Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures (2016)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

192 5.1 Conclusions and Suggested Research 5.1.1 Conclusions This final report is based on research conducted under NCHRP Project 24-39, “Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures.” This research accomplished its basic objectives of evaluating and assessing existing guidelines for the design, installation, monitoring, and maintenance of environmentally sensitive stream bank stabiliza- tion and protection measures. In addition, quantitative engineering design guidance was devel- oped for selected treatments. With the guidance available at the outset of this study, there was a 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 definitive 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 gen- erated by flowing water, and there was concern regarding the difficulties in obtaining consistent performance from countermeasures that rely on living materials. While many biotechnical bank-protection measures have been deployed and have survived for a number of years, there remained considerable skepticism within the engineering commu- nity regarding the performance of these measures when subjected to flood event magnitudes typical of hydraulic engineering design. The applicability of individual measures to varying stream hydraulic and site conditions, the long-term structural integrity of the measure, and the anticipated maintenance requirements are all critical elements that must be understood in order to support sound engineering decisions. In this regard, the research conducted under this study produced significant advances in the state of practice for the design, installation, monitoring, and maintenance of selected environmentally sensitive treatments. Insights were also gained on the relative benefits and potential risks of several widely used treatments. Two environmentally sensitive treatments were subjected to detailed testing in a fully instru- mented hydraulic flume at prototype scale. Results provided definitive quantitative hydraulic data, including velocity, velocity distribution, shear stress, roughness, and erosion for the following treatments: live siltation and live staking installed with a hard (riprap) toe and vegetated mechani- cally stabilized soil lifts with brush layering inserted between the lifts but without a hard toe. Result- ing hydraulic data are applicable to these particular combinations of environmentally sensitive treatments or to the treatment components, alone. Observations and quantitative analysis of per- formance were documented in Chapter 3 and were included in the appraisal of results in Chapter 4. Moreover, the laboratory testing tasks of this study provided proof of concept for an innovative approach to deriving detailed hydraulic data for environmentally sensitive treatments. For the first time, the vegetative components of selected stream bank treatments were installed following C H A P T E R 5 Conclusions and Suggested Research

Conclusions and Suggested Research 193 recommended design criteria, including fabricating the structural component(s), planting the vegetative component(s) and growing them to maturity in a controlled greenhouse setting, and, finally, moving them to a flume for fully instrumented hydraulic testing at prototype scale under a range of flow conditions. As a result of this research, the facility and instrumentation require- ments and the procedures necessary to install and test almost any environmentally sensitive bank-protection treatment were identified and testing protocols were established. While field site investigations generally provide only a synoptic “snapshot” in time of a par- ticular site’s condition and may provide mainly anecdotal design and performance data, the site visit program of this study added valuable insights to the growing body of knowledge regarding the installation and performance of environmentally sensitive treatments. Site visits included 16 sites representing a variety of treatment types in three geographic regions (Southeast, upper Mid- west, and West Coast). The detailed site visit form which was developed for this study provides a wealth of pertinent design and performance data and is provided as a model for evaluating existing treatment sites or in the reconnaissance and selection phase for sites being considered for environmentally sensitive treatments. For this study additional effort was applied to gather- ing design and monitoring information, reports and specifications, cost data, and photographic documentation for each site. Hydrologic and hydraulic data that supported design and influenced the level of functionality achieved was also obtained, where available. The resulting compilation of data for the 16 sites was assembled into a Compendium and presented in a searchable database format that will be useful to both the researcher and practitioner considering the investigation and/or utilization of environmentally sensitive treatments for stream bank protection. The detailed, updated design guidance for three specific treatments, which was presented in Chapter 4, will be of immediate use to the practitioner. This design guidance includes the two treatments tested under this study (live siltation with live staking and a hard toe and VMSE without a hard toe) and an overview and update of guidance for a third widely used treat- ment, vegetated riprap. General hydrologic, hydraulic, and geomorphic considerations as well as site-specific physical processes that influence the design, installation, and monitoring of any environmentally sensitive treatment are included in this standalone presentation to support the design guidelines. The practitioner will also find two detailed case studies of the application of environmentally sensitive stream bank protection treatments employed in conjunction with stream channel restoration projects that supplement the guidelines. One example deals with the application of environmentally sensitive treatments on an arid region perennial river. The second example deals with a smaller stream in a humid region with significant infrastructure issues. The examples illustrate the integration of hydraulic engineering design with the multi- disciplinary approach necessary to achieve project success. In many cases, stream restoration or biotechnical engineering projects require the seal of a licensed PE. By affixing his or her seal to design documents and drawings the PE assumes the responsibility for the accuracy of the design and affirms that the work is within the engineer’s area of expertise and was performed under his or her “responsible charge.” While the seal does not “guarantee” the success of a project, it does attest that the design adheres to the “current state of practice” and was performed with a “reasonable standard of care.” To support the engineer on a multidisciplinary design team and to acquaint the team with the implications of the engineer’s seal, the guidelines include current guidance from FHWA on the use of biotechnical treatments in proximity to transportation infrastructure and discussion of aspects of professional liability in environmentally sensitive design. As a result of this research, updated quantitative guidance and more detailed documenta- tion and guidelines for design, installation, monitoring, and maintenance of environmentally sensitive stream bank protection measures are now available. The research produced practical, implementable guidance that will enhance the ability of bridge owners and other practitioners

