Pollinator plants that will grow in floodland subsoil after construction project

Behind our house the city has just finished a section of sewer pipeline. It was super deep - maybe 20' - and they did not save the topsoil.  After the subsoil was spread out over the 50' wide area they seeded with grass and rye but it is the worst concrete-subsoil stuff I have ever seen, and the not even contractor grass seed is surviving. I feel like this long, open area on ignored municipal property could be turned into something useful (with perhaps a little guerrilla gardening) such as pollinator habitat. Any suggestions for something that would grow in (almost) concrete that could also take some flooding?

Although not a pollinator Rosemary could help out in a few spots. I’ve planted bee balm and oregano in just terrible soil and they done well. Comfrey is always a good choice as well.

Dollar General usually has boxes of wildflower seeds for not very much.  1000 of seed for under $5.00, can't remember exactly the price.

Also blue sage, blanket flower aka firewheel and swamp milkweed would be good additions.