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<br />J <br /> <br />One pier of the bridge was undermined, probably in the flood of <br />1941 and subsequent lesser flows, which rendered the bridge unsafe in <br />the opinion of county officials. A span was druppeu with uynamite un <br />August 1955 so that the structure could no longer be used, <br /> <br />A sidelight of flood flows is the effect of bridge sizes, The Southern <br />Pacific bridge over Gila river at Antelope Hill was built aQout 1925 <br />and therefore the design was influenced by the mammoth flood of 1916, <br />Its length is greater than the adjacent Mohawk Valley Road bridge <br />and greater than necessary for any flow that has happened since, <br /> <br />McPhaul Bridge was constructed by the county and state in 1929 ~ <br />over the Gila on the Yuma to Quartzsite road, now U.S, 95, It is a ~ <br />suspension bridge, 798 feet of span, with approach spans of 57 feet on I <br />the south and 114 feet on the north, Unfortunately, it is of very light 1 <br />construction (designed for one 12,5-ton truck plus 30% impact) and has oj <br />only a 15'-4" clear roadway, After Gila ceased regular flow the bridge <br />was bypassed with blacktop pavement across the river channel and the 1 <br />bridge was used only during flows, In the flood flow (Painted Rock <br />Dam ,elea,e,) of 1966, the Ariwna State Highway Dep"'tment ope,.ted .. <br />the bridge for one-way traffic with flagmen around the clock, The state <br />constructed a concrete bridge and approaches on new alignment in 1967, <br />hence there was no further use for McPhaul Bridge and it has been <br />abandoned, <br /> <br />On Avenue 40, this District and the County installed additional <br />corrugated metal pipe at the Gila crossing during the flood flow of <br />May 1973 so that there are 27 - 54" diameter pipes, It is estimated <br />that the maximum flow here that year was 1937 cfs on May 29. <br /> <br />The same was done at Avenue 20, there are 20 - 54" pipes and <br />4 - 36" pipes, It is estimated that the maximum flow here that year <br />was 1500 cfs on June 25, <br /> <br />These two crossings should now be free from overtopping for any <br />flow resulting from a Painted Rock Dam release of 3,000 cfs, <br /> <br />CHANNEL CLEARANCE <br /> <br />I <br /> <br />Beginning in 1955, it was the desire of the Board of Directors that <br />a lOO-foot swath be kept open along the Gila river channel for flood <br />flow, Due to shortage of manpower and equipment this was not always <br />possible, At the time of the 1973 releases from Painted Rock Dam, <br />the Board decided that this must be done in order to keep the flow <br />confined to the channel so as to lessen damage to adjacent farmland <br />and to provide a faster surface flow thereby lessening groundwater <br />build-up, A crash program was initiated at Avenue 41 and worked <br />downstream to Avenue 16 ahead of the flow. Clearing could only be <br />accomplished in that portion of the channel that was sufficiently free <br /> <br />II . ~ <br />I' <br /> <br />20 <br />