Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures (2016) / Chapter Skim
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A-1 A P P E N D I X A NCHRP Report 544 Findings on Selected Treatments
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A-2 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures McCullah and Gray (NCHRP Report 544) – Summary of Hydraulic Loading, Reasons for Failure, and Research Opportunities DATA AVAILABILITY AND RESEARCH OPPORTUNITIES McCullah and Gray found that availability of design data in terms of sustainable hydraulic loads varied considerably among the 44 techniques included in NCHRP Report 544.
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NCHRP Report 544 Findings on Selected Treatments A-3 COMMON REASONS/CIRCUMSTANCES FOR FAILURE Reasons for failure include excessive shear stress leading to scour and undermining, inadequate anchoring conditions, a poor vegetative establishment environment (e.g., shade, toxic soil/water chemistry, etc) , and poor construction methods.
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A-4 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures 3. LIVE BRUSH MATTRESS HYDRAULIC LOADING Studies have shown that brush mattresses have stabilized a bank in a test flume against velocities exceeding 7 m/s (20 ft/s)
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NCHRP Report 544 Findings on Selected Treatments A-5 COMMON REASONS / CIRCUMSTANCES FOR FAILURE The most likely causes of failure are the following: 1. Inadequate reinforcement from the brush layer inclusions, i.e., too large a vertical spacing or lift thickness for the given soil and site conditions, i.e., slope height, slope angle, and soil shear strength properties, 2.
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A-6 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures RESEARCH OPPORTUNITIES Studies could be conducted to further investigate the spacing between fascines on a slope that provides the optimum stability while minimizing costs, and how they perform relative to coir rolls and straw wattles.
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NCHRP Report 544 Findings on Selected Treatments A-7 COMMON REASONS / CIRCUMSTANCES FOR FAILURE The most frequent reasons for failure of rootwad revetments are flanking and undercutting of the structure. Flanking may occur if upstream or downstream meanders are unstable, causing changing flow directions, the footer log does not extend far enough to protect the entire structure, or the trunk is not keyed in to a sufficiently stable substrate.
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A-8 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures RESEARCH OPPORTUNITIES None identified.
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NCHRP Report 544 Findings on Selected Treatments A-9 13. VEGETATED MECHANICALLY STABILIZED EARTH HYDRAULIC LOADING There appears to be little or no published test data for permissible hydraulic loading of VMSE structures.
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A-10 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures RESEARCH OPPORTUNITIES Some uncertainty exists at present as to the exact permissible shear stresses and velocities for VMSE interfaces. Performance results during high water conditions indicate that VMSE can withstand hydraulic loadings at least equal to those listed in Table 2 for either vegetated coir mats or live brush layers alone.
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NCHRP Report 544 Findings on Selected Treatments A-11 15. VEGETATED ARTICULATED CONCRETE BLOCKS HYDRAULIC LOADING The critical velocity and failure shear stress for ACBs are on the order of 4.3 m/s (14 ft/s)
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A-12 Evaluation and Assessment of Environmentally Sensitive Stream Bank Protection Measures References Cited Above Allen, H and Leech, J.R.
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NCHRP Report 544 Findings on Selected Treatments A-13 Racin, J.A., Hoover, T.P., and Crossett Avila, C.M.
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