This report describes methods and findings of the first phase (pilot study) of a 2-year study of the effect of volunteer woody vegetation on durability of Sacramento River revetments. The study consisted of a literature review, analysis of effects of woody vegetation on revetment performance during the 1986 flood using historical records and aerial photos, and visual inspection of revetments along the Sacramento River between river mile (RM) 84.5 and 119. Federal and Corps of Engineers (CE) regulations specifically address removal of woody vegetation from levee slopes and flood control channels, but vegetation on revetted banks that are not part of a levee is not specifically prohibited. However, current CE maintenance standards as applied to the Sacramento River Flood Control Project prohibit woody vegetation on revetments. Primary reasons that vegetation is undesirable on revetment include potential reduction of channel conveyance, impairment of revetment visibility for inspection, and reduced revetment durability. Only revetment durability was addressed in this study. The literature review revealed little information regarding the effects of vegetation on revetment durability. The propensity of riverbank revetments to support woody vegetation and the habitat value of these plant communities were noted by several investigators. Although incorporation of plant materials in revetments is not standard engineering practice, several sources indicate that living woody vegetation growing through revetments adds strength. Accordingly, revetment designs that include planted or volunteer vegetation have been widely proposed and tested. Several CE field offices permit limited woody vegetation on revetments in particular projects. Although the 1986 flood approached or exceeded record and design discharge magnitudes for much of the Sacramento River Bank Protection Project (SRBPP) reach of the Sacramento River (RM 0 to 194), documented revetment damage due to the flood was extremely limited. A review of Sacramento District files for emergency assistance requests revealed only six damaged sites. Study of aerial photographs, inspection records, and revetment construction dates showed that none of the damaged revetments supported significant woody vegetation at the time of the flood. Five of the six revetment damage sites were located between RM 84.5 and 99.5; four of the five were riprap revetments on convex banks; and only one of the five was damaged severely enough to be repaired by 1989. Visual inspection of the banks of the Sacramento River from a boat in September 1989 (between the Fremont and Tisdale Weirs, RM 84.5 to 119) revealed additional (but slight) revetment damage, primarily to older cobble revetments. The observed damage appeared to be related to geotechnical factors or toe failure; revetment function did not seem to be impaired. Damage rates for revetments supporting woody vegetation tended to be lower than for revetments of the same age located on banks of similar curvature but without woody vegetation. About 70 percent of the bank line of the inspected reach was revetted. About two thirds of the revetment was cobble, and about one third was rock riprap. Seven percent of rhe revetted bank line supported some type of woody vegetation.


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    Titel :

    A Study of Vegetation on Revetments, Sacramento River Bank Protection Project. Phase 1: Literature Review and Pilot Study



    Erschienen in:

    Technical Report ; HL-90-19 phase 1


    Erscheinungsdatum :

    1990


    Format / Umfang :

    8498563


    Medientyp :

    Report


    Format :

    Elektronische Ressource


    Sprache :

    Englisch



    Klassifikation :


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