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Last modified
1/26/2010 10:09:17 AM
Creation date
10/5/2006 4:19:59 AM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Community
Malta Montana
Basin
Statewide
Title
Reconnaissance Report Flood Control for Milk River at Malta Montana
Date
12/1/1991
Prepared For
US Army Corps of Engineers
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />1 <br />1 <br />I' <br />I <br />1 <br />I <br />I <br />1\ <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />To compute water surface profiles for the lev.e alignments, levee <br />alignaent 1 vas used in conjunction with both &lignaents 2 and 3 in place. <br />In other words, alignaents 1 and 3 were combined, as were alignments 1 <br />and 2. Alignment 1 alone would reflect a decrease in water surface <br />profiles when compared to alignments 1 and 3 in place together. The water <br />surface profiles for these alignaenta are shown on plate 5. Th. profiles <br />were computed using encroachment method 1 in HEC-2 for all discharges. <br />The resulting profiles show the respective water surface heights for the <br />10-, 50-. 100-, and 500-year design levee conditio~. It should be noted <br />that the floodway will need to be reestablished prior to construction of <br />any of the levee alignments. <br /> <br />Kateriab and Foundations. Levees protecting Kalta would be located <br />on a large, flat alluvial flood plain area. Soil borings taken in 1966 <br />for a previous study show that the .oil is predollinantly silt with varying <br />amounts of silty clays. Plate 6 shows a typical levea cross section which <br />was used to estill8te construction costs. as described in a later section. <br /> <br />Levee Dedm Features. The total levee height was detemined by <br />adding the water depth for the design flood event and 3 feet for the free- <br />board allowance. Levee heighta ranged froll 2.5 to 13.5 feet. Because the <br />levees protect an urban area, 3 feet of freeboard height was used. The <br />purpose of freeboard allowance is to provide for those factors that cannot <br />be rationally accounted for in dedgn flood profile computatio~. To <br />prevent overtopping in the vicinity of levee drainage structures, an addi- <br />tional 1 foot of freeboard was used for 100 feet on either dde of the <br />structures. Overtopping can occur near bridges because of debris accUIIIU- <br />lations. An additional 1 foot of freeboard was used extending 100 feet <br />on either siele of the bridgea. <br /> <br />A lIinill\lll levee crown width of 10 feet was used. with wider turn- <br />around areas at intervals, to provide access for normal maintenance and <br /> <br />26 <br /> <br />I <br />
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