Evaluation study of natural characteristics of 55km reach of Tigris riverbed material located at the Mosul city area was conducted. The main objective of the study is to analyze the surface and subsurface bed material at the located reach, and to explain the armoring condition in Tigris riverbed. From the result analysis of the field and laboratory work of the collected samples from the surface and subsurface layers of the riverbed material, it was concluded that Tigris riverbed had been reached previously the armoring condition. In general the grain size distribution of the surface layer decreased with distance along the study reach of the river. The riverbed material was approaching the homogeneous condition Finally the surface bed material particles have mainly the disc spherical, cylindrical and blade shape by a percentage of 48.34%, 25.2%, 15.34% and 11.08% respectively. While the dominant size in the surface and subsurface layer was very coarse gravel by percentage of 74% and 36% respectively.
weirs are the most commonly used device in channels for flow measurement and flow regulation due to its simplicity. Conventional rectangular, triangular and trapezoidal weirs are among the most common oldest types of weirs, progress ogee crest weir and cylindrical weirs are started to use in hydraulic engineering. The advantages of the circular weir shape are the stable overflow pattern compared to sharp-crested weirs, the ease to pass floating debris and the simplicity of design. The concern of this paper is to study the effect of size and surface roughness of cylindrical weirs on discharge coefficients (Cd) under different flow conditions. The work was conducted in experimental flume by using three sizes of cylinders and three types of surface roughness. The obtained results show that Cd values will increase with increasing flow rate as well as with decreasing in cylinder diameter; an increase in surface roughness of weir can makes great reduction in Cd value. The h/R effect on Cd values increase with increase in cylinder diameter. An empirical relation was obtained to estimate the coefficient of discharge Cd under different size and surface roughness of cylindrical weirs.
In this study, the establish on laboratory experiments for computing the depth of local scour (d s ) around group bridge pier. For this purpose, fifteen models of bridge piers were constructed and tested, divided into five groups, of each group containing three bridge piers with the same specifications. The diameter of upstream bridge piers (D 1 ) was varied to 2, 4, 6, 8, and 10 cm, and diameter of downstream bridge piers (D 2 ) 10 cm for all. The spacing (S) between the bridge piers was varied three times 20, 30, and 50 cm for all groups. Considering the effectiveness study of upstream flow conditions, the size of diameters of bridge piers, the spacing between bridge piers and medium size of bed material on the maximum scour depth and scour pattern around bridge piers. The study was conductedby employing a physical hydraulic model for bridge piers operated below subcritical flow, clear-water condition and exploitation uniform cohesionless sand as bed material. The experimental results showed the scour depth (d s ) increasing whenever increasing the upstream diameter (D 1 ) of bridge pier and decreasing whenever decreasing the spacing (S) between bridge piers. The dimensional analysis techniques and statistical program were used for locating a new empirical formula with the facilitate of the experimental information; this formula is for calculating the maximum scour depth at bridge piers.
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