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~�~EATON I~9ERY OWNERS~ TA 71 0.3 .w2 S66GT a 1 U. S. DEPARTMENT OF COMMERCE NOAA COASTAL SERVICES CENTER 2234 SOUTH HOBSON AVENUE CHARLESTON, SC 29405-2413 SLOPE STABILIZATION AND EROSION CONTROL USING VEGETATION A MANUAL OF PRACTICE FOR COASTAL PROPERTY OWNERS Property of csc Library Sponsored by. Prepared by: SHORELANDS & COASTAL ZONE Mguerm MANAGEMENT PROGRAM W K I I N G T 0 N S T A T E BloddynamIlr Inc. Washington Department of Ecology D E F RI I T fMB :Olympia. E C 0 L 0 G Y Geotechnical & Biotechnical Engineers Bainbridge Island, Washington PUBLICATION NO. 93-30 MAY, 1993 ACKNOWLEDGMENTS The preparation of this manual was made financially possible using funds appropriated and administered by the Washington State Department of Ecology Shorelands and Coastal Zone Management Program and secured through the National Oceanic and Atmospheric Administration. The authors would like to gratefully acknowledge the numerous technical individuals who provided editorial comments on the manual. We would also like to acknowledge James Scott and Douglas Canning of the Washington Department of Ecology whose shared vision made this manual possible. IMPORTANT NOTICE The contents of this publication are for general information and applica- tionsonlyandshould notbeconstrued as asubstituteforsite specificdesign and installation recommendations from professionals expert in geotechnical, coastal and/or biotechnical engineering practices. Accordingly, Washing- ton Department of Ecology and the preparers of this manual make no representation or warranty of any kind, whether expressed or implied, concerning the accuracy, completeness, suitability, or utility of any infor- mation, apparatus, product, vegetation, or technique presented in this publication and assume no liability. Manual Development: Rian Myers, Myers Biodynamics, Inc. Graphic Design: Rachel Ruud Illustrations: Randy Benedict Contract Officer: James Scott Shorelands and Coastal Zone Management Washington Department of Ecology P.O. Box 47600 Olympia, Washington 98504-7600 A This manual is funded in part by the National Oceanic and Atmospheric Administration. The views expressed herein are those of the author and do not necessarily reflect the views of NOAA or any of its sub-agencies. The recommended bibliographic citation for this publication is: Myers, Rian D. 1993. Slope Stabilization and Erosion Control Using Vegetation: A Manual of Practicefor Coastal Property Owners. Shorelands and Coastal Zone Management Program, Washington Department of Ecology. Olympia. Publication 93-30. INTRODUCTION Puget Sound and its associated coastal waters have created a dramatic system of coastal landforms along which have developed the population centers of Western Washington. It is the natural beauty of this coastal system that continues to place residential pressures on coastlines. Construction practices on and around coastal slopes, in combination with the increasing stormwater runoff from developing properties around Puget Sound, contribute to the acceleration of slope erosion and landslide activity along coastal waterways. Too often, well intended erosion control and slope stabiliza- tion programs do not recognize and incorporate vegetation as a legitimate design tool to address these slope processes. Primarily, these oversights are because the use of vegetation alone (soil bioengineering) or together with other slope stability structures (biotechnical engineering) for slope protection is poorly understood. Therefore, the value of vegetation along a slope is either under-estimated or ignored during the important project planning, design, and agency permitting periods. When properly installed and maintained, vegetation can protect slopes by reducing erosion, strengthening soil, and inhibiting landslides which increase general slope stability. The use of vegetation to manage erosion and protect slopes is relatively inexpensive, does not require heavy machinery on the slope, establishes wildlife habitat, and can improve the aesthetic quality of the property. This publication intro- duces general soil bioengineering practices to coastal property owners so that they may realize the practical and financial benefits of using vegetation to control erosion and help stabilize slopes. u How to Use ThisManual USING THIS PUBLICATION Slope Stabilization and Erosion and library systems. For many Control Using Vegetation provides situations, professional design coastal landowners and govern- assistance should be sought. The ment officials with basic informa- information provided in this tion concerning the nature and publication provides the basic use of slope planting techniques information necessary to make to manage soil erosion and general planning decisions and shallow seated land movements. simple installations on slopes. Information is introduced on site The manual is not intended as evaluation, planning, vegetation a substitute for professional systems, materials, planting geotechnical/biotechnical engi- techniques, and general compat- neering design or site-specific ibility of the installation with consultation. traditional property owner use. This publication is a companion AGENC PERMI document to another Washington Readers working for government State Department of Ecology agencies, whose responsibilities publication entitled Vegetation may involve policy creation, Management A Guidef or Puget geologically hazardous areas, and Sound BluffProperty Owners. development/permit application The publications should be used reviews, can use this manual to together to foster a better under- help them determine whether standing and appreciation for help them determine whether standing and appreciation for projects address vegetative systems the r ole and maintenance oas a viable component of slope vegetation along the coastal zone stability maintenance. Permitting of Puget Sound. The following agencies will find this publication sections present an idealized useful in suggesting alternative scheme of how these publications slope maintenance practices to might be used by landowners coastal land owners who are and local government. unfamiliar with the advantages of COASTAL LAND OWNERS slope planting techniques. This Readers who own coastal property publication may also allow agency and who are concerned about soil personnel to better understand the erosion control and shallow land cause and effect relationship of movement prevention can use shoreline development and the this and other Washington continuing maintenance of slope Department of Ecology publica- stability and erosion control. tions to select and employ general slope protection practices which may be applicable to their property. Additionally, readers can access a wealth of information available through public agencies 2 How to Use This Manual U SELECTING A SLOPE MAINTENANCE PROGRAM The coasts of Puget Sound contain a variety of landforms which can vary greatly in their composition r. and historical use. This makes it difficult to cover all of the prob- lems landowners may encounter on their properties in this general A publication. Nevertheless, this B manual will introduce some gen- A) Backshore Berm eral planting techniques that may B) Low Bank be used alone or in combination c) High Bank C with other revegetation programs 0) Bluff/Cliff and existing natural areas to protect coastal slopes. It is important for you, the property owner, to understand Figure 1. Typical Puget Sound Coastal Slope Profiles. your site characteristics, and the erosion and land movement which slope planting techniques processes which may effect it. m Only then can you begin to select ay proble selution I identified problems. Use Table 1 appropriate protection measures as general guide to the appropri- to reduce potential slope erosion ate slope protection measures for and land movements. your site. The sections on the The first step in the development role of vegetation in slope of a slope maintenance program stabilization and erosion control is to gather basic site information and vegetative planting tech- so that you may better identify niques should be reviewed to and select suitable vegetative determine the specific goals and treatments for problem slope limitations of each technique. areas. The checklist on page 1 This publication addresses only will help you identify and the unconsolidated soil portions organize your slope's key features of coastal zone slopes. Bedrock and characteristics. The back- exposures forming the cliffs of ground information needed to groun infomatio needd to the Puget Sound coastal zone are fill out the checklist is generally t P uget in as tal in are contained in the section - Under- no tis cuse in vegeta- standing Your Property. Use the tic ation beca ues a- checklst asa sumary o yourtion installation techniques are checklisteas valsummarion your not applicable to these areas. The general shapes of Puget Sound Once you have generally charac- coastal slopes are illustrated in terized the existing conditions Figure 1. Use Figure 1 to recog- and uses of your slope, the next nize some of the slope shapes that practical step is to determine are familiar to you. When you * How to Use This Manual RATING KEY TO APPLICABILITY AND COMPATIBILITY GRAPHICS SYSTEM Use the key provided to review the slope management techniques introduced later in this publication and determine which alternatives may be suitable for a general ao slope configuration. Excellent APPLICABILITY COMPATIBILITY Good .. FaIr CONTROL SE. FPor Recommended = L GEOTECHNICAL VIEW compatibility of management techniques with existing or future coastline resource uses. The degree of general applicability or compatibility ranges from Not Recommended E) to Excellent 0 and is indicated accordingly in the graphics window. identify your general slope combination of geologic and shape(s), you can begin to under- environmental influences. stand the behavior of your Additionally, the placement of property and start to account for vegetative components into erosion and landslide processes actively failing slope areas such which may act upon your slope. as landslides or earth flows can You then can implement a not be expected to have any number of vegetative slope short-term stabilization benefits protection measures discussed until these movements are later in this manual, arrested and the sources of the The placement and maintenance problem are eliminated. of vegetation on a slope is In cases where the toe of a coastal important to a slope protection slope is exposed to all but the program. However, there are smallest of Puget Sound wave limits to the stabilization role energies, you must recognize that that vegetation can perform vegetation alone will not stop which must be recognized at the long-term erosion. However, it onset of the planning process. may reduce the rate at which a First, vegetation alone can not slope toe is eroded to a potentially control deep seated earth move- acceptable level. ments that may result from a 4 Unnderanding Your Property � UNDERSTANDING YOUR PROPERTY BedrTill Till Areas covered by Drift deposits proglacia Iakes ? 