2.3.2 Summary of key system components, processes and interactions

Summary

This section presents a conceptual understanding of how geology, hydrogeology and surface hydrology link together. Geology is a key driver of landscape formation and is therefore a controlling factor for many hydrological and ecological processes. It is an important control on processes such as groundwater recharge, discharge, flow dynamics and the interaction between different aquifers, and also influences surface water – groundwater interaction.

Coal mining and coal seam gas (CSG) operations can induce changes in groundwater level and pressure in the vicinity of operations. The spatial and temporal changes are controlled by local hydraulic properties, and are complicated by fracturing and faulting of stratigraphic layers and the constituent rock types. Another potential effect of reduced groundwater level is the change in the magnitude or direction of flow between groundwater and surface water systems, for example, by inducing flow away from the alluvial aquifer that would otherwise discharge as baseflow to a stream.

Major streams in the preliminary assessment extent (PAE) of the Namoi subregion are the Namoi and Mooki rivers, and the Coxs, Maules, Bohena and Pian creeks. All streams within the PAE are temporary, with the exception of the Namoi River. The intermittent nature of the surface water systems means that the management, treatment and disposal of water may affect surface water – groundwater interactions.

A conceptual understanding of the system underpins many activities that are reported in this product including the landscape classification (Section 2.3.3) and the identification of causal pathways (Section 2.3.5). It also forms the framework for the numerical surface water modelling and the numerical groundwater modelling. For the bioregional assessment (BA) for the Namoi subregion, existing two-dimensional conceptual models were used together with three-dimensional representations that were developed during the Assessment to identify pathways between the different components of the hydrological cycle.