River In South-eastern Australia Research Articles

A large-scale field experiment across six rivers illustrates how the effects of resource enrichment are context dependent

Resource supplementation can increase species richness and change the faunal composition of communities, but experiments have produced variable outcomes. An often overlooked element is that species richness can only increase if new taxa can disperse to resource-rich locations and invade established, local communities. We experimentally increased a basal resource (detritus) in six rivers in south-eastern Australia by driving wooden stakes into the riverbed to increase retention of detritus. Control sites were left untreated. Sites were located in agricultural sections with mostly cleared vegetation, but with intact (uncleared) reference sites upstream to provide sources of prospective colonists. We measured channel retentiveness and sampled benthic detritus and invertebrates before and after manipulation. We tested whether: greater retentiveness increased detritus densities, species richness and abundances and altered faunal composition; manipulation sites reached bio-equivalence with reference sites; new species arose from upstream reference areas; and whether outcomes were consistent across rivers. Only three rivers gained increases in detritus densities. All had low pre-existing amounts of in-stream wood compared with rivers that did not respond to treatment. Two rivers (Hughes Creek, Seven Creeks) gained higher species richness and invertebrate densities within 12 months and reached bio-equivalence with reference sites. In contrast, Turtons Creek showed species turnover through replacement of individuals. Only in Hughes Creek was there evidence of successful dispersal from the upstream reference area. The outcomes show that the effects of resource supplementation vary between rivers and suggest that pre-existing conditions (e.g. channel retentiveness) may cause these differences, providing clear evidence of context dependence.

Trends in post‐1950 riparian vegetation recovery in coastal catchments of NSW Australia: Implications for remote sensing analysis, forecasting and river management

AbstractExtensive riparian vegetation clearance occurred in many rivers of southeastern Australia throughout the 19th and 20th century, post colonisation. With improvements in river management practices, coincident with a period of minimal flooding, vegetation recovery of riparian corridors has been occurring since the 1980s in all coastal catchments of New South Wales (NSW). However, the catchment‐by‐catchment spatial pattern and temporal trends, trajectories and rates of vegetative recovery remain unknown. We reconstruct a 70‐year time series of change in riparian vegetation coverage for all rivers in coastal catchments of NSW, utilising historical aerial imagery, Landsat and Sentinel data and a manual digitisation and machine learning method. We quantify and statistically analyse decadal trends in woody and non‐woody vegetation coverage along 19 485 km of stream length in 20 catchments. Across the region, there has been, on average, a 40% increase in vegetation coverage along riparian corridors since the 1950s, with some catchments increasing towards a current day coverage of between 60% and 80%. However, the trends vary by subregion and by catchment. An early logarithmic increase occurred up to 2004 on the North coast, and a recent and accelerated exponential increase since 1995 has occurred on the South coast. After a steep initial increase, riparian corridor vegetation coverage has fluctuated on the Central coast since about 1995. We used these linear, exponential and logarithmic regressions to undertake preliminary forecasts of possible future timeframes of riparian vegetation change, based on several climate, management and natural disaster disturbance scenarios. If the current trend continues, riparian vegetation coverage can reach 70% across the region by 2055. However, if management practices change or catastrophic disturbance events such as fire and flood occur, increases in riparian vegetation coverage could be set back by up to 30 to 40 years.

Snowy River environmental flows post-2002: lessons to be learnt

In 2002, the Australian, New South Wales and Victorian governments agreed to the Snowy Water Inquiry Outcomes Implementation Deed for environmental flows to (in part) restore the health of the Snowy River in south-eastern Australia. This was the first legally binding commitment to deliver annual environmental flows in Australia. Twenty years on, we assess this Deed and its implementation to derive lessons that can inform environmental flows agreements globally. Information from governance documents, flow release data and interviews with stakeholders are used to evaluate the effectiveness of the Deed. The target of 212 GL year−1 from 2012 has not once been reached. In turn, we find that implementation has been hindered by release of too little water, overly complex institutions that lack ownership and accountability, and no provision for review of the Deed. The lessons for effective environmental flow institutions are: (a) set clear, science-based environmental restoration objectives with stakeholders; (b) make roles and responsibilities for implementation clear; (c) enable independent and transparent monitoring, reporting and regulation; and (d) undertake periodic review to incorporate new knowledge, and to adapt to climatic and other unanticipated changes.

