I did more digging and planning and digging on the waterfall project today.
I dug the stream progressively deeper to speed the flow of water across the meadow. This reduces the amount of water that soaks into the ground and avoids the Massachusetts default for low land - muddy swamp.
As the water flows off the meadow plateau, I forced a hard left turn for the water to follow a contour line with very little slope(a small swale,) and widened the cut from bulb shovel width to garden shovel width. This slows the water down, encouraging water to soak in and travel downslope underground.
I may make the channel double the width and slow the water even more. I may make a u-turn at the end of the swale and run another swale the other direction. Or both. Right now, the swale ends abruptly, letting the water find it's way down the hillside to the brook where it came from.
This area of hillside gets better sun than most of the yard, so I tried planting veggies last year. They did not thrive. The hill had been formerly covered by ferns. Today I noted the sandy, silty soil is devoid of plant matter, worms, and the appearance of life below the 3" thick root mass of the ferns. This explains why my vegetables all failed: The soil is devoid of life and a soill food web to transport nutrients. The small soil amendments I did when planting were not enough to sustain vigorous plant life.
In swales watered by rainfall, intermittent water is captured and soaks in. Leaves fall in the dry channel and feed worms. The downslope berm and channel make a good habitat for planted trees and volunteer vegetation while building the soil quality. A continuously watered swale, should be more like a watery ditch alongside a road.
This requires more thinking
My small 40' swale.
I am considering a patch of cat tails for the small pond area on the right and planting a Lotus in the larger pond.