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Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.6. Stream Restoration and Bioengineering

The traditional approach to designing highway structures over water crossings has been based on channel hydraulics, with little consideration of stream stability, causing reduced meanders, costly upstream and downstream erosion problems, water quality impacts, barriers to fish passage, and altering associated wetland and floodplain function. Increasingly, engineers and environmental professionals are turning toward design procedures that minimize disruption of stable stream channels and design in accordance with the natural fluvial geomorphology of rivers. These principles can also be used to restore the physical, biological, and aesthetic characteristics of degraded rivers or help to maintain the natural stream properties for newly constructed projects.

Stream restoration and mitigation is a complex process that addresses the active channel as well as the floodplain and the vegetation along its edges. Geomorphically mature natural channels are dynamically stable and are characterized by an equilibrium of sediment supply and transport. The active channel, floodplain, slope and discharge of natural channels provide the velocity necessary to transport sediment generated in the basin. The aquatic community that resides in the natural channel and along its floodplain has evolved to exploit the features of the channel and to respond to the dynamic equilibrium that has been established. Healthy fish communities tend to exist in productive, dynamically stable channel systems. Such systems provide a suitable mix of habitat features: pools, riffles, bed materials, bank features, aquatic and stream bank vegetation, woody debris, etc. that provide for the basic life requisites of food, reproduction and cover. Therefore, dynamically stable natural channels provide good fish habitat that is sustainable over a wide range of hydrologic conditions. It is generally recognized that natural channels provide optimal sustainable fish habitat for the given natural climate, geology and terrain. Improving fish habitat in natural conditions may not be sustainable over the long term, although short-term improvements are feasible. Natural stream channels are the result of the gradual evolution of the natural landscape and exist in a state of dynamic equilibrium. Natural channels typically lie in valleys with floodplains that attenuate peak flood flows. Their geometry (e.g., channel depth, slope, width, sinuosity, meander wavelength and width-to-depth ratio) can be described by regime equations which depend on the geology and geography of the watershed. This provides a tool that can be used to design channel diversions or realignments in accordance with natural regime conditions and to design watercourse crossings to accommodate natural channel processes. [N]

When changes to the channel, floodplain, vegetation, flow or sediment supply significantly affect this equilibrium, the stream may become unstable and start adjusting toward a new equilibrium state. This transition may take a long time and may substantially change water quality, habitat and adjacent property. Stream restoration re-establishes the general structure, function and self-sustaining behavior of the stream system that existed prior to disturbance, so the stream does not aggrade or degrade and so that it provides the highest level of aquatic habitat and biological diversity possible. To accomplish this, restoration may involve:

  • Removal of the watershed disturbances that are causing stream instability.
  • Installation of structures and planting of vegetation to protect streambanks and provide habitat.
  • Reshaping or replacement of unstable stream reaches into appropriately designed functional streams and associated floodplains.

Bioengineering is the use of plant material, living or dead, to alleviate environmental problems such as shallow rapid landslides, and eroding slopes and streambanks. Plants are an important structural component of bioengineered systems, not just an aesthetic element. This approach to slope stabilization requires a true partnership between engineering geologists, maintenance personnel, civil engineers, and landscape architects. Bioengineering mimics nature by using locally available materials and a minimum of heavy equipment. Hence it can offer designers and roadside managers an inexpensive way to resolve local environmental problems. These techniques can also be used in combination with "hard" engineering techniques such as rock or concrete structures.

The following benefits of bioengineering, or soil bioengineering as it is commonly called, are outlined by: [N]

  • Soil bioengineering work is often the only practical alternative on sensitive or steep sites where heavy machinery is not feasible.
  • Installation of soil bioengineered systems while problems are small will provide economic savings and minimize potential impacts to the road and adjoining areas. Erosion areas often begin small and eventually expand to a size requiring costly traditional engineering solutions.
  • Many designs can be implemented by hand crews.
  • Native plant species are usually readily available and adapted to local climate and soil conditions. Costs might be limited to labor for harvesting, handling, and transport to the project site.
  • Soil bioengineering projects may be installed during the dormant season of late fall, winter, and early spring. This is the best time to install plants and it often coincides with a time when other construction work is slow.
  • Years of monitoring have demonstrated that soil bioengineering systems provide limited initial benefits, but grow stronger with time as vegetation becomes established. Even if plants die, roots and surface organic litter continue to play an important role during reestablishment of other plants.
  • Once plants are established, root systems remove excess moisture from the soil profile. This often is the key to long-term soil stability.
  • Soil bioengineering provides improved environmental functions, such as slope stabilization, stormwater retention, and habitat values.

Nationwide, there is strong support for this natural stability approach from federal and state regulatory agencies involved in the review of highway projects.

 

3.6.1 Planning Considerations for Stream Restoration and Bioengineering
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A literature review for Transportation and the Environment (CTE) and NCDOT by the NCSU Stream Restoration Institute for the Center found that despite research gaps in understanding the goals of restoration, spatial and temporal aspects of structure use and placement, and the reach level hydraulic effects of structures, most authors agree that the process and design of stream restoration should cover the following principle areas: [N]

  • Analysis of channel history and evolution
  • Analysis of cause and effect of change
  • Analysis of current condition
  • Development of specific restoration goals and objectives prior to design
  • Holistic approach to account for channel process, riparian and aquatic function
  • Consideration of passive practices (such as fencing against livestock)
  • Natural channel design to restore function

WSDOT outlines the following stewardship practices when planning and designing bioengineering projects. [N]

  • Evaluate soil bioengineering methods as a possible tool for remediation and restoration of degraded slopes. Soil bioengineering has unique attributes, but is not appropriate for all sites. In some cases a conventional vegetative treatment works with less cost, or it may be best to use a geotechnically-engineered system alone or in combination with soil bioengineering.
  • Evaluate projects that leave exposed slopes, and slopes requiring high maintenance for stabilization, for possible application of soil bioengineering technologies.
  • Include bioengineering technologies as an alternative when evaluating costs.
  • Include a slope stability analysis in plans for large erosional slopes.

