Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures (2016) / Chapter Skim
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From page 90... ...
90 4.1 Overview This chapter contains both general and site-specific guidance for the design, installation, monitoring, and maintenance of environmentally sensitive stream bank protection measures. From a macro-scale perspective, selection and design of an environmentally sensitive stream bank treatment must consider the watershed and river system processes that drive river channel response, including climatic, hydrologic, hydraulic, and geomorphic considerations.
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From page 91... ...
Design Guidelines and Appraisal of Research Results 91 4.2 General Considerations 4.2.1 Introduction Factors that affect stream stability at highway infrastructure can be classified as hydrologic, hydraulic, and geomorphic. Rapid and unexpected changes can occur in streams in response to human activities in the watershed and/or natural disturbances of the fluvial system, making it important to anticipate changes in channel geomorphology, location and behavior.
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92 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures during a period of above average rainfall and runoff than with a single large event. The study of historical wet-dry trends may explain certain complex aspects of system response.
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Design Guidelines and Appraisal of Research Results 93 hampered because related variables such as flow resistance, the form of bed roughness, channel cross-section shape, and sediment discharge also respond to the changing depth. Position and shape of alternate, middle, and point bars can also be expected to change.
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94 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Bed load and suspended load can be described by transport equations as they are usually related to transport capacity. Wash load, however, is dependent primarily on supply conditions.
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Design Guidelines and Appraisal of Research Results 95 regions and for perennial streams in semi-arid environments (Soar and Thorne 2001 and Biedenharn et al.
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96 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures examined for a range of discharges that represent key levels for aquatic habitat, riparian vegetation, channel stability, or flow conveyance (Copeland et al.
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Design Guidelines and Appraisal of Research Results 97 Conveyance. NCHRP Report 544 also contains a special topic on management of conveyance in relation to design of environmentally sensitive stream bank treatments.
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98 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures hydraulic radius in ft, and S is the energy slope. R is equal to A/P, where P is the wetted perimeter in ft, and S is equal to the bed slope when flow is uniform.
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Design Guidelines and Appraisal of Research Results 99 failure of the embankment. Where lateral erosion or increased flood stages accompanying aggradation increase the debris load in a stream, the hazards of clogged bridge waterway, reduced conveyance, and hydraulic forces on bridge superstructures are increased.
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100 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures stream system to various scenarios or future conditions, and (3) physical models or physical process computer modeling using mathematical models such as the USACE HEC-RAS (USACE 2010)
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Design Guidelines and Appraisal of Research Results 101 flow hydrograph is entered as a series of constant flows. Within each flow time step, many sediment transport and cross-section updating time steps are often required.
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102 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Figure 4.3. Evolution of incised channel from initial incision (A, B)
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Design Guidelines and Appraisal of Research Results 103 sediment loads of Figure 4.4. Note that there is an apparent increase of sediment load at stage E (Figure 4.4A)
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104 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Consequently, one of the key factors recommended for evaluation during a field site visit of an existing environmentally sensitive treatment or during the reconnaissance phase for the selection and design of a new treatment is to establish whether or not the channel is vertically stable and, if it is not, what the channel evolution stage for the reach of interest is (see Appendix C, Field Data Forms, Part 2)
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Design Guidelines and Appraisal of Research Results 105 • Vegetation. • Height of bank.
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106 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures where: Rc = Centerline radius of the bend, ft (m) W = Width of the bend, ft (m)
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Design Guidelines and Appraisal of Research Results 107 slope and cross section while posing a threat or hazard to engineered structures and both "hard" and "soft" countermeasures. Some types of lateral instability are shown in Figure 4.7.
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108 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Figure 4.8. Models of flow structure and associated bed forms in straight alluvial channels: (A)
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Design Guidelines and Appraisal of Research Results 109 Secondary currents, which are usually weaker than primary ones, influence the distribution of velocity and boundary shear stress. Markham and Thorne (1992)
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110 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures by longitudinal and transverse currents. This produces a largely down-valley component to meander migration.
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Design Guidelines and Appraisal of Research Results 111 In reaches where geologic controls are exposed predominantly in the bed of the channel, migration rates may dramatically increase because the channel bed is not adjustable. A fundamental assumption of overlay techniques based on aerial photo or map comparison is that a time period sufficient to "average out" such anomalies will be available, making the historic meander rates a reasonable key to the future.
