Home

Chapter 4 - Bank Protection/Erosion Repair guides

1. Protecting property or structures Restoring eroded banks Protecting existing banks from erosion Restoring riparian habitat and improving stream function Determination of the project s necessity must take into account the fact that some erosion is natural and acceptable For example the exposure of roots on a streamside tree is natural and unless extreme it will not hurt the tree If the bank height is less than about eight feet what is easily perceived as bank erosion may be only temporary or even reverse itself as the stream meanders in its floodplain Some erosion repair activities such as bank armoring can destabilize other areas erosive forces are transferred downstream or onto opposite banks eventually causing additional problems A qualified professional may be needed to help determine whether and to what extent erosion is in need of repair STEP 2 HIRE A QUALIFIED EXPERT TO DETERMINE THE APPROPRIATE DESIGN Designing an erosion repair project that maximizes stability and avoids unintended consequences is complicated As noted earlier a stream must have a properly dimensioned bankfull channel in order for it to have long term stability Other critical factors in proper channel design include proper width to depth ratio water velocity sheer stress and channel slope Most property owners do not have the training or expertise necessary to incorporate all of these considerations into project design
2. EIR is required to study the significant impacts of your project on the environment Various alternatives to your project must be identified and evaluated and the environmentally preferred alternative must be selected unless there are overriding circumstances that make the project desirable even though there are significant unmitigated impacts This finding must be made by the approving body of the lead agency along with the findings and MMRP Because there are more alternatives to evaluate there is a slightly longer review period and a requirement to specifically respond to comments For this reason an EIR can be the most time consuming and complicated scenario USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 115 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 7 REFERENCE MATERIALS There is a wide body of literature that STREAM CORRIDOR provides more detailed information on RESTORATION PRINCIPLES these bank protection repair techniques PROCESSES AND PRACTICES We have identified several of the more comprehensive documents A more complete list can be found at http www 4sos org wssupport ws_rest rest_con asp Developed by an interdisciplinary team of stream and watershed management specialists hydrologists engineers and other EPA federal agency and private group representatives A printed document A CITIZE N S STREAMBAN K is available for 71 CD ROM version RESTORATION HANDBOOK se
3. Most erosion repair projects will require permits from federal state and or local regulatory agencies if they entail construction between the banks of a stream Please refer to the Resource Agency Referral List in Section 6 of this Design Guide for a list of all the agencies the types of activities for which they should be contacted and their contact information The San Francisco Bay Area Joint Aquatic Resource Permit Application JARPA consolidates the information that permitting agencies require into a single application The JARPA application can be found at http www abag ca gov bayarea sfep projects JARPA JARPA html The permitting process can take as little as a few weeks to complete but typically takes a few months depending on the complexity of the project and the presence or potential presence of federal of state listed endangered threatened or special status species of plants or animals Typically the U S Army Corps of Engineers the Regional Water Quality Control Board and California Department of Fish and Game will issue permits under federal and state laws while the Santa Clara Valley Water District or the local municipality acts as the local permitting agency IMPORTANT NOTE Bank repair designs that avoid or minimize hardscape and are based on sufficient analysis of the cause of failure and stable channel characteristics almost always receive permits more readily than those that do not Do not he
4. Fascine or wattle bundle Shallow trench with fascine 1 Stake on contour 2 Trench above stakes v2 to of bundles 3 Place bundles in trench 4 Add stakes through and below bundles 5 Cover wattling with soil tamp firmly Wattling to be above grade and 10 20 left exposed USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 95 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 5 BRUSH MATTRESS First the bank must be prepared The eroded slope is graded and smoothed to ensure that all willows are in contact with the soil Then a deep trench 2 ft min is dug at the toe of the bank for the butt ends of the willow branches Wood steel or live willow stakes are partially driven into the soil in rows on three foot centers in the area that will be covered by the mattress After the stakes have been placed live willow branches are put on the bank with their butt ends in the trench Straight branches no shorter than four feet in length and 5 to 1 in diameter are used If the branches are not long enough to reach the upper end of mattress several laye rs may be used however it is necessary to shingle the layers by lapping each new layer over the one below by at least 18 Once the bank is covered by a thick layer of willows cross branches are placed horizontally over the bottom layer These branches are placed against the stakes and then tied to the stakes using wire or string The
5. The cooperative enlisting of neighbors to affect this approach is well worth the effort The typical steps in creating a modified floodplain are Step 1 Identify the appropriate channel width and depth at bankfull level The active channel will contain flows resulting from small frequent rainfall events Step 2 Identify the appropriate elevation for the floodplain area and determine how much space is available and appropriate for widening the banks Step 3 Regrade or lay back the existing bank above the floodplain to a flatter more stable angle usually a 2 horizontal to 1 vertical slope or greater Step 4 Create terraces above the active floodplain to accommodate vegetation Step 5 Plant the terraces with appropriate local native riparian vegetation to stabilize the bank s and create habitat DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 85 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V HOW TO CREATE A MODIFIED FLOODPLAIN IN DEEPLY INCISED CHANNELS A watershed friendly design that recreates a natural floodplain is depicted in Figures 4 and 5 below FIGURE 4 STREAM CHANNEL WITH DEEPLY INCISED STREAMBANKS Deeply Incised Streambanks FIGURE 5 THE SAME STREAM CHANNEL AS FIGURE 4 BUT STREAM BANKS HAVE BEEN REGRADES TO CREATE TERRACES WHERE VEGETATION CAN BE PLANTED Streambank is regraded back to a more stable con
6. The tips should stick out of the crib wall no more than a quarter of the cutting total length The branches are then covered with the gravel cobble mix to the top of the tie backs and the next layer is continued This method is effective on the outside of bends where high velocities are present and in situations where a low wall may be required to stabilize the toe and reduce slope steepness The use of crib walls in a specific location must be considered carefully in the context of the stream s function If placed incorrectly relative to the active channel the bends in a meandering stream can induce considerable damage downstream or on the opposite bank This method does not adjust to toe scour and should be used in combination with soil bioengineering systems and live plantings to stabilize the upper slopes2 DESIGN CRITERIA AND CONSIDERATIONS This method may cause channel scour and erosion of downstream and opposite banks if a modified floodplain is not constructed along the opposite bank It may also cause upstream scour As the logs rot the crib wall can be undercut and eventually fail If the structure fails hazardous rebar and steel cable can be deposited in the river along with the logs and other debris of the structure Source California Department of Fish and Game California Salmonid Stream Habitat Restoration Manual Source Natural Resources Conservation Service Stream Corridor Restoration Prin
7. USE NEAR STREAMS The Guidelines have the force of law and lay out the way CEQA is administered See http ceres ca gov topic env_law ceqa The purpose of the CEQA review is to inform project decision makers of the issues associated with the project to identify significant environmental impacts and reduce them and to disclose to the public the rationale for the decision to approve a project The agency responsible for the CEQA review is called the lead agency and it is usually the agency with the most involvement in the project The local municipality s planning department usually handles the CEQA review however CDFG is also a lead agency for purposes of issuing a Streambed Alteration Agreement Once the lead agency is identified all other agencies that require a permit to be issued for the project whether state or local become responsible Responsible and trustee agencies must consider the environmental document prepared by the lead agency and do not except in rare instances prepare their own environmental documents THERE ARE FOUR POSSIBLE SCENARIOS REGARDING CEQA REQUIREMENTS 1 The project is exempt from CEQA Exemptions are listed in the CEQA Guidelines Specific rules should be consulted but essentially a categorical exemption cannot be used if the project has the potential for an individual or cumulative significant effect on the environment Documentation of exemptions should be obtained from t
8. center of the channel increase the channel s flow and sediment transport capacity and the deep hole is created for fish habitat USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 89 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V ADDITIONAL TOE AND BANK PROTECTION FOR HIGH FLOW VELOCITIES OR CONFINED AREAS In the uncommon situations where water velocities are especially high or where astructure is threatened by its proximity to the bank additional protection or a hybrid approach may be desired PHOTOGRAPH 1 ROCK CROSS VANE STRUCTURE 4 90 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS HOW TO CREATE A MODIFIED FLOODPLAIN IN BROAD FLAT STRETCHES WITH SEDIMENT DEPOSITION In some cases a stream may have experienced heavy sediment deposition over the years In contrast to the deeply incised channels channels with heavy sediment deposition tend to be wide shallow and rather straight Although there may have been fish present at one time the shallow flows make it difficult for them to return Where there is room it is important to restore the nature meanders if possible Streambank is 27 regraded back to a more stable configuration DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V Figures 6a and 6b below show a stream prior to a stream restoration project As you can see the channel was wide shallow and rather straight The bottom drawing shows that the channel was made n
9. circumstances in which it is most appropriate its anticipated environmental value its relative costs and its potential impacts Descriptions are not exhaustive and should only be used in conjunction with consultation from a qualified erosion repair professional the Santa Clara Valley Water District and relevant regulatory agencies Even the most well meaning erosion repair designs can have negative impacts on a stream if they are not planned designed and constructed properly Poorly placed rocks or woody material can cause bed and bank scour erosion excessive sediment deposition and or decreased channel capacity For this reason it is essential that the project is designed to accommodate the site s particular geomorphic location channel form and depth flow velocity and site constraints This typically requires a physical or geomorphic assessment by a trained professional To protect both your property and its value the goals of any streamside bank protection or erosion repair project should be to restore stability and leave the site in a better ecological condition than it was before The first erosion repair method the modified flood plain will provide the best long term ecologically friendly and most stable results Methods 2 through 8 use bioengineering methods Bioengineered bank stabilization methods typically involve two components Regrading the upper streambank to establish or re establish a flood