3 !7 ff Lmil of g acialion T85h OUtwash In Figure 3. Glacial Sediments in the Puget Lowlands (from Downing, 1983. Used with permission of the Washington Sea Grant Program). The locations of Puget Sound beaches which have varying slope coastlines were established by the heights and beach widths. The retreat of the last period of glacial deposits which define the glaciation in the Puget Sound general geologic composition of lowlands. Coastlines are continu- coastal slopes are illustrated in ally modified by coastal marine Figure 3. Glacial till is typically processes and by the gradual the most common geologic unit natural rise in the sea level. along Puget Sound coastlines Today, Puget Sound coastlines and contributes heavily to the boast a range of shore forms sands and gravels deposited on which include high bluffs and beaches. The effect of the slow rock cliffs, tidal mud flats, and rise in sea level over time in the sand and gravel beaches. You are Puget Sound area can be seen probably most familiar with the on Figure 4. common Puget Sound bluffs and their associated sand and gravel 5 *Understanding Your Prop ery a ~~~~~~~~Ya r b e f ~ Yore present Yearsbeoepe,, Mines sanO'Oiredsandng~a C ~~~~1000 Years before present 0 - / ~~~Present / ~~~~~-Meaflseatm ALongsthnre transport v Shoreline v Coastline Figure 4. Coastal Bluff Development. Left: Evolution of a gravel and cobble beach. The longshore transport diagrams illustrate the direction of material movement along the beach. Right: Sea level since the last glaciation (from Downing, 1983. Used with permission of the Washington Sea Grant Program). 6 Understanding Your Property U THE ART OF SITE * SLOPE ANGLE AND HEIGHT EVALUATION To determine the angle Selection of a successful vegeta- of your slope, an easy tion program requires that the method is illustrated in landowner spend time under- Figure 5. It is a simple 2. Read slope angle directly standing waihpeat the point where string standing what is happening device which can be itret h otatr ~ .~intersects the portractor. around their slope. This means constructed with a that you need to start keeping a protractor and a mental list of your observations yardstick. The protrac- on the behavior of your slope and tor is fastened securely note deviations from that typical to a yardstick with a 3. Convert slope angle to 1. Hold device behavior. Observations made string and weight horizontal:vertical ratio. parallel to the during periods of heavy precipita- attached as shown. =3:1 slope lace tion, strong winds, freeze-thaw, When the yardstick is 3o = 1.5:1 heavy wave action, or other local held up and aligned 4S� = 1:1 slope movements are extremely with what appears to Figure 5. Slope Angle Determination. important and empowers you to be the average slope of help provide solutions to your the land, the slope angle can be situation. The Ecology publica- read directly from the protractor. don - Vegetation Management: A This slope angle can then be Guide jor Puget Sound Bluff converted to the appropriate Property Owners will also be horizontal/vertical ratio as shown. helpful to you in performing your site evaluation - particularly as i he quickest way for you to relates to existing vegetation. estimate slope height is to visually estimate the height of some Your site observations should be nearby vertical structure on the grouped into the following slope (i.e. tree or bluff face) and general categories: (1) the nature then estimate how many tree of the slope toe, face, and crest - heights would equal the overall noting the existing slope soil and slope height. vegetation conditions; (2) identify known slope problems or poten- SOIL tial hazardous areas; and (3) note Site specific information noting factors you feel contribute to soil types, thicknesses, and slope erosion and stability moisture conditions is very problems. helpful to you when you select The Coastal Pro both plant species and planting The oastlPrperty Owner techniques to be used in your Checklist provided in this manual program. Observing the types of will allow you to start organizing vegetation already living on the your observations. Additional slope is a good due to slope soil information about your slope site conditions. The County Soil should also be added to the Conservation Service, Soil Con- checklist as necessary. The servation Districts and Coopera- following discussion will aid you dye Extension Agents are good in completing your checklist. sources of information and expertise on soil characteristics. 7 *Undmionnding Your Property *MICROCLIMATE *VEGETATION Puget Sound coastal weather is Evaluation of the existing slope strongly influenced by changing vegetation is the key final topographic and atmospheric observation of the slope because conditions. The degree of it should confirm your previous precipitation, available sunlight, observations. Use the presence temperatures, and wind can of vegetation (or lack of it) to change radically from one coast- confirm or modifyr your site line sector to another and evaluation. Vegetation will exist consequently from site to site. in areas which favor its establish- These factors should be recog- ment. As you identifyr specific nized in your site evaluations and types of vegetation on your slope, planning effort which includes you can consult other references both planting and drainage (see recommended reading control elements. section) to determine the range 8 DRAINAGE ~~~~of environmental conditions Wae DRin andontesoeih (i.e. soils type and moisture, most common agent causing lgtpeeecs t. hc h erosion and slope instability and observed plants tolerate. You should be adequately examined should then be able to confirm during the site evaluation and your original observations. If planning effort. Observations of your observations indicate that your slope's drainage conditions these species should not typically should include a careful search grow on your slope, you may for seepage from the slope face. w antoprrmyuevlais Surface water runoff should also again or investigate whether the be investigated and is best site has recently been disturbed observed during periods of heavy or modified. rainfall. Pipe discharges and uncontrolled drainages across poorly vegetated surface soil are typical slope erosion problems. Visual observation of surface water runoff problems indlude watching for thin layers of water flowing across the slope face. Surface water runoff contained in channels usually starts in small rills in the upper soil horizon and4 then through time erodes into gullies which downcut into the slope. Runoff which concentrates into channels creates greater problems for slope stabilization programs because of the magni- tude of erosive forces. Undertanding Your Property U SLOPE EROSION (e.g. soil type, slope length and Loss of your slope's surface soil steepness, ground roughness, type layers by the action of wind, of vegetation covering the slope, water, and ice are what is referred and exposure to winds). A typical to as soil erosion processes. formation of rills and gullies is Rainfall is the major factor along shown schematically on Figure 6 Puget Sound coastlines. However, Wind and frost wedging erosion wind and frost wedging do act can be reduced by allowing plant upon some exposed slopes. The foliage to cover exposed slope rates of erosion can be controlled areas. The foliage creates a by reducing the sources of runoff physical and thermal barrier to the slope and/or by modifyring which protects the surface soils. the nature of the site conditions which influence runoff rates PUGET SOUND COASTAL SLOPE PROCESSES SOIL - MASS MOVEMENT **-., ~ ~ ~ ~ ~ l.,"'I Rotation Fl SOIL - EROSION ROCK - EROSION Rills/ Seepage/ Wave Action Rock Fall Gullies Frost Wedging Figure 6. Typical Puget Sound Coastal Slope Processes. 9 * Undentanding YourPropemy SOIL MASS MOVEMENT SPECIAL NEEDS AREAS When a downward movement of Should you recognize or suspect relatively intact masses of slope that your property or adjacent material occurs, it is called a mass properties contain any of the movement (instead of erosion). following landforms or slope Mass movements can take the conditions, you should contact form of landslides, earth/debris the appropriate government flows and slumps, and rock falls/ agencies to acquire assistance in earth topples. Figure 6illustrates these technical areas. You may these basic soil movement also want to have consultations processes. These events have been with technical experts in these lumped together by planning areas: agencies and the pubic and are 1) Historical or Recent Land generally called landslides. For slides/Areas designated as simplicity, mass movements will Geologically Hazardous be referred to as landslides in this Geologically Hazardous Areas [A, F] manual. Recognition of active or historical landslide areas is 2) Unstable Slope Fills [A, F] important. Should you believe 3) Planting Vegetation on landsliding has occured or that Slopes Steeper than 1.5 there is the potential for land- Horizontal to 1 Vertical sliding on or adjacent to (33 degrees) [F] your property, it would Iybeu prudent to secure the 4) Coastal Marine Erosion assistance of a profes- [A, B, D, sional geotechnical 5) Wetlands [A, B, C, HI engineer prior to the site 6) Habitat for Endangered, planning process. It is Threatened, Rare Animal important to reiterate Species (e.g. bald eagle or that vegetation can be osprey nests/alternate nests/ used to control shallow perch trees) [E] seated landsliding which is common along coastal slopes. However, it does A - County Planning Office Dept. not address deep seated of Community Development landslide events. Vegeta- B - Washington Dept. of Ecology tion can also be a C - Army Corps of Engineers valuable component of biotechnical engineering D -Washington Dept. of Fisheries E- Washington Dept. of Wildlife design solutions to these F - Geotechnical/Biotechnical Initial shallow-seated landsliding. deep seated potential Professional landslide conditions. Consult a geotechnical/ G - Coastal Engineering biotechnical engineer for design Professional input on stabilization alternatives. H -Weand Professional 10 UndeMnding Your Prope � COASTAL PROPERTY OWNER CHECKLIST WHAT LANDFORM(S) ARE LOCATED * GROUNDWATER ON MY PROPERTY? (check glossary definitions) Is there evidence of groundwater in the slope? H Low Bluff (for this publication, < 10 feet) 1] Seepage or damp surfaces seen on the slope face a High Bluff (for this publication, > 10 feet) ] Active or historical landslides H Low Cliff (not generally applicable to this publication) What are your contributions to groundwater H High Cliff (not generally applicable to this publication) in the slope? H Low Bank (for this publication, < 10 feet) H Water infiltration areas (roof and curtain drains) [1 High Bank (for this publication, > 10 feet) H Septic system El Beach with Backshore Berms of H Irrigation systems Sand/Gravel/Cobbles (marine/estuarine) H Wetlands (check with the County Planning Office) VEGETATION - Is there vegetation on or adjacent to the slope? PROPERTY DESCRIPTION AND If yes, where is it and what are the species. OBSERVATIONS What is the elevation of the house above the high tide water surface? If no, is there evidence of past vegetation? What is the average angle of the slope face? What happened to it and what were the species? Do waves reach the toe of the slope? (check other properties) What are the diameters of beach sediments around the slope toe? (e.g. sand/gravel/cobbles) Has the slope face been recontoured or filled? _ Is there evidence of vegetation movement What is soil material type(s) of the slope? down the slope? FACTORS INFLUENCING SLOPE EROSION � MARINE WATERS AND STABILITY _ Is there a noticeable beach width above the high * SURFACE WATER RUNOFF, WIND water line? AND FROST WEDGING - Are wave energies eroding the toe of the slope? Can the effects of surface water runoff be Are there coastal erosion control visually identified? structures along the beach of your or H Rainfall impact erosion neighboring properties? (e.g. bulkheads) H Soil rills and gullies If yes, are these structures causing erosion? H Winter freeze-thaw evidence Is your property flood prone? H Wind erosion * SLOPE USE [1 Pipe discharge erosion * SLOPE USE How do you use the slope? What does your property contribute to runoff? ] Access to the beach (raillroadstairs/other) [ Significant upland impervious surface [ Vegetation removal for view maintenance H1 Drainage pipe discharge onto slope a Horticultural/garden areas [ Sprinkling/irrigation/hot tub releases H Waste/debris fills H Other H Natural greenbelt induding slope crest Understanding Your Property GENERAL APPLICABILITY ADVANTAGES/ SEEDING CONTAINER LIVE CONTOUR BRUSH DISADVANTAGES (MIXED SPECIES) BARE ROOT STAKING WATTLING LAYERING Rainfall Erosion: Foliage Intercepts railndrops � Runoff Erosion Control: Roots bind surface soil particles 0 Wind Erosion Control: Plants reduce wind exposure * Frost Action Erosion Control: Roots restrain soil movement � Slope Stabilizatlon: Reintorce soil & resists shallow seated landsliding Slope Stabilization: Plants help dewater slope Runoff Erosion Control: Plants * filter soil particles from runoff Immediate Erosion Control/Slope Stabilization Slope Stabilization: Resistance to deep seated landsilding Low Initial malntenance Low long-term maintenance * Low Impact construction Plants prevent slope undercutting by waves Relative low-cost construction Plants combine with other structuralfeatures Aesthetic/wildllfe benefits Table 1. General Applicability of Slope Protection Plant Techniques. The Role ofVegewtaon THE ROLE OF VEGETATION To comprehend the benefits and mechanisms are those processes contributions of how vegetation of water use and movement in the influences soil erosion and slope slope when living plant materials stability, you may think of its role exist in the soil. The general roles as either hydrological or mechani- that vegetation plays in slope cal in nature. The mechanical maintenance and reinforcement contributions arise from the are summarized in Table 2. The physical interactions of either the net effect of vegetation is usually foliage or root system of the plant beneficial to slope stability. with the slope. The hydrological VEGETATION AND SLOPE STABILITY Legend: (+) Beneficial to stability (-) Adverse to stability MECHANISM INFLUENCE Hydrological Mechanisms Foliage intercepts rainfall, causing absorptive and evaporative losses that reduce rainfall available for infiltration. (+) Roots and stems increase the roughness of the ground surface and the permeability of the soil, leading to increased infiltration capacity. - Roots extract moisture from the soil which is lost to the atmosphere via transpiration, leading to lower pore-water pressure. (+) Depletion of soil moisture may accentuate desiccation cracking in the soil resulting in higher infiltration capacity (uncommon around Puget Sound). - Mechanical Mechanisms Roots reinforce the soil, increasing soil shear strength. (+) Tres roots may anchor into firm strata, providing support to the upslope soil mainly through buttressing and arching.(+ Weight of trees surcharges the slope, increasing normal and downhill force components.' Vegetation exposed to the wind which transmits forces into the slope. (Degree of adverse effect Is dependent upon exposure and health of vegetation. Typically a minor consider- (-) atlon for Puget Sound Inland Waterways.) Roots bind soil particles at the ground surface, reducing their susceptibility to erosion. ( Table 2. Vegetation and Slope Stability (Source: Modified from Greenway, 1987). * Tree weight in some situations is benefical to slope stability. Trees should not be arbitrarily cut to "unweight" slopes. 13 * The Roe of Vegeation AN OUNCE OF PREVENTION No amount of slope disturbance followed by replanting should replace rational site planning when it comes to avoiding slope disturbances. Should you have the option, maintain all the native ' .r z vegetation you can and potentially 9<'* . �E~F �~,~cS~- accept the natural retreat of the ���I~~~~~~~t~~~ 4eslope crest. Accordingly, you .... W _ B y itshould plan the location of your residence carefully. Maintaining a greenbelt along slope crests is good practice. Do not assume cutting trees to "unweight" your slope is benefical to slope stability - often it is not. Also, remember as a general rule, do not introduce water onto or into your slope. PLANNING AND INSTALLATION GOALS Since you have now spent time failure planes observing your slope features and Xfailure plans have begun to understand what is happening around your slope, you Figure 7. Root Reinforcement of a Slope. should be able to establish some basic planning and planting goals The protection of the slope which address the problems you against shallow seated landsliding have noted. You should divide is a key benefit of a revegetation the slope into different areas if or existing vegetation mainte- this makes sense based on your nance program. The function that observations. This may allow you mixed vegetation provides by to accomplish different goals in increasing the apparent cohesion those areas. Now is the time for of the surface soil structure of a you to consider any drainage slope is illustrated in Figure 7. improvements to your slope (see The different types of root For More Information). These systems that plants provide can improvements should be compat- strengthen potential shallow- ible with your planting program. seated failure planes on your slope by both fiber reinforcement of the Typically, the slope can be near surface soil and binding soil separated into at least three areas: structure together into a larger the crest, face, and toe. Planting unit through tap or lateral root objectives are usually slightly networks, different in these zones. At the 14 The Role ofVegetation � slope toe, you may be concerned PLANT SPECIES with providing plants which resist SELECTION down-slope soil movements, are An effective method to properly tolerant to wet soils or occasional select plant species involves saltwater spray, and can handle coordinating your site conditions changes to coastal marine deposi- and planting objectives with the tion or erosion processes. On the recommendations of local nursery slope face you may decide to publications and qualified native select plants and planting tech- plant professionals. Plant material niques which tolerate a range of can be both purchased or gathered soil and light conditions, can depending upon your own situa- handle some soil movements, can tion or plant availabilities. Your resist shallow seated landsliding, local native plant nurseries and manage surface runoff, and are state agencies involved in revegeta- compatible with other slope uses. tion programs should be able to Along the slope crest you may assist you in locating appropriate want to revegetate a buffer area planting materials. The Hortus to strenghten soils and reduce Northwest Journal to native plant erosion. Pulling these objectives sources is a valuable resource or together is an important mile- you can contact DNR and SCS stone in your planting effort. for potential plant sources. You Obtain assistance if you find the should use Table 3 in this manual planning process is complicated as a starting point for your plant for your situation. selections. There are still many other species from which to SLOPE PREPARATION choose. It is generally not desirable to select ivy, Scot's broom or other The first task of your planting ornamental exotic plants. Select- program will be to prepare the ing native plants will usually planting area just prior to plant- ng nauve plants wi usually ing, avoiding and protecting increase the success of the planting against wet weather conditions. program and reduce your long- This task requires that soil areas term maintenance requirements. be prepared keeping disturbance Seeding