How fish kills affected traditional (Baakandji) and non-traditional communities on the Lower Darling–

In the summer of 2018–19 mass fish kills occurred in the Lower Darling (Baaka) River in south-eastern Australia. The fish kills received national and international attention and have been the focus of numerous government agency and independent assessments. Although fish kills have previously been recorded in the Lower Darling region, the size and rapid succession of the 2018–19 ‘Menindee’ fish kills made them unprecedented in the Murray–Darling Basin, placing significant pressure on the native fish community. Although the deaths of millions of fish were documented, the significant negative effect that the fish kills had on local communities, particularly the traditional Baakandji people, was largely ignored. The social and cultural aspects of such events can have major non-economic effects on local communities. In this paper we document heart-felt feelings conveyed by local community members. Their sense of loss, despair and helplessness is compounded by frustration regarding water management and policy decision making in the Murray–Darling Basin. However, these tragic events have increased understanding of traditional Baakandji connection to the river and its fish and, together with local recovery efforts, now provide prospects for enhanced community and agency cooperation to improve the health of the lower Darling Baaka River and restore its native fish populations.

The morphology and geomorphic evolution of a large chain‐of‐ponds river system

AbstractRivers with discontinuous watercourses are part of the spectrum of river diversity. Chain‐of‐ponds types contain irregularly spaced, steep‐sided ponds that are separated by preferential flow paths on swampy valley fill. They often contain endangered ecological communities and are receiving greater attention for conservation and restoration. Very little is known about how these river types form, how they have evolved and how they function. Here we present the Late‐Quaternary evolution of one of the last remaining large‐scale chain‐of‐ponds systems in Australia, the Mulwaree Ponds. The chain‐of‐ponds was fully formed by 4.5 ka, with the position and alignment of the ponds being related to the position of pools of a palaeo‐river that is up to 100 ka old. Contemporary hydrogeomorphic processes are insufficient to create the ponds, but sufficient to maintain and keep them open. The phases of evolution for this chain‐of‐ponds system are synchronous with Late‐Quaternary changes in fluvial activity documented for other rivers in southeastern Australia. The ponds at Mulwaree have significant preservation potential over thousands of years. In the current landscape they are rare forms, providing significant grounds for conservation and protection of their distinctive geodiversity. © 2020 John Wiley & Sons, Ltd.

Comparison of historical and modern river surveys reveal changes to waterhole characteristics in an Australian dryland river

Human activities are known to impact the physical template of river channels. These impacts can result from deliberate, direct modifications as well as via indirect processes linked to broadscale landscape change. This study examined changes in the physical template of the Barwon-Darling River, a dryland river in southeastern Australia. Historical longitudinal profiles from the late 1800s were compared with contemporary profiles derived from high-definition, side scanning sonar. Comparisons focused on characterising waterhole features as they are a critical biophysical component of dryland rivers. The use of historical data presented several challenges related to small sample size and suspected sampling bias in the historical survey. However, this study demonstrates that these issues are not insurmountable providing the limitations and uncertainties with the data are acknowledged and data analyses are limited to parameters that can distinguish genuine landscape change. The findings revealed a dramatic change in the physical template of the Barwon-Darling River over a 120-yr period. Waterhole depths and distances between waterholes have been altered significantly. The magnitude and trajectory of change was found to be scale-dependent, with the greatest observable change aligned with the presence or absence of low-level weirs. Waterholes influenced by low-level weirs have increased in depth because of localised impoundment, whilst the distance between deep waterholes (>4 m in depth) has declined substantially. In contrast, the maximum depths of waterholes located outside the influence of weir pools has declined by 1.6 m and the distance between deep waterholes has more than doubled in several reaches. These declines are likely to be caused by sediment accumulation in waterholes associated with anthropogenic increases in sediment flux and a decline in the river's capacity to entrain and transport sediment throughout the system.

Acknowledging the agency of a more-than-human world: material relations on a Snowy River journey

In this article we describe our attempt to challenge our anthropocentric gaze during an outdoor environmental education (OEE) research project involving a 10-day journey with high school students on the Snowy River in south-eastern Australia. Although much contemporary OEE research explores place responsive methodologies that provide possibilities for expanding beyond human centered practices, such movements can be difficult to make. We attempt, through this project, to shift our gaze away from a human-centered viewpoint to understand ways in which new perspectives of journeys, place(s) and learning might be available. To do this we adopt a posthuman/relational materialist approach to explore how the material world is creative of places, people and learning opportunities beyond human centered ways of seeing. We argue for a focus on the more-than-human aspects of places and engage posthuman concepts that allow us to challenge traditional ways of researching. In doing so we seek to uncover and acknowledge the agency of the more-than-human world, and how material places and their elements are valuable in the creation of emergent learning possibilities on an OEE journey. Rather than exact findings, this article is an exploratory journey of thinking OEE in different ways, to explore new opportunities for place and context responsive learning and environmental understanding.

