Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

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Application Note: 2D Hydrodynamic Sediment Transport
   
Two-dimensional models: Since the early 1990s, there has been a shift in computational research towards 2-D models.  Most of the 2-D models are currently available to the hydraulic engineering community as interface-based software in order to allow easy data input and visualization of results.  This added capability has made these models user friendly and popular.  2-D models are depth-averaged models that can provide spatially varied information about water depth and bed elevation within rivers, lakes and estuaries and the magnitude of depth-averaged streamwise and transverse velocity components.  Most of 2-D models solve the depth-averaged continuity and Navier-Stokes equations along with the sediment mass balance equation via the methods of finite-difference, finite-element or finite-volume.
   
Simulation of in-stream sediment capture structures: Sediment transport in a regulated river can be irregular and challenging to deal with due to the presence of large control structures, artificial channelization, and flow regulation.  A study has been conducted on the Spokane River, Washington, USA, and specifically the entrapment of sediment well upstream of the Monroe Street Head End Diversion (HED).  Throughout the operational lifetime of the diversion dam, sediment deposition behind the dam has been a serious problem, at times fouling the penstock intake and costing significant amounts of money and time to remove.  A proposed solution to the problem was to capture sediment well upstream of the HED by placing artificial rock weir structures in the channel.  Rock weirs are aesthetically pleasing and have been found to work effectively in trapping sediment.  Numerical flow simulation was utilized to examine the flow around the rock weirs and to examine the performance of those weirs under a wide range of flow conditions.  The commercial Surface water Modeling System (SMS) software package was utilized here to perform the necessary calculations.  Using SMS, it was possible to resolve the in-stream flow field velocity vectors, which were used to calculate shear stress and examine the kinetic energy and dissipation.  The model was calibrated using field data and the results compared to previous physical models.  The resulting data were used to describe the sediment transport properties of the river and around the structures.  It was possible to give an estimate of the sediment capturing ability of the rock weirs and predict a useful lifetime for the structures.