11/21/2016. STABILIZING EFFECTS OF TREE ROOTS Dependent on Species, Soils, Geology, Hydrology & Slope Moderately Deep Soils Shallow Soils EXAMPLE OF C

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1 STABILIZING EFFECTS OF TREE ROOTS Dependent on Species, Soils, Geology, Hydrology & Slope Moderately Deep Soils Shallow Soils A B A Potential failure plane is reinforced by roots. Anchoring: High Soil Cohesion: High Individual trees are stable without dependence on adjacent trees. Anchoring: High Soil Cohesion: High B STABILIZING EFFECTS OF TREE ROOTS Dependent on Species, Soils, Geology, Hydrology & Slope Shallow Soils Deep Soils C D Moderate if not compromised. Tends to become rapidly unstable when disturbed. Anchoring: Minor C Soil Cohesion: High Unstable soils are deeper than rooting level. D Anchoring: Minor Soil Cohesion: Moderate FIDALGO ISLAND EXAMPLE OF C anchoring: Minor soil cohesion: High 1

2 EFFECTS OF SHEAR STRESS ON TREE ROOTS Site Hydrology Is An Important Consideration SOIL SHEAR STRENGTH TREE ROOTS INCREASE SHEAR RESISTANCE Courtesy of Dr. Roy Sidle DENSE SPACING OF WEAK ROOTED TREES MAY INCREASE SHEER STRESS & CONTRIBUTE TO SHALLOW LANDSLIDE ACTIVITY RED ALDER Illustrations adapted from: Vegetation Influences on Debris Slide Occurrences on Steep Slopes in Japan, Y. Tsukamota and O. Kasakobe back to our scheduled broadcast Trees, Soils, Geology, and Slope Stability 2

3 BIO STRUCTURAL ENGINEERING FOR EROSION CONTROL & SLOPE STABILIZATION INTRODUCTION TO LANDSCAPES ON THE EDGE NOV , 2016 Elliott Menashe Greenbelt Consulting PEOPLE HAVE BEEN USING NATIVE VEGETATION IN ENGINEERING PROJECTS FOR A LONG TIME CHINESE HAVE USED PLANTS FOR EROSION CONTROL FOR 2,000 YEARS Europe Early 1900 s. Cutting and collection of live stems China Early 1900 s. Bundling live stems for use in riverbank Finney, K History of Soil Bioengineering. Masters thesis, Univ. of Oregon. woven willow mattress & brush layering Missouri River, circa after WW II, with increased availability of heavy equipment, civil & geotechnical engineers began depending mostly upon inert materials such as timber, steel & concrete for erosion control the use of vegetation fell out of fashion WILLOW MATTRESS BRUSH LAYERING willow (Salix) species were the most common plants vegetative techniques were used extensively US ARMY CORPS OF ENGINEERS 3

4 Bioengineering for Land Reclamation & Conservation THIS PUBLICATION RENEWED INTEREST IN THE USE OF VEGETATION IN EROSION CONTROL ENGINEERING Published in German by Hugo M Schiechtl In 1973 Translated from the original German and published by the University of Alberta Press in 1980 Biotechnical Slope Protection and Erosion Control, 1982 Donald H. Gray Andrew T. Leiser Biotechnical and Soil Bioengineering Slope Stabilization, 1996 Donald H. Gray Robbin B. Sotir Soil Bioengineering An Alternative for Roadside Management: A Practical Guide Lewis, L USDA Forest Service. Technology & Development Program PUB # SDTDC

5 soil bioengineering & biotechnical measures have been employed in stream bank restoration for decades BRUSH MAT WATTLE Source: USDA Natural Resource Conservation Service SOIL BIO ENGINEERING employs only vegetation or other natural materials to control water, reinforce soils & stabilize slopes live stakes NUMEROUS TECHNIQUES HAVE fascines BEEN DEVELOPED (wattles) wattles live fencing live crib walls live fencing brush live silt fences mattress live pole drains live live check dams stakes brush mattresses Soil Bioengineering techniques logs & used primarily for stream bank dead wood erosion & sediment control BIOTECHNICAL ENGINEERING employs both vegetative & synthetic materials vegetated geotextile green gabions vegetated riprap vegetated crib wall 5

