marlene burr

One advantage to mixing in styrofoam to your basic cob mix is that it weighs a bit less to handle.  That can make handling it a better proposition.  Think it may affect breathability, and drying time..

Goats are the organic way out with blackberries.  They love forage,  and can handle the bank.  Don't leave them too long such that that "over pollute" the stream.   A little us okay,  a lot is problematic for those downstream.  If you can,  consider goat diapers or physically removing poo yourself.  Additionally,  goats leave the roots intact,  so the bank is stabilized.  It will need several "treatments" by goats.  You will also need to plant some thing to take over.  Not sure what is allelopathic to blackberries,  but research couldn't hurt.

Alders are great nitrogen fixers for soils.  They also build soil carbon quickly below ground after they die because they rot quickly.  They often having the misnomer of "weed trees" because the wood rots so quickly and is not usable for structural building materials and fence posts,  but the wood is excellent for interior cabinetry doors and some furniture.   The wood is great for smoking meats and using as firewood in general.  The tree leaves can be used for cattle feed,   and will grow back from stumps.   Many varities grow in many types of soil.  The only downside is that the big trees can topple over easily and be a danger.