VMSE = Vegetated Mechanically Stabilized Earth
Donald Gray, Professor Emeritus Geotechnical Engineering, University of Michigan, my mentor and colleague defines biotechnical as “the combination of structural and biologic elements in a mutually beneficial manner”. In fact, Don help us research and author the NCHRP Report 544 – Environmentally-Sensitive Bank and Channel Stabilization Manual (AKA E-SenSS), which provides over 50 biotechnical or environmentally-sensitive techniques. I wanted my students to be suitably exposed to and knowledgeable of “Biotechnical Erosion Control” methods.
As usual, one of the best ways to learn is by doing so my Shasta College Class, AGNR-66 Watershed Restoration Practicum, designed and built a biotechnical streambank stabilization project during the Stillwater Creek Workshop. We wanted to build a hands-on project that would showcase the College’s abilities. Brushlayering with willows (with or without geotextile inclusions) is, I believe, one of the most important bioengineering techniques – a technique that “is as old as dirt”, which utilizes/demonstrates the engineering principles of “reinforced earth”. Reinforced earth allows one to design/build stable slopes that can be steeper than the materials natural angle of repose. Another plus that I am finding is the reinforcement can replace a bit of the compaction that is usually applied. Plants prefer compaction in the 80%-90% range, so reinforced soil slopes can be a win win with regards to establishing vegetation. Contemporary reinforcements are provided by materials such as “geogrids” – very strong black polypropylene geotextiles (geogrids typically look like the temporary orange environmental fencing though manufactured with many strengthening properties. Well, “back in the day”, ancient China, Rome, and more recently Switzerland/Austria, the soil reinforcements were comprised of plant materials. Willow (Salix sp.) have played a long and successful role in soil reinforcement – imagine a geogrid that can grow and get stronger with time while providing immediate erosion control and environmental enhancements!!!
First thing for our project was to cut and store the willow branches. Brushlayering branches are generally 4′-8′ long. And there is numerous research efforts that indicate soaking willow will increase establishment. I could spend an entire blog giving up all the harvesting, handling, storing, selecting criteria for successful biotechnical construction but maybe later.
Just know it all exists in the Manuals on CD (BioDraw, ESenss, etc). see www.biodraw.com and www.esenss.com. Here my staff, Tara and Christine got to supervise all the willow harvesting. Talk about loving your work! It was nearly impossible to get them back into the office!
When we soaked our bundles of branches, about 25 per bundle, we attracted some local bank beavers to ‘chow down’. They must have felt like somebody delivered pizza to their living room! Beaver cages are often used in Canada but I’ve never had to use one in CA before. Having some Enka mat TRM and orange fencing leftover, we improvised and ‘beaver-proofed’ our bundles!!
Bio Draw 1.0 and ESenSS (NCHRP Report 544) both give design/construction specs for VMSE – often referred to as “burrito wraps” or soil wraps. While they look good on paper, they are quite difficult to build, especially if there is insistence that the outer face of the wrap (lift) is “flat and planer”. The outer face is just too hard to pound or shape smooth before the wrap is made, go ahead, try to build a form or something, but trust me it takes a bit of time and many construction folks will baulk at the design. Note: the linear / flat face is not the most stable, according to Dr. Donald Gray. The outer geogrid will naturally form a more stable catenary curve shape. I refer to it as the “the wrap, when in x-section will look like a beer belly or pregnant tummy” so why fight nature and try to make it absolutely flat at exactly 1.5:1 for instance? Below are typical drawings for VMSE and flapping.
And then this dilemma of constructibility led us to the “Soil Flap Method” – very constructible and very effective. I must give credit to Chris Cummings, PE for Caltrans Dist 1. See our first project using flapping on Buckhorn Summit in the nasty decomposed granite (determined by many to be one of the most erosive soils anywhere – no clay, no cohesion, mucho silts and sands fractions!). Add some brushlayering and some heavy 9 g/m2 Coir netting and long/strong anchor pins or duckbills at the bottom of flap (the tightly-cinched belt below the beer belly) and this technique will give you geotechnical strength, reduced pore pressure (water will weep imperceptivqely and horizontally out the willow branches), and almost 100% effective erosion control (protection against raindrop impact) and sheet erosion (willow tips sticking out provide slope roughness) protection. This is the BOMB technique. And note, no compaction necessary on the face of the slope!! Note the still stable slope after 2 years This area receives over 40″-50″ rainfall and snow per winter.
We couldn’t have done this project without the help of Bruce Lawson and his class. Bruce teaches Heavy Equipment Operations at the College, and he is one of the best dozer operators and human beings I know. Here is a picture of Tara giving Bruce her finger in his chest, all in jest. She broke her finger and it was splinted with wire and tape, We probably should have used a willow branch as the salicylic acid (yes, aspirin comes from willow!) may have relieved the pain.
You can see Bruce operate at Prairie City OHV in this video:
Also I threw in some other photos of projects (Hinton Project) where we built VMSE. See the Dirt Time episodes on Streambank Stabilization, Hinton I and Hinton II.