6 BOTH SOIL BIOENGINEERING & BIOTECHNICAL PRACTICES HAVE LIMITED USEFULNESS FOR LANDSCAPING APPLICATIONS they both depend primarily upon the use of vegetative cuttings LIVE CUTTINGS: need adequate soil moisture a good local source of plant materials have a limited installation period must be dormant when installed have limited ornamental value BIO STRUCTURAL EROSION CONTROL & SLOPE STABILIZATION APPROACH the intentional use of desirable native vegetation species as an integral component in slope engineering applications & projects Vegetation + conventional engineering = an effective long term, integrated solution WHY ARE BIO STRUCTURAL METHODS DESIRABLE IN ENGINEERING? plants provide additional: water runoff management sediment control erosion control shallow landslide resistance provide many other ecosystem services regulatory incentives ESA stormwater no net loss constraints NORTH KING CO PROJECT nd YEAR soil nails geo grid over geotextile coir logs 6

7 NATIVE PLANTS ARE EFFECTIVE ENGINEERING MATERIALS roots provide significant hydrologic, structural & mechanical benefits fibrous roots coarse roots TREES ALSO ADAPT TO ALTERED CONDITIONS engineered structures don t original ground level BENEFITS OF A SUCCESSFUL BIO STRUCTURAL PROJECT GEOTECHNICAL ENGINEERING structural stabilization hydrologic controls surface erosion controls sediment controls ECOLOGICAL RESTORATION invasive plant control desirable vegetation establishment naturalization of the site long term ecologic restoration distant view aesthetic benefits CHRISTINE TASSEFF PHOTO 7

8 BIO SRUCTURAL ENGINEERING ALLOWS USE OF A BROAD RANGE OF PLANT SPECIES groundcovers WA NATIVE PLANT SOCIETY shrubs trees BIO SRUCTURAL ENGINEERING ALLOWS A BROADER RANGE OF PLANTING STOCK CHOICES AND A LONGER PLANTING PERIOD plug tubes USDA FOREST SERVICE NURSERY GEOTEXTILES PROVIDE IMMEDIATE INVASIVE PLANT, WATER & EROSION CONTROL polypropylene reinforced coir nonwoven filter erosion control blanket (ECB) fabrics natural fiber water & erosion control synthetic fiber invasive plant control 8

9 GEO CELL SYSTEMS SOIL NAILS WITH A STRUCTURAL FACING ARE CONDUSIVE TO PLANTING reinforcement & geogrid facing stabilization of unstable slopes with soil nails SOIL NAILS MIMIC SHEAR STRENGTH REINFORCEMENT OF SOIL BY TREE ROOTS soil nail installation RESISTANT ZONE ACTIVE ZONE 9

10 CRIB WALLS NOT ALL MATERIALS & TECHNIQUES ARE EFFECTIVE OR USED CORRECTLY Straw Erosion Control Blanket poor stormwater control extremely short term & temporary shallow rooted grass cover sediment JUTE (BURLAP) OPEN MESH NETTING 10

11 inexpensive often ineffective does not control runoff allows establishment of undesirable species HYDRO SEEDING GRASS ALSO DISCOURAGES ESTABLISHMENT OF MORE DESIRABLE VEGETATION & CAN INTRODUCE NOXIOUS WEEDS ONTO A SITE use of grass should be discouraged in vegetated projects at best only a temporary erosion control solution doesn t prevent noxious weed HYDRO MULCHING establishment 11

12 avoid use of grass & wild flower seed in hydro mulch mixes they often include invasive plants & noxious weeds SOME SOLUTIONS ARE JUST A BAD IDEA SHOTCRETE or GUNNITE Lung Fu Shan Country Park, Hong Kong, China ROCK FILLED GABIONS SOME ENGINEERING STRUCTURES & PROJECTS ARE NOT CONDUSIVE TO A VEGETATION COMPONENT 12

13 SLOPE STABILIZATION PROJECT SITES ARE OFTEN HARSH ENVIRONMENTS US HIGHWAY USGS STRUCTURAL FILL & SITE PREPARATION require the absence of all organic material not a plant friendly environment image courtesy of R.B. Jergens Contractors. REVEGETATION REQUIRES FERTILE SOILS structural fill materials will not grow plants soil characteristics to consider for plant growth: locate stockpiles away from preservation areas Texture Structure Fertility Organic matter content Bulk Density Soil ph Nutrients (as per ASLA LANDSCAPE SOILS SPECIFICATIONS) cover stockpiles to minimize erosion & infestation by invasive plants STOCKPILE & USE NATIVE SOILS STRIPPED FROM SITE 13