10. method should where appropriate be used in conjunction with soil bioengineering or live vegetation plantings in order to stabilize the upper bank and ensure a regenerative source of streambank vegetation The endurance of the structure depends on the species of logs used it might need replacement if vegetative colonization does not take place DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V DESIGN CONSIDERATIONS This method may cause channel scour and erosion of downstream and opposite banks if a modified floodplain is not constructed along the opposite bank It may also cause upstream scour 1 Source California Department of Fish and Game California Salmonid Stream Habitat Restoration Manual 2 Source Natural Resources Conservation Service Stream Corridor Restoration Principles Processes and Practices USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 101 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FIGURE 15 ROOT WATDS AND BOULDERS Log with roots secured within rock toe Toe of bank OHWM Top of bank Top of bank Staked fascine Coir geogrid Live cuttings 2 ft minimum layer heavy loose riprap 3 5 ft minimum diameter rock 1 ft minimum layer of light loose riprap 1 1 ft layer of 14 3 in rounded gravel 2 ft diameter 20 30 ft long log with roots Trench and imbed log bole 12 16 ft minimum distance into riverbed below existing OHWM Secure with
11. stakes are then driven into the bank at least two feet deep After the completion of the mattress the toe trench is filled with appropriately sized boulders and rocks to anchor the butt ends of the branches The brush mattress should be covered with an amount of soil sufficient to ensure a good contact surface between the mattress and the soil leaving some buds and twigs exposed This method forms an immediate protective cover over the stream bank captures sediment during flood flows and rapidly restores riparian vegetation and streamside habitat This measure is not appropriate where toe scour is anticipated in which case boulders may need to be added at the toe DESIGN CONSTRAINTS AND CONSIDERATIONS Branches should be tamped down before tying to create a good contact surface between the soil and the mottress Butt or basal ends of branches must be covered with soil so they can root and to prevent them from drying out Branches should be partially covered with soil This method should not be used on slopes that are experiencing geotechnical failures or other slope instability 4 96 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FIGURE 11 BRUSH MATRESS Live or dead stake Live branches Fascine optiona 7 Ue SS 4 LL USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 97 DESIGN GUIDE 19 GUIDELI
12. than for them to compose the correspondence PROHIBITED ACTIVITIES Before you decide to do work near a creek or river you should consider that it is illegal to place store or dispose of materials of any kind on the banks of or into a watercourse Prohibited materials include dirt soil and concrete pool and spa water paints solvents and soaps yard and animal waste automobile and machinery fluids and firewood and building materials Remember to comply with best management practices that prevent pollution from entering the waterway and damaging the ecosystem DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 11 1 AGENCIES THAT MAY REQUIRE PERMITS Use this chart to help you determine which agency may be involved in your project A checked box indicates that an agency may be involved and should be contacted but does not mean they definitely will be involved Your City s Planning or Public Works Dept Santa Clara Valley Water District Regional Water Wildlife Service Quality Control Board California Fish SWRCB Water and Game Army Corps of Engineers U S Fish amp Involve work on the bank of a river stream or lake Involve excavation of the Involve placement of piers stabilization or erosion control o Q 3 p riparian or other wetland vegetation Involve planting riparian or wetland vegetation Affec
13. the performance of 24 urban stream restoration practices from sites around the Mid Atlantic and Mid west and provides BRASS c o Essex County Government recommendations for improving their Center Box 217 Elizabethtown NY 12932 application in a variety of urban stream or call 518 873 3688 environments It costs 20 Available through the Center for Watershed Protection at http www cwp org 4 116 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS STREAM BANK REPAIR GUIDANCE MANUAL FOR THE PRIVATE LANDOWNER GUADALUPE AND ALAMITOS CREEK This focuses on erosion repair in mercury contaminated streams but it is relevant to a broad range of erosion repair projects Some of the most relevant information from this document is contained in this Design Guide This publication can be obtained from the Santa Clara Valley Water District MAINTAINING CORTE MADERA CREEK A CITIZENS GUIDE TO CREEK SIDE PROPERTY PROTECTION Created for the Town of Portola Valley and its residents to help guide bank stabilization and revegetation efforts along Corte Madera Creek a tributary to San Francisquito Creek The report was created to facilitate communications between the Town and private property owners who wish to address erosion and property loss The document can be found at http www cityofpaloalto org public works jpa projects html GUIDELINES FOR BANK STABILIZATION PROJECTS IN RIVERINE ENVIRONMENTS OF KI
14. the stream channel at the bankfull level by the mean channel depth Width to depth ratio is part of a more complicated concept called entrenchment ratio which is important because it calculates a channel s stability Generally speaking it calculates its stability in terms of its floodplain the larger the floodplain the higher the entrenchment ratio Specifically the entrenchment ratio is equal to the width of the stream channel at twice the maximum bankfull depth divided by the width to depth ratio of the bankfull channel In order to prevent channel incision and maintain a stable stream the ratio of the width of the channel at 2 bankfull heights see Figure 2 to the bankfull width should be a minimum of 2 where the channel is constrained It should be a 3 to 4 ratio at other locations both upstream and downstream This provides sufficient relief and thus prevents excessive erosion of streambed and bank It also prevents damage to bankside properties during 1 year 10 year storm events FIGURE 2 DETERMINING THE APPROPRIATE WIDTH TO DEPTH RATIO Active Floodplain Width at 2 Bankfull Heights Top of Bank n Active Channel Bankfull Stage Height Bankfull Width at Bankfull stage Active Floodplain USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 7 1 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V EFFECTS OF WATER AND SEDIMENT TRANSPORT ON BANK STABILITY Streams adjust
15. themselves to transport as efficiently as possible water and sediment from higher elevations to lower elevations If the amount of sediment available to a creek is significantly increased or decreased the creek adjusts its channel area or cross section to handle the change in sediment In a normally functioning gravel bed stream for example it is not uncommon for the stream channel or portions of the stream channel to downcut and refill significantly from a few inches to 10 feet or more ina single storm event This is one way streams transport their sediment loads clean themselves and temporarily increase their flow capacity With the expanded development in Santa Clara County the time it takes for runoff to reach the streams has decreased which leads to the increase in the amount of water in most streams Some of the specific factors that have led to this increase in water flows are Substantial increases in impervious surfaces such as pavement and roof tops The routing of storm water runoff directly into streams through piped storm drain systems Removal of large areas of streamside vegetation that would otherwise form buffers for runoff and promote infiltration into the soil The stormwater management programs of local municipalities have efforts underway to address these long term issues In the interim however it is important that armoring the channel be avoided on individual properties whenever p
16. A walk along many Santa Clara County streams proves this point It reveals many examples of how individual property owners without professional help tried to control streambank erosion by armoring the bank These measures often fail to address the need to reduce shear stresses in order to keep the bed and banks from eroding Eventually the channel will downcut and in most cases fail Professionals can help avoid this kind of failure prone approach to streambank repair and help identify and address the root cause of the problem USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 77 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V STEP 3 IDENTIFY THE SOURCE OF THE PROBLEM It is important to identify and if possible address that the source of streambank or bed erosion If it is not addressed the erosion repair project may either need to be repeated or expanded in the future or cause other erosion problems upstream downstream or across the stream To identify a potential source one should look for Flow constrictions like bridges or debris that increase downstream velocities and shear stress Existing hardscape or paved over areas that may be increasing velocities downstream Natural or non natural debris that may have redirected the flow into the bank Drainage features that may be directing flow onto or saturating the bank Watershed wide increases in amount and duration of runoff t
17. BANK PROTECTION EROSION REPAIR DESIGN GUIDE INTRODUCTION AND PURPOSE OF THE DESIGN GUIDE This Design Guide is intended to clarify the Chapter 1 of the Water Resources Infrastructure Protection Manual section VIII articles D H Outfalls Pump stations and Site Drainage This Design Guide describes how to address streambank erosion problems and how to use bioengineered methods of bank protection and erosion repair This Design Guide is to be used by local permitting agencies property owners and professionals who design projects on streamside parcels i e civil engineers land use planners landscape architects etc It is intended to Provide guidance for how to design a variety of bank protection projects in places where streambanks are have or may be eroding Promote proactive approach to preventing and resolving serious erosion problems This document is a guide not an instruction manual Erosion repair activities within a stream channel will impact water quality flood protection the stability of adjacent properties and the habitats of many stream dependant species It is for these reasons that these activities require several state and federal permits as well as the involvement of qualified professionals to help design and construct the project in a way that addresses stability and long term water resource protection Examples of more detailed guidance manuals are listed at the end of this document for refe
