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<br />EM 11l0-2-19l3 <br />31 Mar 78 <br /> <br />e <br /> <br />a. Location. Borrow area locations on the river side of a levee <br />are preferable as borrow pits. Borrow area locations within the pro- <br />tected area are less desirable environmentally, as well as generally <br />being more expensive. Riverside borrow locations in some areas will be <br />filled eventually by siltation, thereby obliterating the man-made <br />changes in the landscape. While riverside borrow is generally prefer- <br />able, required lands ide borrow from ponding areas, ditches, and other <br />excavations should be used wherever possible. A berm should be left in <br />place between the levee toe and the near edge of the borrow area. The <br />berm width depends primarily on foundation conditions, levee height, and <br />amount of land available. Its width should be established by seepage <br />analyses where pervious foundation material is close to the bottom of <br />the borrow pit and by stability analyses where the excavation slope is <br />near the levee. Generally, the width of this berm should be about <br />2-1/2 times greater for lands ide berms than for riverside berms. Mini- <br />mum berm widths used frequently in the past are 40 ft riverside and <br />100 ft lands ide, but berm widths should be the maximum possible since <br />riverside borrow areas increase the severity of under seepage effects. <br />In borrow area excavation, an adequate thickness of impervious cover <br />should be left over underlying pervious material. For riverside pits a <br />minimum of 2 ft of cover should be left in place, and for lands ide pits <br />the cover thickness should be adequate to prevent the formation of boils <br />under expected hydraulic heads. Topsoil from borrow and levee founda- <br />tion stripping can be stockpiled and spread over the excavated area <br />after borrow excavation has been completed. This reinforces the imper- <br />vious cover and provides a good base for vegetative growth. <br /> <br />.' <br /> <br />. <br /> <br />e <br /> <br />b. Size and Shape. It is generally preferable to have riverside <br />borrow areas "wide and shallow" as opposed to "narrow and deep." While <br />this may require extra right-of-way and a longer haul distance, the <br />benefits derived from improved underseepage, hydraulic, and environ- <br />mental conditions usually outweigh the extra cost. In computing re- <br />quired fill quantities, a shrinkage factor of at least 25 percent should <br />be applied (i.e., borrow area volumes should be at least 125 percent of <br />the levee cross-section volume). This will allow for material shrinkage, <br />and hauling and other losses. Right-of-way requirements should be <br />established about 15 to 20 ft beyond the top of the planned outer slope <br />of the borrow pit. This extra right-of-way will allow for flattening <br />or caving of the borrow slopes, and can provide maintenance borrow if <br />needed later. <br /> <br />. <br /> <br />4-4. Design and Utilization. <br /> <br />.. <br /> <br />a. Slopes. Excavation slopes of borrow areas should be designed <br />to assure stability. This is particularly important for slopes adjacent <br /> <br />4-2 <br /> <br />e <br /> <br />t: <br />