National Academies Press: OpenBook

Environmentally Sensitive Channel- and Bank-Protection Measures (2005)

Chapter: Chapter 1 - Introduction

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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Environmentally Sensitive Channel- and Bank-Protection Measures. Washington, DC: The National Academies Press. doi: 10.17226/13556.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Environmentally Sensitive Channel- and Bank-Protection Measures. Washington, DC: The National Academies Press. doi: 10.17226/13556.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2005. Environmentally Sensitive Channel- and Bank-Protection Measures. Washington, DC: The National Academies Press. doi: 10.17226/13556.
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1CHAPTER 1 INTRODUCTION Each year, more discoveries are made regarding the impact that human activity and infrastructure have on the surrounding environment. For many years, project designers have included structures that perform well for stabilizing streambanks and decreasing pollution of our nation’s waters by reducing ero- sion. However, many of these structures are missing key com- ponents critical to complete environmental restoration. CHANGING REQUIREMENTS In response to increased knowledge and public concern, regulations and other requirements have been placed on agencies and organizations to implement environmentally friendly and beneficial practices. This requires projects to incorporate components into erosion and sediment control programs that provide improved habitat for the flora and fauna of our waters, produce aesthetic value for roadsides and waterways, and advance the sustainability of stable streambanks and riverine systems. Under many conditions, these “soft” practices are more successful for erosion control than structural “hard” systems and provide the additional benefit of restoring ecological value to streams and rivers. These environmentally sensitive “soft” practices combine with traditional structures to provide engineers with the abil- ity to restore ecological health and stability within the infra- structures so critical to human society. To answer the need for specifications and guidance regard- ing environmentally sensitive channel- and bank-protection measures, NCHRP funded the development of Environmen- tally Sensitive Channel- and Bank-Protection Measures to aid highway engineers, restoration ecologists, watershed hydrolo- gists, biologists, and soil conservationists in designing projects that restore stream and river systems, while protecting property and structures. This report and the accompanying CD are the result of that project. The CD includes typical design drawings, construction and installation specifications, a comprehensive bibliography with numerous links to the documents listed, and an extensive photo gallery of project examples, all based on extensive research and experience. Also included is a software program, entitled Greenbank, that provides users with a reli- able, straightforward approach to selecting these innovative techniques for streambank protection. The program allows users to enter site characteristics and restraints and, using that information, selects the techniques most suited to the project. Appendix A provides descriptions and illustrations of environ- mentally sensitive channel- and bank-protection techniques. Appendix B is a user’s manual for Greenbank. What It Means to Be Environmentally Sensitive There is an ever-growing number of streambank stabiliza- tion practices, and many were considered for inclusion in this report and CD. Most were not included because they offered little in the way of environmental benefit beyond simply reducing bank erosion or channel incision. To be included in these guidelines, techniques had to enhance or protect aquatic or terrestrial habitats, provide aesthetic value, or both. Although aesthetic values vary from person to person, mea- sures were avoided that appeared visually incompatible with naturally occurring riparian features. We generally included measures that facilitated natural revegetation of eroding banks either directly (by planting) or indirectly (for example, by slope stabilization) but were visually unobtrusive. The appearance of banks treated with such measures should even- tually be compatible with naturally occurring riparian features and demonstrate a properly functioning stream system. Often these measures lead to green, verdant, inviting banks that are accessible for recreational use. The techniques included in this report and CD have varying environmental benefits, and those benefits are identified in this report. Interdisciplinary Effort Due to the dynamic nature of any projects within or adja- cent to a stream and the current awareness on the part of designers, the public, and the regulatory community, it is crit- ical that interdisciplinary teams be developed. Members of dif- ferent disciplines provide insight and guidance into specific concerns surrounding a project and can provide the necessary input for project success. Examples of specialists include riparian ecologists, aquatic biologists, geomorphologists, hydraulic engineers, structural engineers, geologists, botanists, biologists, and erosion control specialists. Specialists should be involved early in project development to identify the envi- ronmental benefits desired, to promote communication, and to facilitate the adjustment of project plans and designs.

