You have to resist the urge to pack your stuff up when the sun goes below the horizon, because some of those last, lingering, luminous fingers of light can be some of the most beautiful of the day. You have to be careful when you work, because the light's real pretty, but there ain't much of it, so you're going to have to use a slow shutter speed. I was able to hand-hold this shot, with a one-second exposure, but I don't recommend this-this is where the tripod is your friend.
This is also the water trick at play again. Without the sheen of water as the waves hit the shore, there would be no separation, and no picture. The lengthy exposure helps here. As the water rushes along the beach, it is in motion, and the highlight spreads.
By the way, when you are stuck without a tripod, use anything you can get your hands on to stabilize the camera. Bill Allard at National Geographic is famous for using a beer bottle monopod. If there is nothing around, as there wasn't in this situation, sit down Indian style and brace your elbows on your knees. Or, being at the beach, smush together a towel on the ground and nestle the camera in it. You sacrifice a bit of the ideal camera angle you might have wanted, but you get a frame.