greywater irrigation + check dam+ mulch pit

If somebody isn't advocating it then there must be something wrong with the idea, right?

If one had property where the house was at the top of the hill then ones grey water system is just a simple pipe unloading down the hill. If a simple channel were dug, it results in a man-made stream. Check dams guide the water into mulch pits which are connected in series to increase the distance from the stream that can be planted. This means that no human labor input is required beyond the initial setup to irrigate. Perhaps organic fertilizers (bone meal, blood meal, compost/worm tea, urine, etc) could be poured directly at the grey water output and from there, leached downstream into the growing areas.

Im not a great artist, but i have tried to illustrate the idea. as you can see, its backwards. I imagine that the edges will be planted with crops and the edge of the grey water stream will be planted with fast growing, nitrogen fixing trees to stabilize. between the crops and stabilizing trees, i would like to plant fruit trees and then run chickens and small pigs under that in order to clean up wind fallen fruits.

All of these are permaculture ideas, but i have never heard anyone advocating putting them together. Is there a reason for that? Is there a problem with the concept or is it a "good in theory bad in practice" type of deal?

The thing that jumps out is the slope (which I realize may not be accurately portrayed in the drawing) and the assumption that three diversions will be possible. There's a lot of it depends here, both slope and the infiltration qualities of your soil, so take any advice as not an answer but an indication of what research to do. Grey water is going to enter your system episodically in small quantities--<1 to maybe 40 gallons--so depending on slope, distance and soil characteristics, it may often seep into the ground before getting to the first diversion. Look around the web and you'll see lots of plans for infiltration systems. Many involve pvc or other pipe to get the grey water to the area where you want it and to spread it across a greater area than it would naturally flow. It is important to understand that storage in a tank is limited to 24 hours to minimize bad bacteria growth.

General greywater info (stolen from Oasis Design, a great resource):

Greywater.com—Lots of detailed greywater chemistry info
Greywater Guidelines-Sustainable Sources
Greywater wetland for 500 person university building. Since it also takes rainwater from the roof, the house is a net producer of clean water.
Wetpark - Permaculture greywater purification with a beautiful design
Graywater and rainwater use articles from University of Arizona
Living Wall - Plant growth and greywater purification in confined environments or frost-free areas

dan long wrote:If somebody isn't advocating it then there must be something wrong with the idea, right?

The world we live in is far, far from ideal, and there is a dearth of good ideas. Even when a good idea does come along, it requires marketing and advertising and cajoling and peer pressure until people slowly come around to it. Many good ideas just haven't reached critical mass yet.