18. LINES AND STANDARDS I V 3A EROSION MATS WITH BOULDER OR LOG TOE PROTECTION This method consists of grading the lower portion of the eroded slope at a maximum of 1 5 1 The upper portion of the slope is then graded at a minimum slope of 2 1 and smoothed to ensure that the whole erosion mat contacts the soil Appropriately sized boulders are placed at the toe of the rebuilt bank up to the bankfull discharge water elevation or even slightly higher Voids between the boulders can be planted using live stakes DESIGN CONSIDERATIONS Best for bank slopes of 3 1 or steeper Boulders must be keyed in min 3 feet at the toe of the bank Boulder placement must not constrict the channel cross section or reduce the width to depth ratio Otherwise the repair will likely destabilize the channel The placement of boulders or armoring along the bank may increase turbulence in the area and other areas downstream This could increase erosion USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 93 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 4 CONTOUR WATTLING FASCINES This method consists of tying long bundles of plant cuttings typically willows or cottonwood together with twine and anchoring them in shallow trenches parallel to the stream with wooden stakes When the cuttings develop root systems and mature the plants provide structural soil stability This technique is generally used to manage
19. N REPAIR PROJECT 4 76 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 3 EMBARKING ON YOUR BANK PROTECTION EROSION REPAIR PROJECT This section describes five initial steps to consider in undertaking an erosion repair project This text borrows extensively from the guidance manual developed for the Guadalupe and Alamitos Creeks entitled Stream bank Repair Guidance Manual for the Private Landowner which is cited in the references section INITIAL STEPS Step 1 Establish the Purpose and Necessity of Your Project Step 2 Hire Qualified Professionals Step 3 Get to the Root of the Problem Step 4 Seek Assistance from the Water District Step 5 Secure Permits from the Appropriate State and Federal Agencies STEP 1 ESTABLISH THE PURPOSE AND NECESSITY OF YOUR PROJECT Repairing a stream or bank erosion problem is not a simple or routine task The root cause of the bank failure must first be identified Then the most probable stable channel form and dimensions must be determined based on geomorphology and hydrology as well as hydraulic analyses Only then can a proper solution or repair be recommended Before embarking on any bank stabilization erosion repair project it is important to answer the following questions What is the purpose of this project What are its objectives Is it necessary Some examples of objectives could include
20. NES AND STANDARDS I V 25A BRUSH MATTRESS WITH BOULDER OR LOG TOE PROTECTION First the lower portion of the eroded slope is graded at a maximum slope of 1 5 1 Then the upper portion of the slope is graded at a minimum of 2 1 and smoothed to ensure all willows are in contact with soil Appropriately sized boulders are placed at the toe of the rebuilt bank up to the bankfull discharge water elevation or even slightly higher Live stakes can be placed between the boulders to establish vegetation This method requires a lot of branches Therefore needs to be installed during low flow conditions so that growth can be established Otherwise the branches will wash away DESIGN CRITERIA Boulders must be keyed in min 3 feet at toe of bank Boulders placement must not constrict the channel cross section or reduce the width to depth ratio Otherwise the repair will likely destabilize the channel The placement of boulders or armoring along the bank will increase turbulence in the area and downstream which could cause increased erosion FIGURE 12 BRUSH MATTRESS WITH BOULDER OR LOG TOE PROTECTION 4 98 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 6 BRUSH LAYERING In this method alternating layers of soil and live branches are installed in horizontal rows on the streambank This method is more substantial than brush mattresses and can be used to repair erosion gullies scour holes and
21. NG COUNTY Produced by the King County Department of Public Works Surface Water Management Division Seattle Washington in 1993 This report is an exceptional manual that clearly and comprehensively describes the planning design permitting and construction aspects of bank erosion repair From a technical perspective it is very applicable to California streams This resource including some of its illustrations was used to help prepare this Bank Protection Design Guide DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 11 7
22. SER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 69 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V TYPICAL STREAM FEATURES In a cross sectional view a stable natural stream can be defined by two significant features the bankfull or active channel and the active floodplain See figure 1 below The bankfull or active channel can be defined by the elevation of the floodplain which is formed by the most effective channel forming or dominant stream discharge It is the part of the stream where sediment is actively transported and deposited the part that is capable of containing the most frequent flows The active channel is an important feature because it transports the majority of the water and sediment in the stream system and thus it influences the channel formation over time As seen in Figure 1 the active channel is usually distinguished from the active floodplain by an abrupt change in the slope of the stream bank usually from a vertically sloped plane to the horizontally sloped plane on top of the floodplain Active floodplains are the low lying areas between Top of Bank See Figure 1 and adjacent to the active channel that are subject to frequent inundation during moderate and high flows This area is where sediment is deposited when the active channel s capacity is exceeded during high flows In urban settings active floodplains are often hard to identify due to channel incision and
23. adequate buffer is necessary to protect stream resources In terms of erosion repair projects the use of live plants either alone or in combination with dead or select rock materials can be sufficient to prevent erosion control sediment and provide habitat STREAM FEATURES THAT ARE IMPORTANT TO FISH HABITAT The movement of water through a streambed creates certain natural characteristics or that benefit fish habitat Some of these important features are riffles runs glides and pools Riffles are located in shallow areas or bends in a stream where water flows over rocks Runs are the straight sections between riffles Glides are the transition areas between the downstream end of pools and a run or riffle Pools are usually formed on the outside of bends in a 4 72 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS stream Deep pools are particularly import ant in providing critical fish habitat and refuge areas When the flow in the stream decreases in drought fish can retreat to these pools to wait for the return of higher flows These stream features described above differ from stream to stream depending on stream s geometry and location For example at higher elevations stream channels are steeper narrower and drop at faster rates and may contain series of step pool cascades At a lower elevation however a channel tends to be less steep wider and more sinuous making riffles and pools more com
24. alls are used to reduce sediment input and protect banks in areas where logs are available and boulders are not practical These temporary structures are designed to rot and degrade after live plant material has established itself Cribbing provides protection in areas with near vertical banks where bank sloping options are constrained by adjacent land uses In this method two rows of base logs are placed parallel to the bank in trenches below stream grade to minimize undercutting of the structure Tie back logs are notched into the base logs and placed at regular intervals typically 6 to 8 feet along the base logs Tie back logs are attached to the base logs using re bar pins or cables There should be at least two tie back logs connecting each pair of base logs Once the first row of tie back logs has been connected a second set of face logs is placed on top of the tie backs This procedure is repeated until the desired level of bank protection is achieved As each lift is constructed the face logs and tie backs are filled with a mix of gravel and cobbles to the top of the face log It is not necessary to use topsoil in the fill material DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V but there should be sufficient fine grain material to insure vegetation growth Live cuttings are then laid in to form a complete cover layer These live branches should be long enough to have their butt ends in the soil behind the crib wall
25. amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V ORGANIZATION OF THIS DESIGN GUIDE This Design Guide is organized into two parts and six subsections The Technical Primer part includes useful background information that explains the causes of erosion Homeowners and project developers will likely refer to the Techniques and Guidance part more frequently because it outlines techniques and guidelines for erosion repair CONTENTS PAGE Part Technical Primer on Stream Function and Form 4 68 Section 1 How Streams Function 4 69 Section 2 Typical Causes of Streambank Erosion 4 74 Part Techniques and Guidance for Developing Your Erosion Repair Project 4 76 Section 3 Embarking on a Bank Protection Erosion Repair Project 4 77 Section 4 Introduction to Appropriate Watershed Friendly Design 4 80 Section 5 Detailed Descriptions of Erosion Repair Techniques 4 83 Section 6 Helpful Hints on Obtaining Permits for Stream bank Repair 4 110 Section 7 Reference Materials 4 116 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 67 BANK PROTECTION EROSION REPAIR DESIGN GUIDE PART ONE TECHNICAL PRIMER ON STREAM FUNCTION AND FORM 4 68 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS SECTION 1 INTRODUCTION Before considering bank protection or erosion repair it is necessary to understand the process by which streams form and adjust to their surroundings Streams a
26. areas downstream which could increase erosion FIGURE 14 VEGETATED GEOGRIDS OR SOIL LIFTS Exposed face of geotextile material Live brush Geotextile material Fill material Geotextile fabric Live branches TN Fill material varies Channel bed 4 100 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 8 ROOT WADS AND BOULDERS This method consists of using a combination of boulders logs and live plant material to armor a stream bank It enhances fish habitat and creates a natural looking bank stabilization structure Footer logs are set in a toe trench below the thalweg line the line of maximum depth in a stream with the channel end pointed downstream and the butt end angled 45 to 60 degrees upstream A second log with a root wad is set on top of the footer log diagonally forming an X The root wad end is set pointing upstream and the butt end lying downstream 45 to 60 degrees The apex of the logs are anchored together using boulders re bar or cables Large boulders are placed on top and between the logs at each apex After all the logs and boulders are set in place live plant material such as willows is placed within the spaces of the structure behind the boulders Excavated gravel and stream materials can then be placed over the bank end portion of the structure This method will tolerate high boundary shear stresses if logs and root wads are well anchored This
27. arrower and constructed with a proper width depth ratio at the bankfull level This helped assure the proper transport of sediment through the area by increasing velocities in the active channel The active channel was moved away from the right bank and into the center of the channel corridor creating deep pools for steelhead trout and salmon Brush rolls were used on the top of the right floodplain to accumulate fine sediment and the right vertical stream bank was sloped back and vegetated 08 Deeply Incised An active floodplain is created and then vegetated to promote USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 9 1 stability DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 2 SLOPE GRADING WITH VEGETATION AND FLOODPLAIN TERRACES SPACE PERMITTING This is perhaps the least engineered and often most effective method of long term bank repair because it restores the natural contour and vegetative cover of the stream bank If the bank is undercut or has slumped to a vertical face consider matching the grade of a nearby stable slope Usually a 2 horizontal to 1 vertical slope is considered stable for many soil types and if space allows a 3to 1 slope would be even better Regrading the channel to create terraced banks as described in Section 4 in order to include an active channel and floodplain area is appropriate wherever a more holistic approach to stream restoration is possible As noted ear
