Assignment 3 - Modeling the Sedimentation Rate of the Pearl River Wetlands
Anaytical Modelling
The analytical modelling defines the problem. The influence diagram help exclude parameters, reducing the amount of parameters while the cross-impact matrix and cause-effect diagram gives an insight of the cause-effect relationship of the parameters.
Influence Diagram
The Influence diagram gives a visual aid over multiple parameters, and helps visualize how the different parameters interacts with each other, as seen in fig.1. The influence diagram helps excluding parameters, defining active parameters to include in the cross-impact matrix.
Cause-effect Matrix
Fig.1: Influence Diagram over the parameters interacting with the wetland system.
The most relevant parameters has been defined and put against each other to determine their influence in the Influence Matrix (Table 1). The selected parameters are: Cation Exchange Capacity, pH, Grain Size, Industrial Waste, Tidal Volume, Erosion and Wetland Usage, which is defined as cultivating fish farms and banana plantage.
Table 1: Cause-effect matrix over the selected parameters.
The influence diagram indicates that the tidal volume and the wetland usage are the two parameters with the largest influence of the 7 selected parameters.
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The cause-effect diagram (fig.2) show that the industrial waste and tidal volume are the two parameters that are not influenced by the other parameters, while having the greatest effect on the other parameters. The parameters that correlates with the linear curve have an even cause-effect relation while the parameters below the average curve are more influenced by the rest, leaving the CEC with the lowest effect on the system.
Cause-effect Diagram
Fig.2: Cause-Effect diagram of the relation of selected parameters based upon the Influence Matrix.
Synthetic Modelling
The Synthetic Modelling use multiple criteria evaluation to determine each parameters direct influence on the defined problem, and the parameters' relevance in different scenarios.
Weighting
To use the parameters and achieve a total utility during different scenarios the relevance of each parameter against each other has to be defined, or weighted, as the variable w. Different scenarios has to be defined to evaluate their influence, or utility, on each parameter as the second variable u. Table 2 display the degree of influence the row-parameter has on the column-parameter. The sum represent the weight variable w for each parameter. In this case the parameters with the greatest influence on the system seem to be the tidal volume and wetland usage.
Table 2: O: Selected parameters weighted for their influence upon each other.
Scenarios
To make a multiple criteria evaluation the different scenarios has to be defined. Three scenarios has been used in this exercise:
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Scenario 1: The wetlands has a focus upon plantages, increasing vegetation and root systems while reducing turbulence that the farms would have provided.
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Scenario 2: The wetland has a focus upon fish farms, increasing turbulence while decreasing vegetation.
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Scenario 3: The pH is increased by anthropogenic influences, affecting CEC and wetland usage.
Total Utility & Diagrams
In Table 3 the utility of each parameter for each scenario has been defined and calculated with the weighted sum of the parameter. Figure 3 illustrate the scenarios´ influence on the utility. The erosion, wetland usage and tidal volume are the three parameters with the largest influence on the sedimentation rate within the system for the three defined scenarios. The stacked diagram shown in figure 4 give a clear representation on the influential distribution of each parameter within each scenario.
Fig.3: Example of one of the parameter Utility graphs with relation to each scenario.
Table 3: A MCE of the scenarios, displaying the weighting and estimated utility of each parameter during each scenario.
Fig.4: Stack diagram over the Total utility of each parameter for the different scenarios.
Conclusion
The multiple criteria evaluation of the selected parameters indicate that scenario 1 induce the greatest sedimentation rate within the wetland system, and is foremost influenced by the wetland usage and the tidal volume followed by the erosion. Scenario 3 has the lowest sedimentation rate, and is mainly influenced by the pH and the wetland usage. In scenario 2 and 3 the tidal volume has a minor impact in comparison with scenario 1.