Consider the natural history, cultural, and social issues of the surrounding landscape as well. A proposed soil bioengineering project within a forested landscape, for example, requires knowledge and understanding of:

  • Road construction methods and current maintenance practices.
  • Objective of the bioengineering project - repair, remediation, prevention, habitat, etc.
  • The area's geologic and glacial history.
  • Its propensity for wild fires, wind storms, and floods.
  • Occurrence and trends of natural and management related erosion.
  • Sequence of vegetation removal and revegetation efforts.
  • Fire management history.
  • Soil types and properties
  • Hydraulic and hydrological erosion and scour characteristics.
  • How the area is used by contemporary people and how it has been used in the past
  • What resources (for example, water, native vegetation, non-native vegetation, fish, wildlife) are used by different groups of people
  • What stakeholders are interested in the area and its resources

The following basic planning considerations are good environmental stewardship practice when planning and designing stream restoration and bioengineering projects:

Channel Features
The channel must possess key habitat characteristics including food supply for production, appropriate areas for reproduction, areas for refuge and rest, and linkages between these areas. When designing a channel reach these habitat characteristics need to be considered in relation to the role of the reach in the stream habitat system. Features of the channel that should comply with channel regime relationships and replicate local natural analogues include: [N]
  • Channel morphology: width, depth, pool area, riffle area, sinuosity, meander wave length, bed material, bank material and slope.
  • Habitat substrate: percentage area in boulders (substrate larger than 256 mm), percentage area in cobbles (64 to 256 mm), percentage area in gravels (2 to 64 mm), percentage area in fines (< 2 mm), percentage bed area vegetated; and
  • Habitat structure: type of instream cover, percentage of instream area covered, length of undercut bank, percentage of channel eroding, percentage bank area in debris cover, shading.
  • Riparian Zone: type of riparian vegetation, extent of riparian vegetation. The channel design should produce an overall channel form consistent with that which would evolve naturally under the same conditions. This can be accomplished by comparing stream classification attributes with representative stream reaches that are nearby. The use of natural analogues to determine channel characteristics is recommended wherever possible.
Conveyance Capacity
Flows that entrain sediment, cause bed and bank erosion, and flood the areas adjacent to the channel are important to aquatic habitat. Bankfull discharge is considered to be the flow that determines channel characteristics of width, depth, sediment size and sorting, and channel plan form.

Flows exceeding 1:10 and 1:25 year recurrence intervals are normally the flows that connect the channel to the riparian zone and affect the floodplain features of wetlands, vegetation cover, and sediment deposition. Depending on the type of stream system, the floods greater than the 1:25 year and up to the 1:100 year flow fill the valley bottom, defining the limit of fluvial influence on the landscape. The active channel area should, wherever possible, provide conveyance up to the 2-year return period event. Additional conveyance should be supplied by the riparian zone or floodplain. When site conditions limit the use of a floodplain to convey flows, structural measures such as additional armoring, may be required. [N]

Low Flows
Low flows are defined by the flow duration curve for the watershed. If the data for the derivation of the low flows are not available they can be developed from regional relationships for estimating low flows. Provided a natural channel can support sustainable fish habitat, design guidelines should be incorporated into the channel design based on target fish species. For example, intermittent streams would provide habitat for forage fish or spawning habitat for spring spawners such as arctic grayling or northern pike. Streams with permanent flow could be designed to support target sport fish or other target species.

Human uses
The way the stream is used by various groups of people today, and the ways in which it has been used in the past, are important variables to understand when planning a restoration or bioengineering project. Not only must human uses be considered in assessing the environmental impacts of such a project under NEPA, the National Historic Preservation Act, and other laws, but they may be critical to the design of the project itself, and they may offer particular opportunities for creative cooperative management. For example, a stream may be used by a Native American community as a source of fish, or by an Asian-American community as a source of natural medicines. If possible, it is important to avoid impacting such uses. Also, such communities may be stakeholders whose cooperation will simplify and improve the quality of a restoration project.

Information Requirements

Channel measurements include a site description, cross-sectional characteristics across the channel and valley, an assessment of bed and bank material, documentation of bank vegetative cover, channel profile and channel plantform.

NCHRP Project 25-25, Task 8, was published on-line in 2006, providing guidance on Developing Performance Data Collection Protocol for Stream Restoration.

Site Description
The recommended procedure for characterizing the reach, the riparian zone, and the valley bottom is as follows: [N]
  • Locate the reach to be designed on a map with a scale of 1:2000 for urban areas with contour intervals of 0.3 m. A 1:10,000 scale map should be used for rural areas. Also locate the reach on air photos with a scale of 1:2000, if possible. As air photos of this scale are unlikely to be available unless they are taken specifically for the project, it may be necessary to use smaller scale air photos.
  • Determine the upstream drainage area.
  • Locate the upstream drainage basin and document its condition in terms of land use and level of disturbance. Identify any potential changes to it, including development, impervious surface development, channelization, drainage of wetlands, installation of stormwater ponds, or infiltration fields.
  • Locate the valley and document its width, terraces and breaks in the slope, and any evidence of floodlines.
  • Locate and identify any structures and other modifications to the channel, banks, and floodplain.
  • Locate and map out existing tree cover, shrubs, and understory cover. Locate any debris, stumps, or large boulders in the channel, banks, or floodplain.
Cross-Sectional Measurements
Measurements of channel and valley cross-sections should extend across the valley slope and include the following: [N]
  • Stream width at the time of measurement of the flow.
  • Average depth and maximum depth at the time of flow measurement.
  • Bankfull width.
  • Average and maximum depth at bankfull discharge.
  • Stream entrenchment ratio.
Bed and Bank Material
Assessment of bed and bank material should be carried out by taking the following measurements: [N]
  • Sieve particle size analysis for various samples taken from all representative material types in the section. If bed materials are too large for sieve analysis, characterize the grain size distribution by counting stones.
  • A sketch of the location and a description of the condition of each representative material type.
  • Visual estimates of the percentage of the bed's area covered by boulders, cobbles, gravel and sands, and fines.
  • The area and nature of the vegetative cover on the bed.
  • The particle size data should be plotted as cumulative percent to calculate d 15, d 50 and d 84 of the particle size distribution.
Bank Vegetative Cover
Bank vegetative cover should be documented to include the following: [N]
  • Density and height, using a gridded sampling frame to assess cover and to sample numbers of plants, for the smaller plants.
  • Plant species, associates, and each type's percentage of cover should be noted.
  • In the case of trees, sampling should be carried out at regular intervals along the transect.
  • Location of snags and overhanging vegetation should be noted.
  • The height of vegetation and width of the vegetative buffers along the bank should be assessed.
Profile and Plan Measurements
For the design of a channel, the important variables required include the following: [N]
  • For each station at which the cross-sectional data were gathered, the following should be measured according to a standard datum: water level, bed level, top of bank level, and levels of any terraces. Any historical high water marks should also be recorded.
  • The plan form of the channel should be mapped. The map should include the thalweg's path, cut banks and point bars, mid-channel bars, riffles and pools, snags, and other obstructions.
  • Meander characteristics including wavelength, radius of curvature, and meander belt width and amplitude.
  • All elevations should be placed on the map so that the geometry of all features can be referenced.
  • Depressions, wetlands, and other water storage areas in the floodplain should be mapped.
  • Vegetative cover in the channel and snags should be mapped.
  • Bank vegetative cover, overhanging vegetation, and riparian and floodplain vegetation should be mapped.

