This chapter outlines the current state of the art with regard to modelling of hydrology and fresh water quality and its applicability in relation to several key water management issues. As is clear from this review, the choice of model depends to a large degree on the scale of application and whether the aim is to take into account many driving factors in a complex system, perhaps one as yet unobserved or to consider specific responses to a particular change in a spatially limited context.
- Most of the models discussed here would be relevant to the environmental objectives relating to acidification, ground water, eutrophication and the ultimate aim of ensuring flourishing lakes and streams.
- Generally, conceptual and empirical models might be expected to be more pragmatically useful in a dynamic planning context, particularly if swift responses for use with participatory methods was required, but are less able to give a definitive answer as to the “best” course of action due to equifinality and reliance on previously observed circumstances.
- Bayesian and mechanistic approaches can handle more complex situations where the physical relationships are not all known, but their output is highly dependent on relevant data and models require considerable expertise to set up, thus might be of most use for more strategic impact assessment.
- For specific, local, impact assessment, physically based models can give spatially precise output and capture key inter-relationships including predicting future unobserved cases, but in practice still require calibration to specific circumstances.