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1 Overview In 2005, the results of NCHRP Project 24-19 were published as NCHRP Report 544: Environmentally Sensitive Channel- and Bank-Protection Measures (McCullah and Gray 2005). After conducting an extensive literature review and evaluation of commonly used environmentally sensitive techniques, McCullah and Gray identified 44 techniques for study. Technique descriptions and guidelines for their application were developed. In many respects the work by McCullah and Gray (2005) can be viewed as a starting point and foundation for this project, NCHRP Project 24-39. Even with the guidance provided by NCHRP Report 544, there was reluctance on the part of many engineers to utilize biotechnical approaches to stream bank stabilization techniques. This was due, in part, to a lack of technical training, experience, and defini- tive hydraulic engineering design guidance. In particular, there was a lack of knowledge about the properties of the vegetative materials being used in relation to the force and stress generated by flowing water, and there was concern regarding the difficulties in obtaining consistent performance from countermeasures that rely on living materials. Thus, the objectives of NCHRP Project 24-39 included evaluating and assessing existing guidelines for the design, installation, monitoring, and maintenance of environmentally sensitive stream bank stabilization and protection measures. In addition, quantitative engineering design guidance was developed for selected treatments. Research Approach The research approach for NCHRP Project 24-39 involved the following steps: 1. Completion of a literature review to update the 2005 findings of NCHRP Report 544 and evaluation of current practice with a survey of practitioners. 2. Development and implementation of a laboratory test plan, which involved installing and growing two environmentally sensitive treatments under controlled greenhouse conditions and moving the mature treatments to a large outdoor hydraulic flume for testing and detailed hydraulic data acquisition at prototype scale. 3. Identification of field sites and implementation of a field site visit program to evaluate current practice and performance of environmentally sensitive treatments under a range of geophysical and geomorphic conditions. 4. Compilation of the data acquired from 16 field site visits into a Compendium in a search- able database format to permit practitioners to access a wide range of design, installation, and performance data on commonly used treatments. S U M M A R Y Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures
2 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 5. Development of two detailed case studies that illustrate the integration of hydraulic engineering analysis and design with the multidisciplinary approach necessary to achieve project success when employing environmentally sensitive treatments. 6. Presentation and appraisal of the results of laboratory testing in a standalone format for ease of access by both the researcher and the practitioner (Chapter 3). 7. Presentation of detailed design guidance in a standalone format (Chapter 4) for the veg- etative components of the two environmentally sensitive treatments that were tested in the laboratory, and an overview and update of design guidance for a third widely used treatment. 8. Suggestions for implementation activities to enhance the state of practice for environ- mentally sensitive stream bank protection measures, and discussion of potential areas for additional investigation and research. Appraisal of Research Results Starting with the published results of NCHRP Project 24-19, 16 treatments from the river training and bank armor and protection categories of NCHRP Report 544 were selected for further consideration. Budget and time constraints indicated that only two treatments could be grown and tested in the laboratory flume. For these, certain physical constraints both for growing the treatment in a greenhouse and for transporting the mature treat- ment to the large outdoor hydraulic flume had to be observed. In addition, in selecting the two treatments for rigorous hydraulic flume testing consideration was given to treatments or treatment components that would have the widest applicability nationwide. One treat- ment included a stone (riprap) toe, live siltation, and live staking. The hydraulic data from testing this treatment has broad applicability to either multi-component systems or treat- ments using just individual components (i.e., using live siltation or willow staking, alone) for stream bank protection. The second treatment [Vegetated Mechanically Stabilized Earth (VMSE) without a hard toe] recognizes that many resource agencies tend to discourage, and in some cases prohibit, the use of rock in stream bank protection. Thus, testing the hydraulic limits of a treatment without a hard toe but incorporating fabric-encapsulated soil (FES) lifts with live brush layering between the lifts could have wide potential applicability and interest. It should be noted that the laboratory testing task of this project represents a technological breakthrough in developing quantitative hydraulic engineering design guidance for envi- ronmentally sensitive treatments. The in-channel roughness characteristics of living plants had been tested (by others) in a laboratory flume, primarily to investigate the influence of vegetation on channel roughness characteristics under varying flow conditions. However, the testing of the vegetative components of selected stream bank treatments following rec- ommended design criteria, including fabricating the structural component(s), planting the vegetative component(s) and growing them to maturity, and, finally, moving them to a flume for fully instrumented hydraulic testing at prototype scale under a range of flow conditions represents a âfirstâ in the development of quantitative guidance for environmentally sensi- tive treatments. The results of these tests are presented in a standalone format in Chapter 3. The treatments tested under NCHRP Project 24-39 were designed to respond to specific hydraulic research needs identified by McCullah and Gray in 2005, including: ⢠Live SiltationâResearch into velocities that this technique can withstand would be helpful. ⢠Live StakingâStudies would be valuable regarding the effect live staking has on increas- ing the ability of other measures to withstand higher velocities and shear stresses. ⢠VMSEâSome uncertainty exists at present as to the exact permissible shear stresses and velocities for VMSE interfaces.
