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<br />~~ <br />. <br /> <br />.- <br /> <br />~~.~) <br />..--..:.-" <br /> <br />. <br /> <br />. <br /> <br />:EM 1110-2-1913 <br />31 Mar 78 <br /> <br />past levees have been built by methods of compaction varying from none <br />to carefully controlled compaction. The local economic situation also <br />affects 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 ~ith relatively steep slopes using controlled <br />compaction, ~hile in areas of lo~er property values, poor foundations, <br />or high rainfall during the construction season, uncompacted or semi- <br />compacted levees ~ith flatter slopes are more typical, This is evident <br />by comparing the steep slopes of levees along the industrialized Ohio <br />River Valley ~ith levees along the Lo~er Mississippi River ~hich have <br />much broader sections ~ith gentler slopes, Levees built ~ith smaller <br />sections and steeper slopes generally require more comprehensive inves- <br />tigation and analysis than do levees ~ith broad sections and flatter <br />slopes ~hose design is more empirical. Where rainfall and foundation <br />conditions permit, the trend in design of levees is to~ard sections ~ith <br />steeper slopes. Levee maintenance is another factor that often has <br />considerable influence on the selection of 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 of different requirements for each, As used in this <br />manual, urban and agricultural levees are defined as follo~s: <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) Agricultural levees, Levees that provide protection from <br />flooding in lands used for agricultural purposes. <br /> <br />Ca Levee ~ypes According to Use. Some o~ the more common terms <br />used for levees serving a specific purpose in connection with their <br />overall ptL~ose of flood protection are given in table 1-2, <br /> <br />d, Causes of Levee Failures, Tne principal causes of levee fail- <br />ure are <br /> <br />(1) Overtopping. <br /> <br />(2) Surface erosion, <br /> <br />(3) Internal erosion (piping), <br /> <br />(4) Slides ~ithin the levee embankment or the foundation soils. <br /> <br />1-3 <br /> <br />.;~ '; i,,' >l+lJ <br />