28. as been successfully used with soil nails to stabilize vertical slopes on upper banks where land use constraints preclude regrading of the slope Sheet pile retaining walls have been used in a similar manner Vegetation can be placed on the lower portions of the bank to enhance biotic resources Gunite slope protection causes erosion problems degrades water quality and destroys other beneficial uses Therefore the use of gunite slope protection is discouraged and is included here only for reference USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 109 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 6 OBTAINING PERMITS FOR STREAM BANK REPAIR Taken from the Stream Bank Repair Guidance Manual for the Private Landowner Guadalupe and Alamitos Creeks PRACTICAL POINTS TO HELP YOU OBTAIN PERMITS FOR YOUR PROJECT As noted earlier if you are working in or around a creek or stream you will likely need permits from a local state and or federal agency Below are some practical points to help you obtain permits for your project as quickly and efficiently as possible Following this list is a matrix of activities and the agencies which may require permits for those activities Learn the rules Familiarize yourself with applicable state local and federal agency permitting requirements Determine which agencies may be involved in your project Take time to study the protocols and regulations of the
29. cant problems arise when streams in the lower watershed are confined By lining streams with levees or floodwalls water that would otherwise slowly spread out over a large area of land in a beneficial way accumulates in the channel until it breaches its levee or floodwall potentially causing catastrophic flooding Even if this does not happen a significant amount of sediment may be deposited in the channel after a storm event raising the channel bed elevation This sediment decreases the channel s capacity to handle subsequent storm flow In other words the chance of catastrophic flooding increases with every storm if the channel s sediment is not removed often enough Significant efforts are underway throughout the County to address these issues and to maintain and enhance our remaining natural streams There are also efforts being made to restore and enhance where possible channelized urban drainage ways lt is important to remember that even though a stream may be hardened or modified in a particular location it may remain natural in other areas Over time it may be possible and even essential to restore these streams to a more natural state to improve stability and flood protection for nearby property owners In addition the protection of water quality is critical in all types of Santa Clara County streams both natural and unnatural because they eventually convey water to either Monterey Bay or San Francisco Bay U
30. ccomplish this goal Another hybrid approach is to use cellular confinement or rock on the lower slope and the upper slope can be graded back to a less steep slope and revegetated The rock must be keyed into the streambed to prevent undercutting and failure of the rock slope protection In the cases noted above the use of bank armoring is likely to cause more problems than it will solve because it will not address the root cause of the problem Instead efforts should be made to reduce the water s velocity or redirect it away from the bank using j hook weirs or vanes USE OF GRADE CONTROL STRUCTURES While efforts should be made to construct floodplains flood benches and to consider hybrid alternatives it is also important to consider whether a project should be addressed using a grade control structure For example sometimes bank erosion is a result of channel bed incision which increases the height of a bank and reduces vertical support If a channel is highly incised simply regrading the slope may not be sufficient in the long term and the project will need to address grade control in order to stabilize the bank effectively A variety of structures can be used such as log or rock weirs Newberry weirs and vanes in order to encourage sediment deposition and stabilization of the bed DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USE OF DEFLECTORS Finally in some cases it may be most appropriate to use smaller
31. ciples Processes and Practices USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 105 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FIGURE 17 LIVE LOG CRIB WALLS Live branches Rock fill Live branches placed so not more than 1 4 length extends outside of cribwall Undisturbed bankline Fill material suitable for rooting Rock fill os i m gt 2 i o 4 106 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V TABLE 2 EROSION REPAIR METHODS THAT ARE NOT RECOMMENDED Repair Method Appropriate Slope Appropriate Water IER Veloci Value 12 Concrete Crib Up to 0 25 1 High up to 15 ft sec Negative High Walls depending on size of crib wall openings 13 Articulated Up to 1 1 High up to 15 ft sec for Negative High Concrete Blocks closed cell ACBs low to medium for open cell ACBs 14 Gabions From 0 75 1 upto High up to 15 ft sec Negative High 3 1 lower velocity if planted depending on size and number of planting pockets Concrete 16 Gunite Slope Up to 1 1 High up to 15 ft sec Negative Medium 12 CONCRETE CRIB WALLS All crib walls tend to cause channel bed and bank erosion both in the immediate area and other areas downstream and may also cause erosion upstream Most crib walls eventually fail because they attempt to resolve a symptom of erosion not its cause The use of concrete crib walls is d
32. d not for example be constructed in a way that does not accommodate the beltwidth Doing otherwise increases erosion potential and maintenance costs Meander width is the amplitude of the meander within the beltwidth It is smaller than the beltwidth At a minimum the average meander width of a channel should not be compromised in the lower flood plains In the mid to upper slopes above the valley floor where the natural channel may be fairly straight the beltwidth should also be respected FACTORS THAT AFFECT STREAM STABILITY Several factors affect stream stability They include stream topography the width to depth ratio and extent of channel incision The quantity and movement of both water and sediment in a stream are two of the primary influences on the topography of a stream These materials tend to balance each other within the confines of the stream channel For example erosion on one bank DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V is typically balanced by sediment deposition on the other While the location and extent of the erosion and resulting deposition may change over time the width and depth of a stable stream does not change much Thus any type of erosion repair project must be designed to maintain width to depth ratio in order to ensure long term stream stability while also allowing the streambed to erode and fill naturally A channel s width to depth ratio is calculated by dividing the width of
33. e Water Velocity e ll floodplain 2 Slope Grading 2 1 or flatter for vegetation Low typically up to 6 ft sec Positive ul section 1 5 1 or flatter for boulder section if boulders used eg EN GNE i Wattling 2 1 or flatter for erosion Low Positive ow mat section 1 5 1 or flatter if boulders used 3 Erosion Mats 2 1 or flatter for erosion Generally 1 7 ft sec but can go Positive if planted Low mat section 1 5 1 or flatter up tol 2ft sec if vegetated 5 Bh yer 7 Vegetated Up to 1 1 TI Positive low Geogrids or Soil Lifts 8 Root wads and Medium 10 ft sec or less Positive if planted High boulders 9 Boulder Rock Up to 1 1 preferably 2 1 High up to 15 ft sec less where Negative Revetment voids in boulders are planted Negative to Neutral if planted 10 Cellular Up to 0 5 to 1 Medium to High 5 21 ft sec Neutral Medium Confinement depending on vegetation BEN 11 Live Log Crib Up to 0 25 1 Medium up to 12 ft sec or less Neutral to High if High eme pomo pep 4 84 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 1 MODIFIED FLOODPLAIN HOW TO CREATE A MODIFIED FLOODPLAIN The modified flood plain design provides the optimum solution for long term ecologically friendly and less expensive stability In urban areas property owners typically have short stretches of stream running through their property and often only on one side of the stream
34. eam gravel Be wary of mercury and other Avoid disturbing the creek bed contaminants Disturbed or excavated particularly spawning gravel After project soils in areas where soils are known to completion replace or restore any gravel contain mercury or other contaminants that was moved or removed to maintain should be removed or properly capped if the soil will be exposed to flood flows spawning areas for fish In areas whose soils are known to Take special care when establishing contain mercury remediate the disturbed stream access points because these points or excavated soils if they are exposed to can contribute undesirable sediment to the flood flows Wear protective equipment stream So Consult the Santa Clara Valley Water Use established access point District for disposal guidance wherever possible If it is necessary to create a temporary access point for construction do so as close USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 81 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FOLLOW UP MAINTENANCE Revegetate In areas that have been revegetated replace dead or dying plants and weeds Remove non native plant colonizers Ensure that all plants receive sufficient water Do not neglect stream bank repair after construction is over Minor maintenance activities help ensure a project s success Remove trash and debris Sometimes the accumulation of debris in the channel cause
35. ectiveness on the upper slopes Some tree species such as willows and cottonwoods are more successful when they are closer to the stream Others like oaks enjoy more success higher up the bank Where stream capacity is an issue for flood protection purposes choose vegetation that is flexible and that will not collect debris and slow high flows during flood events Use fast sprouting grass species for more immediate erosion control A regraded slope can be seeded with fast sprouting grass species such as sterile wheat or better yet a native grass sedge seed mix combined with a biodegradable erosion control blanket These species provide more immediate erosion control See Design Guides 4 and 5 for plant species Do not use chemical fertilizers herbicides or pesticides These chemicals can be easily transported to the creek by wind or rain and degrade water quality endangering aquatic life 4 80 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V WATERSHED FRIENDLY DESIGN BEST MANAGEMENT PRACTICES This section provides some tips for stream to the work area as possible in care during construction Proper use of best order to minimize adverse management practices BMPs can have a impacts When the project is tremendously beneficial impact on aquatic complete restore the access Point species and other wildlife human health to as natural and stable environmen
