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59 X(mm) -300 -100 100 300 500 700 900 1100 1300 0 0.50 4.50 50 14.25 27.00 100 40.67 Z(x, t) (mm) 50.00 150 64.08 77.42 99.08 200 124.08 FLOW 148.58 250 300 Figure 7.4. Contraction scour profiles along the channel centerline as a function of time for Test 1 (the numbers in the legend are the elapsed times in hours). It is also noted that the maximum velocity predicted by HEC- in Test 1, as is shown on Figures 7.6 and 7.7. The R2 values RAS in the contracted channel is less than the measured value. were consistently higher than 0.99. The results of tests involv- ing the transition angle and the length of the contraction are 7.5 FLUME TESTS: SCOUR OBSERVATIONS shown on Figures 7.8 and 7.9; Figure 7.10 regroups all of the AND RESULTS measurements taken for the primary tests (Table 7.1). For the uniform contraction scour depth, the average value An example of the measurement results is shown in Figure of the last four points (over a 0.4-m span) in the contraction 7.4 for Test 1. Figure 7.5 shows a sketch of the contraction scour depth profile was used as the uniform scour value. In distribution in plan view. The measurement emphasis was addition, it should be noted that for short contraction lengths placed on obtaining four parameters at the equilibrium con- (Tests 13 and 14), a fully developed uniform contraction did traction scour: the maximum contraction scour depth Zmax, the not exist. The location of the maximum contraction scour, uniform contraction scour depth Zunif, the location of the max- Xmax, is measured from the beginning of the fully contracted imum contraction scour Xmax, and the contraction profile along section. It can be seen that Xmax oscillates at the beginning of the channel centerline. The maximum and uniform contrac- the test but becomes fixed in the late stages. This value was tion scour depths at equilibrium are listed in Tables 7.1 and chosen for Xmax and is the one shown in Tables 7.1 and 7.2. 7.2. These values were obtained by fitting the scour depth ver- An important observation was noted during the tests: the sus time curve with a hyperbola and using the ordinate of the abutment scour never added itself to the contraction scour. In asymptote as the equilibrium value. The fit between the mea- fact, the abutment scour and the contraction scour were of the sured data and the hyperbola was very good for Zmax and Zunif same order of magnitude. Figure 7.11 shows the different A b u tm e n t S c o u r B a c k C o n tr a c tio n S c o u r S e d im e n t D e p o s itio n M a x im u m C o n tra c tio n S c o u r Figure 7.5. Plan view sketch of the contraction scour pattern.