This product details the development of qualitative mathematical models andfor the . Receptor impact models enable the Bioregional Assessment team to assess how changes in hydrology due to may result in changes in .
A receptor impact model describes the relationship between:
- one or more , which represent characteristics of and that potentially change due to coal resource development (for example, drawdown or annual flow volume) and
- a , which is a characteristic of the system (for example, projected foliage cover) that, according to the conceptual modelling, is potentially sensitive to changes in the hydrological response variables.
The outputs of the receptor impact models will help identify ecosystem responses to coal resource development and the need for further local-level studies of ecosystems and their response to coal resource development.
Coal resource developments
Receptor impact modelling for theapplies the two potential coal resource development futures considered in the :
- baseline coal resource development (baseline): a future that includes all coal mines and coal seam gas (CSG) fields that are commercially producing as at December 2012
- in the Namoi subregion there are five open-cut coal mines: Boggabri Coal Mine, Rocglen Mine, Sunnyside Mine, Tarrawonga Mine and Werris Creek Mine; and one longwall mine: Narrabri North.
- coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the
as well as those that are expected to begin commercial production after December 2012
- in the Namoi subregion there are ten : Boggabri Coal Expansion Project, Caroona Coal Project, Gunnedah Precinct, Maules Creek Project, Narrabri South, Tarrawonga Coal Expansion Project, Vickery Coal Project, Vickery South Coal Project, Watermark and the Narrabri Gas Project. Eight of these additional coal resource developments are modelled for the Namoi subregion, with the remaining two mines, Vickery South Coal Project (open-cut coal mine) and the Gunnedah Precinct (open-cut and underground), not being modelled due to insufficient information. Analysis of the impacts of these two developments will be restricted to commentary in product 3-4 (impact and risk analysis).
The difference in results betweenand baseline is the change that is primarily reported in a bioregional assessment. This change is due to additional coal resource development.
Potential hydrological changes have been presented in companion product 2.6.1 (surface water modelling) and companion product 2.6.2 (groundwater modelling) for the Namoi subregion. This product outlines the development and description of the qualitative mathematical models andfor the Namoi subregion that will be applied to determining to, and potential impacts on, in product 3-4 (impact and risk analysis).
development is both qualitative and quantitative due to the complexity and associated with describing relationships between hydrological change and ecological components of the system. The absence of directly relevant theory and ecological response data of potential due to the hydrological changes that may occur in the future requires expert judgement or elicitation to be used in: i) mapping ecological processes and key components (as signed digraphs); ii) constructing qualitative models that predict – as an increase, decrease or no change – response to hydrological change; and iii) selection of ecological indicators (receptor impact variables) from the ecological components or processes and the hydrological regimes (hydrological response variables) that support them. The resulting statistical models quantify how changes in due to coal resource development may potentially impact the in a short-term (2013 to 2042) and long-term (2073 to 2102) period within a landscape class.
Thesupports a variety of and in this they are classified into 29 and allocated to one of six : ‘Floodplain or lowland riverine’, ‘Non-floodplain or upland riverine’, ‘Dryland remnant vegetation’, ‘Rainforest’, ‘Human-modified’ and ‘Springs’.
Qualitative mathematical models anduse these classifications to investigate how changes in hydrology may affect ecosystems. Results that apply the receptor impact models and the potential impact of hydrological changes spatially are reported in Sections 220.127.116.11, 18.104.22.168 and 22.214.171.124 of the impact and risk analysis in companion product 3‑4 for the Namoi subregion.
Two modelling workshops were held to build the qualitative mathematical models and receptor impact models and required input from experts in these landscapes and/or the Namoi subregion. Receptor impact models were developed for landscape classes that experts considered more likely to be at 2.7.3, 2.7.4, 2.7.5, 2.7.6 and 2.7.7.from hydrological changes due to , and for which they had the expertise to inform model development. Commentary on those landscape groups and classes that were not included in the ecosystem modelling is provided in Sections
‘Floodplain or lowland riverine’ landscape group
The floodplain and lowland riverinecontain a collection of landscape and ecological elements exposed to inundation or flooding along a river system including: forests, wetlands and grassy woodlands. The floodplain and lowland riverine qualitative model was developed to capture most of the key linkages within and between the riverine and floodplain habitats. This model informed the (in bold) and for the following landscape classes:
- Floodplain riparian forests (groundwater-dependent ecosystem (GDE) and non-GDE) landscape classes: change in projected foliage cover in response to change in and change in the frequency of
- Floodplain wetland (GDE and non-GDE) landscape classes: probability of presence of tadpoles from Limnodynastes genus in pools and riffles in response to change in the frequency of overbank flows
- Permanent and temporary lowland streams (GDE and non-GDE) landscape classes: average number of families of aquatic macroinvertebrates in edge habitat in response to changes in cease-to-flow attributes of the regime.
