I vote hugelkultur on contour in your garden area. Assuming its not dead flat, in which case build it any direction you like.
Try digging a hole about 2 or three feet deep where you want your garden and see if it fills with water.
That marshy area is basicly a swale already i wouldnt worry about more water catchment for your garden area.
If your water table gets higher than 2 feet for extended periods id be thinking raised beds aswell.
Now if you could make some more dams up that stream from you then we would be talking year round stream.