4.3.6 Limitations of the matrix approach

Despite the elegance of matrix presentation, there are certain limitations which need to be addressed.

• Unless weight-scaled impact scores are used, the comparison of many project alternatives is difficult.

• Scaling the multitude of scores contained in a matrix is also not a tractable proposition, as the ability to independently replicate the method is undermined by a dependence on highly subjective judgments.

• The impact characterization step of the matrix involves subjective prediction as well as assessment.

• There is little opportunity for quantification. However, it is possible to accommodate further detailing in the matrix presentation if prediction/evaluation techniques are separately used.

• While developing matrix structure, it becomes apparent that higher order impacts are not accounted for using this approach.

For example, impacts propagate from one component to another and are not necessarily linked directly with the project activities. In the case of a thermal power plant, waste emissions alter the air quality and the altered air quality in turn affects crops, public health, or materials. A water resources project upstream of a river mouth entering the sea, alters the fresh river flow into the sea and this in turn changes the saline zone of the river mouth. This change in the saline zone influences the marine life feeding near the saline wedge, which influences the income of fishermen as well as the marine ecosystem in general. Both these examples question our rudimentary understanding of impacts. This implies that impacts on the nth environmental component can be due to simultaneous and/or successive changes in the other interlinked components.

There is a lot be learned from this improved understanding of impacts.

• In the case of component-component or secondary impacts, the project activity specificity ends. In other words, if a particular project activity alters a particular component, then, regardless of the project activity, this changed component would affect the linked component. For example, if the temperature of the water of the river is raised above a certain threshold (by any activity) then the fish life in the river would be affected.

• Impacts have non-linear relationships and due to the participation of more than one component in some cases, there is the possibility of a delay in their realization, especially in terms of time. Again, delayed impacts do not mean that the "size'' of the impact is attenuated. It is possible that the size can be bigger, especially if there are processes such as "biomagnification'' or if the receiving environment is fragile (e.g., mangrove ecosystems).

• The matrix style needs to be expanded to allow for component-component interactions. This is technically possible by writing a matrix adjacent to another and so on but it can become rather clumsy if there are multi-component (or multi-order) impacts. One may need here a presentation style which allows one to depict the interconnections in a causal style. Network presentation, discussed later, is perhaps a better choice.

• Writing a single matrix for infrastructure or spatial projects becomes rather difficult. For a thermal power plant, for instance, the impact of waste emissions on air quality depends on whether the region under consideration is mostly downwind or not. If a region (or portion of the neighbouring environment) is beyond a hill, then the waste emissions from the power plant almost get screened. Similar arguments would hold for describing the impacts upstream or downstream of a water resources reservoir. In other words, the impact association attempted in the matrix style assumes homogeneity or isotropy in the region, which is not the case in most situations. This may call for writing more than one (maybe five or six) matrix presentations for a project, describing specific situations happening in the spatial elements. This leads once again to technical as well as communication difficulties. Use of geographical information systems (GIS) coupled with impact assessments methodology becomes an attractive alternative.