Effects of tag type, morphological location and tagger experience on tag retention rates in freshwater fishes

Mark–recapture of fish is often used to inform fisheries or conservation management. Given that variability in tagging efficiencies can affect estimates of population size, it is important that rates of tag rejection are quantified. We double tagged over 45000 large-bodied, long-lived fish in a turbid lowland river in south-eastern Australia. During yearly recapture fish surveys, data on tag rejection were collected. We found that the probability of tag rejection varied as a function of fish species, tag type and tagger experience. Floy tags were more likely to be rejected as dart tags in large-bodied golden perch Macquaria ambigua (6 and 3% respectively), silver perch (18 and 4% respectively) and trout cod (19 and 7% respectively), whereas rates of rejection in the large-bodied Murray cod Maccullochella peelii were similar for both tag types (12 and 10% respectively). More experienced taggers had lower rates of rejection, which varied between 1 and 48% for individual taggers. We trialled three morphological locations for passive integrated transponder (PIT) tagging of fish, with rejection rates lowest for tags implanted in the stomach cavity and highest for those implanted in the pectoral musculature. This study presents the first tag rejection rates for dart, floy and PIT tags for lowland Australian river fish, information that can help guide future monitoring programs.

Sequential fishways reconnect a coastal river reflecting restored migratory pathways for an entire fish community

River regulation infrastructure has been implicated in worldwide aquatic biodiversity loss. In‐stream barriers such as weirs prevent fish migration and the impact can be particularly severe for diadromous species. Fishways are frequently installed on in‐stream barriers to reconnect migratory pathways and rehabilitate diadromous fish populations. Sequential fishways may be necessary in rivers where multiple barriers prevent migration. We monitored a coastal fish community's response to fish passage restoration at 10 predominantly low‐level weirs in the freshwater reaches of the Nepean River in southeastern Australia. Few studies have simultaneously assessed fish community passage at successive fishways within a river system. Prior to the installation of the fishways, there was a gradient of reduced species diversity in an upstream direction including the absence of many diadromous species, despite the regular inundation frequency of most weirs. Following the installation of the fishways, species diversity was still greater in the downstream monitoring sites; however, there was evidence of a positive change in fish community structure in middle and upstream sites. Most notably, three diadromous species rapidly expanded their distribution upstream and one amphidromous species expanded its downstream distribution. This study demonstrates appropriately designed successive fishways can successfully reconnect river systems for an entire fish community, encompassing species with a broad range of swimming abilities and diverse life histories.

Habitat use and movements of Australian grayling (Prototroctes maraena) in a Victorian coastal stream

Riverine fishes are among the most imperilled fauna in the world; however, for many species, there is little or no understanding of their ecological requirements. The Australian grayling (Prototroctes maraena) is a small diadromous fish endemic to rivers in south-eastern Australia that has declined considerably in range and abundance and is listed as threatened nationally. To improve understanding of the species’ movement ecology and to inform the development of conservation management actions, we examined the day-to-day movements and habitat use of Australian grayling (n=7) over 8 weeks by using radio-telemetry. Tagged individuals of Australian grayling typically occupied restricted (i.e. tens to hundreds of metres) reaches of stream, and were mostly located in moderate- to fast-flowing habitats (i.e. glide or run), although, at night, use of slower-flowing habitats (i.e. pools) increased. They also undertook longer-distance downstream movements during a period of increased streamflow. Incorporation of such information into management strategies has the potential to improve our capacity to maintain or re-instate the conditions required to conserve and restore Australian grayling populations.

Clonality disguises the vulnerability of a threatened arid zone Acacia.