Use Characterization
Through consultation with stakeholders, and sometimes appropriate background historical, sociological, ethnographic and archaeological studies, the following information should be gathered:

  • How has the stream and its elements (water, wetlands, channel, meanders, springs, stands of vegetation, fish populations, etc.) been used in the past, and by whom?
  • How are these elements used today, and by whom?
  • What expectations are there about future uses, and who holds them?
  • Who (if anyone) has legal (including treaty) rights to the stream or its resources?
  • Are the various stakeholders willing to participate in restoration and bioengineering?
  • Are there cultural, social, economic, or linguistic barriers to their participation? If so, how can these be overcome?
  • Are there particular areas along the stream, or particular elements within or along it, that require special consideration in planning because of their cultural importance of uses?
Design Steps
Many criteria need to be taken into account for the complex process of designing a channel realignment or channelized section. These include: [N]
  • Discharge capacity (e.g., major flood)
  • Channel stability and sediment equilibrium (channel regime)
  • Riparian zone vegetation
  • Fisheries habitat (possibly species specific)
  • Recreational opportunities (active or passive)
  • Other current uses and use opportunities
  • Aesthetics (viewscapes)
  • Erosion protection

Since these objectives are not necessarily compatible, design conflicts can arise. For example, the objectives for fisheries habitat will affect requirements for vegetation and physical features, recreational and aesthetic objectives could affect topography and vegetation requirements, and the geomorphological features required to provide a stable stream may reduce its capacity during flood events. Physical constraints, such as urban encroachment, may exist and must be considered in the design process. Choosing the right design parameters involves careful consideration of all the objectives for the stream system and the constraints that exist within the valley. Tradeoffs may be necessary to reconcile differences to establish workable design parameters. The recommended design steps are outlined as follows: [N]

  • Step 1: Define Objectives for Design. Identify the objectives to be met in the design. Multiple objectives may include conveyance, fisheries, habitat, recreation, aesthetics, and maintenance.
  • Step 2: Define Existing Conditions. The existing characteristics should be identified and detailed.
  • Step 3: Define Expected Natural Regime. Once the existing conditions are identified, the change in natural regime should be established.
  • Step 4: Identify Inconsistencies. The predicted regime and the existing regime should be compared to identify any inconsistencies and to determine if the stream is in equilibrium.
  • Step 5: Design Parameters for Unconstrained Design. Design parameters for the channel should be developed that will meet the objectives and provide stable, natural conditions.
  • Step 6: Identify Constraints. Identify the constraints to the channel such as property encroachments, roadways, etc.
  • Step 7: Identify Tradeoffs. The constraints and optimum conditions should be compared and the tradeoffs should be identified.
  • Step 8: Develop Final Design Parameters. The tradeoffs should be evaluated and decisions made about selecting design parameters. The design should be compared to the objectives and any shortcomings should be identified.
  • Step 9: Evaluate Design. The design parameters should be compared to the unconstrained condition (see Step 5) and the differences should be evaluated for acceptability.
Climatic Conditions
Climates near the ground can vary considerably within short distances. South facing valley walls, for example, receive more direct sun rays, which cause higher soil temperatures, increased evaporation, more rapid snowmelt in the spring, and generally drier conditions than on the more shaded north facing walls. This difference will influence erosion rates and the composition and vigor of revegetation efforts.
  • Consider precipitation types, amounts, seasonal variation, and duration.
  • Consider temperatures, including seasonal averages and extremes.
Topography and Aspect
  • Slope gradient.
  • Terrain shape (for example, gentle slope to valley or sharp peaks).
  • Elevation of project area.
  • Direction of sun exposure.
Soils
Identify conditions above, below, or within the project site that might have an effect on the project and incorporate these considerations into the design. Consult with the HQ Engineering Geologist to determine need for slope stability analysis. Some categories below will require soil testing to determine.
  • Substrate - take soil probe sample from potential site.
  • Soil types
  • Soil permeability
  • Moisture holding capacity
  • Nutrient availability
Water
Detailed analysis or work in streams or rivers will require consultation with a hydraulics engineer. Work affecting streams or rivers will require consultation with the DOT environmental office.
  • Water velocity: Lateral stream stability
  • Hydrologic regime: general and site specific.
  • If applicable, stream and fish types affected by the erosion site.
  • Location of natural drainage channels and areas of overland flow from road surfaces.
  • Areas for safe water diversion.
  • Condition of ditch line and culvert inlets and outlets.
Erosion Process
  • Evidence of past sliding: deep or shallow failure surface in vicinity.
  • Regional geomorphic trends or slope features (review aerial photos).
  • Type of mass wasting or surface erosion feature.
  • Source of eroding material: road fill slope, cut slope, landing, etc.
  • Trend of site: improving naturally, remaining uniform, or worsening.
Vegetation
Living vegetation is the most critical component of a bioengineered system. Existing vegetation and knowledge of predisturbance plant communities can inform the designer of project limitations, opportunities, and long-term ecological goals. Plants that can resist mechanical stresses of erosion, floods, and landslides, while developing a strong, stabilizing root system are best suited for soil bioengineering applications. The best indicator of which plant materials to consider for the soil bioengineering project is the plants growing on or adjacent to the project site. Deciding which plants to use is affected by the following factors:
  • Site characteristics (topography, elevation, aspect, soil moisture, nutrient levels).
  • Existing vegetation.
  • Intended role of vegetation in the project.
  • Growth characteristics and ecological relationships of the plants.
  • Availability.
  • Locations for plant and seed collection.
  • Plant species and amount growing within and adjacent to project site. It is especially important to identify colonizing species.
  • Logistical and economic constraints.

Plant materials are chosen from among those species available on the site or nearby. Alternatively, it might be possible to salvage like species from a similar area where vegetation is scheduled to be removed. Logistical concerns are important in the selection of plant material.

 

3.6.2 Coordination and Communication on Bioengineering Projects
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The complexity of the project dictates the level at which the following environmental stewardship practices in bioengineering or stream restoration are performed. An interdisciplinary team is typically necessary for all steps. [N]

  • Involve all associated disciplines early in the process.
  • Involve external stakeholders early and throughout the process, including all those who use the channel, wetlands, and associated resources
  • Establish clear project objectives.
  • Conduct predesign field review.
  • Conduct plan-in-hand field review.

 

3.6.3 Available Guidebooks and Research in Progress
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In October 1998, FHWA, AASHTO, and TRB sponsored a scanning review of European practice for bridge scour and stream instability countermeasures. [N] Since that time, state DOTs have undertaken a number of research efforts to establish regionally appropriate guidelines. NYSDOT and NCDOT are among other DOTs that include recommendations for appropriate practices when working near streams in maintenance or construction manuals.

Materials for an accompanying four-day workshop held for 35 NCDOT staff are available from the NCSU Stream Restoration Institute, NCDOT, or CTE.

Maryland's Waterway Construction Guidelines recommends that the planning and design of any stabilization, restoration, or in-stream construction project should include a set of clearly defined restoration objectives, a comprehensive monitoring strategy, and an adaptive management plan. Objectives vary from aesthetic improvements to habitat enhancement to safety and installation of hydraulic structures and roadways. Identifying the objective of the project must be accomplished before the design process can begin. Regardless of the nature of the objective, it should include measurable performance criteria. Performance criteria are quantitative measurements that are made in the stream corridor and compared to the project's objectives and can include parameters such as suspended sediment load and rate of lateral channel migration. A comprehensive monitoring strategy including appropriate baseline studies and timing, frequency, and location of field measurements, is necessary to assess the degree of project success or failure and to determine an adaptive management plan. Options for an adaptive management plan include adjustment or maintenance of individual measures, modification of project goals and objectives, and project redesign.

