North Platte River Flood Storage

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11/U4/U;7 14:1/ I'A3 JU:1 44D 0:f:fl Memo to Roger Patterson Octobcr 21, 2003 Page 2 Yl91lr: tClVr.it t;lJ U!'t'll.L 4 l;KA1VL 1aLA1VL U. UVJ I discussed the City's ongoing F1ood Mitigatioza Plan and the oppoztunilies to mitigate flovd damages on individual properties. I asked if ihere was a possibiliiy that the NWS would raise the flood stage if flood damages to individual propertxes in the impacted area were mitigated. Brian indicated that if the properties of the landowne,?rs that had complaincd to the T1WS were na longer impacted at a stage of 6.0' the flaod stagc could be raised back to 6.07_ This may have been An overly simplistie answer, Uut it was clear that NWS would consider raising the flood stage if aclions were taken to reduce localized flooding. On September 10, 2003, I met wida Jim Hawks, City of Norl'h Platte Utility ManagE;r. Jim was very familiar with the flood stage issue and the types of flooding that have occurredl in the north overbank area just west of Highway_ 83 along the Norch Platte River. Jim identified. the 3 prvperties that had been impacied by flooding and caused the N WS to ]vwer the flood stage. He felt the two main reasons why, these properties are now bei,ng impacted by flood,ing aze: 1. The drainage leading to tiie culvezts under Highway 83 xrxay no longer convey flows. In the past, when property owners complained about flooding, Jim had coozdixkated efforts to make sure the drainway was clear and flow was going under the highway. This is probably noi occurring naw. 2. An old Nebraska Department of Roads (NDOR) diversion dike upstream of the unpactcd properties had bzeached sometune in the last 10 years. It is cleaz from aerial photography that tbere is conveyance north of the dike and that this flow path cou]d directly unpact the propcrties. Jim said that it was unclear what involvement NDOR had with the dike and his attempts to find out if NDOR was respvnsibie For maintenance of the dike were unsucccssful. IIe uidicated that the City would be very i.nterested in exploring mitigation opportunities that would Iead to NWS xaising the flood stage at Nortb. Platte baclc to 6.0'. On October 17, 2003, I met with Don 7isa, NDOR, to discuss the flow characteristics of the culverts under Highway 83 and the upstream diversion dike_ Dan is eurrently resezLrching project plans to determine the capacity of the culverts and detcrmine if the d"zversioin dike was built as part of a project. Based on the alignment of the dike, Don thought it might have becn built to protect the north bridge abutment. The nnost promising flood mitigation options that would lead to the NWS raising the flood stage back to 6.0' appear to be repRiring the breached diversion dike upstream of Highwzry 83, restvring the drainway through ttie Highway 83 culverts, and/or floodproofing the impacted properties. It will be very import:ant to work closely with NWS to ensure that if flood znitigation projects are cnmpleted they wi11 xesult irn the NWS raising the flood stage back to 6.0'.