Long‐lived, widespread plant species are expected to be genetically diverse, reflecting the interaction between large population sizes, overlapping generations, and gene flow. Such species are thought to be resilient to disturbance, but may carry an extinction debt due to reproductive failure. Genetic studies of Australian arid zone plant species suggest an unusually high frequency of asexuality, polyploidy, or both. A preliminary AFLP genetic study implied that the naturally fragmented arid zone tree, Acacia carneorum, is almost entirely dependent on asexual reproduction through suckering, and stands may have lacked genetic diversity and interconnection even prior to the onset of European pastoralism. Here we surveyed microsatellite genetic variation in 20 stands to test for variation in life histories and further assessed the conservation status of the species by comparing genetic diversity within protected stands in National Parks and disturbed range lands. Using herbarium records, we estimate that 219 stands are extant, all of which occur in the arid zone, west of the Darling River in southeastern Australia. With two exceptions, all surveyed stands comprised only one multilocus genet and at least eight were putatively polyploid. Although some stands comprise thousands of stems, our findings imply that the species as a whole may represent ~240 distinct genetic individuals, many of which are polyploid, and most are separated by >10 km of unsuitable habitat. With only 34% of stands (and therefore genets) occurring within conservation reserves, A. carneorum may be at much greater risk of extinction than inferred from on‐ground census data. Land managers should prioritize on‐ground preservation of the genotypes within existing reserves, protecting both vegetative suckers and seedlings from herbivory. Importantly, three stands are known to set viable seed and should be used to generate genetically diverse germ‐plasm for ex situ conservation, population augmentation, or translocation.

Sustaining recovery in red gum, black box and lignum in the Murray River Valley: clues from natural phenological cycles to guide environmental watering

ABSTRACTThe natural flow regime of the Murray River in south-eastern Australia has been fundamentally altered through regulation and extraction, with fewer, shorter floods, changing seasonality of flows and reduced floodplain connectivity. Ecosystems which evolved over millenia show serious stress and decline under the regulated regime. Environmental water allocations being returned to Murray Valley ecosystems to halt the decline and improve river health are not sufficient to re-create missing floods, but aim to mimic key elements of the natural water regime. For floodplain vegetation communities, the missing element is seasonal water availability to maintain condition of mature trees and trigger germination of seedlings. Dominant perennial vegetation species river red gum (Eucalyptus camaldulensis), black box (E. largiflorens) and lignum (Muehlenbeckia florulenta) suffered significant stress and death during the severe Millenium drought (2000–2010), but drought-breaking floods in 2010–2012 replenished soil moisture reserves. A new generation of seedlings germinated, and many environmental watering projects now focus on enhancing survival of these seedlings. Previous studies suggested that timing of phenological stages can indicate key timing for beneficial delivery of environmental water. These findings are being tested at Lower Murray Valley sites, to identify optimum timing for watering to support recovery in floodplain vegetation communities.

Sensitivity of the glochidia (larvae) of freshwater mussels (Bivalvia: Unionida: Hyriidae) to cadmium, cobalt, copper, lead, nickel and zinc: Differences between metals, species and exposure time

Freshwater mussels (Bivalvia: Unionida) are among the most threatened freshwater faunal groups worldwide. Metal contamination is one threat that has been linked to declining mussel population distribution and abundance. This study determined the sensitivity (valve closure) of the glochidia (larvae) of six species of Australian freshwater mussels to cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal rivers in south-eastern Australia (home to ~50% of the population), in a soft reconstituted freshwater (hardness 42mgCaCO3L−1; alkalinity 22mgCaCO3L−1 and pH7.0) over 72h. The sensitivity of each mussel species to each metal increased 2.5-fold with increasing exposure time from 24 to 72h. The most sensitive mussel species (Cucumerunio novaehollandiae), across all metals and exposure times, was ~60% more sensitive than the least sensitive species (Velesunio ambiguus). The relative sensitivity of glochidia to the six selected metals, across all mussel species and exposure times, was: Cu>Cd>Pb>Co=Ni>Zn. Glochidia were most sensitive to Cu and least sensitive to Zn. Quantitatively, the toxicity of Cu was 3-fold more than Cd, 8-fold more than Pb, 14-fold more than Co or Ni and 16-fold more than Zn. The cell surface binding affinities (conditional log K values) of Cd (range 6.65–6.94), Co (6.04–6.29), Cu (7.17–7.46), Ni (6.02–6.29), Pb (6.24–6.53) or Zn (5.96–6.23), pooled for all mussel species after 72h exposure, were positively related to metal sensitivity. The chronic no effect concentrations (NECs) of Cu, Ni and Zn were below (i.e. glochidia were more sensitive than) their national freshwater guideline values, indicating that freshwater mussels may not be adequately protected for these metals in urbanized coastal rivers within south-eastern Australia.

Adaptive Management of Return Flows: Lessons from a Case Study in Environmental Water Delivery to a Floodplain River.

