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.
Combined with the basic characteristics of Suzhou plain river network, two modules are established, one of which is the hydrodynamic module using the water level node method involving gate operation, while the other is the water quality module based on the principle of WASP5 (water quality analysis simulation program5). These two modules were coupled and verified by the monitoring data of Suzhou River network. The results showed that calculation errors of NH þ 4 -N and DO for the model were in the ranges of -15%-13% and -18%-16%, respectively. Despite of the deviations between the monitoring data and simulation result, the calculation accuracy of the model conforms to the practical engineering requirement. Therefore, the proposed coupling model may be useful for water quality simulation and assessment for river network under tidal influences.
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