14 mycorrhizal inoculants improve growth promotes better water and mineral nutrient uptake DIP PLANTS IN INOCULATE SOLUTION inoculated not inoculated SITE ASSESSMENT FACTORS Erosional Processes Physical Site Characteristics topography geomorphology precipitation hydrology soil moisture & fertility elevation slope & aspect stratigraphy fluvial processes shore processes Existing Vegetation Climatic Conditions Socio political Considerations Logistical & Economic Constraints WHAT ARE THE CRUCIAL PROJECT SITE CHARACTERISTICS? FAILED CUT BANK STABILIZATION REFERENCE SITES & INDICATOR SPECIES help define characteristics of the site environment WINDY INVASIVE PLANTS OLD GROWTH STUMP KEEP IN MIND THAT THE PROJECT SITE MAY NO LONGER RESEMBLE REFERENCE SITES SKUNK CABBAGE MADRONE HIMALAYAN BLACKBERRY 14

15 IDENTIFY & PRESERVE VALUABLE EXISTING VEGETATION PROTECT ESTABLISHED NATIVE PLANTS THROUGHOUT PROJECT SITE COIR GEOCELL INSTALLATION, LAKE TAHOE, CA INVASIVE PLANT CONTROL non woven permeable geotextile CRUCIAL TO A PROJECT S SUCCESS HIMALAYA BLACKBERRY DO NOT USE PLASTIC SHEETING! SITE HYDROLOGY IS OFTEN A CRUCIAL CONSIDERATION LIVE POLE DRAINS vegetated interception trenches MAY HELP SOLVE PERCHED WATER PROBLEMS 15

16 HYPOTHETICAL PUGET SOUND BLUFF greatly simplified! seeps SAND topsoil TILL SILT/CLAY PUGET SOUND BASIN SAND/GRAVEL CLAY TILL ADAPTED FROM: LIVING ON THE COAST, US Army Corps of Engineers, 2003 PLANT SELECTION CONSIDERATIONS native to area appropriate to site (sun shade, soils, salt tolerance, etc) favorable spread & reproductive capability superior erosion control value superior root strength (roots with high tensile strength) drought tolerant (once established) commercially available RED FLOWERING CURRANT PLANTING & INSTALLATION CONSIDERATIONS Species selection Plant stock types Locally sourced? Spacing/Density Soil improvement fertility mycorrhizae Irrigation Animal & abiotic damage protection CHRIS MADDEN CARTOON 16

17 THE PROJECT SITE MUST BE STABLE FOR AT LEAST 15 YEARS SHEET FLOW vegetation takes time to become effective OFF SITE INFLUENCES INHERENTLY UNSTABLE Groundcovers: 3 to 5 years Shrubs: 4 to 10 years Trees: 7 to 15 years vegetation becomes more effective over time COIR EROSION CONTROL MAT & NATIVE PLANTINGS use NATIVE plant materials in all biostructural projects better stormwater & erosion control more salt tolerant than ornamentals better rooting capability more drought resistant Rosa nutkana provide better wildlife habitat 17

18 Plant For Multiple Canopy Levels PLANT FOR SUCCESSION (native ecosystem plant community succession & development over time) include both evergreen & deciduous plants overstory canopy understory groundcovers planning, design, permitting & installation of bio structural projects require special skills SEATTLE PROJECT, 2014 BELLINGHAM PROJECT, 2001 some sites are not able to be stabilized STRAIT OF JUAN DE FUCA CLALLAM COUNTY 18

19 thank you ELWHA RIVER REVEGETATION SITE, NOV 2013 BIO-STRUCTURAL ENGINEERING FOR EROSION CONTROL & SLOPE STABILIZATION WITH NATIVE VEGETATION AS A KEY COMPONENT combines: art science engineering & ecological restoration INTRODUCTION TO LANDSCAPES ON THE EDGE design & implementation of projects on Puget Sound shorelines & urban ravines Nov Elliott Menashe Greenbelt Consulting 19