Environmental flow management in a complex, complementary-competitive river system

The exploitation of a river system occurs because of the multitude of benefits that accessible water brings to urban and rural communities. The Opuha and Opihi Rivers (NZ) system is a case study of a strongly regulated system that is progressively but unevenly restoring balanced community and ecological benefits to a river system that had become severely degraded by excessive extraction of water for irrigation, to the detriment of urban water flows, recreation, river based ecological systems, and indigenous fishing rights under traditional food source obligations. The multiple behaviours of the system show a mixture of deterministic, stochastic and emergent characteristics that define it as a complex river system, with a wide range of users where some uses are competitive and some are complementary. System management by regulation, through an adversarial decision process, will typically lead to a management and water allocation regime for a system as a whole that is dominated by deterministic rules. These rules will benefit the stronger stakeholders, so that less influential stakeholders have generally substandard outcomes. A systems approach to allocation can be used simulate the normal stochastic behaviours through strategies that maintain the vitality and diversity of all affected communities with a stake in the river system. The Opuha - Opihi river system, following the construction of a 70 GL storage dam and a 7.5 MW electricity generator in the head waters, is a system that demands a multi-disciplinary analysis of the system behaviours ranging from complex systems theory, economics, community sociology, statistics and risk management, meteorology and ecology through to hydrology to achieve more balanced outcomes for all stakeholders. This paper demonstrates the benefit of applying a stochastic nonlinear dynamical systems analysis to develop a multi-domain system function that recognises the unique structures of this system, and enables an optimisation process for improved user regimes. There is a recognition that the current economically based user regimes should respond more to natural stochastic cycles to achieve optimum multi-user outcomes, and such regimes will ensure that natural cycle based allocations, rather than deterministic allocations, are more robust, better managers of risk (and diversity) and ultimately more sustainable.