Okay then ...
to answer some questions raised -
1. we intend for this to not only have greywater but also combine with rainwater. I'm not sure of the volume of greywater we will have but there will be 4 adults living in the home and possible 2 more depending on circumstances. I had no delusions that the greywater alone would fill the moat. Reading that our greywater addition to the moat will be so small makes me feel like that this is a doable situation for not contaminating any native waterways and for providing moisture for plantings that I don't have to worry about weird stuff being absorbed through the soil.
2. Smell or no smell seems to be a moot point given that the percentage of greywater will be less than 10% of the whole volume of water and we are leaning towards a "pre-moat" area of gravel and reeds to help filter food debris, etc and oxygenate the water.
3. Length and width - Length is pretty set given the space we have. It is 120' from the house to the road, then turn the corner and it's 90' to the drive, 105' to the rainwater wash, and another 80' to the creek. Width and depth are variable at present. Thinking about 4-5 feet wide (difficult for most people to jump in a single bound especially with a steep berm on the other side) and perhaps 3 feet deep. But we've been considering adding fish to the mix after the first 120' run using a net or screen partition to keep them where we want them so we will have to look into what would be appropriate for the type of fish we want to keep.
4. Earthworks - honestly everything we do on our acreage is WORK in capital letters and frankly digging a moat around the edge where there are no trees or roots to contend with and where we can get an excavator in with ease seems much easier than digging a big round pond elsewhere and then contending with the dirt relocation. With the moat we can essentially scrape the dirt out and mound it on one side over a pile of branches and logs, cover with compost, and plant plants.
5. Dumping the water/water absorption ... We'd really like it to be pond-ish if possible, meaning that we would want water in it most of the year if not all year. We have a creek that was seasonal when we bought the place. within 10 days of a rain it was dry again. Fall and winter last year it didn't have enough to even be mud. Then we build a low-water dam... with a continual spill-way on it and it hasn't been dry since. We don't really understand how our two layers of concrete sacks less than a foot high actually created this phenomanom but somehow it did and we aren't arguing with the results. Anywho, the moat, we invision will have a gradual spill to it so that it doesn't flood, in theory, and will add a small trickle to the creek as well at times, maybe. It does get dry and hot here in summer and dry in winter.
6. The purpose of the moat - We had a two-fold purpose in mind. One is to increase the water on the property ... for instance we can build as many ponds as we like so this would just be a different form of a pond. And Two, lol, is not actually about the moat at all but rather the need for the dirt we would remove from the pond. The neighbor to our north is ... how to say this nicely ... an idiot who literally cleared his entire property of trees and filled in all his ponds and sprays his wheat with roundup before harvest and kills any living creature that dares walk across his land ... Naturally we want a barrier between us. On the east is a gravel road. In the summer the dust from the road settles in the grasses and trees and we don't get much infiltration into our property at all but in the winter, when the county mows down all the tall grass for fire prevention, the road dust is insane, Plus the noise from traffic at given times of the day is atrocious. So we wanted to build a berm and then put a fence on top of the berm to abate noise and dust and creepy neighbors. We can only build a 7' fence which isn't tall enough for our landscape but a 7' fence atop a berm would greatly increase our privacy and address our noise issues. I guess there's a 3rd purpose too, to deal with the greywater from the house. It's got to go somewhere.
7. Wildlife issues - I suppose a moat and berm system would work well for some predators but we're not that bothered by wild critters. We have tons of them and figure they were here first. Keeping them out of my chickens is my only goal. I plant extra garden because I know I will lose some. Our goats along with our LGD's are safe by themselves and we fence them up during birthing to protect the babes so that's not really an issue. Our biggest predator is the mountain lion and it would have to be a damn big moat to keep one out. We walk the perimeter every day and keep a look out for tracks. We mainly have raccoons and opossums and deer. We did have a bobcat but they take smaller things like rabbits and our LGD's are about 3x the size of a bobcat so no worries there. Owls and hawks and eagles and peregrins would only increase their population from a moat. Those that fish will have a supply and the water will attract other small critters that they prey on so perhaps a moat like we're discussing would keep them away from our chickens.
All in all this is looking more do-able and less crazy the more I think on it and read other's posts and thoughts on it.
Thanks for chiming in.