Unfortunately there is only one line with elevation marked (750) so it is hard to give you a key point or even a place to start observation.
The way you determine keypoint(s) is to observe where
water begins the downhill journey during a rain event or by the tops of gullies (which is where the water gathers to go downhill).
This upper most point is the keypoint and there would be a
pond placed there, then swales with
berms run at a 1% down hill grade from that point out to intersect the ridge line on either side.
If you happen to know the co-ordinates (gps) for the site, and you post those, I can take a look at the satellite images and give you better help with identifying the important start point(s).
If you are in an area with more than 3 junctions of water passage, then you want a main line setup instead of a key line setup, because that will work better for you.
Redhawk