36. erosion from increased urban runoff On rural streams the active floodplain normally fills approximately every year or two Floodplain filling usually occurs more often in urban areas Vegetation is typically present in the floodplain area as it will become established between the alternating seasonal periods of inundation and sediment deposition Section 2 of the Guidelines and Standards also includes more detailed definitions and sketches showing these features in a variety of settings Important Note A stream s active floodplain is not to be confused with the delineation of floodplain used for flood insurance purposes The floodplain defined for flood insurance purposes is the one percent 100 year flood or the area that has a one percent chance of being flooded to a depth of one foot or greater each year For insurance purposes this equates to a 26 percent chance of suffering some flood damage during the term of a 30 year mortgage FIGURE 1 CROSS SECTIONAL VIEW OF A NATURAL STREAM Active Floodplain Active Channel Bankfull Stage Active Floodplain 4 70 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS STREAM BELTWIDTH AND STREAM MEANDER WIDTH A channel has a certain beltwidth within which it naturally moves This beltwidth can be determined by studying sections of the channel which have not been straightened pre development photographs or adjacent similar channels Levees shoul
37. figuration Active Active floodplain is floodplain 18 recreated recreated 4 86 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS HOW TO CREATE A MODIFIED FLOODPLAIN IN BROAD FLAT STRETCHES WITH SEDIMENT DEPOSITION In some cases a stream may have experienced heavy sediment deposition over the years In contrast to the deeply incised channels with heavy sediment deposition tend to be wide shallow and rather straight Although there may have been fish present at one time the shallow flows make it difficult for them to return Where there is room it is important to restore the nature meanders if possible DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V Figures 6 below shows a stream prior to a stream restoration project As you can see the channel was wide shallow and rather straight The bottom drawing shows that the channel was made narrower and constructed with a proper width depth ratio at the bankfull level This helped assure the proper transport of sediment through the area by increasing velocities in the active channel The active channel was moved away from the right bank and into the center of the channel corridor creating deep pools for steelhead trout and salmon Brush rolls were used on the top of the right floodplain to accumulate fine sediment and the right vertical stream bank was sloped back and vegetated FIGURES 6 STREAM CHANNEL CROSS SECTION VIEW USER MANUAL GUIDELINES a
38. hat may be causing systematic degradation of the creek channel incision which leads to toe failures and bank slumps These underlying causes of erosion could be natural features or constrictions but most likely they are non natural i e human made Oftentimes the source of the problem is an earlier effort to address an erosion problem upstream or downstream Depending on the extent of the problem it may be worthwhile for the property owner to consider a collective effort with neighboring property owners perhaps even including government and or public agencies who own land or rights of way in or near the stream Because actions taken to address erosion in one place can cause problems elsewhere permit applicants should consider the potential impacts on both the downstream and upstream streambed and banks when determining the type of erosion repair measure to use To this end property owners may be asked to provide professional analyses of stream geomorphology and or hydraulics to determine potential negative impacts and recommend ways to prevent them STEP 4 SEEK ASSISTANCE FROM THE SANTA CLARA VALLEY WATER DISTRICT SCVWD For SCVWD s assistance in conducting repair or maintenance contact the SCVWD s Watershed staff at 408 265 2600 There are three different scenarios related to ownership and easement that determine assistance eligibility SCVWD RIGHT OF WAY If the District owns the property where the strea
39. he lead agency Unless a public hearing is required by the local agency for the project a categorical exemption does not require a public hearing The document is simply filed at the county for a specified period 2 A Negative Declaration is issued by the lead agency for the project A Negative Declaration can be issued DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V if the project will have no significant impact on the environment without the need for mitigation measures to reduce a project impact to a less than significant level A public hearing to adopt the findings and the Negative Declaration is required Hint If at any time along the permitting or review process you find that your proposed project can have a significant impact on the environment and by redesigning your project the impact can be eliminated or reduced to insignificant you will save yourself time and money by redesigning your project A Mitigated Negative Declaration is issued for the project This means that there are significant impacts from your project on the environment but mitigation measures during implementation can be adopted to reduce these impacts to a less than significant level A mitigation monitoring and reporting plan is required to identify what who when and where for each mitigation measure thus ensuring that all mitigation measures are implemented A public hearing is required An Environmental Impact Report
40. heir function is not impaired by slight movement from settlement or other adjustments DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V DESIGN CRITERIA AND CONSIDERATIONS Rock should be keyed in approximately three feet below the bed elevation Rock can be graded from larger at the toe to smaller at the upper banks This method may cause channel scour and erosion especially downstream and along opposite banks if a modified floodplain is not constructed along the opposite bank It may also cause upstream scour 729A BOULDER REVETMENT WITH SOIL AND REVEGETATION This method consists of placing soil over the boulders and installing vegetation by staking and or direct seeding Biodegradable erosion control mats are placed over the soil to help control erosion until vegetation establishes itself Special care must be taken while driving live stakes between boulders to avoid damage to the cambium layer of the woody material and to ensure good soil water stake contact Thick rip rap layers may require special tools for establishing staking pilot holes DESIGN CONSIDERATIONS Woody material can be placed using a backhoe with an auger attachment or by driving a steel bar between boulders or by placing rock around durable planting tubes This method may cause channel scour and erosion of downstream and opposite banks if a modified floodplain is not constructed along the opposite bank It may also cause upstrea
41. ir project Finally alternative methods of protecting a streambank are presented starting with how to treat a reach of a stream in a more rural setting where there is room to use a more systemic approach and continuing with a variety of treatments for smaller urban parcels which include a small reach of a stream GOALS PURPOSE OF STREAMBANK PROTECTION ACTIVITIES In general the goals of any bank protection erosion repair activity should be to Maintain or increase stream stability and facilitate transport of sediment and water Avoid localized solutions that repair only a single erosion site but reduce the stability of neighboring stream banks USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 65 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V and cause erosion problems on upstream or downstream properties Enhance and increase native vegetation both in extent and diversity to provide habitat value and help ensure long term bank stability With these goals in mind this Design Guide delineates some general guidelines and issues to consider when embarking on a bank protection erosion repair project as well as a description of various erosion repair techniques This guidance also provides agency staff and streamside property owners with a brief overview of how streams are formed their common characteristics and features and typical causes of streambank erosion 4 66 USER MANUAL GUIDELINES
42. iscouraged This method is mentioned only for reference Concrete crib walls consist of stacked interlocking concrete frames that form a retaining wall Its structural strength is due in part to the composite design of a concrete frame with compacted backfill Crib walls are constructed with open face panels that are planted by live staking This method restricts plant growth to the size of the panel opening As the crib wall slope is flattened and the lattice becomes more open the vegetation potential increases and the allowable velocity decreases because of the exposed soil and vegetation Concrete crib walls perform similarly to live log crib walls Because the crib wall is a rigid structure it is more prone to massive failure in the event of undercutting or settlement USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 107 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 13 ARTICULATED CONCRETE BLOCKS Articulated concrete blocks ACB consists of concrete interlocking blocks that are cabled together to form mats that can be laid on the channel slope and or channel bottom There are two styles of ACBs open cell and closed cell The open cell style allows for vegetation to be recruited into the soil filling each cell Vegetation growth is restricted by the sizes of the cell openings and by the disconnection caused by the cell walls In our arid climate the long term viability of vegetation within the
43. lier the stream bank should always be revegetated with appropriate native plants FIGURE 9A SLOPE GRADING WITH VEGETATION FIGURE 9B CROSS SECTION OF SLOPE GRADING WITH VEGETATION AND ROCK TOE PROTECTION a Rock toe key optional 4 92 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 3 EROSION MATS This method consists of securing geotextile blankets made of biodegradable materials like jute or coconut fiber to channel banks using stakes or staples Biodegradable fabrics are preferable to plastic because they do not inhibit plant growth or act like a net if they are dislodged during a storm The erosion mats provide soft armor protection against erosive forces and are combined with live staking and direct seeding Abrasive sediment debris foot traffic and sunlight will slowly wear snag and tear these fabrics potentially undermining the structure That s why erosion mats are intended to be only the foundation of a vegetated erosion control system In other words the establishment of vegetation is crucial to the long term success of erosion mats DESIGN CONSIDERATIONS Toe protection may be required where significant toe scour is anticipated The bank must be smooth before installing blankets to ensure adequate contact and prevent subsurface erosion The erosion mats must be installed according to manufacturer s instructions in order to prevent failure DESIGN GUIDE 19 GUIDE
44. lls for 60 Available through the This 171 handb k i ide t Center for Watershed Protection at is 171 page handbook is a guide to A restoring eroding streambanks using P p org vegetation and flexible systems It features THE PRACTICE OF WATERSHED installation guidelines sample budgets PROTECTION TECHNIQUES FOR case studies and tips on choosing the best PROTECTING AND RESTORING restoration solution 20 plus 5 shipping URBAN WATERSHEDS At 80 Te onaer eal 8082899982 150 articles are included on all aspects of sos iwla org e 3 watershed protection Drawn from past HOW TO HOLD UP BANKS issues of Watershed Protection Techniques as USING ALL THE ASSETS well as a wealth of other Center papers and An informative well illustrated booklet on reports this 800 page book is organized controlling stream erosion Produced by the around the eight tools of watershed Boquet River Association BRASS a small protection and indexed for easy reference nonprofit group with extensive experience Available through the Center for Watershed in stream monitoring and restoration the Protection at http www cwp org book helps citizen groups tap community URBAN STREAM RESTORATION resources and find success with low cost techniques Techniques covered include streambank shaping grass seedling and live posts planting log cribbing and stone riprap installation To order send 8 to PRACTICES AN INITIAL ASSESSMENT This assesses
