An assessment of Figure 30 ( ). The lowest reaches of the Namoi River were reported to form a losing system, and Pian Creek was classified by as ‘maximum losing’, which the study defined as a river reach where the is separate from the stream due to the presence of an . These findings are generally consistent with previous regional hydrogeological interpretations, including .– for the Namoi river basin was made by as part of the Murray-Darling Basin Sustainable Yields Project using a regional mapping approach. This assessment provided a snapshot in time of the magnitude and direction of hydraulic fluxes to, or from, the major rivers in the Namoi river basin using data from June 2006 (or as close as possible), which was a period of historically low flows in the Namoi River ( ). The analysis and methods are described in . The creek and river reaches in the highland areas of the Namoi river basin, such as the Manilla and Peel rivers (which are east of the boundary), were assessed as gaining reaches. Further downstream, the river reaches change from predominantly gaining in the upper catchment through to losing and back to gaining in the mid-section of the Namoi River, as shown in
employed a combination of hydrological methods to assess – and dominant direction of flux at the river reach scale in the Namoi river basin. The data analyses included:
- comparison of groundwater and stream channel base elevations using a GIS
- the shape of the stream hydrograph and application of a separation filter to streamflow data
- flow duration curves
- vertical connectivity based on nested piezometer hydrographs
- paired stream and bore hydrograph comparisons.
The presence of hydraulic connection between the stream and underlying aquifer was assessed by Figure 31). In areas without bore data within 1 km of the stream, extrapolations were made based on data points further away from the stream. Connection was assumed to exist where the minimum depth to groundwater over the length of the data record (from the 1970s) was less than 10 m. This depth was used as 10 m was the estimated difference between the elevation of the floodplain, where bore levels would be measured, and the base of the stream in the catchment. The minimum depth to groundwater over the length of the data record (since the 1970s) was intentionally chosen to provide a benchmark of where connectivity had at some point in time existed based on the available data. The value of 10 m as the cut-off for inferred connectivity was derived by comparing streamflow gauging station cross-sections on the major streams to the mean elevation of the surrounding 1 km2 area determined from the Australian 9 second digital elevation model ( ) as reported by (this gives a pixel size of approximately 0.06 km2 at the latitude of the ). Although the difference in elevation tends to decrease downstream as the topography becomes more subdued and the floodplains larger, this estimate was considered reasonable given the absence of detailed surveys of the zone and the of using a nine arc-second digital elevation model.through comparing the elevation of the base of the stream channel with the elevation of the groundwater observed within shallow observation bores (<40 m deep) located within 1 km of the stream (
Source: Figure 4-1 in
Figure 31 shows that the streams upstream of Wee Waa were assessed as primarily connected reaches. One exception is the approximate 30 km length of disconnected (non-contiguous) stream reach in the Coxs creek basin between Mullaley and Boggabri, where groundwater levels were reported to have been declining due to the widespread use of groundwater for irrigation ( ). The river reaches downstream of Wee Waa were considered to be disconnected (or maximal losing and/or non-contiguous, depending on the classification system used).
Although thein the Lower Namoi river basin were assessed as ‘disconnected’ from the Namoi River and its tributaries in both the and investigations, it is important to understand the intent of this term. In this ‘disconnected’ is used to describe hydrological systems where the depth to the is more than 10 m below the height of the river bed. also use the term ‘maximum losing’ for the same situation, to indicate that some degree of connection remains between groundwater and surface water in this condition, through an between the surface water system and the watertable. Hydraulic connection occurs between the stream and alluvium in many areas mapped as ‘disconnected’ and stream losses have been shown to play an important role in recharging the underlying aquifers based on the analysis of bore and stream hydrographs and hydrochemical data ( ; ; ). Groundwater mounds are evident adjacent to the Lower Namoi River and its anabranch, Pian Creek, suggesting that streamflows recharge the underlying aquifers. According to other CSIRO investigations ( ), 56% of the Lower Namoi groundwater inputs are from river , mostly associated with flooding inundation, in contrast with the Upper Namoi where only 4.5% is derived from flood recharge. Connectivity is, however, variable and have postulated that the vertical connectivity between the river and the underlying aquifers is poor in some areas, reflecting the migration of the Namoi River channel and associated floodplain deposits, which tend to form low layers.