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112 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures these geomorphic factors and the geotechnical considerations that affect the stability of the channel banks on which the erosion protection measures are to be placed. The vertical stability of the channel directly affects the stability of the channel banks, and the lateral stability of the channel is a function of the hydraulic stresses to which the channel banks are subjected.
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Design Guidelines and Appraisal of Research Results 113 Active bank erosion can be recognized by falling or fallen vegetation along the bankline, cracks along the bank surface, slump blocks, deflected flow patterns adjacent to the bankline, live vegetation in the flow, increased turbidity, fresh vertical faces, newly formed bars immediately downstream of the eroding area, and, in some locations, a deep scour pool adjacent to the toe of the bank. These indications of active bank erosion can be noted in the field and on stereoscopic pairs of aerial photographs.
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114 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Piping. Piping is a phenomenon common to alluvial stream banks.
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Design Guidelines and Appraisal of Research Results 115 growth, location of roads that cause unfavorable drainage conditions, agricultural uses on adjacent floodplain, saturation of banks by leach fields from septic tanks, and increased infiltration of water into the floodplain as a result of changing land-use practices. Various forces are involved in mass wasting.
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116 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Estimating Critical Bank Height. The stability of the bank with respect to mass failure is dependent on soil properties and bank geometry.
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Design Guidelines and Appraisal of Research Results 117 Many river management situations require information on the stability of the channel banks. These may include assessing the stability of existing channel banks, predicting the effect that changes in riparian land use will have, or designing new channels.
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118 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures perpendicular to failure planes. Work by Pollen (2007)
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Design Guidelines and Appraisal of Research Results 119 vegetation on the slope would stabilize the bank even under worst-case conditions. The design was, therefore, implemented and constructed.
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120 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Category Excellent (1-3)
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Design Guidelines and Appraisal of Research Results 121 Quantitative Assessment Inspection of sites stabilized with biotechnical measures should include assessment of three properties of the vegetation: a. Overall health and vitality of the plants, b.
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122 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures so Figure 4.15 shows that predicted soil erosion is more strongly affected by the amount of cover that contacts the soil surface (reducing C-factor from 0.45 to near 0) than the type of vegetation (trees versus grass/weeds)
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Design Guidelines and Appraisal of Research Results 123 healthy understory of shade-tolerant species.
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124 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 4.2.6 Aquatic Habitat Issues Introduction As noted, CRP-CD-58 that accompanies NCHRP Report 544 (McCullah and Gray 2005) contains detailed coverage on a series of special topics relevant to the design of environmentally sensitive stream bank treatments (see also Section 2.1e)
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Design Guidelines and Appraisal of Research Results 125 highway embankments. Sinuous channels with a nonuniform cross section are sometimes altered to become a prismatic trapezoid, and pool-riffle sequences are commonly replaced with uniform runs.
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126 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures single erosion countermeasure, opportunities for increasing either the amounts or quality of fish habitat could potentially pay high dividends both for the environment and in terms of public appreciation and resource agency approvals. Large-scale channel restoration or stabilization work (directly affecting a reach longer than 20 channel widths)
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Design Guidelines and Appraisal of Research Results 127 Geomorphic Context The landforms and hydrology of the upstream watershed directly affect the water temperature and the water and sediment flow regimes that govern habitat quality of a specific river reach. The details of linkages between climate, landscape position, fluvial geomorphology, and hydrology are very complex (see Section 4.2.2)
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128 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures of fish are dependent on the low-energy habitats found on flooded, forested floodplains. Isolation of floodplains from the stream by channel incision, channelization, levee installation, or other forms of structural flood control can be detrimental.
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Design Guidelines and Appraisal of Research Results 129 by providing a relatively high radius compact channel for low flow, and a larger but lower radius cross section during high flows (as observed naturally occurring in valley floodplains)
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130 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures context" means the sum of the physical constraints and the relevant biological constraints. When proposing hydraulic, structural, or environmentally sensitive modifications either to abate erosion or improve biological habitat, solutions should be chosen in light of the specific hydraulic and ecological processes relevant at the site of interest.
