critter had dug under allll the way through, then up out of the ground on the receiving side. So water was spilling into this hole and pouring out the far side under the limestone!

So clearly those late 1800's engineers knew what they were doing installing an over sized culvert and perhaps I am foolish to have tried to alter it. Now I am somewhat afraid to try damming it farther upstream for fear of another giant rain blasting my dam materials down to the culvert and potentially plugging it. I am thankful for nature giving me this worst case scenario before I invest much more time/energy. If anything, I'll start small and far upstream.  

For now, I've pulled the dam and replaced with a trash strainer. I have an air bubbler in the spring pond that's keeping the water clear and have enjoyed a few floats and cold swims this summer at least.

In your picture it looks like the side you partially closed off is the downhill side but I can't tell for sure.  If it is, I would move it to the uphill side.  The thought of causing silt and debris to build up inside your culvert and having to clean it out is unappealing at best.

Theoretically, blocking the culvert turns the road into a dam. It also puts a hell of a lot of water pressure on anything that you try to plug that culvert with.

First, I don't think blocking the culvert is a good idea. It's putting too much water in a place not designed for it. The best you could hope for over time is a washout of the road, followed by sudden inundation.

Much better, I think, to allow the water to move, and to make sure anywhere there's likely to be erosion is a durable surface.

All that water trapped behind a culvert is a lot of work to hold back. Check dams and sediment traps on-contour slow and infiltrate the water before it even hits the watercourse, and as indicated above, even when submerged, such texture takes energy out of the flow, leaving stuff in-place behind the sediment traps and check dams. At the same time, keeping debris and sediment out of the culvert, say with a check-dam made of square hay bales up current of the culvert, keeps water flowing where it should, protecting the roadway infrastructure.

But I am glad the culvert is still there. Sounds like it could have shot right out of the hole it was in and left you down a roadway.

To answer your question directly, yes you can slow the storm water flow. How you do so is critical, though. The goal should be to keep the culvert completely unobstructed, as that's what's keeping an HISTORIC rain event from washing your road away. Instead, obstacles to water flow should be both situated away from the culvert enough to keep it clear, and secured solidly enough that these obstructions aren't washed in to block the flow completely.

-CK

Trace Oswald wrote:
In your picture it looks like the side you partially closed off is the downhill side but I can't tell for sure.  If it is, I would move it to the uphill side.  The thought of causing silt and debris to build up inside your culvert and having to clean it out is unappealing at best.

Must be the angles. This is the uphill/entrance side of things. The far side is a good 12 feed above ground because of all the erosion over the years.

Matt Todd wrote:

Trace Oswald wrote:
In your picture it looks like the side you partially closed off is the downhill side but I can't tell for sure.  If it is, I would move it to the uphill side.  The thought of causing silt and debris to build up inside your culvert and having to clean it out is unappealing at best.

Must be the angles. This is the uphill/entrance side of things. The far side is a good 12 feed above ground because of all the erosion over the years.

I assumed it was, just the picture made it look like that could be the drain side.  

I have a situation a little like yours but less extreme and I have been able to slow the water to a degree with exactly what has been discussed, brush dams.  I like them.  I like the way they look and they are pleasant to build.  I never intend to spend much time on them, but I enjoy walking around in the woods with my dogs collecting material, adding to the dams, and watching them grow bit by bit, so I sometimes end up working on one for two or three hours.  I may not work on it for a few weeks until some day that it is just too nice outside to waste time working, so I'll play with my brush dams again. I find it really enjoyable.

Trace Oswald wrote:
I have a situation a little like yours but less extreme and I have been able to slow the water to a degree with exactly what has been discussed, brush dams.

How do you keep your brush dams in place? I guess I'm gun shy after this rain event we had, thinking that the next one would just blast away anything I could build out of brush. Five inches of rain in a matter of 2 to 3 hours was intense.    

Matt Todd wrote:

Trace Oswald wrote:
I have a situation a little like yours but less extreme and I have been able to slow the water to a degree with exactly what has been discussed, brush dams.

How do you keep your brush dams in place? I guess I'm gun shy after this rain event we had, thinking that the next one would just blast away anything I could build out of brush. Five inches of rain in a matter of 2 to 3 hours was intense.    

The ones up near the top with less water, I usually just pound some branches in and lay bigger sticks/small logs across.  I often wedge or pounds sticks into the ground at a 45 degree angle towards the uphill side.  Then I just pile stuff on and keep poking more brush and sticks in, usually still facing uphill, but also just at random angles.  I just built them up little by little.  As it gets higher, I start angling the sides inward somewhat so it begins to take on kind of a cup shape to capture more water and debris.