WSDOT's Integrated Streambank Protection Guidelines (ISPG)Manual resulted from the 2002 finalization of an effort by WSDOT, the Washington State Department of Fish and Wildlife, the Washington State Department of Ecology, the U.S. Army Corps of Engineers, and the U.S. Fish and Wildlife Service. The ISPG contains chapters on the mechanisms and causes of streambank failure, the best method for selecting appropriate solutions, examples of appropriate solutions, and technical background material. WSDOT has worked with regulatory agencies and other stakeholder to make the ISPG an agreed-upon multi-agency standard, improving bank stabilization efforts while expediting project delivery. The ISPG is part of a series of manuals designed to protect and restore fully functioning marine, freshwater, and riparian habitat in the state and to encourage permit streamlining through the provision of proven, detailed, and well-illustrated technical solutions. Written by professional resource engineers and managers, these manuals - including the ISPG - are geared toward local, state, and federal agencies, elected officials, engineering design consultants, volunteer restoration groups, and riparian landowners. In 2003, WSDOT conducted training based on the ISPG statewide and throughout WSDOT.

In September 2004, Washington State completed Stream Habitat Restoration Guidelines including chapters on Stream Processes and Habitat, Stream Habitat Assessment, Developing A Restoration Strategy, Designing and Implementing Stream Habitat Restoration Techniques, and a variety of Techniques including:

In addition to a Glossary, overviews of Hydrology, Hydraulics, and Fluvial Geomorphology, Construction Considerations, Placement and Anchoring of Large Wood, Typical Permits Required for Work in and Around Water, and Monitoring Considerations are also included.

Federal efforts have included the following:

The latter incorporates and reflects the experiences of the fifteen collaborating agencies and has received the endorsement of and awards from the American Society of Landscape Architects. It is more general than some of the other guidebooks available and is easily applicable nationwide in both urban and rural settings, to a range of stream types. The guide is divided into three principal parts. Part I provides back-ground on the fundamental concepts of stream corridor structure, processes, functions, and the effects of disturbance. Part II focuses on a general restoration plan development process comprised of several fundamental steps. For example, in analyzing stream restoration alternatives, a management summary of proposed activities should be prepared, including an overview of the following elements:

  • Analysis of the various causes of impairment and the effect of management activities on these impaired conditions and causes in the past.
  • Statement of specific restoration objectives expressed in terms of measurable stream corridor conditions and ranked in priority order.
  • Preliminary design alternatives and feasibility analysis.
  • Cost-effectiveness analysis for each treatment or alternative.
  • Assessment of project risks.
  • Appropriate cultural and environmental reviews and their results
  • Monitoring plan linked to stream corridor conditions.
  • Anticipated maintenance needs and schedule.
  • Alternative schedule and budget.

Part III briefly covers Restoration, Installation, Monitoring, and Management. The information lacks detailed design guidance for various stream restoration techniques, but state environmental agencies and DOTs have begun to fill that gap, as will NCHRP 24-19, results of which are due in late 2004.

  • NCHRP 24-19 seeks to fill part of the gap in DOTs abilities to use and rely on environmentally sensitive bank and erosion control measures. Traditional channel- and bank-protection techniques have relied on countermeasures such as riprap, gabions, cable-tied blocks, or grout-filled bags, which may not offer sufficient in-stream functions, such as habitat diversity, fish passage, water quality, and energy dissipation. Environmentally sensitive channel- and bank-protection measures (ESCBMs), such as bioengineering, root wads, large woody debris, riparian vegetation, bendway weirs, and energy dissipaters, are being called for more frequently to protect transportation facilities from erosion, scour, and lateral migration. The CD will include for each ESCBM covered:
  • A review of the technical literature from foreign and domestic sources pertaining to environmentally sensitive channel- and bank-protection measures.
  • Performance data.
  • Examples, charts, tables, figures, drawings, and specifications.
  • Guidance pertaining to selection and application.
  • Critical evaluation of the extent and adequacy of existing information pertaining to the current state of practice for the selection and design of the measure.
  • Upcoming NCHRP projects will cover Riprap Design Criteria, Specifications and Quality Control and Hydraulic Loss Coefficients for Culverts.
  • EPA's Decision-Making Guide for Restoration and a Stream Restoration Glossary
  • Stream Corridor Inventory and Assessment Techniques
  • Assessing Conditions of Stream Corridors at the Areawide Level -- Using Proper Functioning Condition (PFC) Methodology Technical Report
  • TR 1737-12, Using Aerial Photographs to Assess Proper Functioning Condition of Riparian-Wetland Areas
  • TR 1737-15, Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas

The following new state DOT research is in progress:

  • Mn/DOT is undertaking a "Scoping Study for the Development of Design Guidelines for Bioengineering in the Upper Midwest," with research results due in 2006. [N] The project will assess current design methods, clarify current practices, propose areas where better design guidance is needed and outline further research requirements.
  • Georgia DOT is investigating the feasibility of using recently developed stream restoration techniques, specifically in-stream structures, to restore the previous channel geometry and habitat continuity in the vicinity of bridges. [N]) The project will develop a database of the effectiveness of three different materials (rock, wood, and salvaged concrete slabs) for the restoration structures and restoration failures in the region. Results are due in 2006.
  • Florida DOT, in conjunction with USFWS, is also collecting regional data; in particular the agencies are developing regional curves to characterize and stream channel hydraulic geometry (i.e., width, depth, and cross-sectional area) in relationship to bankfull discharge and watershed area and assist in natural channel design for FDOT projects. This study is expected to provide a model for future efforts to analyze streams statewide and result in improved guidelines for designing culverts and bridges to preserve natural bankfull channel dimensions and their associated floodplains and wetlands. Study results are expected in 2005. [N]
  • Nebraska DOR is establishing guidelines about when and where to use vegetation to control erosion on streambanks, how to establish the vegetation, and what types of vegetation are most practical in any given situation. The research team also investigated combined erosion control methods to see if bioengineering can improve the stability and appearance of non-biological erosion control techniques in locations where vegetation by itself provides insufficient protection against erosion. MDT and FHWA are also undertaking research in alternative strategies in stream restoration. [N]

 

3.6.4 Bioengineering Technique Selection
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Selection of the appropriate technique, or techniques, is critical to successful restoration. NCHRP 24-19 Environmentally-Sensitive Channel and Bank Protection Measures will provide guidelines for 44 bioengineering techniques, accompanied by 19 Special Topic guidance documents, and a total of 55 typical drawings in both AutoCAD and MicroStation formats. For each of the 44 different bioengineering techniques, the following information will be provided:

