Threat Effect on asset Knowledge gap Information required Increase in no flow spell occurrence and duration Spells may exceed waterhole persistence time, causing local extinction of aquatic biota Waterhole persistence times in target river valleys Distribution of refugial waterholes across the northern Basin Blank cell Blank cell Blank cell Relationship between spell length and amount of waterhole habitat at the reach scale Blank cell Blank cell Blank cell Water loss rate Blank cell Blank cell Blank cell Waterhole shape and size Blank cell Blank cell Blank cell Connection to groundwater Blank cell Blank cell Blank cell Depth/Persistence relationship Change in the provision of sediment scouring flow events Sediment accumulation in waterholes, leading to reduced volume and persistence Sediment status of waterholes Amount of soft sediment in waterholes Blank cell Blank cell Blank cell Historical rate of sediment accumulation Blank cell Blank cell Effect of flows on sediment dynamics Identification of flow events or other conditions that lead to sediment infilling Blank cell Blank cell Blank cell Identification and quantification of scouring capacity of flows Project purpose This project addresses crucial knowledge gaps (Table 1.1) required to understand if the current EWRs set at the Lower Balonne Floodplain are suitable for maintenance of refugial waterholes, and determines if additional flow indicators are needed. Waterholes in the Barwon–Darling upstream of Menindee Lakes were also investigated, to understand whether particular flow requirements should be specified for this part of the northern Basin.
Bokhara River at Hebel (422209A) 40 127 358 355 (99.2%) Ballandool River at Hebel-Bollon Rd (422207A) 32 131 605 362 (59.8%) Briarie Creek at Woolerbilla-Hebel Road (422211A) 32 145 672 631 (93.9%) Barwon–Darling River valley Blank cell Blank cell Blank cell Blank cell River at Wilcannia Main C (425008) 17 52 321 108 (33.6%) Darling River at Tilpa (425900) 2 179 182 168 (92.3%) River at Louth (425004) 21 39 225 191 (84.9%) Darling River at Myandetta (425038) 6 57 239 206 (86.2%) Darling River at Bourke Town (425003) 5 59 198 91 (46%) Barwon River at Beemery (422028) 4 56 95 70 (73.7%) Barwon River at Brewarrina (422002) 1 113 113 95 (84.1%) Barwon River at Collarenebri (422003) 6 80 161 128 (79.5%)
Environmental Assessment Reach Maximum Waterhole Area (ha) Time-series Maximum Waterhole Area (ha) Refuge Waterhole Area (ha) Persistent Refuge Waterhole Area (ha) Downstream of Beardmore Dam Blank cell Blank cell Blank cell Blank cell Balonne River at St George (422201F) 221.6 43 - - Balonne-minor River at Hastings (422205A) 106.9 18.2 - - Culgoa River valley Blank cell Blank cell Blank cell Blank cell Culgoa River at Whyenbah (422204A) 31.3 0 - - Culgoa River at Woolerbilla (422208A) 16.5 0 - - Culgoa River at Brenda (422015) 160 - 3.7 0 Culgoa River at Weilmoringle (422017) 102.4 - 0.18 0 Culgoa River at U/S Collerina (Mundiwa) (422011) 57.3 1.2 - - Culgoa River at D/S Collerina (Kenebree) (422006) 85.4 0 - - Narran River valley Blank cell Blank cell Blank cell Blank cell Narran River at Dirranbandi-Hebel Rd (422206A) 37.6 0 - - Narran River at New Angledool (422030) 203.8 - 3.8 0.4 Narran River at Wilby Wilby (Belvedere) (422016) 307 - 29.5 3.3 Bokhara River valley Blank cell Blank cell Blank cell Blank cell Bokhara River at Hebel (422209A) 112.5 - 0 - Ballandool River at Rd (422207A) 62.1 - 0 - Biarie Creek at Woolerbilla-Hebel Road (422211A) 40.8 - 0 -
Barwon–Darling River valley Blank cell Blank cell Blank cell Blank cell Darling River at Wilcannia Main C (425008) 589.3 318.6 - - arling River at Tilpa (425900) 382.3 0 - - River at Louth (425004) 284.1 46.3 - - River at Myandetta (425038) 1067.0 511.2 - - Darling River at Bourke Town (425003) 295.7 226.8 - - Barwon River at Beemery (422028) 140.0 81.6 - - Barwon River at Brewarrina (422002) 355.6 355.6 - - Barwon River at Collarenebri (422003) 283.6 168.4 - -
Thirdly, there is an underlying assumption that the data are normally distributed, which is an assumption used in calculating the confidence and prediction intervals. There were no indications in the model validation that this is not the case, but greater sample sizes would yield greater confidence in this assumption. Lastly, the 95% prediction interval appears to be quite large (±121 days), but if the data are normally distributed, the predictions will be on average much closer to the centre of that range (i.e what the model predicts). A 95% confidence interval provides the range in which 95% of values are expected to fall, that is, throughout that range the model should only be wrong in 5% of predictions. Climatic component The driver for natural water loss in waterholes is a combination of evaporation and groundwater. Discerning which of the two loss factors are most important across the river valleys requires further investigation. Presumably there is some correlation with climate, which is a driver for evaporation, but further investigation is required. Other factors such as wind fetch from river orientation may play a large role as well. Also, the Moonie samples were taken in 2009, while the Culgoa and Narran river systems were sampled in 2015. The model could be impacted because of this difference; it may be different because of different conditions during sampling. It is feasible that the relationship may be stronger had the samples been collected in the same time period. Taking the model further Given the success with which this model can predict persistence across three river valleys, the ease of its use and the broad management implications, it would be worth investigating how this model might apply in a wider range of catchments within the Basin. As more catchments are incorporated into the model, the predictions become more robust and the management implications become exponentially greater as more regions can potentially benefit from the model. In order to investigate the effect of climate, the next catchment to be surveyed would ideally have a similar river system in a climatically different location. It may be that by incorporating an element of climate into the model, its accuracy can be increased as will its area of application, though the corresponding increases in complexity may be prohibitive.