194 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures to utilize environmentally sensitive treatments as an alternative to, or in conjunction with, more traditional “hard engineering” approaches. 5.1.2 Deliverables As a result of this research, state DOTs now have documentation (photographs and case his- tories) and guidelines that include selection, design, installation, and maintenance requirements for environmentally sensitive stream bank protection measures including: • A fully documented literature database related to biotechnical/environmentally sensitive treatments. • A Compendium of photographs and case histories of existing projects in a searchable data- base format. • Application examples illustrating the application of environmentally sensitive treatments for a range of hydrologic and geomorphic settings. • Detailed standalone design guidelines to facilitate application of the guidance resulting from this study. The guidelines are presented in a format suitable for FHWA’s HEC-23 and AASHTO guidance documents. • A comprehensive final report. 5.2 Implementation Plan 5.2.1 The Product As described in more detail in preceding sections, the product(s) of this research include guidelines for selection, design, installation, monitoring, and maintenance of environmentally sensitive stream bank protection measures. 5.2.2 The Market The market or audience for the results of this research includes hydraulic engineers and main- tenance and inspection personnel in state, federal, and local agencies with a transportation- related responsibility for selection, design, installation, and maintenance of countermeasures for stream instability at highway facilities, including the implementation of environmentally sensitive protection measures, where appropriate, to satisfy permitting, environmental, and sustainability objectives. These would include: • State Highway Agencies • FHWA • City/County Bridge Engineers • National Association of County Engineers (NACE) • Railroad Bridge Engineers • USACE • USFWS • U.S. Bureau of Land Management • National Park Service • U.S. Forest Service • National Marine Fisheries Service (NMFS) • Bureau of Indian Affairs • Any other governmental agency with highway facilities under their jurisdiction

Conclusions and Suggested Research 195 • Consultants to the agencies above • American Council of Engineering Companies (ACEC) 5.2.3 Impediments to Implementation A serious impediment to successful implementation of results of this research will be difficul- ties involved in reaching a diverse audience scattered among numerous agencies and institu- tions; however, this can be countered by a well-planned technology transfer program. Because of the complexity and geographic scope of channel instability problems, a major challenge will be to present the results in a format that can be applied by agencies with varying levels of engineer- ing design capabilities and maintenance resources. Presenting the guidelines and methods in a format familiar to bridge and highway owners, who are the target audience, will facilitate their use of the results of this research. Using FHWA’s HEC-23 format, which has successfully reached a diverse audience, will help ensure successful implementation. As with the results of any research, there may be segments of the target audience that may be reluctant to adopt or rely on new approaches. Highway engineers may consider the conditions in their state or region “unique.” This concern is addressed by providing illustrative examples at geomorphically diverse sites. 5.2.4 Leadership in Application FHWA. Because of its broad-based mission to provide guidance to the state highway agen- cies, the FHWA would ideally take a leading role in disseminating the results of this research. Through the National Highway Institute and its training courses, FHWA has the programs in place to reach a diverse and decentralized target audience. TRB. The Transportation Research Board through its annual meetings and committee activi- ties, and publications such as the Transportation Research Record: Journal of the Transportation Research Board, as well as periodic international bridge conferences can also play a leading role in disseminating the results of this research to the target audience. TRB could also host a webinar sponsored by interested TRB committees or even the Executive Committee for Design and Con- struction. This would be an excellent forum to roll out the results of this study. AASHTO. AASHTO is the developer and sanctioning agency for standards, methods, and specifications. Thus, it will be important that the research results be formally adopted through the AASHTO process. The AASHTO Standing Committee on the Environment (SCOE) could also utilize the results of this research. As a collective representation of individual state DOTs, AASHTO can also suggest any needed training to be developed by FHWA or others. The AASHTO Task Committee on Hydrology and Hydraulics could provide centralized leadership through the involvement of all state DOT bridge engineers. Regional Bridge Conferences. Regional bridge conferences, such as the Western Bridge Engi- neer Conference or the International Bridge Engineering Conferences, reach a wide audience of bridge engineers, manufacturers, consultants, and contractors. The groups would have an obvi- ous interest in environmentally sensitive stream bank protection measures and their acceptance of the results of this research will be key to implementation by bridge owners. 5.2.5 Activities for Implementation The activities necessary for successful implementation of the results of this research relate to tech- nology transfer activities, as discussed above, and the activities of appropriate AASHTO committees.

