So we recently bought 5 acres on Maryland, and are just getting to know the land. One of the things to be seen is that there is a seasonal stream (some water in it now, not much in the summer) that has cut very deep, near vertical banks. We are talking a channel well over 6 feet deep. While it is cool to see the layers of subsoil and clay, I do wonder if there is a way of slowing this down. I came across a large tree that had fallen, it looked like because it’s roots had been washed away. I’m not sure if this situation came about because of logging - the area is a younger woods- or for some other reason. I know that stabilizing stream banks with plantings is typical, but I’m not sure that plantings at the edge of a gorge will survive, given the fallen tree I saw. The bottom is very soft sand, so it can still get deeper.
Any thoughts?

I didn't read this pdf, but skimmed it. It looks pretty comprehensive. It might contain some helpful information you can use.

Small-scale Solutions to  Eroding Streambanks
http://www.ncforestservice.gov/publications/BYSRGuide2015.pdf

Thanks - but that manual presumes that you have a cleared area. This is in the woods - so there is already a zone that has been left alone for many years. Grading the bank could be done, but would require clearing the banks, which seems counterintuitive!

Here are threads about what we're doing to try to repair our eroded seasonal creek:

https://permies.com/t/51421/Creek-repair-brush-dams

https://permies.com/t/53556/Creek-repair-rock-dams

When we asked the soil conservation guys what to do they told us to grade the banks.  If we had done that, all that soil would have washed down to the neighbors by now because there was no vegetation to stabilize it.

It can slowly be reversed. A line of rocks across the gorge (leading edge slightly buried so water doesnt push it away) will collect sediment. As it fills, add another layer of rocks.

A brush dam will do the same. Tree trimming, branches, brush piled up in the gorge.  It will slow the water. Over time it will catch leaves,  then sediment. It should never really "dam" the water,  just filter stuff to fill it in.

As far as the steep drop off, sloping it is best solution.  This allows grass. The question being when. Doing it now vs waiting til sediment filling is done.

If you fill it to the point that its a smaller drop off, cows can do the sloping for you if you have them.

Can you post some picture of the creek bed,
1) where it "enters" your property
2) where it "leaves" your property
3) where the banks are the least steep (1ft vs 6ft for example)
4) where the banks are the most steep

Without knowing more about your specific problem.

A) Completely fill in the creek bed with rocks aka gabions, water will still flow between the rocks
B) Strategically fill in the creek bed every 50ft aka a dam, sediments will settle behind the dam
C) Slow down the force of the water aka a dam build from gabions, slow down erosion
D) Line the banks with gabion, so that they will not be eroded away
E) Line the steep bank with willow stakes at 45 degree angles, to help stabilize the banks
F) Stop/Reduce the flow of water to the creek upstream, swales/dams/parallel channel/etc  

Out West, this is a pretty common side effect of grazing. Cattle + creeks = steep banks. The forest service uses three strategies to combat it:

1. Brush dams — kind of weaving a little beaver dam in place. Over time, this may collect silt & soil and raise the stream bed.

2. Revegetation  — usually with willows as they can root quickly and create a thick brush that stops animals from furthering the problem.

3. Plug & Pond — this requires heavy equipment, and creates a series of ponds in the existing creek channel while cutting in new, more windy shallow creek paths.

Here are some photos.
Spoke to the upstream neighbor- she said that this summer (admittedly the wettest on record) the 4-foot culvert she had fir her bridge washed out and was carried downstream by the water. So if we try anything to make the stream shallower, we might end up with bigger flooding issues, right?

The best way to address this issue will be to build a series of dams from downed trees and branches.
As others have mentioned you don't want to stop the flow but rather filter the flow, letting any sediment drop out when the flow slows enough.
once you have these established you can then begin to do the bank stabilization with straw mats that you coat with grass and other plant seeds.
These mats can be formed from round bales (hay instead of straw) and held in place with twine and stakes, hay has the advantage of already having some residual seeds.

The dams can start out at a low height which you then build up as you come across more materials.
I am doing this on our north facing slope that was forming a gulley from rain runoff.
At the bottom of the slope I am building a small pond by filling in the current gully and building along the bank upper edge with the exposed rocks from the erosion.
I have short dams at 10 foot intervals from the ridge all the way down to the pond structure.

Redhawk

Thanks for the suggestions!
Do you have any concerns about flooding? Given what my neighbor told me, I am a bit concerned.
I don’t think a pond would be legal on this stream- it is part of a flood system, and even a bridge is iffy, I am told
These picks are all from winter - give the tree canopy, I don’t think grasses would do well.

As long as all you are doing is slowing the water enough to stop the erosion you should not have any issues with any of the government parties that could be involved.
In your case a pond is not part of the system so  that isn't going to be part of the set up.
The wood dams are not going to be solid as if to hold water long term, more like a sieve, since their main objective is to reduce erosion only.

Grasses are but one type of seed to use and there are lots of choices in the form of shade loving and shade tolerant species that you want to mix in with the grasses.
The way such a planting works is the grasses sprout and put down roots then the other plants follow suit, as the light intensity goes away the shade plants take over and establish a meshing root system which holds the soils in place.
The worst thing any drainage system can do is to allow erosion of soil that ends up far down stream, where it can create havoc by filling in pooling structures or plugging up end run drains.

Redhawk