After assessing surface water – groundwater connectivity, the dominant direction of flux was inferred from hydrometric data obtained from 35 streamflow gauging stations on the unregulated stream systems in the Namoi river basin. The results of the analyses are shown in Figure 32. A hydrometric approach was required to infer the direction of flux because of the absence of surveyed field data in the riparian areas of the Namoi river basin, which meant that near-river groundwater elevation and river stage relationships could not be reliably established. A baseflow filter was applied to the streamflow data to estimate the proportion of baseflow using the digital recursive filter, as described in . In addition, the characteristics of the stream hydrograph, based on visual inspection, and flow duration data were analysed. The complete temporal data record was used to assess the dynamic changes in surface water – groundwater interactions over time, as using only synchronous streamflow records would have severely limited the available data pool. This approach was considered appropriate given the objective of characterising changes in surface water – groundwater interactions over the length of the available hydrological record.
Ivkovic (2006) found that relatively larger baseflow indices (meaning that baseflow is a higher proportion of streamflow) and streamflow of longer duration occur in the uppermost reaches of the Namoi river basin. In this area baseflow is contributed from the fractured rock aquifers into which the streams are incised. A decrease in in the downstream reaches was associated with a decrease in flow duration, suggesting that groundwater input maintains streamflow in the upper catchment reaches.
Mapping is at the river-reach scale. Disconnected reaches are where the watertable depth is greater than 10 m from the surface.
Data: Ivkovic (2006)
The hydrometric data were used to infer the dominant direction of flux for the unregulated streams. The dominant direction of flux for the connected regulated streams was classified as losing due to the artificially high stream stage as aof stream regulation throughout the irrigation season (September to March).
The inferred connectivity between the stream and underlying aquifer based on the hydrometric data was cross-validated through the assessment of paired bore and stream hydrograph data and other previous hydrochemical investigations, such asand . These details are further discussed in .
There were some differences in the interpretation of the flux direction between the CSIRO (2007) and Ivkovic (2006) investigations, but these differences can largely be attributed to the use of spanning different observational periods. In particular, the CSIRO (2007) investigation used data obtained circa June 2006, whereas Ivkovic (2006) used the full length of the available hydrological data record (from the earliest data available through to 2003), thus encompassing a broader spectrum of hydrological conditions. Ivkovic (2006) also included a class for variably gaining-losing for the connected aquifer – stream reaches, which the CSIRO (2007) study did not include since they were assessing a snapshot in time. Despite the differences in the CSIRO (2007) and Ivkovic (2006) assessments in relation to the direction of flux, the connectivity mapping is broadly similar, and provides credibility to both mapping efforts at the regional scale.
Additional investigations into Figure 33) were carried out by the University of New South Wales. They used a combination of geological data, geophysical methods, hydraulic data, and groundwater salinity, temperature and water chemistry data ( ; ; ; ; ). The results were consistent with and and indicated that there is spatially and temporally varying degrees of connectivity between surface water and groundwater resources along the river reaches between Boggabri and Narrabri, with predominantly losing conditions during high flows and gaining conditions at low flows. However, have noted that there has been a reversal in the aquifer–stream gradient in the Maules Creek catchment as a of groundwater , with the river now tending to lose water at low flows, rather than gain water.– in the area of Maules Creek and the Namoi River between Boggabri and Narrabri (Namoi groundwater management zones 11 and 5, shown in
Data: NSW Office of Water ()
Product Finalisation date
- 2.1.1 Geography
- 2.1.2 Geology
- 2.1.3 Hydrogeology and groundwater quality
- 2.1.4 Surface water hydrology and water quality
- 2.1.5 Surface water – groundwater interactions
- 126.96.36.199 Observed data
- 188.8.131.52 Previous catchment-scale investigations on stream-aquifer interactions
- 184.108.40.206 Overview of controls on surface water – groundwater connectivity based on previous investigations in the Namoi river basin
- 220.127.116.11 Statistical analysis and interpolation
- 18.104.22.168 Gaps
- 2.1.6 Water management for coal resource developments
- 22.214.171.124 Boggabri Coal Mine (baseline) and Boggabri Coal Expansion Project (ACRD)
- 126.96.36.199 Narrabri North Mine (baseline)
- 188.8.131.52 Narrabri South Project (ACRD)
- 184.108.40.206 Rocglen Mine (baseline)
- 220.127.116.11 Sunnyside Mine (baseline)
- 18.104.22.168 Tarrawonga Mine (baseline) and Tarrawonga Coal Expansion Project (ACRD)
- 22.214.171.124 Caroona Coal Project (ACRD)
- 126.96.36.199 Maules Creek Project (ACRD)
- 188.8.131.52 Watermark Coal Project (ACRD)
- 184.108.40.206 Vickery Coal Project (ACRD)
- 220.127.116.11 Narrabri Gas Project (ACRD)
- 18.104.22.168 Mine footprints
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product