Results from these three separate 126.96.36.199.4).were used to evaluate the combined impact of changes in one or more of these receptor impact variables across the extent of the ‘Floodplain or lowland riverine’ (Section
The floodplain riparian forests receptor impact model predicts that, in relation to groundwater changes, the mean of the average percent projected foliage cover will drop from just under 15% with no change in groundwater level to about 10% if levels decrease by 20 m relative to the reference level in 2012 due to. A change in drawdown over the longer term will have a larger effect on mean projected foliage cover than a change in drawdown over the short term, indicating that potential impacts from changes in hydrology may not be immediate.
In relation to surface water changes, the mean of the average percent foliage cover will increase from just under 12% with no change in the frequency of overbank events to about 18% if the frequency changes to 0.7 (event per year) (relative to the reference level of 0.33 (event per year) in 2012).
The floodplain wetlands receptor impact model supports the experts’ elicited hypothesis that an increase in overbank flows will have a positive effect on the probability of presence of tadpoles. The model predicts that the probability of presence of tadpoles is fairly uncertain across the floodplain wetland landscape classes with values between 0.35 to 0.80 under historical conditions, and as the number of overbank flow events increases the probability of presence of tadpoles would increase to between 1 and 0.60.
The lowland riverine receptor impact model supports the experts’ elicited hypothesis that an increase in the frequency ofdue to additional coal resource development will have a negative effect on the number of families of macroinvertebrates. As the number of zero-flow days increases, the number of families would drop steeply, with values of less than 0.5 under intermittent flow conditions.
‘Non-floodplain or upland riverine’ landscape group
The ‘Non-floodplain or upland riverine’comprises that tend to be in elevated portions of the catchment and include a diverse range of aquatic and terrestrial ecosystems. The upland riverine qualitative mathematical model included all upland riverine classes and the adjacent vegetation, and was developed to accommodate the general lack of hydrological and spatial between the across the . (in bold) and were identified for the following landscape classes:
- Upland riparian forest : change in projected foliage cover in response to changes in and events
- Permanent and temporary upland streams (GDE and non-GDE) landscape classes: average number of families of aquatic macroinvertebrates in instream pool habitat in response to changes in cease-to-flow attributes of the regime
- Upland riverine landscape classes: probability of presence of tadpoles from Limnodynastes genus in pools and riffles in response to changes in cease-to-flow attributes of the surface water regime.
Results from these three separate 188.8.131.52.4).were used to evaluate the combined impact of changes in one or more of these receptor impact variables across the extent of the ‘Non-floodplain or upland riverine’ landscape group (Section
The upland riparian forest receptor impact model predicts that the mean of the average projected foliage cover will decrease with the maximum difference inrelative to the reference level in 2012. However, there is considerable in these predictions as there is an 80% chance that the average foliage cover will lie somewhere between approximately 15% and 30% in the short-assessment period, and somewhere between roughly 10% and 30% in the long-assessment period, with a 6-m drop in groundwater level. The model interpretation also indicates that long-term drawdown will have more effect on projected foliage cover than short-term drawdown.
In relation to change in overbank flows, the upland riparian forest model predicts that the mean of the average of projected foliage cover will increase from just under 24% with no change to about 30% if the frequency increases to 0.8 (event per year) (relative to the reference level of 0.33 (event per year) in 2012.
The upland riverine receptor impact model supports the experts’ elicited hypothesis that an increase in the frequency ofdue to will have a negative effect on the number of families of macroinvertebrates. However, there is substantial variability across the landscape class. Under conditions of constant flow the number of families of macroinvertebrates can range from less than 5 (families) to almost 20. As the number of zero-flow days increases, experts were of the opinion that the number of families would drop quite dramatically to less than 0.5.
The upland riverine receptor impact model predicts that the probability of presence of tadpoles will respond to changes in frequency of zero-flow days due to additional coal resource development. Under conditions of constant flow the probability of presence of tadpoles is predicted to be almost 1 and as the number of zero-flow days increases this may decrease to less than 0.1.
In addition to the upland riverine system, a qualitative model was developed for the non-floodplain wetlands in this landscape group and focused on internally draining lakes in the Namoi, with the Lake Goran ecosystem being the primary focus, but also including Yarrie Lake (both defined as ‘Non-floodplain wetland’ landscape class). A receptor impact model was not developed for this landscape group. Qualitative analyses generally indicate a negative or ambiguous response prediction for most biological variables within the non-permanent wetland ecosystem in response to hydrological changes. Tree and shrub groups were predicted to decline, which leads to negative impacts to habitats for birds, frogs and terrestrial invertebrates. A predicted decrease in wading birds and piscivorous and insectivorous birds leads to a release, or increase, in their prey populations. The potential impact of decreased sheet flow is predicted to lead to a decrease in all forms of aquatic macrophytes and herbivorous birds.
