In version 5 of Infoworks ICM it is now possible to model suspended sediment transport within the 2D domain. This uses the current advection-dispersion model which is already implemented in the 2D engine. The 2D sediment functionality will also calculate Erosion-Deposition rates and update the bed level. What follows is a description of the various 2D modelling options within Infoworks ICM.
Total load methods can be used to represent just suspended load or the combination of bed load and suspended load.
The following Total Load Models are available:-
- Ackers-White revised
- Van Rijn
The following Suspended load models are available (deterministic methods):-
- Van Rijn
- Zyserman and Fredsoe
- Smith and MacLean
Each of these models calculates the erosion-deposition balance near the bed. A maximum carrying capacity is worked out depending on the erosion-deposition model. Deposition occurs when the current sediment concentration exceeds the maximum carrying capacity, and erosion in the opposite situation.
The following approaches can then be used to define the equilibrium concentration at the reference level near the bed in the case of suspended load models:
Lin: Empirical formula based on the Rouse number due to (Lin, 1984).
Rouse Profile: The resulting concentration profile follows an exponential function, assuming the eddy diffusivity varies parabolically with depth. The most widely used approach, especially in rivers.
All options and relevant parameters are specified in the Water Quality and Sediment Parameters
Skin friction method
This is the method by which the skin friction forces acting on the surface of the sediment particle are defined. The available methods are:-
Within the 2D Sediment functionality it is currently possible to specify 2 sediment fractions. These can be modelled independently or dependently. Each fraction should be assigned the following values:-
- Density (kg/m3)
- Settling Velocity-Can be user defined or calculated using a built in model
It is possible to specify a number of sediment settling velocity calculation methods for each sediment fraction:-
- Van Rijn
- Wu and Wang
These are semi-empirical formulas to estimate the settling rate of the deposited sediment. All options and relevant parameters are specified in the Water Quality and Sediment Parameters editor.
The inputs to the 2D sediment model are similar to that of the 1D sediment modelling functionality. Inflows can be associated with a 2D Point Source or 2D Boundary which have associated sediment concentration profiles assigned to them in a pollutograph object for each sediment fraction. Sediment can also be transferred in conjunction with flow across 1D-2D interfaces where they exist. It is also possible to specify sediment initial conditions as described in the below section.
Initial conditions to represent the suspended concentration of sediment for each sediment fraction can be entered using the 2D Initial Conditions. 2D Initial Conditions can also be used to specify bed composition. This can be specified through the depth or elevation of each sediment layer. It is possible to specify a number of different sediment layers:-
- Non-Erodible Layer-This is the fixed level that cannot erode.
- Parent Layer-This is a layer above the non-erodible layer which cannot grow, only erosion will affect this layer.
- Deposited Layer-This will grow or diminish during a simulation as deposition and erosion occurs. The deposited layer sits above the parent layer. Therefore if the deposited layer has been completed eroded the parent layer will begin to be eroded.
- Active Layer-This is the layer at the surface of the bed which represents the material which takes part in the erosion-deposition processes.
Figure 1: Conceptual Representation of the Sediment Layers in InfoWorks ICM
It is also possible to set the initial percentage composition (in terms of mass or volume) of the sediment fractions. For each layer the sum of total composition will be 100%.
In order to simulate 2D erosion and deposition it is necessary to tick the option to do so in the QM Parameters. 2D Sediment transport simulation involve additional calculations compared to a hydraulic only run, therefore simulations will take slightly longer. Typically 2D sediment simulations will take between 5-10 times longer than conventional 2D hydraulic only simulations.
Figure 2: QM Parameters Dialogue in ICM
Currently diffusion is not supported on the GPU engine so it is not possible to undertake 2D Suspended sediment simulations utilising the GPU card.
As part of the 2D Suspended Sediment there are a number of new result variables.
- Carrying Capacity* (Kg/m3)
- Compacted Depth^(m)
- Compacted Depth Parent Layer (m)
- Concentration* 2D (Kg/m3)
- Sediment Depth* (m)
- Deposited sediment depth since beginning of simulation* (m)
- Level^(m AD)
- Rouse number*- (Only for deterministic methods)
- Shear Stress* (N/m2) (Only for deterministic methods)
- Transport parameter* (Only for deterministic methods)
- Volume Concentration*^
- Erosion rate* (mm/hr)
- Dimensionless concentration*
*These results are available for all sediment fractions which are simulated.
^These results are available for all layers in the bed
For version 5 of Infoworks ICM, the 2D engine was enhanced to include suspended sediment functionality. The blog above describes the functionality and the available options currently present. The functionality will be further developed going into the future with the addition of bed load sediment transport functionality to future versions of InfoWorks ICM. Support for the network results objects will also be added as well as the potential to view results in the 3D view.
Lin, B. (1984). Current Study of Unsteady Transport of Sediment in China. Processings of Japan-China Bi-Lateral Seminar on river Hydraulics and Engineering Expierences, (pp. 337-342). Tokyo-Kyoto-Sapporo.