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<br />e <br /> <br />" <br /> <br />. <br /> <br />. <br /> <br />~ <br /> <br />e <br /> <br /><~ <br /> <br />:EM 1110-2-1913 <br />31 Mar 78 <br /> <br />past levees have been built by methods o~ compaction varying from none <br />to carefully controlled compaction. The local economic situation also <br />af~ects the selection of a levee section. Traditionally, in areas of <br />high property values, high land use, and good foundation conditions, <br />levees have been built with relatively steep slopes using controlled <br />compaction, while in areas o~ lower property values, poor foundations, <br />or high rain~all during the construction season, uncompacted or semi- <br />compacted levees with flatter slopes are more typical. This is evident <br />by comparing the steep slopes of levees along the industrialized Ohio <br />River Valley with levees along the Lower Mississippi River which have <br />much broader sections with gentler slopes. Levees built with smaller <br />sections and steeper slopes generally require more comprehensive inves- <br />tigation and analysis than do levees with broad sections and flatter <br />slopes whose design is more empirical. Where rainfall and foundation <br />conditions permit, the trend in design o~ levees is toward sections with <br />steeper slopes. Levee maintenance is another factor that often has <br />considerable in~luence on the selection o~ a levee section. <br /> <br />b. Levee Types According to Location. Levees are broadly classi- <br />fied according to the area they protect as either urban or agricultural <br />levees because o~ different requirements for each. As used in this <br />manual, urban and agricultural levees are defined as follows: <br /> <br />(1) Urban levees. <br />communities, including <br />facilities. <br /> <br />Levees that provide protection from flooding in <br />their industrial, commercial, and residential <br /> <br />(2) <br />~looding <br /> <br />Agricultural levees. Levees that provide protection from <br />in lands used for agricultural purposes. <br /> <br />c. Levee Types Accordin~ to Use. Some o~ the more common terms <br />used ~or levees serving a speci~ic purpose in connection with their <br />overall purpose of flood protection are given in table 1-2. <br /> <br />d. Causes of Levee Failures. The principal causes of levee ~ail- <br />ure are <br /> <br />(1) Overtopping. <br /> <br />(2) Sur~ace erosion. <br /> <br />(3) <br />(4) <br /> <br />Internal erosion (piping). <br /> <br />Slides within the levee embankment or the foundation soils. <br /> <br />1-3 <br /> <br />-------' <br />