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<br />The depth (Y,) in overbank area near the channel upstream of the <br />abutment is 2.0 ft. <br /> <br />K, = 0, 55 <br />K2 = (80/90)0.13 = 0,98 <br />a' = (52 X 2,0)/ 2,0 = 52,8 ft <br />V. = 70/(52 X 2.0) = 1.67 ft/s <br />Fr. = 1.67 / (32.2 X 2.0)0.5 = 0.08 <br />Ys/2.0 = 2,27 X 0,55 X 0,98 X (52,0/2.0)0,43 X 0,080.61 + 1.0 <br /> <br />Ys/2.0 = 2.10, <br /> <br />Y=42ft <br />s . <br /> <br />This scour depth would place the total depth of scour at 11.5 ft <br />below the present stream bed (4,2+5.3+2.0), The last two terms <br />are the contraction scour and the long term degradation. <br /> <br />Comments <br />SCOUR DEEPER THAN THIS may occur! However, if the abutment was set <br />back from the stream bank so that the toe would be back from the bank <br />and the original bank was not disturbed, then y. would be the 2 ft used <br />in the calculations. In this case the scour would be the 4.2 ft from <br />the top of the bank. <br />What to do? <br />Use the total scour depth of 11.5 ft or use ASSHTO GUIDELINES to <br />design the foundations and use riprap to protect the foundation and <br />the stream bank. The reason is that even if the foundation was <br />designed for scour depth of 18 ft the abutment and the stream bank <br />upstream and downstream will have to be ripraped. <br /> <br />Problem 2. <br /> <br />Scour at left bank abutment. <br /> <br />The depth (y.) at the abutment is given as 4.8 ft. This is <br />the flow depth at the top of the bank at the abutment. <br /> <br />K, = 0.55 <br /> <br />69 <br />