Modelling Water Quality to Support Lake Restoration

Abstract

Numerous applications of deterministic models have been used to support decision making in relation to lake restoration actions in New Zealand. The most widely used are one-dimensional, coupled hydrodynamic-ecological models suitable for long-term (multi-year) simulations to explore inter-annual variability and progressive changes in response to restoration actions and global change drivers (e.g. climate change). Three-dimensional models have also been used to examine, for example, spatial variability associated with inter-basin circulation transfers in a deep hydrolake, dispersion of geothermally heated waters in a shallow volcanic lake and a double gyre circulation pattern influencing dispersion of inflows, including a wastewater discharge, to a large volcanic lake. We provide a framework for categorising these applications based on theoretical, heuristic and predictive considerations. Information on model selection, data assimilation and calibration processes presented in this chapter are designed to support increasingly sophisticated modelling approaches, many of which will be supported by autonomous sensor data. The need for these types of models is likely to increase in the future as they are used to support the goals of the National Policy Statement for Freshwater Management (MfE 2014) to maintain or improve water quality. The models will be used to assess the ecological outcomes of potential restoration actions as part of an integrated assessment that includes expert knowledge, economic considerations and social outcomes.