3.4 Impacts on and risks to landscape classes

Summary

The heterogeneous natural and human-modified ecosystems in the Hunter subregion were classified into 26 landscape classes, and then aggregated into five landscape groups based on water dependency: riverine, groundwater-dependent ecosystem (GDE), coastal lakes and estuaries, non-GDE vegetation and economic land use.

Landscape classes that are unlikely to be impacted

Within the ‘Riverine’ landscape group, the ‘Highly intermittent or ephemeral’ landscape class is unlikely to be impacted by drawdown because, by definition, ephemeral streams are not connected to regional groundwater. Ephemeral streams that are directly affected by disruptions to their drainage from excavations at the mine site are likely to be impacted.

All landscape classes in the ‘Coastal lakes and estuaries’ landscape group, except saline wetlands, are very unlikely to be impacted: drowned valleys do not occur within the zone; regulations are in place to limit impacts to seagrass beds from subsidence; and creeks are upstream of developments.

In the ‘Non-GDE vegetation’ landscape group, the ‘Native vegetation’ landscape class is ruled out from impacts because it is not considered water dependent for the purposes of bioregional assessments (BAs).

‘Riverine’ landscape group

The potentially large hydrological changes modelled in some permanent or perennial streams of the Hunter subregion could result in significant ecological impacts. Results from the perennial stream receptor impact model, which uses changes in the probability of presence of riffle-breeding frogs and density of riffle-dwelling Hydropsychidae larvae due to hydrological changes as indicators of change in instream habitats, indicate a potentially significant impact on instream habitat of the Wyong River, and by extension Dora Creek, in the Macquarie-Tuggerah lakes basin. However, when local hydrogeological information is used to constrain the hydrological change predictions in this area, the likelihood of potentially significant changes in instream habitat is low. Elsewhere in the subregion, it is very unlikely that instream habitats of permanent or perennial streams are impacted.

Potentially large hydrological changes are modelled in the intermittent Saddlers and Loders creeks in the Central Hunter and Lower Hunter reporting areas. Results from the intermittent stream receptor impact model, which models changes in the probability of presence of riffle-breeding frog and hyporheic taxa richness in response to changes in zero-flow days, indicate a risk of adverse impacts upon instream habitats in these intermittent systems. Local information is needed to determine the actual risk, having regard to stream condition, habitat diversity, other catchment stressors and recovery potential.

‘Groundwater-dependent ecosystem (GDE)’ landscape group

Potentially large drawdowns are possible in the Macquarie-Tuggerah lakes basin with potential for ecological impacts on wet and dry sclerophyll forests. Around 5.6 km² of wet and dry sclerophyll forest have a 50% chance of experiencing drawdown of more than 2 m. There is little likelihood of impacts on wet and dry sclerophyll forests, based on receptor impact modelling, which predicted only minor reductions in projected foliage cover based on modelled drawdown. There is at least a 5% chance that 10 to 15 km² of dry sclerophyll forests in the Macquarie-Tuggerah lakes basin will be impacted. It is very unlikely that more than 8.6 km² of wet sclerophyll forests or dry sclerophyll forests experience drawdown of more than 2 m. It is very unlikely that more than 5.2 km² of wet sclerophyll forests or dry sclerophyll forests experience drawdown of more than 5 m. The potentially impacted areas are smaller and associated with smaller drawdowns, when local hydrogeological information from the Wyong River catchment is used to constrain the hydrological predictions.

Potentially significant hydrological changes due to additional coal resource development are possible in some areas of forested wetlands. Regional hydrological modelling found that nearly all the riverine forested wetlands in the Hunter and Goulburn basins will potentially experience drawdown of up to 2 m, with about 2.6 km² of the coastal forested wetlands at risk of drawdowns of more than 2 m. It is likely that only small areas (<1 km²) of forested wetlands for which surface water modelling is available are impacted by changes in overbench and overbank flows. Results from receptor impact modelling, which are based on predicted changes in projected foliage cover, indicate little likelihood of impacts on riverine forested wetlands. Riverine forested wetlands along the Goulburn River are identified as ‘more at risk of ecological and hydrological changes’, but the significance of this risk can only be determined through more local information. The ecological impact on the coastal forested wetlands in the Macquarie-Tuggerah lakes basin was not represented in the receptor impact model.

Most of the GDE rainforests are unlikely to be impacted, because if they are dependent on groundwater at all, it is local groundwater sources. The exception is rainforest along the Wyong River and Jilliby Jilliby Creek, the water dependency of which requires further study at a local scale to assess water dependency and potential for impact.

The freshwater wetlands within the zone of potential hydrological change are represented entirely by Keith’s (2004) ‘Coastal freshwater lagoons’ vegetation class. Experts were uncertain about the water dependencies of these systems and their sensitivity to hydrological changes caused by coal mining. The potential for ecological impacts on this landscape class is a knowledge gap.

Semi-arid woodlands, heathlands and grassy woodlands are very unlikely to be impacted because they are located almost exclusively outside the zone of potential hydrological change.

Springs are represented by four assets in the water-dependent asset register. None of these four assets intersects the zone and thus this landscape class is very unlikely to be impacted due to additional coal resource development.

Experts were uncertain about the sensitivity of saline wetlands to drawdown due to additional coal resource development. The potential for ecological impacts on this landscape class is a knowledge gap.