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Design Guidelines and Appraisal of Research Results 131 Department of Fish and Wildlife 2003)
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132 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures More importantly, the type of plants that can survive at various submersions during the normal cycle of low-, medium-, and high-stream flows is critical to the design, implementation, and success of biotechnical engineering techniques. In addition, the combination of riprap and vegetation may be inappropriate if flow capacity is an issue, since bank vegetation can reduce flow capacity, especially when in full leaf along a narrow channel (see management of conveyance discussion in Section 4.2.3)
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Design Guidelines and Appraisal of Research Results 133 Other factors that need to be considered when selecting a design option include climate and hydrology, soils, cross-sectional dimensions (is there sufficient room for the countermeasure?
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134 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures "hard" engineering approach. Biotechnical countermeasures need to be applied in a prudent manner, in conjunction with channel planform and bed stability analysis and rigorous engineering design.
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Design Guidelines and Appraisal of Research Results 135 Slate et al.
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136 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures • Quantitative measurements of key hydraulic variables, and • Condition monitoring of each component before testing and after each test flow event. The two biotechnical bank-protection treatments tested were (see Figures 3.3 and 3.4)
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Design Guidelines and Appraisal of Research Results 137 Figure 4.22. Live siltation typical drawing (McCullah and Gray 2005)
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138 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Cost. An estimated level of effort for installing live siltation ranges from 0.2 to 0.6 work hours per linear foot (0.7 to 2 work hours per linear m)
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Design Guidelines and Appraisal of Research Results 139 and slow velocities during high flows. Cuttings may not grow well if not handled properly prior to installation.
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140 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures (successional reclamation)
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Design Guidelines and Appraisal of Research Results 141 Willow species choice is highly dependent on locale; the best species for a given site are those found growing near the site. Stakes are typically harvested and planted when the willows, or other chosen species, are dormant, although the cuttings can do well other times of year when soil moisture is available.
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142 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures For additional information on performance of live staking installations, see Table 2.10 which lists six sites inspected under Task 6 where live staking was part of the environmentally sensitive treatment implemented. Detailed information on these sites can be found in the Compendium.
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Design Guidelines and Appraisal of Research Results 143 Longitudinal stone toes are well suited for many situations where relatively low-cost, continuous bank protection is needed, and is particularly applicable for ephemeral, narrow, and small- to medium-sized streams. A stone toe is also well suited for areas where the toe is experiencing erosion but the mid and upper banks are fairly stable due to vegetation, cohesive soils, infrequent short-duration inundation, or relatively slow velocities.
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144 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures The key trenches at the upstream and downstream ends should be excavated into the bank at an angle of approximately 30 degrees with the primary flow direction and of sufficient length that flows will not be able to get around them during the design storm. A gentle angle is important for the end keyways, often referred to as "refusals," because it allows for smooth flow transitions coming into and flowing out of the treated reach.
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Design Guidelines and Appraisal of Research Results 145 Construction and Installation. All longitudinal stone toes should be constructed in an upstream to downstream sequence.
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146 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures situation is anticipated or encountered, the problem can be remedied by adding more rock to restore design conditions. Longitudinal stone toes may be flanked during extremely high flows if the key trenches are incorrectly built or if the tie-backs are spaced too widely or are constructed with inadequate amounts of stone.
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Design Guidelines and Appraisal of Research Results 147 Purpose and Advantages. Components and variations of this treatment are also known as FES, brush layering with soil wraps, and vegetated geofabric wrapped soil.
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148 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Figure 4.26. VMSE typical drawing (McCullah and Gray 2005)
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Design Guidelines and Appraisal of Research Results 149 they generally root well from cuttings. Alder, cottonwood (Populus deltoides)
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150 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures overlap sections should be secured in place using wood construction stakes spaced every 3 ft (0.9 m)
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Design Guidelines and Appraisal of Research Results 151 to be the more important factor in the overall performance of the vegetative component. For example, the stair-step configuration of the VMSE creates preferential pathways for high-velocity flow that results in the potential for damage to the coir/jute fabric of the soil lifts.
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152 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures (see Table 2.9)
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Design Guidelines and Appraisal of Research Results 153 Figure 4.28. Vegetated riprap -- bent pole method (McCullah and Gray 2005)
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154 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Figure 4.30. Vegetated riprap with joint planting (McCullah and Gray 2005)
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Design Guidelines and Appraisal of Research Results 155 Environmental Considerations and Benefits There are many environmental benefits offered by vegetated riprap, most of which are derived from the planting of willows or other woody species in the installation. Willow provides canopy cover to the stream, which gives fish and other aquatic fauna cool places to hide.