and planting of vegetation to a minimum according to the should be done carefully. In many requirements of each planting cases, grass and legume seed technique. Once the slope has mixtures will have to be seeded been prepared, you should mark by hand scattering along the face the positions or alignments of of the slope. The seed should then your planned plantings. Excava- be covered with an appropriate tions should be performed mulch material. For large scale concurrently with plant installa- planting on hard-to-reach areas, tions. This will allow installations machines called hydroseeders to proceed effectively and reduce which spray mixtures of seed, your total time on the slope. water, and mulch materials are recommended. These applications are commonly used by the Soil Continued on page 24... * The Role of Vegetation PLANT SELECTION GUIDE* WATER1 LIGHT2 NAME FORM & HABIT MATURE SIZE REQUIREMENTS REQUIREMENTS Red Alder Deciduous tree; seeds Height: 80'+ Moist Full Sun (Alnus rubra) prolifically on bare soil Spread: 40' conditions, , No data Pacific Willow Deciduous multi-stemmed Height: 40'+ Wet conditions, Full Sun (Salix lasiandra) tree; does not spread Spread: 25' Usage high? Scouler Willow Deciduous tree or shrub; Height: 30' Dry-Moist Full Sun (Salix scouleriana) does not spread Spread: 15' conditions, Usage high? Sitka Willow Deciduous tree or shrub; Height: 30' Moist Full Sun (Salix sitchensis) does not spread Spread: 25' conditions, Usage high? Douglas Fir Coniferous tree; Height: 200'+ Dry-Moist Full Sun (Pseudotsuga menziesii) does not spread Spread: 50' conditions, Usage moderate Table 3. Plant Selection Guide (Partial listing of appropriate native plants for erosion control and slope stabilization). 16 TheRok ofVegeration � SOIL ROOTING3 RECOMMENDED PLANTING4 REQUIREMENTS CHARACTERISTICS SPACING CONDITION COMMENTS5 Any soil Fibrous, 10'+ Bareroot seedlings Fast grower in poor mineral Moderately deep up to 3' tall; larger soils; typical 40-50 year plants in containers lifespan; large limbs become brittle; provides food for birds Any soil - Fibrous, 6'+ for rooted plants; Rooted plants to Fast grower in saturated or tolerates shallow Moderately deep 2' for whips or 10' tall in containers; shallowly flooded areas; 25 flooding during and widespread cuttings cuttings 18"-24"; year lifespan - large limbs the growing whips 4' become brittle, tend to break season off; stumps produce long, fast-growing whips; easily rooted Any soil Fibrous, 6' for rooted plants; Rooted plants to Of the willows listed Moderately deep 2' for whips or 10' tall in containers; here, this species tolerates and widespread cuttings cuttings 18"-24"; the driest conditions whips 4'; whips not recommended Any soil Fibrous, 6' for rooted plants; Rooted plants to Fast grower in moist to Moderately deep 2' for whips or 10' tall in containers; saturated soils; widely used and widespread cuttings cuttings 18"-24"; for streambank stabilization whips 4'; whips not recommended Any soil Tap - Modified 10'+ 12"-18" bareroot Generally not considered Tap, Shallow to seedlings; larger a primary species for slope deep and plants in containers face stabilization; high root widespread strength but typical shallow rooting characteristics in thin coastal soils; can be planted in stands in slope crest greenbelts; good eagle and osprey perch and nest trees; potential for wind throw in thin or disturbed soils 17 * The Role of Vegetation PLANT SELECTION GUIDE (CONT.) WATER' LIGHT2 NAME FORM & HABIT MATURE SIZE REQUIREMENTS REQUIREMENTS Northern Black Deciduous; Height: 100'+ Moist Full Sun Cottonwood does not spread Spread: 40' conditions, (Populus trichocarpa) Usage high Red-Osier Dogwood Deciduous shrub; Height: 20' Moist-Wet, Full Sun (Cornus stolonifera does not spread Spread: 20' No data Sun/Shade or Cornus sericea) Black Twinberry Deciduous shrub; Height: 10' Moist, Full Sun (Lonicera involucrata) does not spread Spread: 8' No data Ninebark Deciduous shrub; Height: 15' Moist, Full Sun (Physocarpus capitatus) does not spread Spread: 10' No data Sun/Shade Cascara Deciduous tree/shrub; Height: 25' Moist, Full Sun (Rhamnuspurshiana) does not spread Spread: 15' No data Salmonberry Deciduous shrub; Height: 8' Moist, Sun/Shade (Rubus spectabilis) spreads by underground Spread: 6' No data Full Shade runners to form thickets Hooker Willow Deciduous shrub; Height: 20' Moist-Wet, Full Sun (Salix hookeriana) does not spread Spread: 15' No data Red Elderberry Deciduous shrub; Height: 15' Moist, Full Sun (Sambucus racemosa) does not spread Spread: 10' No data Sun/Shade Full Shade 18 The Role of Vegetation � SOIL ROOTING3 RECOMMENDED PLANTING4 REQUIREMENTS CHARACTERISTICS SPACING CONDITION COMMENTS' Any soil - Fibrous, 6'+ for rooted plants; Rooted plants to Fast grower in moist to tolerates shallow Shallow to deep 2' for whips or 10' tall in containers; saturated soils; also widely flooding during and widespread, cuttings cuttings 18"-24"; used for streambank the growing extensive whips 4' tall stabilization; potential for season wind throw Any soil - Fibrous, 3'+ for rooted plants; Rooted plants to Attractive shrub that tolerates shallow Shallow 2' for cuttings 6' tall in containers; produces bright red stems flooding during bareroot & cuttings the growing 18"-24" tall season Any soil Fibrous, 4'+ Rooted plants to Produces yellow twin flowers Shallow 6' tall in containers; and black twin-berries; some bareroot 18"-24" tall success reported from cuttings Any soil Fibrous, 4'+ Rooted plants to Produces masses of tiny Shallow 6' tall in containers; white flowers which change bareroot 18"-24" tall to reddish seed clumps Any soil Tap, 4'+ Rooted plants to Shiny, black berries are Moderately deep 6' tall in containers; favored by Cedar Waxwings bareroot 18"-24" tall Any soil Fibrous, 4'+ Rooted plants to Spreads quickly once Shallow 4' tall in containers; established; berries provide bareroot 6"-8" tall; food for a variety of cuttings 18"-24" songbirds Any soil Fibrous, 3'+ for rooted plants; Rooted plants to 6' A horticultural variety, Moderately deep 2' for cuttings tall in containers; "Clatsop," has been developed bareroot & cuttings by the Soil Conservation 18"-24" tall; whips Service for its vigor, disease 4'; whips not resistance & attractive foliage; recommended salt spray tolerant Any soil Fibrous, 4'+ Rooted plants to Produces red, non-edible Shallow 6' tall in containers; berries; some success reported bareroot 18"-24" tall from woody cuttings 19 * The Role of Vegetation PLANT SELECTION GUIDE (CONT.) WATER' LIGHT2 NAME FORM & HABIT MATURE SIZE REQUIREMENTS REQUIREMENTS Douglas' Spiraea Shrub; Height: 8' Moist-Wet Full Sun (Spiraea douglasii) spreads by seed & Spread: 6" conditions, underground runners No data to form seed Snowberry Deciduous shrub; Height: 4' Dry-Moist Full Sun (Symphoricarpos albus) spreads by underground Spread: 3' conditions, Sun/Shade runners to form thickets No data Full Shade Salal Evergreen shrub; Height: 3' Dry-Moist Sun/Shade (Gaultheria shallon) spreads by underground Spread: 3' conditions, Full Shade runners to form thicket No data Ocean Spray Deciduous shrub; Height: 10'+ Dry-Moist Full Sun (Holodiscus discolor) does not always spread Spread: 6' conditions, Sun/Shade aggressively No data Vine Maple Deciduous shrub; Height: 15'+ Moist Sun/Shade (Acer circinatum) does not always spread Spread: 10' conditions, Full Shade aggressively No data Kinnickinick Low-growing shrub; Height 8" Dry conditions, Full Sun (Arctostaphylos Uva-ursi) spreads to form a dense, Spread: 6" No data evergreen carpet Thimbleberry Deciduous shrub; Height: 4' Moist Full Sun (Rubus parviflorus) spreads by underground Spread: 4' conditions, Sun/Shade runners to form thickets No data Indian Plum Deciduous shrub; Height: 10' Moist Full Sun (Oemleria cerasiformis) spreads by underground Spread: 6' conditions, Sun/Shade stems to form open stands No data Full Shade Evergreen Huckleberry Evergreen shrub; Height: 6' Dry-Moist Sun/Shade (Vaccinium ovatum) does not spread Spread: 3' conditions, Full Shade No data 20 TheRoleofVegeration � SOIL ROOTING3 RECOMMENDED PLANTING4 REQUIREMENTS CHARACTERISTICS SPACING CONDITION COMMENTSS Any soil - tolerates Fibrous, 3' for rooted plants; Rooted plants to Spreads quickly & shallow flooding Shallow 2' for cuttings 6' tall in containers; aggressively in most sites during the bareroot & cuttings growing season 18"-24" tall Any soil - tolerates Fibrous, 2'+ Rooted plants to Tolerates high winds and shallow flooding Shallow 24" tall; bareroot often grows on vegetated during the 6"-18" tall slopes overlooking salt water growing season Any soil - tolerates Fibrous, 2'+ Rooted plants 4" to Widely available; difficult to shallow flooding Shallow 12" tall establish; slow growing; during the tolerates salt spray growing season Any soil - tolerates Fibrous, 4'+ Rooted plants to Produces attractive sprays of shallow flooding Moderate 2' tall in containers; creamy-white flowers; will during the bareroot 6"-12" tall root spread growing season Any soil - tolerates Fibrous, 8'+ Rooted plants to 4' Large specimens widely shallow flooding Moderate tall in containers; available; spreads by root during the balled & burlapped and seed growing season plants to 10' tall Any slightly Fibrous, 2' Rooted plants in Widely available evergreen acid soil Shallow containers ground cover; tolerates salt spray Any soil Fibrous, 3' Rooted plants in May be difficult to find in Shallow containers some native plant nurseries Any soil Fibrous w/horizontal, 4'+ Rooted plants to 4' Male and female flowers are underground runners, in containers; on separate plants; only Shallow bareroot 6'-8' tall female flowers produce the attractive "plums" Slightly acid Fibrous, 3'+ Rooted plants to Attractive, but slow growing; Shallow 2' tall in containers difficult to establish; tolerates salt spray 21 * The Role of Vegetation PLANT SELECTION GUIDE (CONT.) WATER' LIGHT2 NAME FORM & HABIT MATURE SIZE REQUIREMENTS REQUIREMENTS Nootka Rose Deciduous shrub; Height: 6' Moist Full Sun (Rosa nutkana) spreads by underground Spread: 3' conditions, runners to form thickets No data Red Currant Deciduous shrub; Height: 8' Dry-Moist Full Sun (Ribes sanquineum) does not spread Spread: 6' conditions, Sun/Shade No data Wax Myrtle Evergreen shrub; Height: 15' Dry-moist Full Sun (Myrica californica) does not spread Spread: 