Weir management : challenges, analysis and decision support.

If humanity is to make the best of this planet then it is crucial that we develop the capacity to implement the most effective environmental management practices. Essential is a holistic approach to management, as is advocated by integrated catchment management (ICM),
which proposes that catchment management issues will be best dealt with when interventions are planned together at the catchment scale and all stakeholder interests are
given consideration during decision making. The issue of weir modification is a good example of a problem that would benefit from these principles. Many stakeholder interests are affected by weir modification, and if effective and fair weir modification decisions are to be made, all must be used to evaluate alternative weir
modification options. So that decision makers can make the most of the synergies and avoid the conflicts that can occur between interventions, they need to know how multiple weir modifications interact. To do this decision makers must be able to manage and utilise a large amount of information and use it to help them make effective decisions. The objective of the research presented in this thesis is to develop an approach to the management of weirs in the Don Catchment that is holistic both a spatial sense and in terms of the assessment of alternative management options. An evaluatory framework for weir modifications is formulated by adapting published typologies of river ecosystem services (ESs). The prediction of how catchment interventions affect sociocultural ESs is recognized as a particularly challenging to the application of this framework because their qualitative and subjective nature makes them hard to predict. Bayesian Networks (BNs) are identified
as a potential solution as they use probabilities to describe the relationships between variables. A BN was built to predict how weir modification affected weir danger and weir fun for canoeists by utilising the knowledge of canoeing groups. It is concluded that despite a number of caveats, BNs offer a potentially important method for allowing sociocultural ESs to be predicted in decision making processes. The consideration ofthe complex interdependencies multiple weir modifications can have is recognised as another of the challenges facing weir management decision making. A
spatially explicit modelling approach is developed that can account for the interactive effect multiple weir modifications have on river connectivity for several river species in the Don Catchment. Expert judgement and hydrological modelling are used to discriminate between
different levels of habitat quality for European eel (Anguilla anguilla) and Atlantic salmon (Safrna safar). Several strategies to increase connectivity in the Don Catchment were explored. It was found that each had its own set of winners and losers, indicating trade-offs
between species need to be considered when planning connectivity enhancements. The modelling approach shows the interdependent effects of weir modifications are vet:
important in determining habitat accessibility, particularly the cumulative effect of multiple
fish passes.
A decision support system (DSS) dubbed the Weir Tool was constructed through the integration of the canoeing BN and the river connectivity models. As it is generally
assumed that if DSS are employed, improved decision making will result, this assumption was tested in a controlled experiment. In contrast to expectations, users of the Weir Tool learnt less about the environmental issue of weir modification compared to the control
group, and did not make more effective decisions.