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- 1. Sediment Model for GESZ (Good Ecological Status in river Zenne) Shrestha N.K.; De Fraine B.; Bauwens W. Department of Hydrology and Hydraulic Engineering Vrije Universiteit Brussel nashrest@vub.ac.beJuly 14, 2011 Sediment Model for GESZ 1
- 2. Presentation Layout Introduction. Objectives. Theory. Sediment module as OpenMI component. Experiments. References.July 14, 2011 Sediment Model for GESZ 2
- 3. Introduction Sediment has crucial role on Nutrient budget. Sedimentation of suspended solids can be a major pathway for transfer of nutrients from surface to bottom and same applies for resuspension. Sediments offers abundant surface area for the adsorption of various hydrophobic substances. Modelling of sediment dynamic is essential to evaluate the ecological status of river Zenne.July 14, 2011 Sediment Model for GESZ 3
- 4. Objectives To model the transport, distribution, deposition and resuspension of suspended solid. More specifically, Deposition of solid materials during dry weather flow (DWF) and subsequent scour during wet weather flow.July 14, 2011 Sediment Model for GESZ 4
- 5. Theory (1) Shear Velocity: expresses the shear stress in a link as a velocity. With, u* = shear velocity g = gravity R = hydraulic radius S = slope of energy line v = cross-section velocity n = manning’s coefficientJuly 14, 2011 Sediment Model for GESZ 5
- 6. Theory (2) Critical Diameter: dividing diameter between motion and no motion. Shield’s Criterion (1936): is based on an empirically discovered relationship between two dimensionless quantities. θ = Ratio of shear stress and submerged weight of grain: R* = Renoyld’s number: With, u* = shear velocity s = specific gravity g = gravity d = particle diameter ν = kinematic viscosity of waterJuly 14, 2011 Sediment Model for GESZ 6
- 7. Theory (3) Shield’s Diagram in programming point of view: Approximated using two straight line segments bound to a central polynomial approximation all in log-log plot. This approach is not very practical to work with.July 14, 2011 Sediment Model for GESZ 7
- 8. Theory (4) Soulsby and Whitehouse (1997): Proposed an algebraic expression that fits Shields’ curve closely and passes reasonably well through the extended set of data that became available more recently. This approach is used in this model. Ordinate: Abscissa (dimensionless grain size): Relationship between θ and D*:July 14, 2011 Sediment Model for GESZ 8
- 9. Theory (5) Soulsby and Whitehouse (1997) provides direct means to obtain θ and u* that corresponds to a given particle diameter. For the inverse operation, i.e., to get dcr corresponding to u*, the equation u*(d) must be solved for d. For this Newton-Rhapson iteration is used with bisection process (to refine possible interval for critical diameter; hence fast convergence).July 14, 2011 Sediment Model for GESZ 9
- 10. Theory (6) Deposition and erosion calculations in the new model: The sediment is divided into a number of classes. The number of classes is configurable. Each single class is treated individually and behaves uniformly to erosion and deposition (i.e., a class erodes or deposits in its entirety). Consider the class i of the sediment, bound on the lower side by diameter di and bound by diameter di+1 at the upper side. Three situations can arise: 1) If di > dcr , all the sediment of class i that is in suspension is deposited to the bed: With, SSc = Suspended sediment concentration SSc(i)t = 0 BSm = Bed sediment mass BSm(i)t = BSm(i)t-1 + SSc(i)t-1 * Volume Volume = Volume of water in linkJuly 14, 2011 Sediment Model for GESZ 10
- 11. Theory (7) 2) If di+1 ≤ dcr, all the sediment of class i that is on the bed will be eroded and enter suspension: SSc(i)t = SSc(i)t-1 + BSm(i)t -1 / Volume BSm(i)t = 0 3) If di < dcr< di+1, the state of the class i is not modified: SSc(i)t = SSc(i)t-1 BSm(i)t = BSm(i)t-1July 14, 2011 Sediment Model for GESZ 11
- 12. Sediment model as OpenMI component (1) <?xml version="1.0"?> <LinkableComponent Type="GESZ.SimpleQualityComponent.DiscreteQualityComponent”Assembly="..OutputGESZ.SimpleQualityComponent.dll"> <Arguments> <Argument Key="InputFileSWMM" ReadOnly="true" Value="GESZ-8.inp" /> <Argument Key="InputFileTSS" ReadOnly="true" Value="TSS-GESZ-8.txt" /> <Argument Key="KinematicViscosity" ReadOnly="true" Value="1e-6" /> <Argument Key="SpecificGravity" ReadOnly="true" Value="1.45" /> <Argument Key="MaximumParticleDiameter" ReadOnly="true" Value ="3.0" /> <Argument Key="Resolution" ReadOnly="true" Value="20" /> <Argument Key="StorageUnitName" ReadOnly="true" Value="WWTP_Bxl_North" /> <Argument Key="TSSRemovalEfficiency" ReadOnly="true" Value="100.0" /> <Argument Key="SlopeRatingCurveForTSS" ReadOnly="true" Value="0.5749" /> <Argument Key="InterceptRatingCurveForTSS" ReadOnly="true" Value="16.93" /> </Arguments> </LinkableComponent>July 14, 2011 Sediment Model for GESZ 12
- 13. Sediment model as OpenMI component (2) Input Exchange Items (Expects): Inflow (all nodes) Outflow (all nodes) Flow (all links) Volume (all links) Shear velocity (all links) Output Exchange Items (Provides): TSS (all links and nodes) Critical diameter (all links) Bed mass (all links)July 14, 2011 Sediment Model for GESZ 13
- 14. Experiments (1) Implemented in Non-navigable Zenne. Distance over 20 km Resolution = 20July 14, 2011 Sediment Model for GESZ 14
- 15. Experiments (2) Specific gravity (eg: 1.0 → no sedimentation,1.4 →slight sedimentation, 2.4 →heavy sedimentation) Input of TSS (constant 100 mg/l for 2 days) Fictitious particle size distribution (maximum particle diameter 3.0 mm) →July 14, 2011 Sediment Model for GESZ 15
- 16. Experiments (3) Results for S = 1.0 (no sedimentation) Flow Simulated TSS Concentration Profile plot of Simulated TSS ConcentrationJuly 14, 2011 Sediment Model for GESZ 16
- 17. Experiments (4) Results for S = 1.4 (slight sedimentation) Flow Simulated TSS Concentration Profile plot of Simulated TSS ConcentrationJuly 14, 2011 Sediment Model for GESZ 17
- 18. Experiments (5) Results for S = 2.4 (heavy sedimentation) Flow Simulated TSS Concentration Profile plot of Simulated TSS ConcentrationJuly 14, 2011 Sediment Model for GESZ 18
- 19. References Shields A. (1936): Anwendung der Ahnlichkeits-Mechanik und der Turbulenzforschung auf die Geschiebebewegung. Preus Versuchsanstalt Wasserbau Schifffahrt Berlin Mitteil 2b. Soulsby RL., Whithouse R. (1997): Threshold of sediment motion in coastal environments. In: proc. Pacific Coasts and Ports Conf. 1, University of Canterbury, Christchurch, New-Zealand. pp 149-154.July 14, 2011 Sediment Model for GESZ 19
- 20. Thank you for your Attention!!July 14, 2011 Sediment Model for GESZ 20

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