One problem, FWIU, is that the levees themselves are basically just mounds of dirt. Adding something on top of a levee won't do much good if ANY water gets under the new thing you added. Instead, the flow under the new object will quickly erode the levy below it and may--especially if the erosion allows the object to fall through--result in a larger breach than if the "repair" had not been attempted.
I was really thinking more in the lines of a long flat metal beam structure formed with large crossbeams and smaller crossbeams that could stretch from one wall to the other and then place sand bags so that the current doesn't just wash the bags away. Oh well I'm not there just an idea.