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<br />Floodplain Description <br />Sta. 424 + 70 to 470 + 00: Sheets 1-3 <br />The floodplain in this reach is narrow. Channel slopes and flow velocities are <br />high. No structures are located in the floodplain in this reach, therefore damages <br />are primarily due to channel erosion. Some pavement damages are also <br />expected due to road overtopping, <br />Near the intersectton of U.S. Highway 40 and State Highway 93, the flow <br />overtops the roadway and splits. The split flow option of HEC-2 was used to <br />model Highway 40 as a weir in order to compute the discharge lost from the <br />main channel. The lost flow follows an independent flow path unrelated to the <br />main channel profile, until it re-enters the main channel downstream. The <br />downstream discharge in the main channel below the flow split was reduced by <br />90 cfs to account for lost flow. <br />The two culverts under the Mobile Premix Driveway and the driveway to the <br />south are both of inadequate capacity to convey the 1 DO-year discharge. The <br />roadway at both locations is overtopped during the 100-year flood. <br />Sta. 414 + 70 to 424 + 70: Sheet 3 <br />The floodplain in this reach is mostly in an undeveloped open space with the <br />exception of one residential property located on the fringe of the floodplain. The <br />culvert under Zeta Street at the lower end of the reach is undersized. <br /> <br />Reach <br /> <br />L-13 <br /> <br />L-12 <br /> <br />v. FLOOD HAZARD AREA DELINEATION <br />General <br />The delineation of flood hazard areas for the 100-year flood has been performed for this study <br />The results of this analysis are found in the attached plan and profile drawings. The 10-year <br />profile has also been computed and plotted on the plan and profile drawings. <br />100- Year Floodplain Description <br />The 100-year water surface elevations and floodplain limits determined in the study represent <br />estimates based on future development and the current channel geometry in the basin. As a <br />result, they may differ from the floodplain limits identified in earlier studies. <br />The following is a reach by reach description of the 100-year floodplain beginning in the upper <br />portion of the basin and moving downstream. The floodplain of the main stem of Upper Lena <br />Gulch will be described first, followed by Pleasant View Tributary and Apex Gulch Refer to <br />Figure 2 for reach locations. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />3 <br /> <br />I <br /> <br />I <br />