'Riverine' landscape group

The total length of streams in the riverine landscape group within the zone of potential hydrological change is 3138 km, 63% of which is in highly intermittent or ephemeral streams, which were considered predominantly rainfall-dependent and not encompassed in the definition of water-dependent adopted for the BAs. For BA purposes, an ephemeral stream is defined as a stream that flows only briefly during and following a period of rainfall, and has no baseflow component. Thus groundwater changes due to additional coal resource development are unlikely to have a significant impact on ephemeral stream hydrology. Interception and storage of local runoff on a mine site can impact ephemeral streamflow; however, since communities associated with ephemeral streams are adapted to high runoff variability and respond opportunistically to water when it is there, they are considered less vulnerable to changes in catchment runoff. A qualitative model was developed for streams in the ‘Highly intermittent or ephemeral’ landscape class (ephemeral streams; Table 5), but was not progressed to a receptor impact model.

The qualitative models for the perennial, intermittent and ephemeral streams all include a riparian habitat component. For perennial streams, this model node (circles in the signed digraphs in the subsequent sections) serves as a linking node to the forested wetland GDE qualitative model. Along intermittent and ephemeral streams, this node could represent the connection to a dry sclerophyll forest, rainforest or other landscape class qualitative model. Similarly, the frog nodes in the perennial river model and the forested wetland model represent another point of connection, reflecting the interconnectedness of the landscape classes. In other words, while the riverine qualitative models are largely self-contained, they include components that enable them to be linked to other qualitative models, representing other parts of the landscape. Of course, not all possible interconnections between the riverine qualitative models and other landscape class models are represented, as this was not the objective of the model building process.

Receptor impact modelling, described in Section 2.7.3, focuses on perennial streams and intermittent streams (Table 5). The ‘Lowly to highly intermittent’ landscape class designation in Table 5 combines the two intermittent riverine landscape classes (‘Lowly to moderately intermittent’ and ‘Moderately to highly intermittent’) that were defined from the flow regime classification methodology (see Section 2.3.3 of companion product 2.3 for the Hunter subregion (Dawes et al., 2018)) on the basis that both are variably connected to groundwater. For the purposes of developing the qualitative model, it was agreed at the workshop that a single model could represent both landscape classes.

The discretisation of the stream network into landscape classes, based on flow regimes that broadly reflect connection to groundwater, was considered useful for differentiating between different instream ecosystems. In some streams, the modelled hydrological changes indicate the possibility of a switch from perennial to intermittent or ephemeral flow, or from intermittent to ephemeral flow. In other words, a change in landscape classification. The expert elicitations for the intermittent and perennial stream models include hydrological change scenarios consistent with these sorts of flow regime changes. Thus, a receptor impact model for, say, perennial streams can be used to predict the response of a receptor impact variable to a change to intermittent flow. The differences between the components and relationships represented in the perennial stream, intermittent stream and ephemeral stream qualitative models indicate potential ecosystem changes where the predicted hydrological change indicates a landscape class change.

Last updated:
18 January 2019
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