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<br />EM 1110-2-1913 <br />31 Mar 78 <br /> <br />Table 1-2. Classification of Levees According to Use <br /> <br />Type Defini tion <br /> <br />Mainline and tributary levees Levees that lie along a mainstream and <br />its tributaries, respectively. <br /> <br />Ring levees <br /> <br />Levees that completely encircle or "ring" <br />an area subject to inundation from all <br />directions. <br /> <br />Setback levees <br /> <br />Levees that are built landward of exist- <br />ing levees, usually because the exist- <br />ing levees have suffered distress or <br />are in some way being endangered, as by <br />river migration. <br /> <br />Sublevees <br /> <br />Levees built for the purpose of under- <br />seepage control. Sublevees encircle <br />areas behind the main levee which are <br />subject, during high-water stages, to <br />high uplift pressures and possibly the <br />development of sand boils. They nor- <br />mally tie into the main levee, thus <br />providing a basin that can be flooded <br />during high-water stages, thereby <br />counterbalancing excess head beneath <br />the top stratum within the basin. Sub- <br />levees are rarely employed as the use <br />of relief wells or seepage berms make <br />them unnecessary except in emergencies. <br /> <br />Spur levees <br /> <br />Levees that project from the main levee <br />and serve to protect the main levee <br />from the erosive action of stream <br />currents. Spur levees are not true <br />levees but training dikes. <br /> <br />1-4 <br /> <br />. <br /> <br />4 <br /> <br />:< <br /> <br />. <br /> <br />. <br /> <br />- <br /> <br />. <br />