  • Description
  • Purpose
  • Planning
    • Useful For Erosion Processes
    • Spatial Application
    • Hydrologic / Geomorphic Setting
    • Conditions Where Practice Applies
    • Complexity
    • Design Guidelines / Typical Drawings
  • Environmental Considerations / Benefits
  • Hydraulic Loading
  • Combination Opportunities
  • Advantages
  • Limitations
  • Materials And Equipment
  • Construction / Installation
  • Cost
  • Maintenance / Monitoring
  • Common Reasons / Circumstances For Failure
  • Case Studies And Examples
  • Research Opportunities
  • References

Bioengineering techniques are grouped into four major categories, viz., 1) River Training Techniques, 2) Bank Armor and Protection, 3) Riparian Buffer and River Corridor Treatments, and 4) Slope Stabilization. The CD will include a rule-based selection system that relates the hydraulic, geotechnical, and environmental constraints of each technique to site conditions and project constraints to aide the user in selecting an applicable measure. Also included will be reference material "hot-linked" within the various design criteria provided. The material will be considered state-of-the-art when it is due out in late 2004 and will cover the following practices: [N]

Example 6 : Environmentally Sensitive Channel- and Bank-Protection Measures to be Included in NCHRP 24-19

River Training

  1. Spur dikes
  2. Vanes
  3. Bendway weirs
  4. Large woody debris structures
  5. Stone weirs
  6. Longitudinal stone toe with spurs
  7. Longitudinal stone toe
  8. Coconut Fiber Rolls
  9. Vegetated gabion basket
  10. Live cribwalls
  11. Vegetated Mechanically Stabilized Earth
  12. Live siltation
  13. Live brushlayering
  14. Willow posts and poles
  15. Trench fill revetment
  16. Vegetated floodways
  17. Meander restoration

Bank Armor and Protection

  1. Vegetation alone
  2. Live staking
  3. Live fascines
  4. Turf reinforcement mats
  5. Erosion control blankets
  6. Geocellular Containment Systems
  7. Rootwad revetments

Bank Armor and Protection, cont.

  1. Live brush mattresses
  2. Vegetated articulated concrete blocks
  3. Vegetated riprap
  4. Soil & grass covered riprap
  5. Vegetated gabion mattress
  6. Cobble or gravel armor

Riparian Buffer and Stream Corridor Opportunities

  1. Live gully repair

Vanes with J hooks

  1. Cross Vanes
  2. Boulder clusters

Slope Stabilization

  1. Diversion dike
  2. Slope drain
  3. Live pole drain
  4. Chimney drain
  5. Trench drain
  6. Drop inlet
  7. Fascines with Subsurface Drain
  8. Flattening
  9. Stone - Fill Trenches

Special Topics

  1. Bankfull Discharge
  2. Bio-Adaptive Plant Response
  3. Checklist/Guidelines for Effective Design
  4. Combining Techniques
  5. Designing Stone Structures
  6. Ecological Aspects of Bridge Design
  7. Geotextiles and Root Penetration
  8. Harvesting/Handling of Woody Cuttings
  9. Management of Conveyance
  10. Optimal Compaction and Other Strategies
  11. Physical Aquatic Habitat
  12. Proper Functioning Condition
  13. Resistive (Continuous ) vs. Redirective (Discontinuous )
  14. Revetments to Resist Wave Wash
  15. Self-Launching Stone / Well Graded Stone
  16. Sources, Species, and Durability of Large Wood
  17. The Key to Stability is the Key
  18. The Role of Geotextiles and Natural Fabrics

 

3.6.5 Bank Protection and Stabilization Techniques
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Streambank stabilization affects many of the structural characteristics and functions of a stream. These impacts can be viewed as either adverse or beneficial, depending upon the perspective of the individual assigning values to the system. The prevailing philosophy in ecosystem management is that physical alterations of the structure and character of an ecosystem are most significant if they also impact process-based functions. Erosion control measures are most likely to impact morphological evolution, sediment processes, and habitat, and are least likely to impact the stream's hydrologic character and the chemical processes and pathways.

River functions most likely to be impacted by stabilization measures include stream evolution processes, riparian succession, sedimentation processes, habitat, and biological community interactions. Those least likely to be impacted include the functions related to hydrologic balance and chemical and biological processes.

Bank protection practices are designed to protect the stream bank from erosion or potential failure. Bank protection practices include practices that are structural in nature, as opposed to practices often grouped as bank stabilization, which tends toward less structural and more vegetation-reliant techniques such as bioengineering, to stabilize streambanks. Bank protection practices are used along stream reaches where eroding streambanks threaten private property or public infrastructure or where available space or highly erosive flows are a constraint.

The most common examples of bank protection practices are rootwad and boulder or riprap revetments. Fact sheets on Bank Protection Techniques, provided by the Washington Department of Fish and Wildlife, cover the following Structural Techniques:

  • Anchor Points
  • Roughness Trees
  • Log Toes
  • Roughened Rock Toes

Bank stabilization practices generally involve regrading the stream banks to a stable angle and geometry, followed by the use of vegetative plantings and biodegradable materials to stabilize the streambank and prevent future bank erosion. Widely used practices within this latter group include coir fiber logs, live fascines and willow plantings. A Caltrans Stormwater Fact Sheet on Stream Stabilization is available online. This source describes Best Management Practices that can reduce the discharge of sediment and other pollutants and minimize the impact of construction activities on watercourses

A number of the following techniques are also used in river training or channel restoration, are reviewed here rather than in those later sections.

Riprap

Riprap usually refers to natural stone (i.e., cobbles, boulders, or broken stone), used for shoreline, streambank, or streambed armoring for erosion control. Riprap has many advantages over other bank protection techniques including: low cost, relatively simple construction techniques as necessary, easily repaired, ability of vegetation to grow between rocks, increasing stability of the bank and improving habitat value of the structure, and performance is not impaired. [N]

Riprap structures can have ecological benefits and can even be used specifically to improve the quality of riverine habitat. Stabilizing stream channels with riprap can reduce sediment loads, improve water quality, and allow re-establishment of riparian vegetation. Stone used in riprap structures provides hard substrate habitat that can be important in some sand bed streams where it might be limited, and spaces between riprap stones provide velocity refuge and cover for aquatic invertebrates and small fishes.

Generally, streams with healthy riparian vegetation communities and the habitat features associated with such communities (shade, relatively stable undercut banks, large woody debris, etc.) will be harmed ecologically from the addition of riprap structures. On the other hand, habitat may be improved on streams where natural hard substrate is rare or lacking. Systems with excessive erosion due to anthropogenic causes are most likely to benefit ecologically from riprap. According to the literature, the impacts for coldwater fisheries are predominantly adverse, whereas impacts for warmwater organisms are overwhelmingly beneficial. [N] Although a number of variables are involved, this general trend appears to be related to the character of the habitat afforded by the riprap relative to the habitat it replaces and the other habitat in nearby reaches. In most of the warmwater systems studied, coarse hard substrate was very limited, so the addition of riprap provided a habitat niche that was rapidly exploited by a number of species. [N] The Washington State Department of Fish and Wildlife produced a Literature Review of Revetments and found predominantly adverse effects in these cold water environments. [N]

Design Considerations and Practices for Minimizing Environmental Impacts from Riprap

Careful planning can minimize impacts due to construction, and design features can often be incorporated into riprap structures to improve their habitat value. According to the U.S. Army Corps of Engineers, most of the impacts associated with armoring a streambank are the same regardless of whether the armor material is riprap, concrete, vegetation, or a synthetic product; material-related impacts are generally associated with the habitat characteristics of the structure, and the influence of the structure on riparian vegetation. [N]

Impacts associated with the use of riprap as an erosion control measure can be minimized by modification of structures and incorporation of the following environmental stewardship practices. Similar modifications can be employed to minimize the impacts associated with riprap used as toe protection in a slope stabilization project.

