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Last modified
1/25/2010 6:25:31 PM
Creation date
10/4/2006 11:11:57 PM
Metadata
Fields
Template:
Floodplain Documents
County
Weld
Community
Windsor, Laku Landing
Stream Name
Cache La Poudre River
Basin
South Platte
Title
HEC-2 Study of Laku Landing
Date
2/4/1992
Prepared For
Laku Landing
Prepared By
CWCB
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />. <br /> <br />. <br /> <br />. <br /> <br />Hydraulic Analysis of Proposed Conditions <br /> <br />4 <br /> <br />"'0 <br /> <br />Loku""'" <br />ExiItin!~ <br />~1396!lOJXX) <br />0.00 <br /> <br /> .,,, <br /> .,'" <br />] <br />.i .,,, <br />. <br /> 47>0 1\ ~.,.". <br /> \ <br /> --/" <br /> ."" <br /> <br />'7W <br />u" <br /> <br />"'"'' <br />"""- <br /> <br />....... <br /> <br />411$.00 <br /> <br />11:>9.3) <br /> <br />Figure 3. Current FIS Study of Existing Conditions <br /> <br />in question halfway downstream to the previous cross section and halfway upstream to the next <br />cross section. Once this total surface area was found, the different areas of land that had different <br />roughness characteristics were weighted using the percentage their area was of the total area. This <br />weighting technique was used to achieve a single 'n' value for each channel or overbank area, <br />eliminating the need for horizontal descriptions of Manning's 'n' using the NH card. <br /> <br />Hydraulic Analysis of Proposed Conditions <br /> <br />The motivation for performing this study is due to the fact that two lakes are being created in <br />the flood plain. During an intermediate regional flood, the lakes will fill with water, and then the <br />flood waters will continue downstream, except that now the flow will be over the water in the lakes <br />instead of the ground which used to occupy the lakes, and water has a roughness considerably less <br />than that of ground. For existing ponds within the scope of the current FIS study, Simons Li & <br />Associates used a Manning's 'n' roughness value of 0.02. <br /> <br />Figure 4 can be used to determine the area halfway to the upstream and downstream cross <br />sections which we will call the cross sectional related area. The total surface area of the lakes at <br />Laku Landing is 34 acres, and the total cross sectional related horizontal surface area is 119 acres. <br />The computer program used to create these drawings is also capable of calculating the area of <br />polygons using triangular decomposition. <br /> <br />In computing the new <,rea weighted roughness for cross section #139690 it is important to <br />realize that the portion of land that the lakes will occupy has a roughness very close to the total <br />computed existing roughness of 0.062. Before we purchased the land, for several years there has <br />
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