8' conditions, Sun/Shade No data Native Plant Annual and perennial grass Height: 1'-2' Dry-Wet Species/mix Seed Mixes and forb mixes available Spread: varied conditions, dependent Medium - high *Table 3 based on information from: Myers Biodynamics staff experience; Binns, 1980; Stevens & Vanbianchi, 1993; Kruckeberg, 1982. FOOTNOTES 'WATER REQUIREMENTS 2LIGHT REQUIREMENTS 3ROOTING CHARACTERISTICS Dry - Once established, tolerates dry Full Sun - Requires sun throughout Fibrous - Lacks a central root; root soil conditions during the the day mass composed of fibrous growing season Sun/Shade - Requires shade for about lateral roots Moist - Requires moist soil throughout 1/2 the day Tap - With a stout, central main the growing season Full Shade - Requires shade root Wet - Tolerates saturated soil throughout the day Shallow, Moderate, Deep refers to relative year-round rooting depth (influenced by soil and Usage - Relative water uptake by plant groundwater conditions) [e.g., high or no data] 22 TheRoleofVegetation U SOIL ROOTINGs RECOMMENDED PLANTING4 REQUIREMENTS CHARACTERISTICS SPACING CONDITION COMMENTS, Any soil, Fibrous, 3' Rooted plants to Thickets of spring stems prefers rich soils Shallow 2' tall in containers; create a formidable barrier; (not extensive) bareroot to 18" tall; produces attractive, pink cuttings 12"-18" flowers followed by large, red hips; tolerates salt spray Any soil Fibrous, 6'+ Rooted plants to 4' One of our finest ornamental Shallow tall in containers; natives; produces clusters of (not extensive) bareroot to 18" tall white to red flowers Slightly acid, Fibrous, 10'+ Rooted plants to 10' Tolerates salt spray; high with organic Moderate wildlife usage matter Species/mix Fibrous, Apply as Seed Woody plant seeds also dependent Shallow recommended available (success typically low); very slow to establish; avoid exotic commercial mixes; seed mixes typically used in conjunction with other vegetation plantings; typically short-term erosion control technique 4PLANTING CONDITION SCOMMENTS Sizes given are those that are generally Growth rate; ornamental & wildlife value; found in nurseries; other sizes may also wind/salt spray tolerance; maintenance; be available average life span 23 * The Role of Vegetation Continued from page 15. Conservation Service and other to slope plantings. Mulch protects agencies. against rain and wind while seeds Where broadcast seedngs are are germinating and plants pro- made, time of seeding for grasses pogating. It also reduces loss of and legumes is very important. soil moisture during extended dry Seeding should be avoided in periods. Because of the severe July, August, and September nature of most coastal slope areas, wherever possible as extensive a mulch cover addition is neces- drought periods can occur. sary if vegetation is to be estab- Legumne-based mixtures should be lished from seed. seeded as early as possible but no A wide variety of mulches can be later than mid-June. Grass-based used. These range from scattered mixtures can be seeded before and straw to sprayed fiber. More after July through September. It common materials and methods should be realized that healthy, may include: hay or straw (1V/2- herbaceous ground covers may 2 tons/acre), jute netting, plastic require an initial fertilizer applica- netting (not recommended), tion to achieve higher successes. manure or compost (not recoin- Select native species and use a mended), wood fiber, or fiber slow-release formulation (do not matting. Check with your local over fertilize). Soil Conservation Service office, Woody plant materials should nursery people, or garden and come from plant stock which is farm centers to get more informa- dormant and should be planted tion on local availability or immediately. Materials can be suitability for your situation. installed up to 48 hours after One other short-term anchoring cutting if they are kept cool and method which has helped to moist by covering cuttings with stabilize slopes during vegetation moist mulch. establishment in some areas sus- Willow, cottonwood, and dog- ceptible to shallow soil move- wood can be planted as cuttings ments involves "naiing down" a or saplings and are particularly slope face with 5 foot metal fence good for seep zones and other wet posts. The posts are driven areas of slope faces. However, perpendicularly into the slope face avoid planting willows near artifi- in a grid pattern with 10- 15 feet cial drains because their roots seek spacings between them. The posts water and may eventually dog or are cross-connected with heavy disrpt he rais. henplanting wire or cable which has the effect other shrubs and trees on slope o yn h niesoefc areas, consult qualified nursery together from top to bottom and people to determine appropriate side to side. The posts should be species for your conditions. driven in almost all the way into the ground, wired, and then the MULCHING slope should be planted and Mulching of seeded or planted mulched. areas is of particular importance 24 Planting Program U PLANTING PROGRAM PLANTING ZONES edge is currently cleared, a strip Without using more advanced may be left undisturbed and a stabilization techniques, the revegetation program imple- maximum slope to be considered mented. for vegetative stabilization is 0SOEFC (i.5Hi. ThoriotloIvearticany Vegetation should be established god plant IV) Ther foremany on patchy and barren slope faces good pl~~ants minthformo or terraces to reduce erosion. grasses, vines, shrubs, admnrPlanting practicality depends trees that can be used for slopegralontecrcerfth stabilization projects. Plant s loeatlnd patiecularacte of the selection is dependent upon the slope, angl.d slperiual of t.he I goals of your erosion control slopdeagrees) sholdope ofns.5HiV program and site conditions. the dividing linel betcosierend Typically, effective programs manageablen slope bewend aslp incorporate structural diversity manaeabep enough tand veeaslope in plant selections (trees/shrubs stepeouldhb dificut orgtaimossbl with goun spcovers).ns to establish without employing mix o f species. ~~other reinforcement techniques. * SLOPE CREST If room exists at the top of a The vegetation along the edge slope, low slopes can be graded of the top of the slope serves as back to a gentler configuration. a protective buffer for the slope 3H:1IV or flatter slopes are ideal face. If possible, you should bcueteesoe a epe maintain or reestablish a greenbelt paedndpanted wthwesesloed a epe whichwouldprovie a bffervehicles. However, in most coastal between the slope face and resi- areas, slopes are too steep or too dential structures. This is particu- high for mechanical planting larly important in areas where techniques. Slope regrading may slopes are too steep and too high be neither economically feasible for economically feasible stabiliza- nor technically desirable for the tion methods. For example, some idvda rpryonr coastal high bluffs in residential idvda rpryonr arma along Seattle, Tacoma, Various species and mixtures of Edmonds, and Port Townsend species can be planted on slope waterways may be too severe to faces and expected to succeed in attempt stabilization. In cases like this rather severe environment. these, you may choose to main- These include seed mixtures of tain a strip of dense natural grasses and legumes and a range vegetation along the bluff edge. of shrubs and minor trees. The roots of the vegetation can Large trees should be used on the strengthen a bluffs resistance to face of slopes sparingly and with slumping or sliding. If the bluff caution. Should these trees 25 * P4neing Pogam collapse because of undermining dynamic changes in the coastal of the root system by erosion or shore system. Vegetation at the by windthrow, large volumes of slope toe can sometimes help earth can be disturbed by the reduce marine erosion to tree roots when they pull from the manageable levels. slope. The resulting large, bare areas are opened to further PATN IE arerosinwhc mare oenedanger Late fall and early spring are erosiontwhich mayendandeget , usually the best times for slope Newadjacentre should and vion . installations. During these periods generally be established on the pat r eidrat h New maor tres shoud notplants are semi-dormant, the face of coastal slopes. Existhe slope soils are easiest to work, and faejof coastre slouldsbe Existi g vegetative cover is at a minimum. mjoritoredeforsins shofuldbercly If slope moisture is an installation ting and toppling. If the trees polm aluulypoie h monitred or sins o undecut-problem, fall usually provides the become unstable, they should be slope cut before they fall. Root systems should be left intact to bind the MAINTENANCE soil for a short period of time Use the Ecology publication - while new live, well-rooted vege- Vegetation Management: A Guide tation establishes itself. Establish- for Puget Sound BluffProperty ing new vegetation prior to felling Owners to plan for a range a tree would be advantageous to maintenance considerations in the slope protection program. your erosion control program. * SLOPE TOE Most programs do not have In those situations where the significant long-term maintenance bottom of your slope is suscep- requirements. tible to frequent or periodic wave attack, vegetation alone will not be adequate as an erosion control tool. In such cases a form of structural toe protection may also be required. If the toe is not subject to coastal marine erosive forces, trees and woody shrubs can be useful in resisting upland landsliding and tolerating the 26 Planting Techniquesfl PLANTING TECHNIQUES When you review the following It is always advisable to consult planting techniques remember additional resources prior to that the descriptions are meant to undertaking your site work. introduce general slope planting Additionally, these and other techniques to coastal landowners. techniques may be combined with As a result, a technique may not structural/mechanical slope be adequately discussed to the stabilization designs (biotechnical level of detail required for your engineering) which are also unique property characteristics. beyond the scope of this manual. Six GENERAL PLANTING TECHNIQUES SEEDING LIVE STAKING (MIXED SPECIES) CONTAINER OR BARE ROOT CONTOUR BRUSH WATTLING LAYERING AVOIDANCE/RETREAT OR BiOTECHNICAL SOLUTIONS 27 * Planting Techniques SEEDING * DESCRIPTION AND * PLANNING