  • When used as an armor material, minimize riprap impacts by reducing the height of the protection, by increasing the slope of the embankment, and by sizing the riprap to afford adequate habitat within the aquatic environment.
  • Plant the interstices of a riprap revetment with woody vegetation.

Measures to reduce the impacts associated with flow deflection structures incorporating riprap include the following:

  • Carefully locate the deflection structures to minimize impacts to the riparian corridor
  • Modify the structure design in order to generate desired habitat characteristics within the aquatic environment.

Structure designs that result in diverse conditions or that restore or generate necessary habitat can produce generally positive impacts. The size and gradation of stone for both flow deflection and armor structures can be adjusted to reduce impacts in some cases. Most impacts caused by energy reduction structures are related to the height of the structure. High structures significantly decrease the energy and water surface slope, induce sediment deposition upstream and scour downstream, and can present a barrier to the migration of aquatic organisms. These impacts can be minimized by the following measures:

  • Replace single structures with a series of low-head structures.
  • Incorporate structural modifications to improve sediment continuity and fish passage.
Construction Practices to Minimize Adverse Environmental Impacts from Use of Riprap

Construction methods used to place revetments should be carefully reviewed to ensure that they do not contribute to environmental degradation. Construction of a typical riprap structure requires extensive use of heavy equipment, and steps should be taken to minimize damage to riparian vegetation and instream habitats.

  • Plan movement of construction materials to minimize impacts to riparian vegetation outside the area of interest.
  • Conduct riprap placement so as to preserve existing trees along the bank that are not in danger of windthrow or toppling.
  • Regulate equipment operation on the upper banks to minimize soil compaction in the riparian zone, which leads to plant mortality.

Common methods of riprap placement include hand placing; machine placing, such as from a skip, dragline, or some form of bucket; and dumping from trucks and spreading by bulldozer. Hand placement produces the best riprap revetment, but it is the most expensive method except when labor is unusually cheap. Steeper side slopes can be developed with hand-placed riprap than with other placing methods.

  • Where steep slopes are unavoidable (when channel widths are constricted by existing bridge openings or other structures, and when rights-of way are costly) consider hand placement.
  • With machine placement release sufficiently small increments of stone as close to their final positions as practical.
  • Minimize rehandling or dragging operations to smooth the revetment surface, as this tends to result in segregation and breakage of stone, and can result in a rough revetment surface.
  • Avoid dropping stone from an excessive height as this may result in the same undesirable conditions.
  • Minimize riprap placement by dumping and spreading as a large amount of segregation and breakage can occur. In some cases, it may be economical to increase the layer thickness and stone size somewhat to offset the shortcomings of this placement method.

Timing of construction is important when managing for certain impacts.

  • Construction activities should generally be avoided when they will disrupt spawning or nesting activities of nearby sensitive species.
  • Designs that incorporate vegetation may require that the installation occur during the dormant season.
  • Construction activities should generally be abandoned when flows are sufficient to heighten the risk of catastrophic failure.

NCHRP 24-19 will outline environmental stewardship practices for implementing Cobble or Gravel Armor, Vegetated Riprap, and Soil and Grass Covered Riprap. Currently available on-line guidance includes:

Gabions

Gabions are stone-filled wire baskets that are used to protect the stream bank from erosive water currents. NCHRP 24-19 will provide guidance for the use of Vegetated Gabion Baskets and Vegetated Gabion Mattress. Meanwhile, guidance is available on-line on implementation of gabions from the Maryland Department of the Environment.

Toe Protection

Toe Protection consists of reinforcing bank toes with vegetation, bioengineering methods, or rigid engineering techniques to ensure the dynamic or rigid stability of the stream corridor. NCHRP 24-19 will have forthcoming information on Longitudinal Stone Toe with and without Spurs. Maryland and Alaska have online resources for toe protection as follows.

Vegetated Concrete Blocks

Vegetated Articulated Concrete Blocks or Cellular Concrete Blocks are precast perforated concrete blocks which stabilize slopes or streambanks but also allow vegetation to establish itself through openings in the block. [N] NCHRP 24-19 will provide practice guidance for Vegetated Articulated Concrete Blocks. Meanwhile, practice guidance for implementation is available on-line from Florida:

Live Crib Walls

Live Crib Walls are hollow, box-like frameworks of untreated logs or timbers filled with riprap and alternating layers of suitable backfill and live branch layers and are used for slope, streambank, and shoreline protection. [N] They are sometimes used in channel restoration or river training as well. Environmental stewardship practices for live crib walls and vegetated cribbing are available online in the form of fact sheets and guidelines from the following states:

Root Wads

Root Wads are a streambank protection technique that provides immediate riverbank stabilization, protects the toe of slope and provides excellent fish habitat, especially for juveniles. Root wads are particularly well suited for higher velocity river systems and riverbanks which are severely eroded. They provide toe support for bank revegetation techniques and collect sediment and debris that will enhance bank structure over time. Because of their size, root wads usually require the use of heavy equipment for collection, transport and installation. [N]

NCHRP 24-19 will cover rootwad revetments. Environmental stewardship practices for live crib walls and vegetated cribbing are currently available online in the form of fact sheets and guidelines from the following states:

Live Staking

Live plants can be incorporated into a riprap structure to enhance its habitat and aesthetic value. Live staking (i.e., planting live woody vegetation) of the riprap interstices is common, and root wads can be incorporated into a riprap structure. The woody vegetation enhances the habitat value of the structure, and as an added benefit, it can also increase bank stability and reduce chances of structure failure. In areas where aesthetics are especially important, the stone above the normal high water level can be covered with soil and planted in grasses. Cuttings (live stakes) are the most beneficial means of adding vegetation to riprap structures.

  • Cuttings should be prepared from woody plants that root adventitiously (e.g. Salix spp.), obtained from as near the site as possible, and should be free from obvious signs of disease.
  • To root effectively, cuttings must have good soil/stem contact, (difficult to achieve in many riprap structures) and must be placed to a depth sufficient to access groundwater during drought.
  • Woody cuttings or posts can be placed through many riprap sections using a stinger mounted on an excavator. The stinger creates a pilot hole into which the cutting is inserted. A recently patented procedure allows the installation through riprap of plants that are encapsulated with soil, greatly improving survival, as a lack of soil contact within the riprap section is a leading cause of mortality for plants installed with a conventional stinger. Alaska has added information online under the heading of Dormant Cuttings.

