Woods Tea has some good suggestions. We've used some of those shrub types for just such a project.

So here's a little something to consider: I do tons of "stream restoration" for my job up here in sconnieland. And let me tell you, the DNR folk all are of a mind to reduce tree canopy. I know that sounds wrong, and I'm still not sure I'm down with it, but that's what they always want to do in such cases. So basically-and this may be going beyond what you are willing or able to do-the process consists of carefully removing some of the trees along the bank, not because they are problematic in and of themselves, but for two other reasons. First, these projects almost always call for a regrading of the bank back to a more moderate slope which is inherently more stable, and those trees right along the bank can prevent this. Then, with the increased sunlight now flooding in, herbaceous plants are installed thickly to hold the bank. We use a wide array of species, everything from ostrich fern (probably not native to your part of the world) to sedges, grasses, woodland forbs, etc. In the worst cases-or portions thereof-we will also use things like coir logs and Bio D-Blocks, a proprietary coir product with flaps that are pinned down before the next tier is installed. Think big $$ for that method, but sometimes, it's all that will work. And then, in the very worst spots, we may "hard armor" the bank using large riprap, but experience has shown that when you armor a channel, you are just pushing the erosion downstream to wherever the armor ends, so that is used sparingly.

Like I said, probably a bit more than you are able to do, but do consider more than just trees, as much as I hate to say that. Some of the other plant types can do good service in holding a bank.

The situations I discuss are parts of a mid-sized city's flood and stormwater control system. As such, flood control is job one. And while I actually hate some of the things we have to do, there's always mitigating aspects of the projects that make it tolerable and often, downright fun. So, we may remove trees along a stream bank, which just strikes me as so very wrongheaded, but then we plant all kinds of stuff later and if anything, some day that site will be even the richer for it. Things like large tree trunks that have fallen across the channel are to me completely natural and full of wildlife habitat potential, but they may restrict flow in a big rain, and that could mean somebody's basement is flooding further up the watershed. So such items have to be removed religiously. Things like that. We did one large-scale project where nearly one mile of stream was restored from what it had been-a ditch alongside a county highway- back into a squiggly meandering brook. In the process, a gigantic old snag which must have been home to hundreds of animals was right in the way of regrading, so that got removed. Broke my heart but you know, since we've done this work, complete with "wetland depressions"-in effect little manmade wetlands-the wildlife has just exploded. It seemed like it took frogs one day to find all this new habitat!

+oM