FUNCTIONS CONSIDERATIONS Seeding involves the application Drilling soil holes into the slope of grass, forb, and woody plant area can reduce the seed quantities seed mixes to slope areas. Seeds required. Practically, this method may be applied to slopes by is best used on mild slopes, in broadcasting seed mixes onto the smaller prescription areas, and for slope by hand or by placing seed woody plant seed stock which is into small holes placed into the more expensive that grass seed slope. Hydroseeding is also mixes. Typically, a 3-inch another option used for hard to diameter by a 4-inch deep hole is access locations. Seeding creates a good size for the planting hole. a shallow fibrous rooting zone in Make sure surrounding soil is the upper foot or so of the surface loosened around the hole so that profile which binds near-surface future root systems can develop. soils and protect soil surfaces Drop a slow release fertilizer from surface water runoff, wind, capsule to the bottom of the hole and freeze-thaw erosive forces. and cover with about 31/2 inches Seeding is usually applied in of soil. Then place about 20 seeds combination with other planting into the hole and cover the seed techniques to address most as directed by the seed supplier. erosion control issues. Broadcast seeding is the most common application method employed in projects. Seeds are scattered uniformly by hand onto the slope. If the application area soil has been roughened slightly, seed germination will be more successful. It is also impor- tant to make sure precipitation does not wash seeds down the slope. Mulch seed immediately to keep seeds from being blown and washed away, or eaten by wildlife, and to keep the surface soils moist. Fertilize areas as required by mix directions. Hydroseeding is another applica- tion method that uses seed mixed Figure 8. Seeding (grasses shown here) with erosion control mulch. with water, fertilizer, and some- times mulches to spray apply the mixture onto expansive or hard to reach slope areas. 28 Planting Techniques * LIMITATIONS APPLICABILITY COMPATIBILITY Good for mild erosion problems or in combination with other L. X* rooting systems of grasses and techniques~~~~~~~~~~~~~~~~~~~~~~~~. Th shallow....-.. .'..v forbs do not significantly increase BLUFF srzK AEUDAWS the shear strength of the surface LUFF .CRU soil profile and limit landsliding. Woody plants seeded into slopes [ _ need five to ten years to begin to A \ develop extensive rooting net- AR, TEI IE works. Woody plant roots do a jLOW MARIN ES better job providing root rein- forcement of the surface soils but are le s s effective th an native grass mixes at reducing erosion at the soil surface. Seed germination for all species require that soils to be kept moist. Seeding should include mulching to achieve adequate erosion control. Seed nixes using combinations of wild strawberry, wild ginger, oxalis,=:> ,2 sword fern and bracken fern have -: been reported to be more success- ful than grass-based mixes for some sites. a ADVANTAGES AND DISADVANTAGES Advantages: Seeding can be quickly applied to slopes, materials are inexpensive, and technique is compatible with many slope situations. Disadvantage: Seeding does not readily self-repair eroding slope Slope seeding with long straw mulch and juts matting. areas. Seeding is not adequate to be used alone for highly eroded areas or for shallow seated landslide stabilization. 29 P Planting Techniques CONTAINER OR BARE ROOT PLANTING * PLANNING Space as recommended. CONSIDERATIONS Spacin and sonpeantl. Use rooted pant materials when you need a fast action program for specific slope areas. This allows you to avoid the critical germination period for seeding programs or root development period for cuttings. Place material into positions on the slope during the fall or spring. When placing material in holes make sure you loosen the root ball or in the case of base root plants, make sure roots are not bound or bent upwards in the holes. Install Figure 9. Container/bare root planting (single or bunch planting). according to the specific require- ments of each plant or plant a DESCRIPTION AND grouping. It is common practice FUNCTION to prune the plants after installa- Container and bare root planting tion which will allow a greater involves placing single or bunches percentage of available plant of rooted plants into excavated energy to be used for developing holes on the slope. This method healthy rooting systems. can be used for woody plants or Because the immediate slope for non-woody plants which will stabilization expectations of using eventually spread into a uniform rooted materials are often too root coverage. Container and high, it is a good idea to use plant bare root plant material can be groupings or bunch plantings. purchased directly from nurseries This method allows you to or gathered from other sites and place plants which have slightly propagated by the landowner. different rooting and foliage Transplants from nearby areas characteristics which may (away from the slope) can also be strengthen the overall reinforce- used. Rooted plant materials offer ment program. Bunch planting the property owner the most also allows the plants best suited immediate solution to developing for the slope environment to an erosion control and slope eventually dominate the plant stabilization program that can secure a slope. 30 Planting Techniques community. Finally, in cases APPLICABILITY COMPATIBILITY where one species used is not .: 1 L i healthy or has been recently -.i plninhuereous speciesus dino {_.. [........_ _. . . ~....... F4ii...._ stressed, you have provided some :\ safety factor in your planning by . planting numerous species. 01 lei BLI Mulching around the plants is L . L recommended as a minimum. A i J ] * LIMITATIONS [ h i Container planting does not " '..'t s, address gully erosion control - T i~~l Lo.~..~ ~~~ CIE,.''ElOICHNIC'L WIIOIF Vt%'~, IEW g'~"' problems. Landowner must identify available plant sources ahead of time to have the quantity, species, and rooted condition necessary for the progra m. Container plants can be relatively expensive, - ADVANTAGES AND DISADVANTAGES Advantages: Well developed rooted plant materials installed for faster slope stabilization, typically higher plant success, minimal slope disturbance using planting holes. Disadvantages: Relative cost of materials, hard to install into some mulching systems, initial watering requirements. Container plants (Red-osier dogwood and Salal shown). 31 * Planting Techniques LIVE STAKING * DESCRIPTION AND * PLANTING FUNCTION CONSIDERATIONS Live stakes are sections of woody Woody plants which have good plants that are cut into lengths rooting characteristics make good and placed into the slope. The staking plant stock. Stakes are plant material is installed during generally 2 to 3 feet long and 1/2 the fall or spring when the to 1112 inches in diameter and can original plant (and consequently be collected from sections or cuttings from it) are dormant. branches of plants from donor The plant materials used for sites. Stakes should be flat cut on stakes are usually hardy species the top and diagonal cut on the which root easily and eventually bottom so they will be installed grow into mature woody shrubs correctly. that reinforce the soil structure of Stakin can be used alone and the slope. (See Table 3 for some w h g cutting species alternatives.) ohrpatn ehius Typically, if stakes are used alone on the slope they will be spaced across the slope as recommended for each species and slope situation. Each row should have Space as recommended. Spacin dependedl the same spacing but should Spacing dependent on plant selection and slope angle. alternate stake positions so that if you look down or up slope no two consecutive rows should have stakes directly above or below one another (a diamond pattern). Stake rooting will be most effective if the stake is not posi- tioned vertically but positioned at an angle off horizontal so that rooting can occur more effectively along the entire below ground length as shown on Figure 9. Length =2-3 ft.Stakes are typically be placed into predrilled holes using rebar sections which are slightly smaller than the diameter of the stakes. Gently tap stakes into holes with soft mallets or other instruments. Remove the top section of the stakes that get damaged during installation. It is good practice to 32 Plandng Techniquesfl mulch the staked area after the APPLICABILITY COMPATIBILITY installation is completed. Live staking is also used with contour wattling to secure wattles stake installation is the same as __S~~~~~~~~~~~~~~~~~~~~~~."'......'3...._..:.___:. along a contour. The method of stake installation is the same as HI G . . . .. A~l.... . U ^c"~ o~L ~ ,pELF described for independent stakes. L liMiTATiONS 1 E Used on slopes of 1.5 horizontal to 1 vertical or flatter. The best c/':'.--..?A '1 * OEOTECSNICAL WU.DUFE time for staking installation is fall JJ LoWN � 1 GN .. installation is ~~~~~~ES'iUARINE $TERUC'1JRES EORE8OWS and spring which requires careful planning to perform slope work in this time period. Often the planting period for many projects is planned for the summer and early fall and this typically results in low propagation of the cuttings and ultimately poor slope protection performance of the vegetation system. Live staking does not provide an immediate solution to slope stabilization. ADVANTAGES AND DISADVANTAGES Advantages: Stake sources are plentiful and inexpensive, can be planted with minimal surface preparation/disturbance, can be placed into irregular (but stable) slope surfaces, helps reduce slope soil moisture. Disadvantages: Does not solve existing erosion problems (excluding benefits from associ- ated mulch), staking is not a short-term solution to slope instabilities. Live stake installaton. 33 * Planting Techniques CONTOUR WATTLING � PLANNING Spacing varies from CONSIDERATIONS 4-10 feet depending Woody plants which are particular- 1) Excavate email trench along slope ly suitable to contour wattling are 1)~~~~~~ Ecvtsmltrnhaong slp oite dogodandion contour. Place live stakes along x willow, red-osier dogwood, and trench edge on 3-foot centers trench edge on 3-fooll cent ers ~snowberry. Wattling is generally (see section on live stakes). considered good for slopes of 2) Placewattlesintotrench with . 