Applicability A variety of concerns regarding the applicability of these techniques have been expressed by highway engineers. It is imperative that project designers consult with specialists knowledgeable of local conditions to enhance the success of their project. As an example, the correct selection of a species of willow or cottonwood adapted to the local region is critical to the success of many of these techniques. Climate zone will also dictate the growing and dormant periods of those species. It is also extremely important for designers to understand the specific ecological issues surrounding a particular water body and to design structures with those concerns in mind. For example, a threatened or endangered species of fish in a par- ticular area may have specific requirements, which would be identified by local agency representatives. It should be noted that the knowledge gleaned from the case studies included in the CD is applicable to projects all across the nation, since the projects were installed in a variety of sit- uations across a broad range of stream and river types. These guidelines are not meant to replace or disregard the abundance of available engineering data, equations, or design protocol. It is critical that factors such as scour depth, tractive force, and design high water be determined for each particular project and be incorporated into project design. Sustainability of Environmentally Sensitive Techniques Concerns are widespread throughout the industry regard- ing the longevity and strength provided by environmentally sensitive techniques. Extensive research was performed to obtain reliable information regarding hydraulic loading lim- its for each technique discussed. It was found that many of the techniques will be just as strong as, if not stronger than, “hard engineering” counterparts. One source (Escarameia, 1998) classifies bioengineering alone as light, meaning soft practices are known to withstand mean cross-sectional veloc- ities no greater than 1 m/s (3.3 ft/s). However, many bio- engineering techniques and most biotechnical practices have been documented to withstand much higher local velocities. Structures such as riprap are usually enhanced rather than weakened by combining a “hard” technique with “soft” com- ponents. The CD provides tables regarding velocities sustained by each specific technique and the sources of the information. It was found that many of the techniques can withstand velocities up to 3.5 m/s (12 ft/s). Data Availability and Research Opportunities Data availability was found to vary considerably amongst the techniques. Each technique was assigned to one of three levels based on the amount and quality of available data and the number of successful case studies and examples found 2 throughout the nation. These level designations provide guidance to the user for selecting each technique. For exam- ple, Level I techniques may be selected for use in situations where a higher level of confidence is desired, whereas Level III techniques may be used in trials or situations where exper- imentation is more acceptable. This report found that major opportunities exist for study- ing particular components of installation and the impacts individual techniques have on project success. The need exists for more performance data, such as allowable veloci- ties for some techniques and the amount of vegetative cover required to reach project objectives. As a result of the exten- sive literature review performed and expert input and testi- monials, research opportunities are identified in the detailed descriptions of each technique on the accompanying CD. The CD provides the information and guidelines needed to design and install structures and practices that will stabilize streams and rivers while providing the improved habitat and ecological health needed for a better environment. This report documents the procedures used for gathering the infor- mation needed to establish these guidelines. PROJECT TASKS The project commenced on May 1, 2001. This Final Report describes the work carried out from the inception of the project through November 30, 2004. The various tasks outlined in the Work Plan included the following: Task 1—Literature Review and Agency Survey Task 2—Formulation of Work Plan Task 3—Interim Report Task 4—Execution of Approved Work Plan Task 5—Preparation of Supporting Tools Task 6—Final Report These tasks are enumerated and described in greater detail in Chapter 2. The results of the literature review and evalua- tion are described in Chapter 3. The literature review includes an evaluation of multiple information sources: books, conference proceedings, agency technical reports, agency guidance manuals and handbooks, and websites. The research team discussed the appropriate term for the entire suite of channel- and streambank-protection measures at some length and decided that technique was more appro- priate than measure or countermeasure. It was recognized that some treatments may be applied outside the highway right-of-way to mitigate and enhance stream morphology or corridor and habitat values. It was observed that some bank- protection procedures do not entail construction of some- thing, but instead may actually require deconstruction, for example, slope flattening and regrading—a fundamental approach for stabilizing slopes, including streambanks. In light of these considerations, the word technique is used below to refer to all types of environmentally sensitive channel- and bank-protection measures.

The project research team developed a survey form (ques- tionnaire) that was sent to state DOTs and some representa- tive regulatory agencies asking about experiences relevant to this project. Responses to the survey are summarized in Chapter 4. The survey revealed information about the most common problems or concerns with environmental tech- niques for channel-erosion control, the most common tech- niques employed, and qualitative and quantitative data for a variety of techniques. Selected environmentally sensitive channel- and bank- protection measures (techniques) are described in Chapter 5. The project research team identified and narrowed down the list of candidate techniques to 44. These techniques are grouped into four major categories, namely, (1) River Train- ing Techniques, (2) Bank Armor and Protection, (3) Riparian Buffer and River Corridor Treatments, and (4) Slope Stabi- lization. The work plan called for preparation of guidelines for each technique. The research team initially focused efforts on the preparation of brief summaries (fact sheets) for each technique, which would provide short descriptions of each method in addition to preliminary data. It was decided, how- ever, that these fact sheets were redundant to longer guide- lines, and work was terminated on them. A brief description and schematic drawing of each technique can be found in Appendix A. Chapter 5 lists all the subjects discussed in rela- tion to each of the techniques on the enclosed CD. These sub- jects include the technique’s category and propose, detailed design guidelines and specifications, and so forth. 3 In addition to the techniques discussed, the research uncovered many subjects of direct relevance and applicabil- ity to the entire spectrum of environmentally sensitive channel- and bank-protection work. These special topics— ranging from management of conveyance and combining techniques to protecting and improving aquatic habitat and the role of geotextiles and natural fabrics—are also listed in Chapter 5. The accompanying CD includes the discussion of each of these special topics. The accompanying CD also includes other important information, such as case studies and a photo gallery. The case studies give detailed descriptions of past projects that included environmentally sensitive techniques, the results of the projects, and observations regarding project perfor- mance. The photo gallery includes photos from case studies, examples, and more in an easy-to-access format for the user. A rule-based technique selection system for use by DOTs or consulting engineers is described in Chapter 6. The system contains a set of rules relating the strengths and weaknesses (hydraulic, geotechnical, and environmental) of each tech- nique to relevant site characteristics. This system, entitled Greenbank, is not intended for designing bank protection but rather to assist the user in selecting a reasonable technique or countermeasure. Greenbank provides the user with a short list of appropriate techniques for closer consideration and pro- vides references and justifications for these outputs. Appendix B, Greenbank Decision Support Tool User’s Guide, discusses the information provided by the software in more detail.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 544: Environmentally Sensitive Channel- and Bank-Protection Measures examines environmentally sensitive channel- and bank-protection measures and includes recommended design guidelines for their application and a selection system for helping to determine the most appropriate channel- and bank-protection measure. The selection system is presented as an interactive software program entitled “Greenbank,” which can be found on the accompanying CD-ROM (CRP-CD-58). The selection system software (CRP-CD-58) is available for download in an ZIP format

Download the NCHRP CRP-CD-58 in ZIP format.

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