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156 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Vegetated Riprap with Brush Layering and Pole Planting (Figure 4.29) : There are two methods of constructing brush layered riprap; one involves building up a slope, and the other works with a pre-graded slope.
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Design Guidelines and Appraisal of Research Results 157 Common Reasons/Circumstances for Failure Flanking, overtopping, or undermining of the revetment due to improperly installed or insufficient keyways is one of the biggest reasons for failure of riprap. Improperly designed or installed filter material can also cause undermining and failure of the installation.
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158 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures The restoration area is located approximately 25 miles downstream of Cochiti Dam on the Rio Grande in what is designated as the Santa Ana Reach (Figure 4.31) of the Pueblo of Santa Ana (Pueblo -- a sovereign tribal nation)
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Design Guidelines and Appraisal of Research Results 159 channelization works, and the construction of upstream dams (for example, see Lagasse 1980, Salazar 1998, Richard 2001, USACE 2002a, Grassel 2002, Sixta 2004, Ortiz 2004, Ayres Associates 2006a)
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160 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures have induced scour of the remaining jetty-jack fields exposed along the eroding river banks resulting in undercutting and burial of the jacks. Hydromodification Hydrology in the Middle Rio Grande Valley (i.e., Cochiti Lake to Elephant Butte Lake)
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Design Guidelines and Appraisal of Research Results 161 Annual Hydrographs at Albuquerque Gage Date D is ch ar ge (c fs) Figure 4.34.
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162 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures federally-listed plant species are likely to occur within the project area, and none have been detected by USACE and Pueblo biologists. Stakeholder Activities The Pueblo has implemented an ecosystem-based restoration program, designed to reverse the impacts of 60 years of flood and sediment control and channelization projects on the Middle Rio Grande and restore a healthy, functioning Rio Grande ecosystem.
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Design Guidelines and Appraisal of Research Results 163 Channel and Stream Bank Stabilization Measures In 1998, the Reclamation investigated routine bank stabilization measures where active bank erosion persistently threatened the riverside levee on the east side of the Rio Grande about 0.5 miles downstream of the Jemez River confluence. Rather than continue long-term maintenance, a more permanent solution to the problem was sought in coordination with the Pueblo of Santa Ana.
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164 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures of the river channel within the GRF itself. Guide banks were added to the design to maintain a favorable upstream channel alignment (Ayres Associates 2003 and USACE 2008)
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Design Guidelines and Appraisal of Research Results 165 accommodates some channel movement and allows for the erosion of the bar surface and deposition of new material at any location across the active width. The left bank of GRF #2 was tied into the existing channel bank along the bosque and has a 3H:1V slope.
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166 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Figure 4.39 presents a representative cross section of the Bed Sill design. The Bed Sill was constructed at a constant elevation across the channel.
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Design Guidelines and Appraisal of Research Results 167 GRF Riprap. The riprap components of the GRFs were designed to withstand the hydraulic forces associated with the 100-year flood (22,300 cfs)
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168 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures that the overbank velocities and associated shear stresses are less than those in the main channel. The same gravel used to provide the filter on the bank slopes was used as the bedding under the overbank armor.
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Design Guidelines and Appraisal of Research Results 169 Figure 4.41. Typical sections of bank transitions (Ayres Associates 2003)
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170 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Native species were selected with regard to hydrologic regimes and corresponding depths to water table that occur along the slope of the upper bank. Guidelines for pole planting similar to those in Section 4.3.1 were followed.
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Design Guidelines and Appraisal of Research Results 171 of coffer dams, dewatering of the structure sites, and in-channel excavation as well as installation of access roads and staging and stockpiling sites. Pertinent Data.
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172 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures GRF #3 Physical Characteristics Length of GRF (in-river portion) 400 ft Width of main channel portion Approximately 240 ft Width of overbank portion Approximately 170 ft Thalweg elevation at crest 5054.0 ft, NGVD 29 Thalweg elevation at toe 5052.0 ft, NGVD 29 Longitudinal slope 0.005 Sheet pile driving depth 12 ft below final grade Length of buried guide bank 385 ft Length of bank transitions 50 to 210 ft Material Quantities Item Unit Upstream Transitions Main GRF Downstream Transitions Guide Bank Totals Geotextile fabric SY 1,330 14,780 1,320 - 17,430 Granular filter CY 425 3,050 410 - 3,885 Riprap, Type 1 CY 1,660 8,450 1,290 - 11,400 Riprap, Type 2 CY 500 2,060 170 230 2,960 Vinyl sheet pilling SF - 7,460 - - 7,460 FES LF 1,020 1,600 352 - 2,972 Type 1 willows LF 1,020 1,600 352 - 2,972 Type 2 willows LF - - - 385 385 Type 1 seed mix SF 6,630 10,400 2,288 - 19,318 Type 2 seed mix SF 6,630 10,400 2,288 - 19,318 Type 3 seed mix SF 1,658 2,600 572 - 4,830 Table 4.6.