1.5H:1V or less. The installation ends overlapping. Secure dead stakes through middle of wattles of wattles along slopes requires a at 2-3 foot centers. Sr greater degree of planning prior to 3) Pull excavated soil down into installation. Generally, wattles are and around wattles leaving approximately 20% of wattle area placed horizontally in shallow located above slope surface yet in trenches along preselected align- contact with soil. Walk on wattles to compact and achieve good 3 ments on the slope at a single soil-wattle contact. contour elevation. The wattles are 4) Move upslope to next trench placed into the trenches and alignment and repeat processa partially covered creating what appear like slope terraces. Wat- Figure 10. Contour wattling tling installation along a slope face should progress from the slope toe * DESCRIPTION AND upslope to the crest until planting FUNCTION is complete. Contour wattling is an erosion Wattles are created by laying plant control planting method which materials length wise between two can also be used to stabilize very bucking horses (or modified saw- shallow soil structure against horses). Plant materials should be landsliding. The method involves about ]/2 - 1P/2 inches in diameter packing lengths of woody plant and about 4 to 8 feet in length. material into cables or bundles Butt ends and top ends are usually (sometimes called live fascines) laid alternately until a bundle has about 8 to 10 inches in diameter. been created that looks like an 8 Wattle (yive fascines) The bundles are laid continuously to 10 inch wide cigar. Bundles are Dead stake along slope contours as shown in then tied together using untreated /Live stake Lie/tk Figure 10. The cabling effect lengths of twine. This process is Minimum along the slope helps to intercept repeated until you fabricated the angle io surface water runoff and route it length of wattling necessary to laterally before it creates erosion finish a contour length. Next you problems. The wattles help trap live stake the downslope side of sediment by creating barriers the trenches to hold the wattles in (living fences) to protect down the trench overlapping the ends of Fgndetail. slope areas against material falls bundles slightly. Place dead stakes or erosion. (2 foot long section of a 2 x 4 stud cut diagonally) through the wattles 34 Planting Techniquesf every two feet. Finally, pull the APPLICABILITY COMcPATIBILITY soil from the trench excavation F down into the wattles and com -nI K pact into the trench by walking on the bundles. Make sure there is good soil-plant contact aroundBLF and in the wattle. 0I ...IJi I E OR Ll About 80 percent of the wattleL 1 WJI should be buried below the exist- t H/1 ing soil surface as shown in Figure 11. Leave the remaining area AO~EXCL WlLF above the existing soil surface [ESKI~NE TRUA~RIEA then cover with soil to intercept water and create mild slope terraces. At this time it is good to excavate the next upsiope trench and then repeat the process. It is important to get the plant materials into the trenches before they have a chance to lose critical stem moisture. Seeding and mulching should follow immedi- ately after installation. * LIMITATIONS There is a significant quantity of plant material required for this technique. Installation is best per- formed with a labor crew of 3 to 4 people. The technique is time consuming if quality work is performed. For dry sites, summer watering maybe initially necessary. *ADVANTAGES AND DISADVANTAGES: Advantages: Good erosion control technique, can be used to manage mild gully erosion, can serve as Wattle construction, slope drains when wattle cables are angled slightly. MK of species or speciessore Disadvantages: On steep or long slope lengths, high runoff velocities can undermine wattling near drainage channels, can dry Untreated twine ties out if not property installed,Fi u e1.Wtldta. covered, or maintained.Fire1.Wtldta. 35 P Planting Techniques BRUSH LAYERS Spacing varies from Layering provides the best tech- 4-10 feet depending nique to achieve soil reinforce- I) Excavate trench so that on site conditions ment to resist potential shallow- approximately 1/4 of average 7 seated landsliding events. Brush brush length extends beyond slope face. Do not over excat layers act as live fences to capture 2) Lay an appropriate mix of Zsh A debris moving down the slope. species and/or brush species ' L 'N'IN from different sources along trench sidewall. CONSIDERATIONS 3) Pull excavated soil down into This technique can be very dis- trench and compact soil into 2 ~ ri~0, ruptive to native soils and can the original slope configuration. trigger movements Slightly mound soil behinduring brush layers. installation. It is important to 4) Move upslope to next trench perform installation in phases and alignment and repeat process. not to excavate more area than is necessary to install plant materials. If there are large quantities of Figure 13. Brush layering. loosened soils on the slope, * DESCRIPTION AND layering is a good slope stabiliza- FUNCTION tion approach. Also, if imported Brush layer planting consists of soil material will be used to restore live woody plant material placed eroded areas, brush layering into the slope face along trenches should be considered. It is best to excavated along slope contours install materials into the imported as shown in Figure 13. This fill area and avoid disturbing technique is most applicable to existing soil structures. Use brush areas subjected to cut or fill layering on slopes up to 1.5H:iV operations or areas that are or in highly eroded gully areas. highly disturbed and/or eroded. Plant material should be prepared Spacing 4-10 feet. Flow direction Spacing dependent rw~ ~~~~~o f_-ieldl conditions. Minimum angle = 101 -9 ~~~~11 14L Gully section looking up-slope. Length = 2-6 ft. Figure 14. Brush layering detail. Figure 15. Brush layering for gullies. 36 Planting Techniques as described under contour APPLICABILITY COMPATIBILITY wattling except for the length of the collected material. .... ('LIMITATIONS '1!..~~....?}~...i.. Not good for dense, stiff soil : . structures. Not recommended as -] E01 A] 'I ." a solution to gully erosion control .... unless technique shown on Figure 15 is used to rehabilitate gullies. *: ADVANTAGES AND, :.... . ...:.....:.. DISADVANTAGES: W| LOWEINK CAR Advantages: Good immediate soil reinforcement and slope dewater- ing function, good erosion ~IE control capabilities for dry debris. Disadvantages: Labor intensive procedur e, technique is intoler ant to development of water channels (rill s an d gullies). Therefore , use technique for appropriate site conditions. Brush layering in fill unit. AVOIDANCE/RETREAT OR BIOTECHNICAL SOLUTIONS Although avoidance is not truly a If structures can be relocated, planting procedure, it should b e greenbelts and low-impact slope discussed as a viable technique to planting may proceed with less weigh when it comes to slope ris k t o structures. restoration ~ ~ ~ rstraio usin getechica resto ration using geotechnical Biotechnical engineering solutions engineering design tabil ity use both vegetation and inert construction. For some sites it structural designs to address steep will be more economical for slopes greater than 1.5H: IV, home-owners to relocate struc- known landslide areas, compli- tures away from slope crests than cated drainage issues, and slope to mobilize construction crews to restoration programs. perform traditional advanced geotechnical slope stabilization. 37 * For More InJermation FOR MORE INFORMATION Elizabeth C. Miller Library Planning and Center for Urban Horticulture Engineering Departments: 3501 NE 41st Street Washington Department of Seattle, WA 98195 Ecology (WDOE) 206/543-8616 Continuing Education Continuing Education Washington Sea Grant Program 206/685-8033 Environmental Protection Agency (EPA) National Oceanic and International Society of Atmospheric Adminstration Arboriculture, Pacific NW Chapter (NOAA) P.O. Box 15729 Seate, WA 981157 U.S. Army Corp of Engineers Seattle, WA 98115 206/365-3901 U.S.DA. Soil Conservation Service District Offices Washington State University Plant Amnesty Extension Offices 906 NW 87th Street Washington State Department Seattle, WA 98117 of Fisheries (W.D.F.) 206/783-9813 ~206/783-9813 ~Washington State Department of Wildlife (W.D.W.) Puget Sound Water Quality Authority P.O. Box 40900 Washington D.O.E. Olympia, WA 98504 Shorelands Publications: Olympia, WA 98504 8001547-6863 Vegetation Management A Guide for Puget Sound Bluff Property Owners Washington Native Plant Society Marine Shoreline Erosion: P.O. Box 576 W 987Structural Property Protection Woodinville, WA 98072 Methods Shoreline Bluff and Slope Stability: Management Options Note: This section and the glossary developed jointly with the Department of Ecology - Shorelands and with Elliott Menashe, 1993. 