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Show Mill Creek Flood Not as Big As Earlier Flow Estimates Failure of the Mill Creek bridge east of Moab was not caused by a record-sized flood, but by inadequate design, Grand County Commissioners were told Monday. Mon-day. Utah Department of Transportation Commissoner Sam Taylor of Moab told the Commission that a second stream-bed measurement by UDOT hydrologists, backed up by stream flow estimate figures from the U.S. Geological Survey had indicated that the flood which destroyed the bridge was gauged at only 3,200 cubic feet. The bridge was designed for the "fifty year flood," which was calculated at 5,200 cubic feet per second. Early measurements of the flood size listed it at 5,600 cubic feet per second. Those measurements were double-checked double-checked after a number of observers in the DOT, and in the community questioned the flood size. "Our final investigation showed that the bridge failed at 60 percent of design capacity," Mr. Taylor told Grand County officials. Major factors involved in the inadequacy inade-quacy of the design included the removal of rock-fence barriers around the north abutment due to funding limitations in the Grand County and Moab City Collector Road Fund; in increasing the angle which the bridge crossed the creek without lengthening the structure, and due to the failure of an old CCC check dam which washed downstream, lodged above the new bridge, and diverted flood waters directly at the north abutment which was undermined and dropped. Mr. Taylor stated that the Utah Transportation Commission, meeting in Bryce Canyon last Friday, had agreed to program funding -- estimated at $150,000 for the removal of the damaged structure and construction of a new bridge, and Grand County agreed Monday to provide matching funds of up to $15 thousand. Design crews are currently working on the plans, which should be completed by Sept. 1, Mr. Taylor said. The hew structure will be forty feet longer than the one with was destroyed, and it will rest on caisons planted on concrete bearing pedestals poured ten feet below the creek-bed. Approaches constructed in the initial phase of work will be utilized in the new construction. Grand County is currently constructing a temporary creek crossing with culverts to serve until the new bridge is done next spring. A temporary pedestrian walkway is also being considered by Grand County and Moab City, to get children from the Hecla Subdivision area across the creek to Southeast Elementary School. in lain . - ijiw ui immmvm mr'nivfl |
