A Strategic Approach to Water Quality Modelling

This paper examines the linkages between water quality modelling and resource management and suggests a strategy to ensure models are useful. Far too often models are developed and implemented to address poorly defined problems and in many cases introduce undue complexity that is not supported by the available data. We must be aware that models are only tools to assist resource mangers to make better decisions. Models should be appropriate to the level of detail required to provide a useful answer within timeframe constraints that resource mangers have. The strategy to model water quality may be divided into four main steps. Firstly, based on environmental values and uses, and water quality guidelines determine water quality objectives. Secondly, identify the major management issues taking into account the severity of water quality problems and the key drivers. This includes the setting up of an adaptive modelling framework to develop strategies to address the water quality objectives. Thirdly, select appropriate combinations of models taking into account data, scale, and time step and model complexity considerations. Finally, assess the uncertainty within the analysis to demonstrate whether results are within sufficiently robust to provide a useful answer. There are many water quality models available that can be applied to a variety of problems. Selecting the appropriate suite of models is a difficult exercise. This paper reviews and classifies the types of models available, and also discusses data requirements, scale, applicability and complexity of these models. Consideration is given to the relationship between water quality constituents and the order in which they need to be modelled. This categorisation gives an indication of the applicability of models to answer particular types of resource management questions and also identifies areas where models are currently inadequate or not available.