For the ones with more water, I dug into the banks a couple feet on either side of the gully area and lay a log across with the ends sticking into the bank for more support.  Then I just build them the same way.  

Your water flow may be more extreme than mine is, so I'm not sure if what I do will work for you.  Mine haven't washed out yet, but several have filled completely with silt, sand, debris, whatever.  In the areas where that has happened, the waterway is much, much wider now, so I'm assuming it is absorbing more water before it runs off, so it has served it's purpose for me.  I'm hoping to saturate the area and create springs further down stream on my land, but in may be a couple years before I know if that is working.

Can you give us a photo of the downstream side please?
On reflection messing with something thats has done well for so long may be unwise.
But maybe some improvements can be achieved where the erosion is and all will be wqll

I would take the screen off that culvert.

Why? Liability. I have very little tolerance for the risk of liability.

I have no idea who built it, what they accounted for in the design, who owned it, etc. But, if i were the cash strapped owner of the road, and, say, 5 years from now, the road blew out over the culvert? Its very easy to blame "oh, the guy downstream put a screen up which blocked the debris and caused the culvert to fail, so he should have to pay". True? Who knows, and who cares, but road fixes are expensive, and usually the last person to touch something is the one blamed.

Honestly, if i were redesigning a culvert, i would always make it bigger than existing - no one complains after the first financial pinch about the bigger culvert, but bigger culverts are less likely to trap debris, and less likely to fail. And are easier to clean.   And culvert maintenance is something many places skimp on. Not to mention if the road debris head downstream onto your property and damage something... Nice to be able to blame the road owners and maybe have insurance pay something.

Anyway- i would personally do whatever you want do downstream of it (within reason and safety), but leave the liability for that culvert with the road owners. I like baffling erosive flow to slow it rather than trapping it, in most cases, which slows water down to make it less powerful rather than allowing it to build up (safer in an unengineered solution).

John C Daley wrote:Can you give us a photo of the downstream side please?
On reflection messing with something thats has done well for so long may be unwise.
But maybe some improvements can be achieved where the erosion is and all will be wqll

Here is the downstream side. As you can see, the culvert is a good 12 feet above water level. If you look at the exposed tree roots on the far side, that's about where the original railroad fence shot across the hole and continued at ground level on the side I was standing on. Which tells me that this culvert used to be at ground level and has, since 1872, scoured a massive hole in the earth down to ground-water level. On the one hand, that's nice because it's scoured out a nice 5 foot deep swimming hole that stays full of spring water. On the other hand, when the rain really gets rolling it continues to cause more erosion further downstream.

I made a concrete block weir where the "pond" empties and becomes a stream, but even that got blasted out by the last big rain. So having observed this and tinkered with it, I think my course of action will be very long term. Experimenting next with small brush dams as far upstream as I can where the water will not have gained much momentum yet. And just keeping my strainer clean from trash and natural debris. No more hubris and big damn building from me :)  

Catie George wrote:I would take the screen off that culvert.

Why? Liability. I have very little tolerance for the risk of liability.

I have no idea who built it, what they accounted for in the design, who owned it, etc. But, if i were the cash strapped owner of the road, and, say, 5 years from now, the road blew out over the culvert? Its very easy to blame "oh, the guy downstream put a screen up which blocked the debris and caused the culvert to fail, so he should have to pay". True? Who knows, and who cares, but road fixes are expensive, and usually the last person to touch something is the one blamed.

Honestly, if i were redesigning a culvert, i would always make it bigger than existing - no one complains after the first financial pinch about the bigger culvert, but bigger culverts are less likely to trap debris, and less likely to fail. And are easier to clean.   And culvert maintenance is something many places skimp on. Not to mention if the road debris head downstream onto your property and damage something... Nice to be able to blame the road owners and maybe have insurance pay something.

Anyway- i would personally do whatever you want do downstream of it (within reason and safety), but leave the liability for that culvert with the road owners. I like baffling erosive flow to slow it rather than trapping it, in most cases, which slows water down to make it less powerful rather than allowing it to build up (safer in an unengineered solution).

Valid concerns for sure. But this culvert goes under an old railroad grade and is entirely on my property. I did get very scared and learned my lesson when it came to partially damming it. It could never overtop the railroad grade because it's at least 20 feet tall above the culvert. But from what I'm seeing, the water still has the ability to work it's way around the culvert and undermine things in other ways. So my current course of action, which I believe to be safe, is to just use this screen to keep garbage and natural debris out. I will have to keep it clean so it does not become a dam.