Laserfiche WebLink
<br />J <br /> <br />J <br /> <br />Based on the HEC-2 model prepared by the SCS, the eXlstmg channel through the bridges falls <br />approximately 1.9 feet from an elevation of 3980,0 upsrream of Hl,v"'{ 6 to an elevation of 3978.1 <br />do\,,mstream of the DPRR, In order to limit the extent of the bridge \\idening at HWY 6, the proposed <br />channel through the bridges will be lowered about l,5 feel. Tne proposed channel lowering will <br />require a drop structure upstream of H\VY 6, <br /> <br />Ideally, the excess material generated from the major channel improvements in the \'icinity of HWY 6 <br />and the DPRR. in addition to the low flow channel further dO\'lllstream. would be used to construct the <br />north and south levees, However, the material must be tested to determine if its physical properties <br />will achieve the goals of a flood conrrollevee, <br /> <br />Two additional levees are required upstream of H\VY 6 to eliminate the Pa\\nee Creek overrlows, <br />Levee Number 2 will begin at HwY 6 and generally continue west to a poim about .~OO feet west of <br />CR. 35, From there the levee will turn north and tie into a narural high point approximately 1.000 feet <br />to the north, A gravel driveway along the 1,000 feet reach will need to be raised about 3 feet to allow <br />access to a residence west ofCR. 35, The overall length of Levee NUITIber 2 wij] be 2,bout 3,760 feet <br />and it will range in height from 1 fOOl to 5 feet. <br /> <br />Levee )lumber 3 will begin at a natural high point 1.200 feet west of CR. 35 and continue for about <br />),2-+0 feet due west to a point about 1.200 feet west of CR. 33, The levee will range in height from] <br />foot to 5,) feet. According to the existing HEC,2 modeL the lOa-year water swface elevation <br />upstream of CR. 33 for both existing and proposed conditions is 4009, This water surface elevation is <br />equal to the elevation of CR. 33 at the intersection with the gravel driveway located 500 feet north of <br />Pawnee Creek. Therefore. CR. 33 will have to be raised to elevation 4012 to provide 3 feet of <br />tree board during the 100-year event. The road raise will be:;in aboU! 100 feet north of the gravel <br />driveway and continue south for about 500 feet to a point whee CR. 33 is at eievation 401.2, Levee <br />Number 3 will be located on the north side of a residence near CR, 33 leaving several structures on the <br />channei side or'the iewe, However. based on spot elevations from the mapping. it does not appear <br />that the structures are within the I OO-year residual floodplain, <br /> <br />Finally, three ring levees will be required to protect individual residences which are currently located <br />in the 100-year tloodplain, The ring levees wi!! have milder slopes along the iandward side so they <br />will be less noticeable to the homeowners, .-\s an alternative to the full height ring levees. a <br />combination ring levee and floodwa1l could be used to minimize the height of the ievees surrounding <br />the residential strucrures, The floodwa!! would be :0 feet tall and made of 6" X 6" lOngue and groove <br />timbers, Typical cross,sections or' both the standard levees and the ring levees are shown on Figures <br />12 and 13 <br /> <br />In the summer of 1996 the UPRB, completed the improvements :0 their bridge to meet the proposed <br />i OO-year flow conditions, However. the UPRR constructed the bridge over the existing channel cross- <br />section so thar the area under the new bridge is not increased umil the channel improvements proposed <br />in this study are completed, Costs have been included in the estimate for the channel improvements <br />and for soil cement erosion protection under the new railroad bridge, <br /> <br />37 <br />