38 Glossay � GLOSSARY APPARENT COHESION BLUFF enough to transmit the thrust of The resistance to soil particles An unvegetated high bank flooding by lateral compression separating from one another which composed largely of unconsolidated and capable of sustaining the weight is independent of soil particle deposits with a near-vertical face of overlying strata or man-made forces. overlooking a body of water. structures without losing its BANK BLUFF CREST structural integrity when arched BANK BLUFF CREST The rising ground bordering the Upper edge or margin of a or exposed to loading. sea, a river, or lake. Also see shoreline bluff. DECIDUOUS BLUFF and CLIFF Losing leaves or needles in the fall. BLUFF FACE BEACH The sloping portion of a high bank. DRAINAGE (SOIL) The zone of unconsolidated The rapidity and extent of the material that extends landward BLUFFTOE removal of water from the soil from the low water line to the place The base of a bluffwhere it meets by surface runoff and by down-draw where there is marked change in the beacflow through the soil. Also, the material or physiographic form, or BUFFER natural and artificial means for to the line of permanent vegetation A protective strip of vegetated land. improving this removal by a system (usually of surface and subsurface conduits. the effective limit of storm waves). CLEAR-CUT The seaward limit of a beach is the A timber harvest method which EARTHQUAKE extreme low water line. A beach removes all the trees on an area A sudden motion or trembling includes FORESHORE and in one operation. in the Earth caused by the abrupt BACKSHORE. CLIFF release of slowly accumulated strain ~~~~~~CLIFF . (by faulting or by volcanic activity). BEARING CAPACITY A high, very steep to perpen-dicular The load per unit area which or overhanging face of rock rising EROSION the ground can safely support above the shore. The wearing away of rock or soil without excessive deformation. and the movement of the resulting COASTAL ZONE . particles by wind, water, ice, or BEDROCK The sea-land fringe area bordering gravity, but usually excluding gravity, but usually excluding A general term for the rock, usually the SHORELINE where to coastal Mass Movements. solid, that underlies soil waters and adjacent lands exert a or other unconsolidated, surficial measurable influence on each other. EVERGREEN material. COHESION A plant which retains its needles or of mdi- leaves for more than one growing BIOENGINEERING The internal resistance ofindi- season. In soil applications, refers to the vidual soil particles to separate use of live plants and plant parts to from one another. EXTREME HIGH WATER reinforce soil, serve as water drains, (EHW) COMPETENCE The average height of the highest act as erosion prevention barriers, (1) In hydrology the ability of a tidal waters reached during the year land promte denwernowar ,o , current of water or wind to over a 19-year period. transport particles, emphasizing BIOTECHNICAL the particle size rather than the FEEDER BLUFF In slope stability engineering, amount, measured as the diameter An eroding shoreline bluff which refers to the use of both live plant of the largest particle transported. supplies material to accreting material and inert structures to (2) In structural geology a sediment shorelines. stabilize and reinforce slopes. or rock layer, rigid and strong 39 * Glossary FLOW INTER-DEPENDENT OVERSTORY A MASS MOVEMENT involving A group of plants which growing The portion of a forest that rapid flowage of wet soil, rock, together protect each individual forms the upper crown cover. and displaced vegetation as a from disturbance by wind, erosion VISCOUS mass down a slope or or other natural processes. Often PERCENT SLOPE a channel; including mudflow, shallow rooted trees will remained by 100) debris flow, and earthflow. windfirm because they form a wide, between the vertical and the horizontal distance for a given spreading root mat. FORMATION - (GEOLOGIC) slope; e.g., a 3-foot rise in a 10-foot The ordinary unit of geologic map- INTERSTICES horizontal distance would be a 30 ping recognized by field criteria Openings or spaces in rock or soil percent slope. consisting of a larger, persistent, that are not occupied by solid and mappable strata of predomi- matter. POORLY SORTED na.ndy~ one.kindof~ rock~ or .Unconsolidated deposits that nasediment type. INTERSTICES OR FRACTURES consist of particles of many sizes The flow of rain water into soil mixed together in an unsystematic GEOTECHNICAL material. manner so that no one size fraction Refers to the application of civil predominates. JOINT engineering technology to some engin eering technology to some A crack (parting or fracture) RILL aspect of the earth . formed in rock by movements A tiny drainage channel cut in a GEOTECHNICAL STRUCTURES normal to the cracks and without slope by the flow of water. Can Along coastal slopes, refers to slope shear movements (by displacement) develop into a gully with continu- protection designs such as retaining of the rock on either side of the ing erosion. wall, revetments, and designed crack. RUNOFF slope recontouring. LANDFILL That part of the precipitation that GULLY (1) The solid waste disposal process appears in uncontrolled surface Large intermittent drainage chan- using land as the final disposal site. streams, drains, or sewers. It is nel developed from the erosion (2) A fill area specifically for the the same as streamflow unaffected forces of drainages occuring from purpose of creating additional dry by artificial diversion, imports, surface water runoff. land, usually accomplished by storage, or other works of man covering a wet or swampy area or in or on the stream channels. HARDPAN slope face with sand or other A hard, impervious, often clayey suitable material SATURATED layer of SOIL lying just below the A condition in which the INTER- surface. Sometimes synonymous MASS MOVEMENT STICES of a material are filled with for TILL. A unit movement of a portion of a liquid, usually water. the land surface down a slope as a IMPERMEABLE SLIDE, a FLOW, or SOIL CREEP SEISMIC Having a TEXTURE that does not in which gravity is the main driving Pertaining to earthquakes or earth permit fluids to move through it force. vibrations, including those that are freely. man-made, e.g., explosions and NATURAL LANDSCAPE underground nuclear blasts. INFILTRATION ELEMENTS The movement of water or The natural watercourses, topogra- SHEAR STRENGTH solutions into or through a rock or phy, hydrology and vegetation Resistance to lateral movement or soil through its INTERSTICES or which comprise a particular site. failure along a potential failure fractures; the flow of rain water surface. into soil material. 40 Glossary � SHORELINE STRATIGRAPHIC SECTION UPLAND The intersection of a specified Any sequence of rock units found A general term for elevated land plane of water with the BEACH; it in a given region (the oldest at the above the beach which lies above migrates with changes of the tide. bottom and the youngest at the the EXTREME HIGH WATER SLIDE top). level. A MASS MOVEMENT resulting TABLELANDS WETLANDS (BIOLOGICAL) from failure of SOIL or rock along The tops of bluff areas usually Lands transitional between a rotational or planar surface. developed for homesites. terrestrial and aquatic systems where the water table is usually SLOPE TENSILE STRENGTH at or near the surfaces or the land is The inclination of the land surface Resistance to rupture or failure due covered by shallow water. from the horizontal percentage of to tensile forces or pulling. slope is the vertical distance divided WETLANDS by the horizontal distance, then THINNING (JURISDICTIONAL) multiplied by 100. Tree removal in a forest stand that Land forms which support under reduces tree density and numbers in normal conditions a predominance SLUMP a given area. Most discussions of ofhydrophytic (wetland) vegeta- A SLIDE characterized by a rotary thinning stress increased growth tion, hydric (wetland) soil types, movement of a generally indepen- and yield of timber. and wetland hydrology. Typically, dent mass of rock or earth along a they are jurisdictionally defined as: curved slip surface. TILL POORLY SORTED and generally "Those areas that are inundated or SOIL unstratified sediments, deposited saturated by surface or groundwater In engineering work a soil is any directly by and underneath a at a frequency and duration earthen material, excluding hard glacier. Usually very hard and sufficient to support, and that bedrock, composed of 1) loosely compact, with good bearing under normal circumstances do bound mineral and organic capacity and low permeability. support, a prevalence of vegetation partides, 2) water, and 3) gases. typically adapted for life in In agriculture, a soil is the loose TOE OF SLOPE saturated soil conditions (Federal surface material capable of See BluffToe. Interagency Committee for supporting plant growth, and UNCONSOLIDATED Wetland Delineation, 1989)". having properties resulting from Said of sediment whose particles are WINDTHROW the integrated effect of climate and loose and not cemented together. Trees blown over by the wind. living matter on the decomposition Usually caused by thinning or of bedrock and surficial deposits. UNDERCUTTING ad The removal of material at the base SOIL ARCHING of a steep slope or cliff or other A phenomena that transfers lateral exposed rock by the erosive action soil pressure to adjacent rigid of waves, running water, or sand- members (trees, piles, etc.) laden wind. anchored in an unmoving soil or rock zone. UNDERSTORY Trees or other plants which tolerate SOIL CREEP reduced-light conditions and The gradual and steady downhill normally grow beneath the forest movement of soil and loose rock canopy. material on a slope. STRATA A layer of soil. 41 REFERENCES Albright, Rick. et al. 1980. Coastal Zone Atlas of Washington, Volumes I 6& I1. Washington Department of Ecology. Binns, W.O. 1980. Trees and Water. Arboriculture Leaflet No. 6, Forestry Commission Research Station, Surrey, England. Canning, Douglas J. 1991. Sea level rise in Washington state: State-of- the-knowledge, impacts, and potentialpolicy issues. Shorelands and Coastal Zone Management Program, Washington Department of Ecology, Olympia. Canning, Douglas J. 1991. Shoreline bluff and slope stability: Management options. Washington Department of Ecology. Shorelands technical assistance paper No.2. Chandler, R.J. 1991. Slope Stability Engineering. Institution of Civil Engineers. Thomas Telford Publishing Company. Clemens, Robert H. et al. 1970(?). The Role of Vegatation in Shoreline Management: A Guide for Great Lakes Shoreline Property Owners. Great Lakes Basin Commission. Downing, John. 1983. The Coast of Puget Sound. Its Processes and Development. University of Washington Press, Seattle. Gray, D.H. and A.T. Leiser. 1982. Biotechnical Slope Protection and Erosion Control. New York: Van Nostrand Reinhold. Greenway, D.R. 1987. Vegetation and Slope Stability - Chapter 6 In: Slope Stability. John Wiley and Sons Ltd. Kruckeberg, Arthur R. 1982. Gardening with Native Plants of the Pacific Northwest. Douglas & McIntyre Publishing. Menashe, Elliott. 1993. Vegetation Management: A Guide for Puget Sound Bluff Property Owners. Washington Department of Ecology. Rahn, P. 1986. Mass Wasting - Chap. 6 In: Environmental Geology. Elsevier Publishing Company, New York, N.Y. Schwab, G.O. et al. 1966. Soil and Water Conservation Engineering, Engineering. New York: Wiley. Stevens, M. and R. Vanbianchi. 1993. Restoring Wetlands in Washington State. Washington Department of Ecology. Terich, Thomas A., Maurice L. Schwartz, and James Johannessen. Version 2.0 1991. Coastal Erosion Management Annotated Bibliographies on Shoreline Hardening Effects, Vegetative Erosion Control, and Beach Nourishment. Shorelands and Coastal Zone Management Program, Washington Department of Ecology. 42