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Flood Data <br /> Flood warning and flood forecasting services in the Elk River area are provided by the National <br /> Weather Service Forecast Office at Minneapolis. Technological support is provided by a staff of <br /> professional hydrologists at the North Central River Forecast Center also located in <br /> Minneapolis. <br /> Lead time between distribution of flood forecasts and arrival of the flood crest may range from a <br /> few hours to several weeks, in the case of snowmelt. Lead time for crests resulting from rainfall <br /> is normally 3 to 7 days, depending on the area and magnitude of the storm. <br /> Floods of record in the Elk River Basin have historically occurred in March, April and May as a <br /> result of rapid snowmelt. The worst conditions will occur when rainfall accompanies the <br /> snowmelt. The most common indication of a potentially hazardous spring flood will be a <br /> snowpack greater than 18 inches in the drainage basin. If a rapid warming trend occurs under <br /> these conditions, a flood is highly probable. The peak flood flow under these conditions will <br /> generally occur about 7 days after the start of snowmelt, which allows adequate time for <br /> preparation. The worst conditions will occur if a rainstorm accompanies the warming trend. <br /> Under these conditions, advance notice may be reduced to a few days or less, depending on <br /> the area, magnitude, and distribution of the rainfall. <br /> When the reservoir elevation is high or during floods, the City of Elk River should maintain <br /> communications with the National Weather Service in Minneapolis. The National Weather <br /> Service will provide details regarding river stages and flows upstream from the dam and <br /> anticipated weather conditions. <br /> Whenever conditions that may cause a flood appear to be developing, the City should keep in <br /> touch will all of the sources mentioned above in order to maximize lead time for flood <br /> preparation at Elk River Dam. The City should also coordinate efforts with the National Weather <br /> Service and local agencies in disseminating flood information to residents in the flood plain. <br /> Structural Drawings <br /> Structural drawings can be obtained by request from Elk River Municipal Utilities. <br /> Gate Operation <br /> This section describes the radial gate operation plan during flood or other periods of high water <br /> elevation. The gates should always be operated in general accordance with the operation plan <br /> described here, or in a separate Inspection, Operation, and Maintenance Manual. During <br /> extreme floods, some deviation from the operation plan may be required. Such deviation should <br /> only be permitted when the reservoir water surface rises very rapidly and normal gate operation <br /> procedures are impractical. A complete description of the gate operation plan is presented <br /> below, with a graphic following: <br /> • Always clear the downstream area of any personnel at or near river level before opening <br /> a gate. <br /> • When the reservoir level reaches elevation 875.0 feet and rising, open Gate No. 2 <br /> (middle gate) approximately 6 feet. To open the gate 6 feet, the electrical operator <br /> should be engaged for approximately 8 to 9 minutes. The gates can also be opened <br /> manually with the handwheel: 670 rotations of the stem nut will open the gate <br /> 66 <br />