Abstract
In this investigation, scour in long contractions phenomenon was studied
experimentally. For this purpose, forty laboratory experiments were carried out in
a laboratory channel .Two different river sand sizes of 0.653 mm, 1.040 mm were
used to conduct the experiments with standard deviations of 2.151 and 3.474
respectively. Three different ratios of contraction (B1/B2 =4,3 and 2) and three
different angles of contraction (θ=10,15 and 20 degrees) were tested. For each
case, the discharge was changed four times from 10.4 Liter/sec to 47.6 Liter/sec.
Data analysis showed that depth of scour (ds) depends mainly on contraction
ratio (B1/B2), densimetric particle Froude number (Frο) and geometric standard
deviation (σg). Results of this study showed that there is a strong linear direct
relation between the ratio of the contraction channel width and the depth of scour.
Also a direct relationship was found to describe the effect of discharge on depth of
scour. The results showed that there is no effect of contraction angle on the scour
depth in long contractions. Also, an empirical non-dimensional relationship was
obtained to determine depth ratio (Y2/Y1) in long contraction with correlation
coefficient (R2) = 0.9343.
The results of the present investigation were compared with those of other
investigators showing a good agreement among them