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Design Guidelines and Appraisal of Research Results 173 the appropriate season as scheduled by the Pueblo. The Pueblo is required to obtain all permits applicable to any repair work.
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174 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Construction. During construction, it was noted that materials were either improperly or inadequately placed or that, in some cases, the size or gradation of bedding materials used in a number of locations were not as specified.
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Design Guidelines and Appraisal of Research Results 175 Richard, G
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176 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures were indicated by high-flow velocities that resulted in both bank and channel erosion. Degraded stream beds and frequent and severe peak flows diminished aquatic habitat.
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Design Guidelines and Appraisal of Research Results 177 corridor in the form of roadway crossings, utility poles, manholes, storm sewer outfalls, and culverts. The primary bank erosion process is fluvial erosion; limited amounts of mass failure occur where the channel has simultaneously incised and impinged against a high bank.
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178 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Creek. Hydraulic modeling of the 100-year event indicated that maximum velocities occurred at bankfull flow, and that these velocities ranged from 2.75 ft/s to 7.75 ft/s, varying by reach.
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Design Guidelines and Appraisal of Research Results 179 loading to downstream waters by 50%, to increase habitat quality for fish and wildlife, to control stream velocities, and to stabilize stream banks. Project measures included stream bank stabilization, channel bed erosion controls, and storm water detention basins.
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a. Graded bank, stone toe, and upstream-angled rock vane shortly after construction.
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Design Guidelines and Appraisal of Research Results 181 g. Cuttings planted in coir fiber ECB showing initial growth shortly after planting.
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182 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Mistakes and Learning Curve. Construction was scheduled for winter months to take advantage of frozen ground, but an unusually warm, wet winter complicated construction operations due to muddy conditions.
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Design Guidelines and Appraisal of Research Results 183 much of this stone had been moved or dislodged, both along stone toes and at the small drop structures. Some local erosion was noted at one site immediately downstream from a protected bank likely due to a poorly designed transition from the protected bank to a convex bank (point bar)
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184 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures References Arlinghaus, D
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Design Guidelines and Appraisal of Research Results 185 sensitive stream bank stabilization and protection measures, 16 treatments from the river training and bank armor and protection categories of NCHRP Report 544 were selected for further consideration (see Appendix A for a summary of issues related to hydraulic loading, common reasons/circumstances for failure, and research opportunities for these 16 treatments as identified in NCHRP Report 544)
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186 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 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.
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Design Guidelines and Appraisal of Research Results 187 The following sections highlight relevant observations that contribute to advancing the current state of practice for environmentally sensitive design based on the survey of practitioners and the field site visits conducted under this study. 4.5.2 Observations from the Survey of Practitioners Under Task 2 a survey form was prepared, approved by the NCHRP project panel, and distributed by email to 319 individuals representing all 50 state highway agencies (DOTs)
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188 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 4.5.3 Observations and Lessons Learned from the Field Site Visits Introduction Under Task 6, field investigations were conducted at 16 sites where a variety of environmentally sensitive treatments had been installed and monitored. The sites were grouped in three specific regions as follows: • Southeast (Mississippi)
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Design Guidelines and Appraisal of Research Results 189 Live siltation: • As a biotechnical practice live siltation can be self-mitigating as it establishes into a row of riparian shrubs. At the Alamitos Creek site in Northern California, cuttings of Baccharis (mule fat)
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190 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures Observations on the installation and performance of "Tray 2" (VMSE without hard toe -- see Chapter 3 and Figure 3.4) are summarized below.
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Design Guidelines and Appraisal of Research Results 191 • At the Nichols Arboretum site the live stakes in the riprap have not fared well. Many stakes were damaged when driven through the rock blanket to plant them in interstices.
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