Vegetated Geogrids

Levees (Dikes)ApproachConstruction CostSoft Hard Low HighMaintenance CostAdaptabilityLow High Low HighDescriptionLevees or dikes are earthenembankments designed to furnish floodprotection during periods of seasonalhigh water. As such these structures aredesigned to withstand the loading fromwater pressure for a period of days toweeks. Longer time periods will requirean earthen damn. The major differencesbeing that levees can only remainsaturated beyond the limit of capillarysaturation for a short period, leveesfrequently must be constructed onfoundations that are less than ideal, andlevees typically use whatever fillmaterial is available locally. Majormodes of levee failure includeovertopping, surface erosion, internalerosion, and sliding. Under strongcurrents and/or wave action levee sideslopes themselves must often beprotected by the techniques discussed inthis document.Design and ConstructionBasic steps in the design of a leveeinclude detailed subsurfaceinvestigations of both the levee site andthe borrow site. This will helpdetermine the strength of the foundationas well as the fill material. Geometricparameters including crest height, crestwidth and side slope are set based onfactors such as expected flood crestelevation, soil stability, and practicalconsiderations. Once cross-sectionshave been set, the design should beanalyzed for seepage, slope stability,settlement, and trafficability of thesurface.Figure 22: Typical levee cross-section.DRAFTFigure 23: Constructed levee.Construction of a levee begins withclearing, grubbing, and if necessarystripping the site. Any loose or softareas should be removed to create astable foundation. Once the site isprepared, fill material is added in lifts.Depending on the type of levee beingconstructed, compaction may berequired between lifts. Once the desiredgeometry is achieved, surface protectioncan be added. Common choices includevegetation, rip-rap, and concrete.