I have red hill and wandering Jew succulents that are literally growing in a stream of water. Been in there a couple months now. If anybody knows about succulents they generally hate too much water.. Also kept century plants and many others alive for months at a time in this stream on the property. With no root rot. The key is constant flow to provide an aerobic environment to the roots. Similar concept as hydroponics. Most people automatically think flooding will kill a plant. Not necessarily, but yes stagnant water most definitely will. Maybe add a cheap aerator system to the lower root zone if you know it’s gonna flood for months at a time in certain spots. Lol idk, just a though. You can also stuff the bottom of the planting pit with sticks, logs, large mulch, rocks hard clay and sand, and this has worked well with holes that only flood up until that bottom level with those mentioned materials. Then backfill with a normal mix on top of that level.
A cheap mix I use in Fl is 50% native sand maybe with a bit of clay, 40% topsoil and or leaf compost and or sphagnum peat moss, 5% pulverized limestone, 5% composted or semi-composted coffee grounds (Starbucks will give u huge bags for free). Just remember to fertilize often because this mix is honestly pretty devoid of Nitrogen and probably some micros. Most things on that list you can find at Lowe’s and if a bag has a rip they’ll mark it down 50% regardless of how much fell out usually. At my Lowe’s anything under 5$ is marked down to 1$