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<br />This discharge exceeded the all time record discharge of 55,500 cfs that occurred <br />in 1947 and was nearly double the peak discharge that occurred in 1993, The <br />estimated frequency of the event at Hamburg is .005 percent chance exceedance <br />with an average return interval of once in 200 years. <br /> <br />On Wednesday, June 17th, additional staff gages were installed at the <br />Highway 333/lnterstate 29 underpass and at Ditch 6 at the Highway 333 bridge. <br />These staff gages were installed to monitor the Ditch 6 ponding area due to the <br />flow over the 1-575 tie back. There was concern about water backing into Hamburg <br />from the ponding area. Locals used flood fight measures to block culverts through <br />1-29 and prevent water from backing through those and sandbagged across the <br />Highway 333 underpass and near the Ditch 6/Highway 333 crossing. Observations <br />at these gages indicated that water was flowing into Ditch 6 from the ponding <br />area. The Ditch 6 pumps were shut down on June 17'h due to concerns of running <br />out of fuel and not being able to get additional fuel to the pumps because of the <br />levee overtopping. On Thursday June 18th the pumps were refueled and the pumps <br />restarted. <br /> <br />. <br /> <br />Figures 5-9 are the hydrographs for this event for the East Nishnabotna River <br />at Atlantic and Red Oak, Iowa, West Nishnabotna River at Hancock and Randolph, <br />Iowa, and Nishnabotna River at Hamburg, Iowa. <br /> <br />20 <br />