196 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 5.2.6 Criteria for Success The best criteria for judging the success of this implementation plan will be acceptance and use of the guidelines and recommendations that result from this research by state highway agency engineers and others with responsibility for design, maintenance, rehabilitation, or inspection of highway facilities. Progress can be gaged by peer reviews of technical presentations and publica- tions and by the reaction of state DOT personnel to updated FHWA guidance documents and NHI training courses. The desirable consequences of this project, when implemented, will be more efficient plan- ning, design, maintenance, and inspection of highway facilities considering the range of both traditional engineering techniques and environmentally sensitive techniques available to address problems related to stream bank instability at highway facilities. The ultimate result will be a reduction in damage to highway facilities attributable to stream instability and reduced long- term costs and environmental/ecological impacts of countermeasure installations. 5.3 Applicability of Results to Highway Practice Approximately 82 percent of the 600,000 bridges in the National Bridge Inventory (NBI) are built over waterways. Many, especially those on more active streams, will experience problems with scour, bank erosion, and channel instability during their useful life (Lagasse et al. 2012). The magnitude of these problems is demonstrated by the estimated average annual flood dam- age repair costs of approximately $50 million for bridges on the Federal-Aid system. Highway bridge failures caused by scour and stream instability account for most of the bridge failures in this country. A 1973 study for the FHWA (Chang 1973) indicated that about $75 mil- lion were expended annually up to 1973 to repair roads and bridges that were damaged by floods. Extrapolating the cost to the present makes this annual expenditure to roads and bridges on the order of $300 to $500 million. This cost does not include the additional indirect costs to highway users for fuel and operating costs resulting from temporary closure and detours and to the public for costs associated with higher tariffs, freight rates, additional labor costs, and time. The indirect costs associated with a bridge failure have been estimated to exceed the direct cost of bridge repair by a factor of five (Rhodes and Trent 1993). Rhodes and Trent (1993) document that $1.2 billion was expended for the restoration of flood-damaged highway facilities during the 1980s. Although it is difficult to be precise regarding the actual cost to repair damage to the nation’s highway system from problems related to stream instability, scour, and erosion the number is obviously very large. The guidelines and recommendations that resulted from this research pro- vide guidance to bridge owners for design, installation, and life-cycle care of a range of environ- mentally sensitive countermeasure alternatives that provide effective, reliable, and predictable protection while reducing environmental and ecological impacts. The end result will be a more efficient use of highway resources and a reduction in costs associated with the impacts of stream instability on highway facilities. 5.4 Suggested Research The findings of Chapter 2 and the interpretation and appraisal of testing results in Chapter 3 are reflected in the design guidelines and supporting information in Chapter 4 of this final report. Updated and enhanced guidance for the design, installation, and monitoring of envi- ronmentally sensitive stream bank protection measures were developed under NCHRP Project 24-39. Laboratory testing of two environmentally sensitive treatment configurations contrib- uted materially to the quantitative hydraulic engineering guidance available for the design and