Pilliga (upland and lowland) region
The Pilliga and Pilliga Outwash represent a unique set of ecological systems within the 2.7.3).. It was considered appropriate to develop a set of separate ecological models for the Pilliga to improve the assessment of potential ecological . The for the Pilliga region included riverine (9.8% of upland streams and 13.1% of lowland streams), the ‘Grassy woodland GDE’ landscape class (8% of the zone), and the non-floodplain wetlands landscape classes (<0.2% of the zone). Key ecological processes in both upland and lowland riverine landscape classes were captured together in the Pilliga riverine qualitative mathematical model. A qualitative model for the ‘Grassy woodland GDE’ landscape class was also formulated, but no quantitative modelling was developed as it is considered less sensitive to hydrological change given its reduced reliance on and (see Section
The riverine classes in the Pilliga region have a unique set of conditions such as: sandy beds, temporary flow with some permanent pools above highly stratified sandstone, and channels that often form shallow and poorly defined ephemeral wetlands.(in bold) and were identified for the following :
- Pilliga riverine (upland and lowland): change in projected foliage cover in response to changes in cease-to-flow attributes and groundwater
- Pilliga riverine (upland and lowland): average number of families of slow-water macroinvertebrates in instream pool habitat in response to changes in cease-to-flow attributes and groundwater drawdown.
The Pilliga riverinepredicts that percent foliage cover will decrease as groundwater drawdown increases due to . The mean of the average percent projected foliage cover will decrease from just below 25% with no change in groundwater level, to about 20% if the levels decrease by 150 m relative to the reference level in 2012. In relation to surface water changes due to additional coal resource development, the model predicts that the mean of the average percent projected foliage cover will decrease from just under 25% under constant flow to about 10% if the number of increases to 180 (days per year).
In relation to number of families of aquatic macroinvertebrates, the Pilliga riverine receptor impact model predicts that an increase in zero-flow days and/or cease-to-flow days will have a slightly negative effect but will vary across landscape classes. Under conditions of constant flow, the number of families of macroinvertebrates will range from 15 (families) to 20 and as the number of zero-flow days increases the number of families would decrease with values between 13 and less than 10 for very intermittent flow conditions (zero-flow days of greater than 150).
The model predicts that the number of families of macroinvertebrates will decrease as groundwater drawdown increases due to additional coal resource development. Under conditions of no change in groundwater level, the number of families is predicted to be just under 12, decreasing to about 6 if levels decrease by 55 m relative to the reference level in 2012.
‘Rainforest’ landscape group
The ‘Rainforest’ 184.108.40.206). Given the limited resources and the limited extent of this landscape group in the zone, a was not formulated. Thus, potential ecological impacts are not quantified, but can be inferred from modelled changes in groundwater across this landscape group.is distinguished primarily by its vegetation structure and composition and is predominately ‘Dry Rainforest’ or ‘Western Vine Thickets’ (both threatened vegetation classes in NSW). 4 km2 of the ‘Rainforest’ and 0.3 km2 of the ‘Rainforest GDE’ landscape class are within the . A qualitative model was developed for this landscape group given the conservation values surrounding the vegetation types common to this group. This model identified as being critical to supporting many biophysical components of the (Section
‘Springs’ landscape group
The ‘Springs’is comprised of two : ‘Great Artesian Basin (GAB) springs’ and ‘Non-GAB springs’ denoting the hydrological of the to the underlying . The ‘GAB springs’ landscape class is associated with sedimentary sequences of the GAB and can be characterised as ‘discharge’ or ‘recharge’ springs.
Two of the seven ‘GAB springs’ in the Namoi 220.127.116.11). Given the nature of these springs and their limited extent in the zone of potential hydrological change, a was not formulated for this group. Any changes in groundwater drawdown across the extent of these springs can be used to infer potential ecological , however these cannot be quantified.are located within the . Given their location on the eastern edge of the Pilliga region, these springs were considered to be ‘recharge’ springs; that is, their source of water is from localised from nearby sandstone outcrop areas. A qualitative mathematical model was formulated for a typical recharge GAB spring that included the associated terrestrial and aquatic . This model identified as the critical variable driving ecological function in this system (Section
Limitations and gaps
The limitations and gaps surrounding evaluation ofresponses to changes in and regimes are discussed. It emphasises that the degree to which ecological modelling can inform impacts across the extent of a particular is limited by the available expertise, the evidence base that informs the model, and the coverage of hydrological modelling, particularly with respect to the surface water. Some specific limitations include:
- a limited understanding of the nature of groundwater interactions between riverine and terrestrial ecosystems for the Pilliga region; a more complete picture of the hydrological connections among the Pilliga riverine, vegetation and wetland elements is considered a key priority for future work
- a paucity of surface water hydrological response information for the upland riverine reaches and very little coverage of the entire stream network in the Pilliga region
- the degree to which species within the ‘Rainforest’ access groundwater given that this habitat occurs in elevated parts of the .
The receptor impact modelling described in this product culminates with the creation of(functions) that are subsequently applied in product 3-4 (impact and risk analysis) for the Namoi subregion, and result in predictions that translate the potential hydrological change to indicators of potential ecosystem change.
- 2.7.1 Methods
- 2.7.2 Prioritising landscape classes for receptor impact modelling
- 2.7.3 'Floodplain or lowland riverine' landscape group
- 2.7.4 'Non-floodplain or upland riverine' landscape group
- 2.7.5 Pilliga riverine landscape classes
- 2.7.6 'Rainforest' landscape group
- 2.7.7 'Springs' landscape group
- 2.7.8 Limitations and gaps
- Contributors to the Technical Programme
- About this technical product