My pond varies by a foot or so most every year. The trick to starting vegetation that likes a certain range of water coverage is to plant several (4 or so) in a particular area with the first planting on the high side of the bank, next a few inches lower, third, forth and so on a bit further down in the water column. 4 might be excessive depending on your water level variance, but this allows them to get their roots established so they won't be so susceptible to low or high water conditions.

My pond has the Duck Potato (Arrowhead), Thalia Dealbata, & Pickerel Weed as emergence. It took a couple years of buying some of them to get them to take well. I'd bet I had a 50-60% success rate, but now, 5 years later, I have strong clusters of the PW & TD. The arrow head came on naturally and tend to not cluster, but are spread out in more solitary plants.

I have rather steep banks and would make a tight ring of rocks below the water and dump a bucket of good soil into the ring, then plant my plants in them. This helps keep the soil from sliding down the steep bank and gives the roots something more than a hard bottom to grow in. To this day, I still dump some soil in the rock ring pile every spring to supplement the loss of soil. My clusters have escaped the rock rings and are making the surrounding areas their own. I doubt the adding of soils is really necessary any more.