Have you thought about a rain garden/dry creek bed?

Our entire residental block has drainage issues but happily, wonderful and cooperative neighbours as well. Together we are working on solutions. So far, we all have been very satisfied with the results.

I have installed two french drains on my property. The one in front runs along the property line, collecting the run-off from two houses as well as channeling water from a low spot in the middle of both our yards.

In back, water is collected from another downspout and from the very busy sump pump. On my property there, it runs under the grass and garden. When it reaches the fence, it diverts to the side street, picking up the run-off from connections to three other houses along the way.

In the middle of the block, where there is huge, water collecting wrinkle in the terrain, causing water problems for another 6 neighbours, we are in the process of creating yet more french drains and trenches. Instead of diverting the run-off to the street - an impossibility in any case - the natural dip at the junction of those properties will purposely be deepened and widened, creating an intentional "wetlands". The excavated dirt already has a new home as a berm for yet someone else's landscape.

We hired a contractor friend with a bobcat and loader who quickly dug the trenches and took care of the excavated dirt. Considering the time involved and the volume of dirt to be moved, the modest cost was well worth the price. That cost was shared equally by all of us. We bought our own sleeved weeping tile and gravel individually because of the different lengths needed. As well, we each decided on how to finish the visible part of the drains on our own properties.

I've linked pictures of my own drains. You can tell from the parched grass that they are not being used right now, lol

But, having said all that, I don't know how a french drain would help in this case. We used them to divert standing water in a relatively flat landscape. Your run-off water HAS a place to go with - ahem - enthusiasm.

I would suggest a variety of other options including a berm at the start of the slope, terracing, imbedded large boulders, stabilizing landscape fabric, lots and lots of varied plantings. If you don't want to use an expert, there is a plethora of resources on the internet and at the library. Have fun.

Here is a link that might be useful: french drains

Erosion is from speed and volume. Anything you can do to keep water from joining together to make more, any time you can disperse water, and anything you can do to slow the speed of water will reduce erosion.

Dywells for your downspouts, reduced steepness of slope, swales or catch basins with a deep sump to allow for a slight pitched pipe to release the water so that it does not get trucking down that slope....

Step 1 is to understand the problem(s).

problem 1: you say the wood cipcs get moved by the rain. You are using "tripple shredded" mulch. This is fine mateial that is easily moved around. Use course wood chips instead. This will slow the water down and move less easily. On my 45 deg slop, they don't move.

problem 2: it seems as if the whole backyard slopes to one corner. As long as the slope remains, water will follow the slope. Change the slope or interrupt the slope. Level out the back yard.

Leveling is not always each, so you can consider changing the direction of flow. If you create a channel running perdendicular to the flow, it will alter the flow. This could be a dry river bed. When it rains, the water will fill the dry river bed and follow it's direction.

problem 3: water in the back cornder. It looks like you have a wooded area behind your house, in which case this is probably niot a problem. maybe the slope stops at your back fence preventing water to flow out of your property.

The non-grass area right now looks like mostly weeds or very younge plants. If you plan to turn this into a garden, better soil, plants, rocks and better mulch will all slow down the movement of water so it is no longer a problem.

Based on what you have said and the pictures. I would tend to build a swale or dry river bed along the wooden fence, heading to the back corner. In the back corner, build a drain that goes under the back fence and into the woods. A dry river bed can be straight and functional, or it could become a very interesting feature of the garden as it meanders aroud. Add a pond or rain garden to collect the water. You have lemons - make lemonade.

This is a lot easier than a french drain.

I think the solution depends on your ultimate goals for this area. To me, it looks like an unfinished part of a yard--a naked fence...nothing in particular planted--waiting for someone to finish it. Too shady for grass. If you just want it planted, there are plants that would hold the soil against erosion, but they must be protected until they are established.

You should tell us goals and where the property is located...what zone? In my opinion, you do not need french drain or any expensive structure.