Live staking BMP fact sheets and resources online include:

Live Staking, Willow Posts, and Poles, to be covered in NCHRP 24-19

Large Woody Debris

Research on the effect of wood structures includes both biological and hydraulic study. Large organic debris or large woody debris has an important influence on stream process and morphology by hydraulically controlling areal sorting and storage of sediment, spacing of pool-riffle sequences and channel geometry. [N]

Two studies in wood placement examine the effect on trout habitat. [N] Both papers report increases of trout fry and biomass associated with large woody debris. Hilderbrand et.al compared the effect of random design and human judgment-based placement of large wood structures. Their most significant finding was the 146 percent increase in pool area associated with systematic placement opposed to 32 percent pool area increase in random placement. [N]

The Washington Department of Fish and Wildlife has produced guidance on Anchoring and Placement of Large Woody Debris that is available on-line. Another Washington document also has guidance on Large Woody Material (p. 88).

Live Fascines

Live fascines are groups of dormant branches bound together to create a log-like structure that will root and grow, quickly providing plant cover. The bundle is used to revegetate and stabilize slopes, secure the toe of streambanks, or provide a transition from one revegetation technique to another (e.g., a brush mat to a live siltation). Bundles are planted in shallow trenches and provide immediate physical protection to a site before plant growth begins. Bundles create small shelves that collect native seeds and water. [N] Environmental stewardship practice guidance on implementing these techniques will be available from NCHRP 24-19 and is currently available from the following states:

Brush Layering or Branch Packing

Brushing Layering is a revegetation technique which combines layers of dormant cuttings with soil to revegetate and stabilize both streambanks and slopes. It is one of the best techniques for these purposes. Living and non-living brush layers provide fish habitat. Branches are placed on horizontal benches that follow the contour of the slope and provide reinforcement to the soil. Steep slopes and streambanks are better stabilized when a biodegradable revegetation fabric is used to hold the soil in place between the plant layers. Additional stability is provided when the front of the soil layer is seeded with grass while the woody plants are becoming established. [N] This technique is sometimes used in channel restoration or river training as well.

Branchpacking is another similar revegetation technique which consists of alternating layers of live branch cuttings and compacted backfill to repair small, localized slumps and holes. One of its advantages is that as the plant tops grow, the branchpacking becomes increasingly effective in reducing erosion and runoff. The trapped sediments then refill slumps or holes while the roots stabilize the surrounding area. [N]

Environmental stewardship practices for brush layering are available online in the form of fact sheets and guidelines from the following states:

Brush Mattresses

Brush mattresses are a revegetation technique that provides a protective covering to a slope as soon as it is installed. A brush mat can be constructed with dormant branches of willows and poplar that will root and grow. Alternatively a brush mat can simply be constructed with any brushy, woody branches to provide effective slope protection from erosion. A brush mat is often combined with other revegetation and/or protection techniques which are used to secure the toe of the slope including root wads, live siltation, bundles, coir logs and spruce tree revetments. [N] Brush Matting/Live Brush Mattresses will be covered in NCHRP 24-19. Environmental stewardship practice guidance on implementing these techniques is currently available from the following states:

Coir Fiber Logs

Coir fiber logs are constructed of interwoven coconut fibers that are bound together with biodegradable netting. Commercially produced coir logs come in various lengths and diameters, and the product needs to be selected specifically for the site. Fiber logs composed of other sturdy biodegradable materials may function equally as well.

Applications for coir logs occur in many streambank, wetland and upland environments. The log provides temporary physical protection to a site while vegetation becomes established and biological protection takes over. The logs can provide a substrate for plant growth, protect plants growing adjacent to the log, can be used as a transition from one revegetation technique to another, and used to secure the toe of a slope. Both the upstream and downstream ends of the coir log(s) need to transition smoothly into a stable streambank to reduce the potential to wash out. [N] NCHRP 24-19 will offer environmental stewardship practice guidance on Coconut Fiber Rolls. Meanwhile, guidance is available on-line in the form of fact sheets and design specifications from the following states.

Ditch Lining, Turf Reinforcement Mats, and Geocellular Containment Systems

Ditch lining provides a long/short-term erosion resistant lining of the ditch flow line and side slopes utilizing biodegradable or non-biodegradable geo-textile fabrics and/or angular rock to stabilize ditches and channels from erosion and soil particle movement. [N] NCHRP 24-19 will provide environmental stewardship practice for Turf Reinforcement Mats, Erosion Control Blankets (covered in this document under Erosion Control), and Geocellular Containment Systems.

Research on the use of compost blankets in stream rehabilitation projects has found that although flood events completely submerged the compost blankets and much of the staked vegetation, the compost blanket held in place while some of the woody vegetation was destabilized and/or washed won stream. [N] It may be advantageous to have the compost contained (e.g., in a sock), because rising stream levels submerge the compost. [N] The Washington Department of Fish and Wildlife has produced guidance on Planting Considerations and Erosion Control Fabric that is available on-line.

Other available resources from North Carolina and Washington include:

Other Vegetative Streambank Stabilization and Bank Protection Practices

Shields et al studied the effect of specific woody vegetation combined with rock bank protection finding native woody species, especially willow, to be best adapted to streambank environments; however, success of vegetation was successful only in reaches where the streambed was not degrading and banks were stabilized by grading or toe protection. [N] In a similar study, Shields et al combined stone placement with willow planting in a deeply incised sand channel. Stage-discharge, channel geometry and grain size were unaffected, though average depth of scour holes and pool habitat increased along with fish number and size, woody vegetation cover, mean depth and width. Additionally, they reported the occurrence of erosion beneath stones. [N] Shields et.al. also conducted a study on the addition of spurs to stone toe protection indicating a modest increase in overall pool width and habitat availability, and local effects on depth. [N]

Environmental stewardship practices in streambank stabilization and vegetation are included in on-line fact sheets and guidance from the following states:

Bioengineering Techniques provided by the Washington Department of Fish and Wildlife, cover the following:

  • Woody Plantings
  • Herbaceous Cover
  • Soil Reinforcement
  • Bank Reshaping

NCHRP 24-19 also has forthcoming guidance on Large Woody Debris Structures as well as a discussion using "Vegetation Alone" in protecting stream banks.

Borrow

This item consists of supplying, loading, hauling and satisfactorily placing additional material necessary to complete embankments to subgrade and other features of the work. Materials should be obtained outside the limits of the ROW.