Conclusions and Suggested Research 197 performance of these two treatments and their vegetative components. Compilation of data, documentation, observations, and lessons learned from the site visit program added to the grow- ing body of knowledge on design, installation, and performance for these techniques (see, for example, Goldsmith et al. 2014). Additional research to extend the results of this study could sup- port wider application of environmentally sensitive techniques. The following suggested topics would extend the results of this study. • The laboratory testing tasks of this study identified the facility and instrumentation require- ments and developed testing procedures and protocols for obtaining treatment-specific hydrau- lic engineering design and performance data. Testing to determine the hydraulic response of additional commonly used environmentally sensitive techniques is warranted. These would include (in order of priority based on reported use by practitioners): – Vegetated riprap. Generally good performance was reported for this technique. Slope erosion and drought were the most commonly reported causes of substandard behavior. Laboratory testing of the effects of root structure on rock sizing and improved techniques for installing vegetation without disrupting the function of the filter is warranted. Testing of the relative effectiveness and hydraulic response of the methods commonly used to in- stall this treatment (see Section 4.3.3) could contribute to the wider use of this bio technical technique. – Live fascines. This treatment consists of bundles of branch cuttings placed in long rows in shallow trenches across a stream bank slope on contour or at an angle. Fascines are intended to grow vegetatively while the terraces formed will trap sediment and detritus, promoting further vegetative establishment. Common reasons for failure include toe ero- sion and/or flanking. The appropriate spacing between the fascines on a slope, appropriate toe protection, and the performance of fascines relative to coir rolls and straw wattles could be investigated. – Coconut fiber rolls. Coconut fiber rolls are manufactured, elongated cylindrical structures that are placed at the bottom of stream banks to help prevent scour and erosion. The co- conut husk fibers (coir) are generally bound together with a geotextile netting. Common reasons for failure include excessive shear stress leading to scour and undermining, inad- equate anchoring conditions, and poor vegetative establishment. Some permissible velocity and shear stress data are available (see McCullah and Gray 2005), but data on optimum configurations and anchoring could improve performance. – TRM. TRMs are similar to ECBs but are more permanent, designed to resist shear and trac- tive forces. TRMs are a biotechnical technique intended to work with vegetation (roots and shoots) in a mutually reinforcing manner. While maximum flow velocity for unvegetated TRM has been shown to reach 8 ft/s, data for permissible velocity and shear for mat/vegetation combinations is not currently available (McCullah and Gray 2005). – Customized techniques. The laboratory testing approach developed and validated under this study could contribute to the design of new/innovative biotechnical designs or custom- ized combinations of various techniques and configurations. Combinations of hard and soft biotechnical components and a variety of vegetation types for high-value, high-risk projects could be tested and optimized with the resulting treatment-specific hydraulic data. • For NCHRP Project 24-39 both 1-dimensional and 3-dimensional velocity data were acquired for all test runs. Budget constraints limited the analysis of hydraulic data to only the 1-D velocity data. During each flow, 1-D point velocity measurements were taken at each transect at 20%, 60%, and 80% of the total flow depth, and also as close to the bed as possible. Dur- ing each flow, 3-D acoustic Doppler velocimeter measurements were taken at selected loca- tions where the probe could be positioned within the submerged willow vegetation. This 3-D acoustic Doppler velocimeter data are available for additional analysis and development of appropriate conclusions. However, in acquiring this data some difficulties were encountered,

198 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures particularly in proximity to vegetation clusters. The 3-D measurements were scattered in time and space, and near-bed measurements may be suspect. • Environmentally sensitive stream bank protection measures are clearly viable on perennial streams of the arid Southwest such as the Rio Grande (see Section 4.4.2). However, addi- tional effort could be allocated to the unique aspects of applying these techniques to ephem- eral streams of the arid Southwest. A logical starting point would be publications and guidance from the USDA Plant Materials Centers in this geophysical region, including the Los Lunas Plant Materials Center in New Mexico and the Tucson Plant Materials Center in Arizona. For example, the Los Lunas Center notes that in areas served (the semi-arid and arid Southwest region) environmental conditions in the region, including low precipitation, high-intensity rainfall, wind, extreme topography, and varied land uses, combine to produce a variety of problems needing plant material solutions. Among the Center’s major conservation goals are erosion and sediment control and riparian restoration. Similarly, the Tucson Center mission statement includes current conservation needs such as erosion, drought, water quality, wild- life habitat, and wildfire damage. The Center develops and evaluates adapted plant materials and technologies to serve the needs of its service area.