Vegetated Geogrids

layer is prepared consisting of a geosyntheticmembrane and a layer of smallrocks, or gravel. The main armor unitsare then placed on the filter layer, withlargest rocks along the bottom of thebank. Extra protection is typicallyrequired at the toe of the structure and atthe flanks to prevent erosion in thesecritical areas.Revetments can be costly, ranginganywhere from $500/lf to $2,000/lf.Construction costs are a function ofstructure dimension, as well as theavailability and coast of transportingmaterial to the site.The individual rocks comprising arevetment can be prone to damage,displacement, or deterioration. Thisreduces the overall effectiveness of thestructure, and makes surrounding areasmore susceptible to future damage. Forthis reason, periodic inspections arerequired to identify misplaced ordeteriorated armor stones so that theycan be repaired before the damagebecomes too severe.AdaptabilityIn terms of adaptability, revetments arefairly flexible. Adding individual armorunits to extend an existing structure isusually possible, although expensive.Given the significant costs involved withthe mobilization/demobilization of theheavy equipment required forconstruction, consideration of futureconditions is most efficiently addressedprior to initial construction.AdvantagesRevetments have many advantages overother engineered shore protectionapproaches, among them are:• Individual armor units are given anallowance for movement withoutcausing the structure to becomeimpaired.• The installation is straightforward;however it does require the use ofheavy machinery.• Revetments have low maintenancerequirements and damages can beeasily repaired.• Revetments are adaptable and can beadjusted or modified to continue toprovide protection in the future.• They can withstand relatively strongcurrents.• The void spaces within the structureprovide some habitat function ascompared to shear, impervioussurfaces.DisadvantagesRevetments have many disadvantagescompared to other engineered shoreprotection approaches, among them are:• Scouring occurs at the toe and flankof the structure and can increaseerosion downstream.• Material cost and transportation canbe expensive.• Large voids due to poorly placedrocks can be a hazard.• Access to the shoreline isaltered/disrupted.• They have a significant impact onthe local landscape and can disruptsediment transport.DRAFTSimilar TechniquesAlternatives may include: gabions,bulkheads, rootwad revetments, treerevetments, green walls, and crib walls.