Its roots only hang down about a centimeter at most usually, its will probably survive even with some water movement, and its pretty cool i use it in most of my water features, except waterfalls. Duckweed will work also, and both help to filter and maintain water in small water features. But dont put duck weed in anything you arent sure you want it in, it will spread much faster then even the natens....also i've discovered duck weed will actually grow on land if its humid and moist enough. Not sure if it will spread but it survives....i like the natens better...but if you have a feature that the natens wont live in, try the duck weed its a lil hardier.
Everything I've ever written is/was just my opinion!