Integrated assessment of wetland water budget and hydroperiod for quarry development

ABSTRACT: The assessment of quarry development requires a multi-disciplinary approach to address the range of water-related concerns. The fundamental issue is that many of the effects of development, including quarry, stream and wetland impacts, cannot be easily separated into surface and groundwater components. Climate variation and storage add further complexity. Even a multi-disciplinary approach often lacks a consistent quantitative framework. Traditional analysis strategies may include steady state groundwater modelling, lumped parameter hydrologic modelling and a conceptual water balance model to link the various sub-models together. Unfortunately, differences in the underlying assumptions, scale, resolution, time step and mass balance can significantly affect predictive accuracy. Monte-Carlo analysis can be used to explore uncertainty, but the fundamental sub-model limitations cannot be overcome with a fragmented approach. Integrated surface water and groundwater models can address the complete hydrologic cycle in a manner that rigorously addresses the processes, spatial and temporal interactions. Applied skillfully, variable resolution integrated models can address detailed engineering scale design issues within the full watershed context. With an integrated approach, there is no need for artificial assumptions and partitioning of surface and groundwater. Precipitation is applied as a transient input, and the model is calibrated to observed heads, stream stage and total measured flows. Through the development of integrated models for numerous quarry development applications, we have developed new strategies for effects analysis that evaluate the behaviour of the site under a range of possible seasonal and inter-annual climate conditions. By comparing integrated transient simulations of each scenario under the same long-term climate set, the subtle and complex changes in hydrologic conditions can be determined. The benefits of this approach include a comprehensive assessment within an integrated framework. While sensitivity analysis is difficult due to long simulation times, the transient comparison provides unique insight into system behaviour across a range of real (observed) climate conditions that is much more useful than a hypothetical parameter variation. Examples of this approach indicate an exceptional match to long term measured stage, soil and groundwater levels and stream and quarry flows.