45. m is located District staff will visit the site to inspect the erosion determine if and how it should be addressed and then if need be take appropriate measures to do so SCVWD EASEMENT If the District has an easement on the section of the stream needing repairs District staff will visit the site to inspect the erosion Easements generally provide the District with the necessary rights to perform the work The District can make repairs within an easement after assessing the extent of the erosion the infrastructure affected the available funding and the need to conduct other work on District property PRIVATE OWNERSHIP If the stream is under private ownership District staff is generally available for a visit to the site however this availability will depend on the number of requests received and staff resources Staff can provide advice on an approach to use but the District will not design or construct the project Requests for technical assistance for minor erosion repair work can be submitted to the District via their web site at http www valleywater org Water Watersheds streams and floods Taking care of streams Service request form cfm To negotiate an agreement for assistance on a substantial repair project contact the District s Watershed staff at 408 265 2600 4 78 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS STEP 5 SECURE PERMITS FROM FEDERAL STATE AND OR LOCAL RESOURCE AGENCIES
46. m scour 1 Source California Department of Fish and Game California Salmonid Stream Habitat Restoration Manual Source Natural Resources Conservation Service Stream Corridor Restoration Principles Processes and Practices USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 103 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FIGURE 16 BOULDER REVETMENT WITH SOIL AND REVEGETATION Varies depending on gaps in riprap Riprap Up to 48 in long live stakes 1 2 in diameter with two lateral buds above grade Bottom of stakes to be in native soil Channel bed 4 104 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 10 CELLULAR CONFINEMENT SYSTEM Soil cellular confinement system geocell is a polyethylene plastic cellular system where structural strength is developed by the composite design of soil plant roots and the plastic s cellular configuration This system is available in eight inch deep honeycomb mats that can be installed in offset vertical layers to create terraced planting areas The honeycomb cells are filled with soil moderately compacted and planted with woody vegetation and grasses The structure functions similarly to a crib wall structure This method can also be used in combination with slope grading and vegetation on the upper slopes This method can foster the development of vegetation 11 LIVE LOG CRIB WALLS Live log crib w
47. mon The combination of riffles runs and pools is extremely important for fish because it provides different feeding spawning and or nursery areas These stream characteristics should be preserved restored and enhanced where possible as appropriate to the stream topography in any type of erosion repair effort DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 73 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 2 CAUSES OF STREAM BANK EROSION All streams erode to some extent as a part of natural processes Natural erosion is typically caused by 1 Hydraulic forces that remove bank material 2 Geotechnical instabilities 3 Or most commonly a combination of both these two forces HYDRAULIC FAILURES Hydraulic failures occur when the force or velocity of the water is greater than the natural cohesion of the soil In other words the forces that bind the soil together are overcome by the water Some visible features of hydraulic failures are erosion near the bottom or at the toe of a stream bank or alteration of the streambed Changes in the direction of flow constrictions increases or decreases in the amount of sediment and increased amount and duration of flow from impervious areas can all accelerate erosion of the stream bank or alteration of the streambed and in turn hydraulic failure Some of the sediment that is introduced in
48. mp STANDARDS FOR LAND USE NEAR STREAMS 4 87 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V POSSIBLE VARIATIONS ON THE FLOODPLAIN APPROACH RESTORING NATURAL STREAM MEANDERS Where there is sufficient room in the stream channel it can be very helpful to modify the channel in a way that restores natural stream meanders The diagram below shows how a creek channel can be narrowed and reformed with more meander As noted earlier a proper width depth ratio at the bankfull level is created and a modified floodplain can be constructed In this example three J Hook rock structures were installed with brush rolls on the right bank floodplain to divert the water away from the bank and into the center of the channel construct narrower meandering channel cut slope back and vegetate i Ce v brush p gt 2 brush P i Aue 3 rock J hook weirs 4 88 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS ADDITIONAL TOE AND BANK PROTECTION FOR HIGH FLOW VELOCITIES OR CONFINED AREAS In the uncommon situations where water velocities are especially high or where a structure is threatened by its proximity to the bank additional protection or a hybrid approach may be desired Placement of rock boulders at the toe of the slope along with placement of riparian branch cuttings such as willows into the spaces between the boulders into the soil or earth filled mats can a
49. nate or reduce as many potential health concerns and environmental impacts as possible Consider environmentally superior alternatives described in the previous section These methods are also generally easier and much faster to permit Incorporate the suggestions you receive during early consultation Employ a qualified design consultant with specialized expertise in stream analysis and design Pay attention to details Follow all the rules and listen to agency staff guidance Respond promptly to requests for information Be on time for meetings with representatives of the regulating agencies Do not cut corners Get in writing all dates procedures fees etc Be willing to negotiate Recognize that government regulators may have a great deal of authority over your project but that they are willing to negotiate You should be too 4 110 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS When in doubt ask If you are not sure whether your project needs a permit or whether it is regulated at all ask Going ahead without following the proper guidelines will ultimately cost you time money and goodwill Keep good records Keep notes of conversations and meetings Ask for interpretations of rules to be written by the agency representatives An easy way to do this is to confirm conversations by E mail Remember agency staff time is limited it is easier for them to review or comment on your understanding
50. oard and California Department of Fish and Game and federal agencies such as the Army Corps of Engineers and U S Fish and Wildlife Service to name a few For projects with an aquatic component such as work near a creek or stream a single application called the San Francisco Bay Area Joint Aquatic Resource Permit Application JARPA has been designed to replace individual applications for state regional and federal agencies As suggested earlier consider taking advantage of this consolidated Regional Water Quality Control California Fish Army Corps of Engineers E o tc N Q 2 a Q application to streamline the project permit application process If a project requires local approval such as that of the local city government or Santa Clara Valley Water District be sure to check with these agencies about what to include in the application since the JARPA document does not consider local agency requirements CALIFORNIA ENVIRONMENTAL QUALITY ACT Prior to obtaining permits for a project a California Environmental Quality Act CEQA review will be required if the project is undertaken by a public agency or if a public agency needs to issue a permit for a project CEQA is found in Section 21000 et seq of the Government Code and the CEQA guidelines are found in Section 1500 et seq of the California Code of Regulations 4 114 USER MANUAL GUIDELINES amp STANDARDS FOR LAND
51. olve a septic leach field near a creek or wetland Require a water well near a creek or wetland Involve work within historic o existing coastal wetlands Remove water from a cree for storage or direct use on non riparian land materials be generated and or stored on site Take place in adjacent to in a building adjacent to or near a river that has been designated as wild and scenic under state or federal law gt lt E __ LLLLL E Eo Bo ges USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 113 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V Planning or Public Santa Clara Valley Works Dept Water District Your City s Require water to be diverted from a river stream or lake for the project or activity Affect water quality deposition of silt an increase in water temperature a change in the pH level or in some other way Occur in an area where endangered or rare plant species are thought or known to occur Occur in an area where endangered or threatened fish bird or animal species are thought or known to occur SAN FRANCISCO BAY AREA JOINT AQUATIC RESOURCE PERMIT APPLICATION As discussed earlier projects in or near creeks and even intermittent streams can be regulated by many agencies the local city government local agencies such as the Santa Clara Valley Water District state agencies such as the San Francisco Bay Regional Water Quality Control B
52. ossible for several reasons First bank armoring prevents channels from adjusting to high flows and can increase the probability of flooding Bank armoring also causes accelerated flow velocities and turbulence along banks which then induces more erosion on unarmored banks Finally because armored banks cannot adjust to changing stream conditions they are prone to undercutting IMPORTANCE OF VEGETATION AND RIPARIAN BUFFERS The roots of well established vegetation not only protect the surface of stream banks but also penetrate deeply into the ground helping to stabilizing it Lack of vegetation close to a creek bank can contribute to slope instability and failure due to overbank drainage or soil saturation In addition to providing bank stability streamside vegetation filters pollutants shades and cools the stream increases infiltration reduces flash runoff and provides habitat for wildlife A variety of scientific studies of the minimum and optimum width of a vegetated buffer along a stream indicate that a width of 10 feet is not enough to provide adequate filtration or habitat A study by U S Fish and Wildlife indicates that in order to effectively remove pollutants a buffer of 50 feet is needed Other sources recommend a vegetated buffer that is 2 to 5 times the width of the stream channel While there is ongoing discussion about the most appropriate width for vegetated buffers it is conclusive that at least some
53. other significantly scoured areas The buried branches take root to reinforce the substrate while the tips produce vegetative top growth that protects the bank surface This method can also be used in combination with a rock toe vegetated geogrid or live cribwall as described later in this section FIGURE 13 BRUSH LAYERING DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V DESIGN CONSTRAINTS AND CONSIDERATIONS Installation is best done during dry periods or low flow conditions since construction requires earthwork A large amount of branches are needed for this method AT TIME OF INSTALLATION ina USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 99 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 7 VEGETATED GEOGRIDS OR DESIGN CONSIDERATIONS SENLEIETS Boulder placement must not constrict This method is similar to brush layering the channel cross section or reduce the but adds even more stability by wrapping width to depth ratio Otherwise the engineered soil lifts in biodegradable repair will likely destabilize the channel erosion control fabric or geotextiles between layers of live branches This method is useful where site constraints don t allow the slope to be laid back Boulder or log toe protection can also be incorporated into the design where site conditions warrant Armoring or the placement of boulders along the bank will increase turbulence in the area andother