Drains and Trenches

NCHRP 24-19 project lists the following areas in slope stabilization to be discussed in the upcoming publication due in late 2004. Drainage practices discussed as part of this project, NCHRP 25-25(04) include:

  • Diversion dike
  • Slope drain
  • Live pole drain
  • Chimney drain
  • Trench drain
  • Drop inlet
  • Fascines with Subsurface Drain
  • Flattening
  • Stone - Fill Trenches

Wire Mesh/Cable Net Slope Protection

Wire mesh has been used to control rockfall on actively eroding slopes since before the 1950s. More recently, cable nets have been added to the toolbox as well. Washington State DOT recently attempted to take the field beyond the regular empirical methods, engineering judgment, and experience to incorporate research on existing performance, testing of critical system components, system failures, typical loading conditions, and analytical models to describe these. The guidelines were developed to support the design of these systems for a variety of loading conditions; specifically, they provide design guidance on site suitability, characterizing external loads, fabric selection, anchorage requirements, and system detailing. [N]

 

3.6.6 River Training and Channel Rehabilitation Techniques
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Grade Control Structures

Grade control structures are designed to maintain a desired streambed elevation. They can be either used to raise the stream invert to reverse past channel incision or to maintain the channel invert at a current elevation. Common examples of grade control structures are rock vortex weirs and rock cross vanes and step pools.

Low-head stone weirs (LHSW) are boulder structures that extend across the entire bed of a stream channel, and have an effective height of less than 3 ft. The structures are primarily used to prevent streambed degradation, reduce the energy slope to control erosion, create backwater for reliable water surface elevations, and increase aquatic habitat diversity.

Unlike traditional grade control structures, which can adversely impact fish passage, habitat, recreation, and other environmental functions, LHSW are designed to provide stabilization and riffle and pool habitat, reoxygenate water, establish desired substrate characteristics, improve local bank stability, and enhance habitat diversity and visual appeal. LHSW structures are flexible in that their design characteristics can be altered to achieve specific objectives and to address unique site characteristics. LHSW structures are designed to remain stable under the full range of anticipated flow conditions, and to permit fish passage.

All LHSW structures obstruct the flow, creating a backwater area upstream that, at least temporarily, serves as a pool and reduces upstream erosion. Most concentrate the energy losses in a scour hole or dissipation basin immediately downstream of the structure. They can be designed to arrest bed degradation, or can have virtually no effect upon this phenomenon. The extent to which these and other characteristics are manifested depends upon the structure dimensions, shape and orientation, material, and the character of the stream.

A common configuration for conventional LHSW structures is a V-shaped structure with the apex pointing upstream, a depressed central region to serve as a low-flow notch, and boulders or riprap as a foundation with the ends keyed well into the banks. The dimensions can be varied for effect, but the structure height is commonly set at about the bankfull elevation at the banks, and is generally 0-2 ft above the bed at the apex.

The V-shape is intended to concentrate flows in the central portion of the channel and minimize the velocity gradient near the banks. The friction generated by the water flowing over the weir crest causes the streamlines to "bend" approximately perpendicular to the crest alignment. This phenomenon only persists for a narrow range of flow depths (generally less than one fifth the structure height), so on an LHSW with a sloping crest, the effect varies with discharge.

Log and Check Dams

Log and check dams are used to pool water and for grade control. The pooled water is used either to create aquatic habitats or to trap sediment runoff from work sites or drainage ditches along the roadside. Following are examples of these dams available online.

Flow Deflection/Concentration Practices

Flow Deflection/Concentration Practices are designed to change the direction of flow or concentrate flow within the stream channel. The practices within this group may be used to deflect flow away from eroding stream banks, concentrate the flow in the center of the channel, redirect water in and out of meanders, or enhance pool and riffle habitats. Common practices within this group include rock vanes and log vanes.

Stream Deflectors

Vanes

Bendway Weirs

Bendway Weirs are an important tool in current multi-purpose erosion control, stream restoration, and habitat improvement projects. A series of upstream-angled low-elevation stone sills (Bendway Weirs) are designed to control and redirect currents and velocities throughout a bend (and the immediate downstream crossing) of a river or stream. The U.S. Army Corps of Engineers provides an Overview of bendway weirs, What Is A Bendway Weir?, How Do They Work?, Advantages, A Real-World Example, Design Considerations, History, Theory, and Design, and Applications for Bendway Weirs (Case Studies) along with technical assistance contacts.

Following are some guidelines available online that cover Weirs and Sills:

NCHRP 24-19 Environmentally-Sensitive Channel and Bank Protection Measures will be forthcoming in providing guidelines for the following techniques in the area of River Training (Stream Restoration, Channel Relocation):

  • Vanes
  • Weirs
  • Spur Dikes
  • Bendway Weirs
  • Stone Weirs

Boulder Placement In-Stream for Habitat Creation

Maryland's Fact Sheet on Boulder Placement describes guidelines for placing boulders in stream channels to encourage riffles and pools and to provide habitat and spawning areas for aquatic life. When properly utilized, boulder placements create small scour pools and eddies which can be used as rearing areas for various species of fish. They can also help restore meanders and pools in channelized reaches and to protect eroding streambanks by deflecting flow. Boulder placements are most effective when used in moderately wide, shallow, high velocity streams with gravel or cobble beds and stream reaches with pool densities less than 20 percent. See guidelines for further details. [N] NCHRP 24-19 will also have information on Boulder Clusters available online in late 2004.

Other Flow Redirection Techniques

Flow Redirection Techniques provided by the Washington Department of Fish and Wildlife, cover the following:

  • Groins
  • Buried Groins
  • Barbs
  • Engineered Log Jams
  • Drop Structures
  • Porous Weirs

 

3.6.7 Stream Restoration Evaluation and Monitoring
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DOTs evaluate and monitor stream restoration efforts to help determine whether the design objectives have been met and in order to identify needed adjustments to design parameters, installation procedures and/or stabilization methods. The following areas are typically monitored:

  • Proper functioning of stabilization and grade-control structures.
  • Check channel stability by measuring dimension, pattern and profile; particle-size distribution of channel materials; sediment transport; and streambank erosion rates. This is usually accompanied by a reassessment of stream morphology, using permanent cross-section measurement areas.
  • Biological response (i.e., vegetation, macroinvertebrates and fish).
  • Whether the specific objectives of the restoration have been met.
  • On a site-specific basis, shading and temperature are occasionally monitored as well.

Resource agencies generally require photo-documentation to supplement the above. Monitoring often occurs at least once a year for five years after construction.

CTE and the NCDOT developed the evaluation and monitoring recommendations for stream restoration projects as noted in the Appendix:

 

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Continue to Section 3.7 »
 
Table of Contents
 
Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.1 Beyond Mitigation: Projects to Achieve Environmental Goals
3.2 Context Sensitive Design/Solutions
3.3 Avoiding Impacts to Historic Sites
3.4 Designing to Accommodate Wildlife, Habitat Connectivity, and Safe Crossings
3.5 Culverts and Fish Passage
3.6 Stream Restoration and Bioengineering
3.7 Design Guidance for Stormwater and Erosion & Sedimentation Control
3.8 Drainage Ditches, Berms, Dikes, and Swales
3.9 Design for Sustainable, Low Maintenance Roadsides
3.10 Designing to Reduce Snow, Ice, and Chemical Accumulation
3.11 Designing to Minimize Air Quality Problems
3.12 Design and Specification for Recycling
3.13 Designing to Minimize Noise
3.14 Lighting Control/Minimization
3.15 Design for Sustainability and Energy Conservation
3.16 Safety Rest Areas, Traveler Services, and Parking Area Design
   
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