Summary 3 The laboratory testing task does not represent the only contribution of this study. The synthesis and survey of current practice accomplished as part of this NCHRP Project 24-39 study updated the 2005 findings from NCHRP Report 544 and concluded that hydraulic design criteria were still scarce and, with few exceptions, rely on the literature that was sum- marized within NCHRP Project 24-19. The available hydraulic criteria were drawn from a variety of sources and varied in quality at that time from qualitative anecdotal rules of thumb to isolated spot measurements of velocity. Sixteen site visits to existing field installations of a variety of treatment types in three geographic regions (Southeast, upper Midwest, and the West Coast) were also completed. A highly detailed site visit data form was developed and completed for each site, and signifi- cant additional effort was applied to gathering design and monitoring information, reports and specifications, cost data, and photographic documentation for each site. Additional effort was devoted to obtaining hydrologic and hydraulic data that supported the design and influenced the level of functionality achieved at each site. While much of this infor- mation was qualitative and anecdotal, observations from each site visit provided insight into best management practices, and, in several cases, into failure mechanisms and les- sons learned that will improve the state of practice. Moreover, the site visit reports and data obtained were assembled into a one of a kind Compendium of information to pro- vide easy access for the practitioner to a wealth of experiential information on environ- mentally sensitive treatments. The Compendium is presented in a searchable database format to permit the practitioner to employ structured query language (SQL) in searching the database. General hydrologic, hydraulic, and geomorphic considerations and site-specific physical processes that influence the design, installation, and monitoring of any environmentally sen- sitive stream bank protection treatment are presented in a standalone format in Chapter 4. The site-specific physical process topics include bankfull discharge and conveyance; assess- ing the stage of evolution for incising channels; analyzing aggradation, degradation, and lat- eral channel stability; predicting meander migration; guidance for protecting the upstream and downstream âflanksâ and âtoeâ of a stream bank treatment; and estimating toe down requirements and hydraulic stress on a bendway. Geotechnical considerations, guidance for monitoring the success of the vegetative component(s) of environmentally sensitive treatments, and aquatic habitat issues that can influence the design and installation of any treatment are also discussed in Chapter 4. Detailed, updated design guidelines for three widely used treatments are the focus of Chapter 4. These include the two treatments tested under this study and an overview and updated guidance for vegetated riprap. These design guidelines are presented in a format that addresses the following specific topics: (1) purpose and advantages, (2) design and hydraulic design parameters, (3) materials and equipment, (4) construction and installation, (5) cost, (6) maintenance and monitoring, and (7) common reasons for failure. Of the two treatments tested in the laboratory, one (live siltation and live staking with a stone toe) met or exceeded all performance expectations. The second treatment (VMSE without a hard toe) exhibited vulnerabilities to damage and soil loss under the same conditions of discharge and longitu- dinal slope. In addition, two detailed case studies of the application of environmentally sensitive stream bank protection measures employed in conjunction with stream channel restoration proj- ects are presented in Chapter 4. One example involves the application of environmentally sensitive techniques on an arid region perennial stream. The second example deals with a smaller stream in a humid region with significant infrastructure issues. The examples illus- trate the integration of hydraulic engineering analysis and design with the multidisciplinary approach necessary to achieve project success and include, by example, additional guideline
4 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures topics such as hydrologic and hydraulic design parameters, performance and longevity, and ecological issues. For the engineer involved in the multidisciplinary design of an environmentally sensitive treatment, Chapter 4 also provides current guidance from FHWA on the use of biotechnical treatments in proximity to transportation infrastructure. In addition, for the Professional Engineer (PE) on a design team aspects of professional liability in environmentally sensitive design are explored. As a result of this research, updated quantitative guidance and more detailed documen- tation and guidelines for the design, installation, monitoring, and maintenance of envi- ronmentally sensitive stream bank protection measures are now available. This research produced practical, implementable guidance that will enhance the ability of practitioners to utilize environmentally sensitive treatments as an alternative to or in conjunction with more traditional âhard engineeringâ approaches.