54. pact fish habitat and might therefore require mitigation However downed trees and logs can often deflect high flows causing serious bed and bank erosion destroying fish habitat and degrading water quality For these reasons downed trees and logs need to be removed quickly Plant between October 15 and March 15 In order to minimize irrigation requirements and ensure that plants receive sufficient water for natural propagation plant in the fall and early winter Where soils are dry and water is limited irrigate as needed until the rainy season Do not introduce invasive non native vegetation species into the watershed Non native invasive plants are a serious problem because they often inappropriately constrict water flows and overtake native plant species See Design Guide 2 for more on invasive non natives Instead use locally collected native species for revegetation and replacement plantings Plant selection and density should be informed by a survey of natural areas on the same creek that have a similar ecological setting This can inform you as to what species would be found in the area and an approximate population density See Design Guide 4 and 5 Plant according to moisture needs using different types of vegetation on the upper and lower sections of the stream bank Plants have different tolerances for the wet conditions at the toe of slope They also vary in drought tolerance and erosion control eff
55. plain with terraces where possible Planting native riparian vegetation on the streambank and terraces in order to restore and provide long term stability If soft methods of protection are not feasible due to highly erosive forces then there is probably a channel dimension hydrology and or morphology problem Hard bank protection can cause more erosion and damage in the channel along the downstream and or upstream banks as well as on the opposite bank of the repair site Any consideration of the use of hardened materials should be with caution and with an assessment of the impacts that may occur Erosion repair methods 9 thorough 11 incorporate bank armoring which should be avoided The use of log and rock flow deflecting structures as described in method 1 is less expensive and a more environmentally friendly way of protecting banks from erosion Detailed guidance of these methods is beyond the scope of this Design Guide but should be considered by the design professional Erosion repair methods 12 through 16 are NOT recommended However they may be necessary when the site is constrained or where the water volume velocity bank steepness and resultant erosive forces necessitate the use of more extreme methods USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 83 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V TABLE 1 PREFERRED EROSION REPAIR METHODS Repair Method Appropiiate Slope Appropriat
56. re shaped by a combination of forming forces that include Gravity or the slope of the channel banks Friction which is a function of vegetation the soil s type and particle size and the channel s pattern and profile Velocity the speed of the water flow Quantity the volume of water flowing and sediment moving through the stream Over time streams move and shift in response to changes in these forming forces That is why streams do not naturally tend to flow in a straight line Instead they meander in search of equilibrium with their forming forces adjusting to changes in water flow and sediment transport These changes can have both natural and non natural causes CHARACTERISTICS AND HISTORY OF STREAMS IN SANTA CLARA COUNTY Some streams in Santa Clara County are still in a natural condition while others have been straightened or channelized in response to land development activities and flood control needs Throughout the County human made channels were created to contain the flows that once naturally fanned out over the valley floor carrying with them nutrients and sediment and creating alluvial fans and fresh water marsh habitat These human made channels were created to accommodate the use of land for agriculture or urban development and to ameliorate flooding conditions DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V HOW STREAMS FUNCTION Experience has also shown however that signifi
57. rence MOVING TOWARD SOFT MORE SYSTEMIC METHODS OF BANK PROTECTION EROSION REPAIR Traditional methods of controlling erosion have relied on hard structural practices such as covering banks with interlocking concrete blocks and building retaining walls However these techniques often have negative impacts on streams In many cases these methods are also expensive and ineffective in the long run Recommended instead are soft or bioengineered bank stabilization methods A bioengineered approach involves the planting of native streamside or riparian vegetation combined with the strategic placement of logs or minimal rock where necessary and regrading of steep slopes wherever possible in order to produce living systems that minimize erosion control sediment and provide habitat The natural attributes of plants when combined with stabilized bank slopes provide better dynamic stream systems than stationary hard structures An objective of this Design Guide is to protect and where appropriate restore streambanks and related stream resources Where suitable it encourages a systemic approach to streambank protection and stream restoration This Design Guide starts by describing how streams function typical features of a stream and importance of riparian vegetation It then discusses typical causes of streambank erosion and recommends basic measures to be considered when planning and designing a bank protection erosion repa
58. restricted cell openings is problematic However open planting areas can also be constructed into the ACB mats by creating an opening in the mat by removing some of the blocks The open areas can be revegetated with shrubs and trees Irrigation is necessary to aid plant establishment This method will create channel and bank erosion both down and upstream of protected areas It is environmentally unfriendly and prone to failure When it fails steel cables and stakes hazardously protrude from the mats into the channel This method is not appropriate for small erosion repair sites and is discouraged because of the limited potential for biotic resources 14 GABIONS This method consists of placing large wire baskets filled with rocks on channel banks either as mattresses or stacked in layers that resemble steps Gabions can sometimes naturally revegetate if adequate water and soil are available Gabions can also be revegetated using planting boxes Planting boxes are gabion cells that are left open to bare soil and revegetated with shrubs and trees Temporary irrigation may be provided to the planted vegetation in order to aid its establishment But wire baskets can deteriorate over time and may be harmful to fish Gabions are very hazardous and unfriendly to native fish especially salmonids which often try to spawn in gabions below the water line The basket wire deteriorates quickly and the fish are injured on the baske
59. rock toe 4 102 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 9 BOULDER ROCK REVETMENT Rock rip rap is a method for armoring stream banks with boulders that prevent bank erosion Rock riprap can be used at the toe of the slope in combination with other vegetative methods on the upper portions of the bank Rock can also be used for drainage outfall structures Rip rap footing is laid in a toe trench dug along the base of the bank The size of the rock is determined according to the expected velocity in the channel and can vary from 6 to 18 for velocities up to 10 feet per second up to 24 minimum for higher velocities Large angular boulders are best suited for this purpose because they tend to interlock The rock s specifications must meet certain standards in order to assure that it is structurally sound A gravel blanket that is at least one foot thick should be placed under the rock rip rap on slopes of 1 1 or greater This prevents underlying soil from being washed out which leads to slope slump and failure during periods of high flow Geotextile fabrics should be avoided since they prevent the natural establishment of vegetation This method should where appropriate be used with soil bioengineering systems or live vegetation to stabilize the upper bank and ensure a regenerative source of streambank vegetation A major benefit of this method is that the components are flexible and t
60. s erosion on nearby banks So Regularly remove debris such as trash and human caused debris Do not put yard waste in the creeks or on the banks where leaves and clippings can wash into the stream elf mulching Use biodegradable erosion control blankets on bare slopes or if it is too late in the season to establish vegetation The blankets will last for 1 to 3 years while natives reseed Monitor the success of natural revegetation before taking aggressive action to revegetate Woody debris from the site might make for suitable mulch Use bark and other wood products or fabric blankets above the high water line to prevent erosion of bare soil after construction is completed Use weed free certified mulch Do not use Eucalyptus Walnut or Tree of Heaven They produce an allelopathic compound that can be toxic to plants and aquatic organisms Be careful when trying to control rodents Burrowing rodents may be a nuisance and can damage levees on streams but do not use rodenticides Their effect on the local habitat is too destructive Instead consult County Vector Control 4 82 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 5 DETAILED DESCRIPTIONS OF EROSION REPAIR TECHNIQUES Described in this section are 16 different types of erosion repair methods Each description contains a brief overview of the repair method the
61. se agencies Refer to their web sites Read staff reports permit conditions and studies relating to your project or similar projects Contact the agencies in charge of granting permits for your project You may need to obtain different permits for your project from a number of agencies Contact the agencies that may need to issue a permit for your project to determine who will be involved Ask about the agency s permitting process obtain relevant forms and discuss potential timelines for obtaining your permits Do not expect to get schedule commitments at this stage but at least get an idea of the how the process works and a feel for how long it may take Write a complete project description A complete project description is crucial Include drawings photographs and other supporting materials to assist the regulatory agencies in understanding what your project entails Photographs and descriptions enable them to provide guidance and direction before a site visit can be scheduled Consult early and become familiar with agency staff Consultation with permitting and regulatory agencies should begin as early as possible An in person meeting is the best way to discuss your project Try to have plans maps photographs of the project location and other information available at the meeting You can also request that a staff person meet you at the site Reduce adverse environmental impacts Design your project to elimi
