Vegetated Geogrids

installations. First, the bank must beexcavated down to the expected depth ofscouring and a rock footing placed. Thefooting should extend out into the riverto prevent scouring at the toe of thestructure. The first level of timber logsis then placed on top of the rockfoundation, with subsequent levelsplaced perpendicular to the previous.Each successive layer is nailed to theprevious. Once the desired height isreached, the structure can be backfilled.Typically rock is used to fill the cribframe up to the base flow water level,with layers of branch cuttings and soilinterspersed between each layer oftimber above the base level.Figure 21: Live crib wall installation.The capitol cost of installing a live cribwall is moderate to high compared toother shoreline hardening methods.Costs can range from $100-$400 perliner foot.exception of increasing its elevation.Excavating the top layer and addingadditional sections is straightforward,however care should be taken tominimize the impact to existingdeveloped root systems.AdvantagesLive crib walls have many advantagesover other engineered shore protectionapproaches, among them are:• They can be used on banks that havevery steep slopes.• The necessary materials are easilyobtainable.• These structures can withstandrelatively high velocities and shearstresses.• They are effective against preventingbank erosion on faster flowingstreams.• They are more aesthetically pleasingthan many traditional shorelinehardening approaches.• They are more ecologically sensitivethan most shoreline hardeningtechniques.DRAFTDisadvantagesLive crib walls have many disadvantagescompared to other engineered shoreprotection approaches, among them are:Once the structure is constructed, itshould be examined early on to makesure that the roots of the live cuttings aredeveloping. Beyond that there isminimal maintenance to be performedon a crib wall.Adaptability• Installation and construction iscomplex and requires heavyequipment.• Crib walls are not designed to resistlarge lateral earth stresses so themaximum height of the wall islimited.Once constructed, it is difficult tomodify a live crib wall, with the