Hey Everybody,

We’re thinking of doing a series of posts about different Erosion & Sediment Control and various Streambank techniques.  Kind of a basic knowledge, information-rich, get-to-know-your-tools type of thing.  So, let’s give it a go shall we?

Let’s talk Live Silitation! 

TWO QUICK NOTES

• The above video clip is a part of our Willow Creek Project DVD.  Would you like to use Dirt Time video in your training or presentations.  Get it touch with us here.
• All of this information below is taken from, and is covered in more depth, in our Erosion Software program ESENSS (check it out here).

DESCRIPTION

 Live siltation (also known as Vertical Brush Layering) is a revegetation technique used to secure the toe of a streambank, trap sediments, and create fish rearing habitat. The system can be constructed as a living or a non-living brushy system at the water’s edge.

PURPOSE

Live siltation helps to secure the toe of a streambank, and trap sediments.

CONDITIONS WHERE PRACTICE APPLIES:

Live siltation is an appropriate practice along an outer bend with sufficient scour or toe protection.

PLANNING

Useful for Erosion Processes:

• Toe erosion with upper bank failure
• Scour of middle and upper banks by currents
• Local scour
• Erosion of local lenses or layers of noncohesive sediment
• Erosion by overbank runoff
• General bed degradation
• Headcutting
• Piping
• Erosion by navigation waves
• Erosion by wind waves
• General bank instability or susceptibility to mass slope failure
• Erosion by ice and debris gouging 

Spatial Application:

• Instream
• Toe
• Midbank
• Top of Bank

 Hydrologic / Geomorphic Setting

• Resistive
• Redirective
• Continuous
• Discontinuous
• Outer Bend
• Inner Bend
• Incision
• Lateral Migration
• Aggradation

Design Guidelines / Typical Drawings:

Cuttings should be placed adjacent to the water’s edge to ensure effective sediment trapping and velocity reduction at the toe of slope. At least 40 branches per m (12 branches per ft) should be installed.

ENVIRONMENTAL CONSIDERATIONS / BENEFITS

This is a very effective and simple conservation method using local plant materials. This technique is particularly valuable for providing immediate cover and fish habitat while other revegetation plantings become established. The protruding branches provide roughness, slow velocities, and encourage deposition of sediment. The depositional areas are then available for natural recruitment of native riparian vegetation.

HYDRAULIC LOADING

This technique may be used for velocities up to 2 m/sec (6.6 ft/sec), but velocities should be at least 0.25 m/sec (0.8 ft/sec) for the system to function properly.

COMBINATION OPPORTUNITIES

Live siltation techniques can be constructed in combination with rock toes, Rootwad Revetments, Coconut Fiber Rolls, Live Fascines, and Brush Mattresses.

ADVANTAGES

This is a very effective and simple conservation method using local plant materials. This technique is particularly valuable for providing immediate cover and fish habitat while other revegetation plantings become established. The protruding branches provide roughness, slow velocities, and encourage deposition of sediment. The depositional areas are then available for natural recruitment of native riparian vegetation.

LIMITATIONS

If using a living system, cuttings must be taken during the dormancy period.

MATERIALS AND EQUIPMENT

Natural stone, willow wattles, logs or root wad revetments are needed for toe and scour protection. The live siltation will require live branches of shrub willows 1-1.5 m (3.5–5 ft) in length. The branches should be dormant, and need to have the side branches still attached. Any woody plant material, such as alder, can be installed for a non-living system.

CONSTRUCTION / INSTALLATION

Construct a V-shaped trench at the annual high water (AHW) level, with hand tools or a backhoe. Excavate a trench so that it parallels the toe of the streambank and is approximately 0.6 m (2 ft) deep. Lay a thick layer of willow branches in the trench so that 1/3 of the length of the branches is above the trench and the branches angle out toward the stream. Place a minimum of 40 willow branches per m (12 branches per ft) in the trench.

Backfill over the branches with a gravel/soil mix and secure the top surface with large washed gravel, bundles/coir logs, or carefully placed rocks. Both the upstream and downstream ends of the live siltation construction need to transition smoothly into a stable streambank to reduce the potential for the system to wash out. More that one row of live siltation can be installed. A living and growing siltation system typically is installed at AHW. A non-living system can be constructed below AHW during low water levels. If it is impossible to dig a trench, the branches can be secured in place with logs, armor rock, bundles made from wattles, or coir logs.

COST

0.7-2 work hours per linear m (0.2-0.6 work hours per linear ft), plus willow stock if not readily available on site.

MAINTENANCE / MONITORING

During the first year, the installation should be checked for failures after all 1-year return interval and higher flows, and repaired as necessary. During summer months of the first year, ensure that cuttings are not becoming dehydrated.

COMMON REASONS / CIRCUMSTANCES FOR FAILURE

Cuttings will not promote siltation as well if not located at the water’s edge. If located further up the bank, cuttings may dry out, and will only trap sediments and slow velocities during high flows. Cuttings may not grow well if not handled properly prior to installation. See The Special Topic: Harvesting and Handling of Woody Cuttings for proper handling instructions.

For more information, pictures, diagrams and examples, sure to check out our erosion software program E-SenSS (click here)

We’re picking up where this workshop left off.  More info coming soon…

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.

Merry Christmas!

John 

Over the course of Sept-Nov 2008, John and I made frequent visits over to Alberta, just outside of Calgary.  The Alberta Department of Infrastructure and Transportation (AIT) hired John to consult, design and deliver a very big, very impressive BioEngineering workshop.  And of course, we were there with cameras (due to the great support of AIT).

BlinkWorks is on the homestretch of the video edit, and the episodes should be available quite soon.  But, we wanted to give a sneak peek and show a rough cut of the first 5 minutes.  This early footage gives a pretty good idea of what the project entailed.

The workshop centered around a project that aimed to save Highway 2 (a major highway connecting Fort McCleod and Calgary) from being undercut by Willow Creek.  A harmless enough looking waterway, Willow Creek had developed the devious little habit of eating away its banks toe, which led to major landslide failures.

In the past, we did similar projects for AIT up in Hinton Alberta.  Check out our ‘Hinton’ episodes in Season 1 and Season 2.

We’ll definitely be posting more material soon.  And of course, stay tuned to find out when the entire video is released.

Or better yet, send me an email through the contact us link and we’ll let you know as soon as its released!