62. sitate to contact agency representatives early in the design process to determine whether you need a permit from their agency and to discuss potential repair options if you do DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 79 DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V SECTION 4 GENERAL GUIDANCE FOR WATERSHED FRIENDLY DESIGN USE VEGETATION TO RESTORE AND MAINTAIN STABILITY Revegetation of the streambank is one of the most common and often the most effective way to prevent erosion along a streambank This is because roots bind soils together which prevents erosion while leaves provide protection from rain splash erosion In addition the exposed trunks and stalks provide resistance to stream flow because they slow the water and decrease its erosive energy An added benefit is that vegetation provides ideal habitat for birds and other animals Vegetation planting methods commonly used include cuttings transplants live staking and direct seeding including hydro seeding Maintain streamside trees Avoid pruning trees unless it is necessary to the survival of the plant or the protection of existing property and or infrastructure as trees can critical shelter and shade for stream wildlife Do not remove affixed logs Logs that have been permanently or securely affixed to the streambank provide valuable habitat Their removal could negatively im
63. structures designed to redirect high velocity flow away from eroding banks and into the center of the channel Examples include spurs kickers deflectors vane dikes etc and they should be considered as a way to train flows and reduce the amount of engineered bank protection The photographs below provide some guidance on how and when these devices can be used Detailed guidance of these methods however is beyond the scope of this Design Guide but should be considered by the design professional For a rock cross vane structure boulders are placed in an upside down V shaped structure in the stream This V shaped design serves to slow water velocities near the banks and direct the flow toward the center of the stream The banks then become depositional areas instead of erosion areas At the same time the increased velocities in the center of the channel actually increase the channel s flow and sediment transport capacity reducing the risk for infrastructure flooding during high flow events Finally the rocks in the center serve as a channel grade control The drop off just downstream of the rocks creates a deep hole which slows flows and can provide an excellent fish hold and hide habitat even at very low flows The rock J hook structure is used to protect one side of the river bank by directing flows from that side to the center of the stream As with the rock cross vane structure the increased velocities in the
64. surface erosion It works well in straight stream sections and wherever flow velocity is low DESIGN CONSIDERATIONS The long bundles trap and hold soil on banks by creating small dam like structures effectively segmenting the slope length into a series of shorter slope lengths This method enhances the opportunities for locally native species to colonize and therefore should where appropriate be used with other soil bioengineering systems and live plantings Reinforcement at the toe of bank may be a limiting factor Contour wattling does not work well in locations where slopes are undergoing geotechnical failure 724A CONTOUR WATTLING WITH BOULDER OR LOG TOE PROTECTION Appropriately sized boulders are placed at the toe of the rebuilt bank up to the bankfull discharge water elevation or slightly higher Voids between the boulders can be planted using live stakes DESIGN CONSIDERATIONS Boulder placement must not constrict the channel cross section or reduce the width to depth ratio Otherwise the repair will likely destabilize the channel The placement of boulders or armoring along the bank may increase turbulence in the area and other areas downstream which could increase erosion 4 94 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V FIGURE 10 CONTOUR WATTLING So AFTER TOPSOIL COVERING Q
65. t property and public services condition as possible Prevent soil at construction entrances from being When restoring a damaged section tracked onto streets near of a streambank imitate natural work sites stream features such as channel meanders appropriate width and depth and vegetation This will stabilize the channel Details of this concept are CONSTRUCTION BMPS Control dust Dust can be a nuisance and have an adverse impact on water quality included in Section 5 of this Design Guide To control dust Observe work windows In channel e Water active maintenance areas work should generally be conducted so that they are sufficiently moist during the dry season between to prevent dust June15th and October 15th to minimize negative impacts to plant and wildlife Sometimes these dates will Sweep any paved access roads of visible soil material vary depending on the wildlife species Cover trucks hauling sediment in the area Do not use heavy equipment ensure that their tailgates are during spawning or migration seasons closed and brush off any as it can destroy fish habitat excess ditt If construction during periods of stream flow can not be avoided include measures Store and secure materials to separate area of disturbance from Remove all building materials debris stream flow to minimize turbidity lumber et cetera within 2 days of in stream completing the project Avoid removing in str
66. t native plants wildlife or fisheries Result in stormwater discharge into a creek or wetland Divert or obstruct the natural flow or change the natural bed or bank of a creek or wetland nvolve repair rehabilitation or replacement of any structure or fill adjacent to a creek or wetland Involve placement of bank protection or stabilization structures or materials e g gabions riprap concrete slurry sacks Involve building any structure adjacent to a creek or wetland enhancement attraction or harvesting devices and activities Q N a n a o NE P E HE 4 112 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V Your City s Planning or Public Santa Clara Valley Water District Works Dept Regional Water Quality Control Board Wildlife Service SWRCB Water California Fish and Game Army Corps of Engineers U S Fish amp Use materials trom a streambed including but not limited to boulders rocks gravel sand and wood debris Require the disposal or deposition of debris waste or any material containing crumbled flaked or ground pavement with a possibility that such material could pass into a creek or wetland Involve the removal of any materials from or add fill to a creek or wetland nvolve grading or fill near a creek or wetland Involve a bridge or culvert Involve utility pipe lines Inv
67. to the stream will naturally deposit on the bottom of the stream Over time this may raise the bottom of the stream and reduce the capacity of the active channel forcing the water to spread out laterally This causes erosion and steepening of the stream banks This can also occur when a stream is starved of sediment typically by dams or erosion control structures and the excess energy that would have been used to transport sediment is now free to erode bed and banks This condition typically occurs with the construction of hardened channel linings or with the addition of other types of instream debris sediment or detention basins that trap sediment In this case the erosion down cutting and steepening of the streambed and banks occurs below the lined section or instream basin causing the eroded sediment to settle farther downstream Nonetheless the impact on the stream is similar Thus for hydraulic failures the most effective erosion repairs are accomplished by addressing the root cause of the failure which may include installation of measures to redirect flow increasing the erosion resistance of the bank by planting vegetation on the bank or adding protection to the toe of the stream bank GEOTECHNICAL FAILURES Geotechnical failures occur when gravitational forces are greater than the strength of the soil These failures are usually caused by over steepened banks and or excess moisture in the soil This res
68. ts sharp wire barbs Furthermore the baskets used to line or armor the banks of streams cause bed and bank erosion They often undercut or fail due to slumping of the soil on which they are constructed The use of gabions is discouraged and are rarely permitted by the Department of Fish and Game except in extreme situations The material is included here for information 4 108 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 15 SACKED CONCRETE Sacked concrete slope protection consists of burlap bags filled with concrete and placed against channel banks Sacked concrete does not provide any revegetation potential However it offers the opportunity to contour walls around existing vegetation such as tree wells Sacked concrete should not be used because it causes erosion degrades water quality and destroys other beneficial uses It is included here for reference There may however be extreme circumstances where site constraints vertical slopes and high velocities preclude all other options DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V 16 GUNITE SLOPE PROTECTION Gunite slope protection consists of a pressurized concrete mixture sprayed over an eroded bank The gunite can be textured colored and formed for aesthetics to mimic natural rock Reinforcing steel may be placed against the bank prior to spraying This is not an acceptable method of erosion repair but is included here because it h
69. ults in the movement of earth better known as a landslide Near a stream the likely causes of this type of failure are a high groundwater table poorly designed surface drainage systems such as those that drain surface runoff directly over the top of the stream bank leaking swimming pools and leaking septic systems or water lines which saturate the stream bank Thus for most geotechnical failures what must be addressed is the source of the water that s causing excess moisture in the vicinity of the stream bank COMBINATION FAILURES The third type of failure is a combination of hydraulic forces and geotechnical instabilities Hydraulic failures often lead to geotechnical failures As the toe of the stream bank erodes or the channel cuts downward because of hydraulic forces the bank effectively increases in height and becomes too steep and unstable Sometimes the upper portion of the stream bank fails from lack of support and slides into the stream This process is well described in the document Maintaining Corte madera Creek A Citizen s Guide to Creek side Property Protection which was prepared by Phil Williams and Associates in Collaboration with H T Harvey and Associates for the San Francisquito Creek Joint Powers Authority They write The higher a bank is the flatter the angle must be to prevent slumping For example most 4 74 USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS soils will s
70. upport a three foot high vertical bank but if the river cuts a deeper channel say five feet the bank will collapse under its own weight A five foot tall bank would need to be graded to a lower gradient to be as stable as a three foot vertical bank and a ten foot high bank would have to be excavated to an even lower gradient to be stable The higher the bank the lower the stable gradient becomes The best remedy for this problem the problem of an over steepened bank experiencing both hydraulic DESIGN GUIDE 19 GUIDELINES AND STANDARDS I V and geotechnical failures combines several steps The first step involves regrading the slope to a more stable angle which is why it is called laying it back The second step involves reinforcing the toe where necessary with biotechnical methods such as logs and rocks The third step involves reducing erosive energy on the bank by planting the bank so that it does not become over steepened again For an illustration see figure 3 below FIGURE 3 LAYING BACK A STREAMBANK TO INCREASE STABILITY Streambank is regraded back to amore stable p configuration Active floodplain is recreated hes Deeply Incised Streambanks Active floodplain is recreated USER MANUAL GUIDELINES amp STANDARDS FOR LAND USE NEAR STREAMS 4 75 BANK PROTECTION EROSION REPAIR DESIGN GUIDE PART TWO TECHNIQUES AND GUIDANCE FOR DEVELOPING A WATERSHED FRIENDLY EROSIO

Chapter 4 - Bank Protection/Erosion Repair guides

Contents

Download Pdf Manuals

Related Search

Related Contents