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<br />000827 <br /> <br />ponds and retUrnS 10 the river al the boal ramp, Currently split /lows only return to the <br />river at the boat ramp when the boat ramp is submerged, This will be true for <br />proposed conditions also, <br /> <br />The boat ramp and adjacent parking area and properties are not protected from any <br />/Iood condition or any level of inundation by the existing levee because the boat ramp <br />itself is a notch in the levee. The levee upstream prevents a split /low condition <br />betWeen approximately 11,000 and 35,000 cfs, when the boat ramp is submerged by a <br />backwater. The backwater over the boat ramp above 11,000 cfs is the controlling water . <br />surface elevation for the proposed design, . therefore that water surface elevation will not <br />change from the existing levels experienced, No modifications are being performed at <br />the outlet, The proposed change will be a /low through condition for /lows between. <br />11,000 and 35,000 cis, Because the /lows are routed through a pond and a /Ioodplain <br />area before renirning to the main channel at the submerged boat ramp, increased <br />sedimentation at the boat ramp due to /low through is not ellpeeted. In fact sediments <br />assoaiated with the former backwater condition may be reduced. With the submergence <br />of the boat ramp during an induced /low-through condition, scour at the boat ramp is <br />ellpeeted to be insignificant as the backwater curve will absorb the energy of the /low. <br />Most energy of the induced /low-through will be dissipated in the constructed notch and <br />in the first pond. . <br /> <br />The 1,000 cfs estimate of /low through the notch is the maximum flow expected for.. <br />conservative calculations of scour in the notch. This was estimated conservatively.high <br />at a 40,000 cfs discharge, and the entire boat ramp, parking area and road into the site <br />will begin to be submerged when this occurs and the contribution of flows overtopping <br />the existing levee low points will be as .significant or greater than /lows through the <br />notch, <br /> <br />The launChing and parking area currently ellpc:nences /low-through at flood levels, and <br />inundation will be essemia1ly the same under proposed conditions. The project does <br />not creaie a new river channel because the channel currently ellists which backwaters <br />above 11,000 cfs and /lows through above 35,000 cfs. . The project allows it to flow- <br />through between 11,000 and 35.000 cfs, Increased .velocities at the boat ramp are . <br />possible, but insignificant because the area will be submerged whenever this occurs. <br />Inundation will not change ellcept within the Ela Wildlife Sanctuary as a mild slope of <br />. the water surface from the notch to the boat ramp, <br /> <br />Sedimentation will likely be reduced at the boat ramp, but as an insignificant change, <br />Turbulence and impairment to boat launching activities will occur only dUring flood <br />events similar to ellisting conditions. Flooding of the parking lot and boat ramp or any <br />property other than the Ela Wildlife Sanctuary will not change since the levee has <br />already been removed by construction of the boat ramp. The only possible impact <br />outside of the Ela Wildlife Sanctuary associated with the project may be 10C3lized scour <br />at the boat ramp and this is unlikely because of the submerged condition of the boat . <br />ramp .during flow through conditions. <br /> <br />6 <br />