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<br />Problem 2. <br /> <br />What decrease in the dj.scharge through the bridge is needed to <br />reduce the contraction scour to 2 ft? <br /> <br />Yz = ( <br />9 <br /> <br />X <br />25,900 <br /> <br />)617 (398)0.69 (0.024)0.37 <br />389 0,024 <br /> <br />= 1.22 <br /> <br />Ys = 11 - 9 = 2.0 ft <br /> <br />x ) 6/7 <br />25,900 <br /> <br />= 1. 22 <br /> <br />( X <br />25,900 <br /> <br />= 1.22 7/6 <br /> <br />X = 32,000 cfs <br /> <br />Decrease is 43,600 - 3; ,000 = 11,600 cfs <br /> <br />Problem 3. <br /> <br />Contraction scour for relief bridge in left approach. <br /> <br />Estimate scour using Lc.ursens Case 3 equation. This equation is <br />for vertical wall abutments. <br /> <br />Ys= 0.13 [ <br />Y, <br /> <br />Q <br />1 7 <br />Dm3 y,6 /<"2 <br /> <br />6 <br />." <br /> <br />- 1 <br /> <br />(7: <br /> <br />Qrelief bridge = 43,6CO - 32,000 = 11,600 cfs <br /> <br />Y, <br />Wz <br />D50 <br /> <br />= 2.8 it <br />= 200 ft <br />= ,00098 ft Use material under <br />relief bridge. <br />= 1.25 X D50 = 0.00123 ft <br /> <br />the soil layer at the <br /> <br />Dm <br /> <br />66 <br />