Most of the time, having a drainage easement run through your yard does not mean that you can't fence portions of it. You just can't impede the flow of water, just as your back neighbor's chain link fence doesn't (because it is above ditch centerline and runs in line with flow of water.) A fence of yours abutting it would be approximately the same. It is where a fence crosses the ditch -- such as might happen at the corners of your yard -- that a healthy gap below the fence must be maintained so water can flow below it, unimpeded. But being realistic about this, privacy fencing is barely going to make a dent in your privacy needs on account of the elevations involved. If it was I, I would assess fencing based on security needs and achieve screening via another method, primarily tall shrubs. Wouldn't those that achieve 12' to 15' height do the job? If so, that's all you need. Of course, in selecting shrubs you'd need to take into account the light conditions so that they prosper. Sometimes, in cases like this, a plant is selected that survives sun or shade and will work throughout the entire area, simplifying the hedge. Sometimes, groups of different plants -- each appropriate for the given light condition -- are used for a more varied effect. You'll weigh what you do against your overall back yard design objectives. Sometimes people have the idea that shrubs will grow painfully slow and take forever to do the job. I think in most cases, it's opposite. But a huge amount of how fast they grow depends on the care they receive during the establishment phase (first two--three years.) If they get plenty of supplemental water and fertilizer on a regular schedule, they will likely grow quickly, making your privacy concerns soon disappear. I'm showing a possible bed line for the back boundary zone. (Does star on tree mean it be removed?)

I'd start by researching with your town what can be done on your easement. For instance, can you put up a fence of any kind such as a wire fence that would restrict a dog but allow sight and water flow? Are there limits on what you can plant? Woodies, herbaceous? Does the backyard easement start where the dirt ends or is that the property line? I can't tell if the star is giving both the side and back boundary or just the side. What do you want to do with your backyard other than have a dog? A patio or entertainment space or a spot for kids to play or lush gardens or . . . For now, have your meeting with the engineer and find out if the city has a written policy on drainage easements so it's clear what you can and cannot do in those spaces. Get grass seed and preferable straw down quickly so that you keep erosion from happening and seed can start growing before it gets too hot. Consider mixing in some annual rye grass to help with protecting the soil while perennial grasses fill in. Once you have a clear idea on the limitations the easement will create and have a wish list beyond the dog and screening from the neighbor's slider, come back and let us know so you can get suggestions.

Once I ordered a dump truck load of driveway gravel for a project I was doing at home. Within mere minutes of it being dumped at the road edge a storm struck up and a gazillion gallons of rainwater washed the entire load down the street and into the ditch. I got literally none of it. My point is that a "dry stream bed," being mainly gravel, might not necessarily be the best erosion control device since it washes if enough force comes. It may work fine if the conditions are not too harsh, but where an "impressive trench" can already be dug, and with the slope that exists here, I'd say you may be needing some other remedies. It can be difficult to give good advice about drainage problems on a forum because, first and foremost, we need to understand the site and its surroundings -- which is a lot of detail -- and many/most homeowners are unable to provide it. If a landmark is mentioned as part of the description, or as a problem spot, we should also see it corroborated in a photograph. As a starting point, the overall property is much easier to understand if it is put in the form of a plan .... a "map" of the property, on which then arrows showing the direction of water flow can be drawn, and notations of the problem spots made. Those could be supported by complete photographic scenes which pan the area with slightly overlapping shots (so we see from one end to the other how things fit together.) The easiest way to begin is by capturing a Google Earth image of the property. Use a paint/drawing program to draw on it. (The line tools can be used with a mouse.) Or trace the basic features onto paper and use a pencil to draw on it. Steps, in and of themselves are not going to solve an erosion problem. Actually, steps and retaining walls are capable of creating erosion problems if they are improperly laid out, which is common.

Do you know why it's collecting there in the first place? Do you know what the development/county/city plan is for the surface drainage of your property and the surrounding property? If so, you should drain to there. As for calculating gravel needs for a french drain, it's pretty much length * depth * width, minus the volume of the drainage pipe. Your edges aren't going to be perfect, so add in some extra for that. However, a french drain may not be the right solution, and even if it is, you'll still need a way to keep silt and debris from building up inside it and/or a way to clean it out. Drainage is complicated, and I would recommend either a ton of reading or consulting a professional if you want it done right. This is one of the best comprehensive writeups that covers drainage. Don't be put off by the fact that it says it's written for golf courses. Drainage Systems for Golf Courses Dr. Ed McCoy Ohio State University