2.7.3 'Floodplain or lowland riverine' landscape group


The ‘Floodplain or lowland riverine’ landscape group occupies a land area of approximately 6% of the Namoi subregion assessment extent and makes up around a quarter of the entire length of the stream network across the assessment extent. There are four lowland riverine landscape classes that capture differences in surface water (temporary/permanent) and groundwater (groundwater-dependent ecosystem (GDE)/non-GDE) regimes across the assessment extent. The floodplain landscape classes contain a collection of landscape and ecological elements exposed to inundation or flooding along a river system including riparian forests, wetlands and grassy woodlands.

The zone of potential hydrological change for the Namoi subregion contains all four of the riverine landscape classes, with the largest by length being the ‘Temporary lowland stream’ (2062.2 km) and ‘Permanent lowland stream’ (979.6 km) classes. All six of the non-riverine landscape classes occur within the zone of potential hydrological change with the largest classes by area being ‘Floodplain grassy woodland GDE’ (421.7 km2 or 6% of the zone) and ‘Floodplain grassy woodland’ (121.3 km2 or 1.7% of the zone). There is approximately 1% of ‘Floodplain riparian forest GDE’ and 1.6% of ‘Floodplain wetland’ and ‘Floodplain wetland GDE’ landscape classes within the zone of potential hydrological change. An overview of those aspects of riverine, groundwater and floodplain ecohydrology relevant to the Namoi subregion is presented to provide context to the ecological modelling presented thereafter.

A qualitative model was developed for this landscape group that captured some of the key linkages within and between the riverine and floodplain habitats. From this model, key hydrological response variables were selected for a subset of the landscape classes. There are two landscape classes in the ‘Floodplain or lowland riverine’ landscape group (non-Pilliga region) where groundwater drawdown was assigned as a hydrological response variable: ‘Floodplain riparian forest’ and ‘Floodplain riparian forest GDE’. The corresponding receptor impact variable for riparian forests was identified as change in projected foliage cover. The frequency of overbank flows was identified as being an important driver of the riparian ecosystem (‘Floodplain riparian forest’ and ‘Floodplain riparian forest GDE’ landscape classes) as well as the off-channel water bodies or floodplain wetlands (‘Floodplain wetland’ and ‘Floodplain wetland GDE’ landscape classes). The experts at the quantitative modelling workshop considered the presence of tadpoles from the Limnodynastes genus as the appropriate receptor impact variable for floodplain wetlands.

The cease-to-flow attributes of the surface water regime were considered as critical hydrological response variables for the lowland riverine landscape classes and were assigned: annual number of zero-flow days (averaged over 30 years) and annual maximum zero-flow spells. Assemblages of macroinvertebrates in the edge habitat were deemed to be appropriate receptor impact variables for gauging impacts on these cease-to-flow attributes of the flow regime.

Last updated:
6 December 2018
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