I have been asked to bid on a project to control creek bank erosion and flooding. The creek is fairly fast moving and temporarily floods the homeowner's yard after a hard rain. The adjacent homes do not have this problem due to topographical differences and, in one case, a retaining wall. (Interestingly, the neighboring retaining wall was built by an engineer several years ago and has caused an eddy which has eroded the bank downstream).
The homeowner asked if I could place boulders along the bank to stop the erosion and prevent flooding. The stated goal is a natural look, i.e. "not a wall." The creek bed is limestone, and the bank features several trees and lots of tangled roots. The section of bank involved is approximately 80' long and the limestone creek bed varies between 1-3' below the bank edge.
Homeowner called the local authorities, who advised she could modify the bank as she saw fit provided the creek was not obstructed. I plan to verify this information myself to be certain.
I think boulders and an appropriate selection of plant material is the solution to this problem, and will achieve the natural look the client is after. That said, I am wary of tinkering with the natural course of the creek-- in particular, I don't want to create a flooding/erosion problem for the neighbors. I am half tempted to consult an engineer before submitting a plan.
Maybe I am over thinking this, but I want to be careful here. In particular, I am looking for suggestions about the type of preparation that can/should be done before placing the stone (or that can be done without causing significant root damage-- the goal is to preserve the existing trees). Any other suggestions/warnings are greatly appreciated as well. Thanks!
You are gonna wanna bring in an stream bank engineer FOR SURE!
Where I am it is required.
This is a pretty simple stream bank restoration, and planting is going to play the major part.
Remember the lesson of the neighbor, rocks increase turbidity, increasing downstream erosion. And that water will move most rocks. It is a tenacious force.
Coir wattles, willow bundles that is what I would expect. This is a fun field, it is neat to work to restore natural process. And one of the processes is the eventual undermining of the existing trees. It won't be soon but it is bound to happen. I guess it all depends on the low water mark. It the tree can continue to stabilize itself during the low water periods, and your stream bank restoration works to take the brunt of the scouring power of the water the trees will last beyond your clients attention span. (life expectancy)
I't will be a fun project, slightly out of our average comfort zone. Keep growing!
It doesn't look like there are any dissenting opinions on the stream bank engineer recommendation. I agree that is the appropriate first step, and hopefully, the client will appreciate the reasons why it is necessary.
I'm going to go look at this creek again today- it should be over the banks now that all the snow we got this weekend is melting, and I'll have a better idea of what is involved here.
Any thing you add (hard armor) to the stream will cause disturbances behind it. Natural plantings with soft reinforcment would be my way with a few hard items Ie: boulders, flatstone, logs, ect. Looking at your pictures I can't tell what the stream velocity is and can't recomond a product just from them. But NA Green has a web site that allows you to look up products and compaire them. Be carefull on plant material choices, you might be able to use wet land plants installed in a choir log along with a TRM that extends into the water to support submergent plants. I would look at extending the TRM to the high water mark and a bit beyond it.
I'm jealous!! These are the types of projects I use to work on when I lived in California.
I'm not sure if alot of willow grows in your area, but we used willow all the time in CA and it works great. Willow walls, willow baffles, willow waddles...all great stuff.
I would talk to a stream engineer in your area and look at some different options. Seems like some baffles and/or rock wing deflectors might be worth researching into...to help trap sediment for those trees, but still allowing water to pass through.
Or maybe a willow wall. It's weakest it's first few years, but when it grows it can do better than rock. If not enough sun, we even tried dead brush walls in Washington. T-posts held back a bunch of dead brush tied with wire which would trap sediment....but, your creek looks a little too big for something like that to stay in place and plus...it's not very pretty.
If you go with rocking the bank, just make sure you got a solid, deep toe. I recommend putting some erosion control blanket behind your rock wall and definately sprig some vegetation in-between the rocks. Always overestimate the force of water--its stronger than you think. And as my old foreman always said..make your structure bomb proof. Also, be sure to find the high water mark...you don't want the water to go behind your structure and erode behind it. Have fun!
Our company is participating in a "flagship" type of certification program here in Michigan that gives landscape professionals, building contractors and others instruction on state laws, DEQ permitting and best practices for environmental quality for shorelines and waterways. We'll be completing the program in June, but unfortunatly we're located more than an hour from GR. The contact for this website should be able to point you to a participating professional from your area.
Just found out that indeed, I was right. There isn't a way to stop the roots from growing once they are dead, and someone recommended that I get a backhoe, get them darn roots out and move on with new dirt. Sheesh!