Thanks to the clarification and inspiration gained from attending Permaculture Voices, I've been thinking about things through a different scope. Standing in the backyard this afternoon I was thinking about how a 'keypoint' is essentially a place where there is a higher concentration of water. Applying keyline design to the keypoints enables you to more effectively manage and control water so that it slows, spreads, and sinks across the landscape, instead of rushing aimlessly to the nearest gutter.
While my understanding is that keyline design was developed and tailored more towards larger, sloping landscapes, I believe that keyline design can be applied on a smaller scale. In a residential setting, we can collect water from our roofs, parking lots, etc. These points of collection can serve as keypoints. From the keypoints, swale-like mulch basins can transport excess water throughout the landscape. In essence, this is a rain garden, but one which more intentionally applies keyline design.
Until this realization, I'd been slightly dismayed by having such a flat yard to work with. I think this was partly due to much of my looking into water harvesting/storage was more applicable to sloping landscapes. While I'd felt competent in my understanding of how to manage water in sloped landscapes, managing water on flatlands has been a bit of a grey area for me. But with today's epiphany, I am feeling as if flatlands allow for a looser prescription of water harvesting/storage practices. Sloped landscapes beckon for contour lines, swales, and keypoint ponds, whereas in the flatlands, I think the designer has more discretion as far as where to direct water and how to manage it.