Next installment, after Christmas, I’ll cover some of the things we learned about Stillwater Creek, the evaluation of the old state-of-the-art streambank stabilization techniques (circa 1970) and how they (gabions and tires) are unraveling today, and more tips from David Derrick. Stay Tuned!
And you heard it here first, on Watchyourdirt.com
Comments ??? Please let us have it.
Now remember, the intent of the project was to “move the thalweg stream-ward”. The big issue of secondary importance was trying/implementing the construction method of “Self-Launching” rock. The emergency nature of the project and the environmental sensitivities were the primary design “drivers”. RSP (Rock Slope protection) – Rip rap in Caltrans jargon, would not be allowed by the Resource Agencies. Other design constraints were water quality and both instream and gravel bar habitat protection. In other words, we would not excavate the river bottom and we would not excavate the gravel bars.
So, this was a perfect opportunity to utilize the self-launching (graded, poorly sorted) rock as described in NCHRP Report 544, and place clean rock on the existing river substrate. This is how the Longitudinal Stone Toe Protection (LSTP doing double duty as the construction access road) was built. And then the redirective Rock Vanes, attached to the LSTP, were installed to re-direct and manage the THAWEG. So, if the thalweg and high energy stay away from the bank and out to the middle of the channel, then the project is a success. See for yourself how it is working.
David Derrick, upon seeing these photos commented ” I like that thalweg”. I like it too, it is over 60′ streamward of the bank and last winter the thalweg was at the toe of the bank. Also notice in the photos the slow velocity and low energy of the flood waters over the terrace.
Thalweg management, adding roughness (the willows, live siltation, live poles, and a flood bench), and a flood bench can sometimes replace RSP for an Environmentally-Sensitive approach to streambank protection. please note that the vertical bank will be addressed in subsequent projects.
Any comments or questions out there? Please use the comment bar and let us know what you think.
The Stillwater Creek Stream Workshop was a huge success.
Over 36 professionals attended the 3.5 day workshop hosted by Shasta College and organized by the Shasta College Foundation and Sacramento Watersheds Action Group (SWAG). We had some Military people from Kansas, almost 10 professionals fro Caltrans, CA Fish and Game was represented (2 wardens attended), a City of Roseville planner, and many more.
David Derrick, from Bovina, Mississippi (yup, Bovina, right near Vicksburg, home of the USCOE Waterways Experiment Station), was in super great form. For those of you who haven’t caught David teach about streams, well …..so sad. Scott Thompson, SC Foundation stopped by and commented about david, “that guys is a great instructor!”. But hey, you can catch him next year as we plan to make this a yearly affair. The entire workshop was about practical application and experience. Both David and myself have designed and built tons of projects, which we have dutifully documented and monitored through the years.
The College provided bus transportation (and oh, the lunches provided by the College were deeLISH) so we could visit Sulphur Creek, a Redding Urban Salmonid stream that SWAG started restoring in 1996. The attendees got to see restoration and biotechnical techniques that are over 10 years old (Newbury Rock Riffles, Viffles, Rock Vanes, Live Siltation w/ LPSTP).
If these sound foreign to you well, I taught some modules on biotechnical EC/ Bioengineering and all the attendees got free copies of NCHRP Report 544 / ESenSS – Environmentally-Sensitive Streambank Stabilization (this CD has all the practices (54) that are environmentally-sensitive alternatives or enhancements to traditional rip rap, including digital drawing files, BMPs, design criteria, case studies, photos etc.)
Besides the classroom instruction by David and myself, the real high point(s) were the field trips out to Stillwater Creek that bounds the College campus to the East. We all got to “Read The Stream” with David’s help – through the eyes of an experienced stream and river guy. There was a lot to see too, or more correctly, a lot NOT seen. Such as proper stream function. There was almost no large wood in the stream, even though wood was probably an important component to proper stream function. David help us see that there were a lot of other components like overhanging branches and “dragging limbs”, no substrate complexity like pools and riffles.
We learned a lot about “Roughness”, not the Manning’s n – type, but instead David explained how the vegetation, rocks, pools/riffles etc provide the necessary roughness during high flows to dissipate stream energy while relatively smooth banks (no veg, riprap, etc.) will erode or accelerate the stream energy. More on this in upcoming blogs!
The stream was / is incised at a Stage 3-4 on the Channel Evolution Model. David and I spent significant time explaining geomorphic features and stream energy, and the resulting dis-equilibrium. This reach of creek was a classic example showcasing the state-of-the-art streambank stabilization practices circa 1960-1970s, e.g., Gabion baskets, tires, or rock places along a straightened reach of stream that is separated from it’s floodplain and then historically gravel mined for good measure! Yes, this reach of Stillwater Creek will provide a “learning laboratory” for many years to come. It is also has very valuable potential as critical Salmonid habitat if restoration projects are implemented.
And this is exactly what Shasta College, the Shasta College Foundation, and SWAG want. To restore the habitat and stream function while providing a hands-on learning laboratory. We want to offer more workshops, at least on an annual basis. What would you say if Shasta College offered curriculum in Stream Restoration?
Give us your feedback please.
And stay tuned for more information. We are going to offer additional Stillwater Creek blog topics over the next few weeks.