Using earthworks and keyline principles to maximise water for ponds and dams.

If one was building ponds/dams (on the keypoint of a valley) for aquaculture or habitat, I would assume you would try to drain water towards the dam, and that water retention techniques such as swales, rock/ brush dams. and keyline ploughing would reduce the amount of water reaching the dam. But increasing runoff, and 'draining' areas to a dam couldn't be good for the land (at least not in the Australian climate). Overall, would swales and check dams in the gully above the keyline raise the water table, benefitting the dam more overall? Is water quality better in a primarily groundwater fed dam compared to a runoff and rain fed dam? Would keyline ploughing would be better below the dam, as it actively moves water to the primary ridge, away from the gully, to benefit vegetation? From an ecosystem point of view, it is good to have as many niches as possible, so it is important to rehydrate soil while balancing that with the creation of waterbodies.

Reading more about keyline, and I realise that the aims of keyline do not fully match up with a complete permaculture/polyculture, but is more directed towards increasing arable pasture :
"According to Yeomans (the originator of the keyline concept), swampy bottomland results from mismanaging the water upstream.  To correct the problem, you dig a swale (an on-contour ditch) along the keyline so that water doesn't whoosh right down into the swampy bottom, but instead flows gently (along a 1% downhill slope) to drier areas to the side.  This is known as a spreader swale, and it's what folks mean when they talk about moving water from the valleys to the ridges --- you're not technically bringing water uphill, but you are moving it from a wetter area to a drier area.  The result is a more productive, damper area to the side of the keyline, and a more productive, drier area in the flat zone directly downhill" (https://www.waldeneffect.org/blog/Keylines/).

A permaculture might actually look to accentuate the swampiness of a certain area to increase the edge effect and create more niches. Keyline farming would likely look to move that water away and soak it into the soil of the adjacent ridge. Both look to increase soil water retention, but keyline farming is more focused on uniform hydration.

I still think the geographical basis of keyline is useful in judging the placement of permaculture earthworks. My amended questions are;
Is the keypoint (usually) the optimal place for dams?
Do earthworks above the keyline that allow for filtration of water into the soil negatively or positively impact water levels of dams below?

What we did when we wanted to increase the amount of water going to our pond was to make a trench that was long, wide and smooth though getting deeper as it neared the pond.

There were rock blocking the path of this trench that had to be removed.

I went thru a decade or two of building dams every chance I got, following keyline principles: "Slow it! Spread it! Sink it!" This was after a childhood fascination with wetlands and parents that allowed me to have zones in the yard where I could dig and model and build. I often had an opportunity to work on a scale way smaller than classic keyline work. That's great: you develop the chops you need. I had ample opportunity to experiment with appropriate vegetation as well. Not many of us have the chance to work on 400 or 4,000 acres of mild slopeing land.  In retrospect, it's all good, but there's a long learning and dues paying timeline. Note that Australia generally is a pretty old continent without a lot of mountains, volcanos, and big rivers.  In North America, hold on to your wild dreams and proceed slowly, don't get in a hurry. We have a very active continent and Big Shit Happens. I have done big plantings that peceeded an unexpected record hot, drout summer, and worked my tail off getting water to my young trees. ( I learned to plant with watering tubes of bamboo ( biodegradeable and the drip line puts moisture right in at the root zone)  In my lifetime I have participated mandatorily in tornados, volcanic eruptions, record snow events and floods. Canoeing down the street happens... Observe! Find people who have been building ponds, doing wetland restoration, ANYTHING remotely related, and get your hands dirty, and grab opportunities for learning. Anywhere you are, your headwaters is your roof: start in zone 1! direct downspouts to filtration? absorbtion swales, (do not flood your basement!)  work on your planting chops and develop your guilds of useful plants and work on learning how to build stable infiltration systems. Then find opportunities for volunteering on wetland restoration projects and the like, and learn to dig like a woodchuck and plant like a beaver (a beaver dam is a living engineering structure, eh?)