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<br /> <br /> <br />" <br /> <br />FIGURE 4. - Highline Canal out of its banks and flooding across Bible Park in southeast Denver, May 6, 1973. <br />Photograph by L. Scott Tucker, executive director, Urban Drainage and Flood Control District (Denver). <br /> <br />" <br /> <br />kinetic energy, and along entrenched reaches, <br />especially at places where channels had been <br />constricted by artificial landfilling along the <br />banks. According to Fred Watts, Deputy Direc- <br />tor of Public Works for Denver, the South <br />Platte "just ate away all of Platte River Drive <br />between Yale and Mississippi" (quoted from <br />the Rocky Mountain News, May 9, 1973). Along <br />this reach the channel of the river had been <br />greatly constricted by filled land. Three weeks <br />after the storm, the South Platte was still run- <br />ning bankfull and was too high to permit close <br />inspection of scour effects along its banks. The <br />South Platte had, in fact, surged over its banks <br />again on May 22 after having receded to a level <br />below flood stage in Denver a week earlier. <br />In downtown Denver, the 15th Street Bridge <br />across the South Platte River collapsed when <br />its center-support pier was undercut by scour <br />(fig. 5). Collapse of the bridge, moreover, sev- <br />ered eight telephone cables and disrupted tele- <br />phone service between downtown Denver and <br /> <br />northwest Denver, parts of Arvada, Broomfield, <br />and Boulder. The four-lane bridge was less than <br />10 years old and had survived the 1965 flood <br />and the heavy runoff of 1969. According to City <br />Engineer Jack Bruce (The Denver Post, May <br />7, 1973), it was the bridge least expected to <br />faiL When the center pier went out, the bridge <br />collapsed inward, trapdoor like, from both <br />abutments. <br />Although no other bridges failed within the <br />city limits of Denver, bridges and culverts were <br />among the chief casuaities of the flood else- <br />where, and their failures added greatly to the <br />cost of the storm. Bridges and culverts are par- <br />ticularly vulnerable because they form channel <br />constrictions which increase the velocity and <br />the competence of the stream. Bridges and cul- <br />verts, moreover, tend to increase the severity of <br />flooding when dammed or blocked by trapped <br />debris. Such blockages backed water into build- <br />ing basements and first-floor levels in many <br />parts of the metropolitan area, blocked and <br /> <br />7 <br /> <br />