Question 3. What is the persistence time of waterholes in the Lower Balonne and Barwon–Darling? Findings: The average persistence time for modelled waterholes in the Culgoa River valley was 377 days (maximum 587 days at Weilmoringle GS). The average persistence time for modelled waterholes the Narran River valley was 355 days (maximum 637 days at Angledool). In the Barwon–Darling, the persistence time, based on uncalibrated models, ranged from 1083 days (Hell’s Gate) to 1953 days (Akuna/Weir 20A). Modelled waterhole persistence times were validated by remote sensing analysis (Chapter 2). What does this mean? Modelled waterholes in the Lower Balonne do not persist as long as previously thought; the majority of waterholes did not persist longer than one year and none persisted beyond two years. Question 4. Does groundwater influence the persistence time of waterholes in the Lower Balonne and Barwon–Darling? Findings: Groundwater contribution to waterholes along the Narran and Culgoa rivers is minor. Groundwater interaction maybe be greater in the Barwon–Darling, but does not contribute significantly to waterhole persistence. What does this mean? Groundwater interactions did not need to be explicitly included in the calibration of persistence models for the Lower Balonne (Chapter 3). Question 5. Does sedimentation affect waterhole persistence in the Lower Balonne and Findings: The average depth of accumulated soft sediment in the Lower Balonne was 25 centimetres (approximately 11 per cent of average maximum waterhole depth in the Narran and Culgoa Rivers). The average depth of accumulated soft sediment for the Barwon–Darling was 28 centimetres (approximately 4 per cent of average maximum waterhole depth in the Barwon–Darling). Waterholes in the Lower Balonne were shallower than the Barwon–Darling. What does this mean? Additional findings from sedimentation rate analysis will be provided in a supplementary report. Question 6. Can the persistence time of waterholes across the northern Basin be predicted using a generic model? Findings:
Table 7.1 Knowledge gaps and their corresponding outputs. Threat Effect on asset Knowledge gap Information required Information gathered Output Blank cell Blank cell Blank cell Distribution of refuge waterholes across catchments Remote sensed mapping of waterholes present in satellite images that captured no flow spells across the assessment reaches Comprehensive map of refuge and persistent waterhole locations across the northern Basin Blank cell Blank cell Blank cell Relationship between spell length and amount of waterhole habitat at the reach scale Remote sensing analysis of amount of wetted habitat in waterholes following no flow spells of a range of durations Relationship between spell length and available waterhole habitat was investigated Blank cell Blank cell Blank cell Water loss rate Depth change using data loggers Climate data Calibrated waterhole persistence models for scenario assessment. Maximum persistence times for assessment of consequence and incorporation risk assessment. Simple generic persistence measures for rapid estimates. Increase in no flow spell occurrence and duration Spells may exceed waterhole persistence time, causing local extinction of aquatic biota Waterhole persistence times in the target river valleys Waterhole shape and size Bathymetric mapping to develop a digital elevation model Blank cell Blank cell Blank cell Connection to groundwater 222Radon, conductivity and stable isotope sampling to detect groundwater inflow Blank cell Blank cell Blank cell Depth/Persistence relationship Comparison of depth/persistence relationship between river valleys and catchments Model to predict persistence using depth measurement
Change in the provision of sediment scouring flow events Sediment accumulation in waterholes, leading to reduced volume and persistence Sediment status of waterholes Amount of soft sediment in waterholes Sediment probing to establish depth profile of soft sediments Sediment profiles of representative waterholes Historical rate of sediment accumulation Aging of subsamples from sediment cores Analysis is ongoing. To be provided in a supplementary report. Blank cell Blank cell Effect of flows on sediment dynamics Identification of flow events or other conditions that lead to sediment infilling Analysis of sediment core stratigraphy and links to historical flow/climate data Analysis is ongoing. To be provided in a supplementary report. Identification and quantification of scouring capacity of flows Not covered in this project