Tjyylli

This is often a complex legal situation due to regulations that affect (in many parts of the world) what you can do in or near a body or stream of water even if the land next to it or around it belongs to you; not to mention the fact that you are fighting with a force that has literally shaped the planet, and it's inexorable and quite capable of undoing many things you try to do to stop it, if, in fact, it is even legal for you to try to do those things. If the stream also is a property BOUNDARY, the legal implications of trying to move it get even more complex.

The "wire mesh" you describe is most probably gabions, which are empty wire cages which are stacked and filled (pretty much by hand, which has taken a novice contractor or two by surprise, to their cost) with rocks. Another common technique is "rip rap" which are simply large rocks layed over the face.

Your only legal option in many places would be to think about moving your fence back before it's undermined. Trying to get plant material established on the eroding slope is another approach, but many jurisdictions are less fond of people planting highly invasive species often selected in the past for that purpose, so you may need to stick with native/local species. Or, you may be able to perform some work after having hearings/meetings with the Authority Having Jurisdition over such activities in your area (conservation commission, department of environmental protection, etc.)

Legal issues aside (that's not our pigeon here), a reliable way is dry mix sand bagging:-

Pick a low quality concrete sans water, place it at your leisure and let the rain /moisture make it go off. It's a common civil engineering technique, and very efficient in terms of cost, effort and design experience. It also requires very little ground preparation, which for gabions can be quite some effort as the're regular shapes. Eventually the bags rot away and the concrete remains.

Been there , done that; my creek ( Plum Creek, Highland IN) was 30ft. width and embankment was 40 ft. high. I "coated" it with railroad ties, bricks, and many cuttings of trees and bushes. To reach my height I used 3 tiers of RR ties with slopes between. It required a lot of stuff and work. Yours looks much more manageable. Look for affordable rip-rap ;aka brick, cinder block, broken concrete, large size gravel, etc, to break the current . I used reject bricks from a nearby factory that sold them very cheap. For my larger project I used 24 yards/ about 48 tons. I suggest the mesh you have seen on highways and hold it in place with your rip-rap. Then stick a bunch of cuttings of trees that grow well in your location , early spring will work best . Then throw out a bunch ( 50 #) of seed like annual rye grass ( best in the fall ). If you like gardening it could be a great hobby area. Depending on how fast and high the stream gets ; two rows of railroad ties near the waterline will give you about 16" of "seawall". Depending on your budget , there are many options available for seawalls. If rainwater is eroding gullies ;they can be slowed with grass sod, but sod will need some sunlight. This answer is from the perspective of what one person can do without power equipment, other than a 10 wheel dump truck to deposit stuff at the top.

What I’ve seen commonly done is either large rocks or large chunks of concrete dumped to protect the area eroding.

You say it is slow moving, so I’m betting the erosion primarily happens during/after rains causing high, fast moving water. I think you’ll want pretty large rocks/concrete at the base (like maybe 2.5’ or 3’). If you own the other side, you can help straighten that section out by excavating that area.

As mentioned in another answer, there may be legal issues since the creek is a waterway. In the US, you would have Federal and probably state laws involved (many other countries have similar laws about waterways, even if you own the property). I would not try to fill the creek bed back in without approval, even if it is technically your property.

What you really want here is a retaining wall that has some sort of better resistance to the creek. Ideally you would want something like a concrete wall (say 4ft above the water line, extending below) along the creek bed with some sort of support rods running back into the earthen hill (lest the hill push the wall over). You could add some retaining wall ceramic bricks above for support and aesthetics. Since this would control erosion, it should get regulatory approval.

The catch here is this is probably no longer a DIY project. I would want a professional company to come and do the work since

• they would know and comply with any environmental laws


• they would have the equipment to rebuild the hillside (you'll need some excavation and rerouting of the creek bed)

Ignoring the problem won't work either, since these kinds of problems only get worse over time. It may not stop with just your fence...

Not sure where you are, but definitely check with some local authorities, such as your state (if in the US) Department of Natural Resources or equivalent, or the federal Natural Resources Conservation Service. Most modifications will need some sort of permit, and a lot of places have programs available to help landowners with such issues- I know us in the environmental/conservation fields do NOT like to see such erosion occurring!

Here's a guide our DNR has produced, maybe some information would be of use?
https://www.iowadnr.gov/portals/idnr/uploads/water/stormwater/streambankmanual.pdf

Adding to some already good answers, I'd emphasize using vegetation to help stabilize the bank. Only one answer (https://diy.stackexchange.com/a/162118/76258 - a great one) mentioned that so far.

My construction experience is limited but I have seen streambank stabilization done in various forestry operations. Vegetation and riprap is the key technique stabilizing remote stream banks that are near forest roads or for some other reason are being intervened with to mitigate erosion. Dropping logs, woody debris, and stones into the river banks as directed by local expert ecologists/biologists. Planting fast-growing trees that spread roots and shoots to stabilize soils, like shrub willows. The goal is to slow up the water and break up its flow path, to reduce the volume and velocity of water chiseling away at the river bank. Upstream of the erosion-prone area is important to consider and work with if possible, as conditions there (e.g. channelization to prevent flooding upstream) can exacerbate the problem at your area of interest. "We're all downstream."

Even for these more local-nature-based options it'd be wise to consult with your local environmental department to learn from their expertise on your area's unique hydrology and geology and regulations. They are interested in making these situations better, as erosion is bad for you, the area's real estate overall, and downstream environmental quality. These kinds of situations are easy to make worse, e.g. channelizing streams seemed like a good option for many cities that are now finding it's important to let floodplains do what they are naturally inclined to do: periodically flood. Vegetation and riprap is a fairly safe, time-tested/nature-proven way to mitigate erosion, but done haphazardly these techniques could cause immediate or long-term problems as well.