For many floodplain rivers, reinstating wetland connectivity is necessary for ecosystems to recover from decades of regulation. Environmental return flows (the managed delivery of wetland water to an adjacent river) can be used strategically to facilitate natural ecosystem connectivity, enabling the transfer of nutrients, energy, and biota from wetland habitats to the river. Using an informal adaptive management framework, we delivered return flows from a forested wetland complex into a large lowland river in south-eastern Australia. We hypothesized that return flows would (a) increase river nutrient concentrations; (b) reduce wetland nutrient concentrations; (c) increase rates of ecosystem metabolism through the addition of potentially limiting nutrients, causing related increases in the concentration of water column chlorophyll-a; and (d) increase the density and species richness of microinvertebrates in riverine benthic habitats. Our monitoring results demonstrated a small increase in the concentrations of several key nutrients but no evidence for significant ecological responses was found. Although return flows can be delivered from forested floodplain areas without risking hypoxic blackwater events, returning nutrient and carbon-rich water to increase riverine productivity is limited by the achievable scale of return flows. Nevertheless, using return flows to flush carbon from floodplains may be a useful management tool to reduce carbon loads, preparing floodplains for subsequent releases (e.g., mitigating the risk of hypoxic blackwater events). In this example, adaptive management benefited from a semi-formal collaboration between science and management that allowed for prompt decision-making.

Impoundment constraint of fish niche diversity in a temperate Australian river

Dams constitute a major threat to aquatic ecosystems world-wide by modifying habitat and impairing opportunities for many freshwater fish. Subsequently, there can be a loss in fish diversity and change in the species distributions and population structure that ultimately contribute to changes in trophic structure and ecosystem function. In this study, stable isotope analysis (SIA) was used to compare trophic interaction and niche space of five fish species residing upstream and downstream of a significant barrier (Tallowa Dam) on the Shoalhaven River in south-eastern Australia. Significant reduction in niche space was found among predator/prey species residing in upstream habitat, implying limited dietary opportunity. Mixing calculations for Macquaria novemaculeata confirmed ontogenetic differences upstream and downstream of the dam. Causal mechanisms for this variability in trophic structure include habitat modification and/or discontinuity in river connectivity. SIA provides a useful tool for demonstrating the effect of barriers and/or impoundments on aquatic ecosystems, and for developing future monitoring programmes to evaluate restoration strategies.

Spatial partitioning in the use of structural woody habitat supports the cohabitation of two cod species in a large lowland river

Many freshwater fish worldwide have been shown to use Structural Woody Habitat (SWH) for a variety of reasons. The mid reaches of the Murray River, a large lowland river in south-eastern Australia, was surveyed by boat electrofishing, to investigate the use of SWH type (hollows, rootmass and solids), SWH distance to bank (near bank, intermediate to bank and mid-channel) and the interaction between SWH type and distance to bank. The study found that Murray cod catch per unit effort (CPUE) increased in near-bank areas when hollows were a component of the SWH. The CPUE of trout cod was higher when hollows were present. However, the interactions between distance to bank and hollow SWH were complex and dependent on presence or absence of rootmass. The species-specific interactions between SWH microhabitat and distance to bank found within this study has important relevance for stream managers. The common practice of realigning SWH favours Murray cod over trout cod, which could have negative consequences for the endangered trout cod. More broadly, managers may need to consider a balance of SWH type and where it is placed in the river for the species they are targeting when rehabilitating rivers via the introduction of SWH.

Predicting natural instream woody-habitat loads across large river networks

Past waterway management practices worldwide involved extensive removal of instream woody habitat (IWH) and riparian vegetation. The importance of instream woody habitat for healthy aquatic ecosystems has now been recognised, with management approaches reversed to reintroduce instream woody habitat and replant riverbanks. Knowledge of natural or pre-disturbance IWH loads is useful to guide such restoration programs; however, such datasets are often unavailable. In this study, natural IWH loads were mapped along 105km of undisturbed rivers in south-eastern Australia. This field dataset was modelled, using boosted regression trees, against geomorphic, environmental and climatic variables to predict natural IWH loads in rivers across Victoria. Mapped natural IWH loads averaged 0.029m3m–2 (±0.005), ranging from 0.083 to 0.002m3m–2. Natural IWH volumes were predicted to range from 0 to 0.102m3m–2. Distinct IWH loading trends were noticeable over larger spatial scales. Eastern Victoria showed relatively lower natural IWH loads than did western Victoria. Because many stream restoration efforts do not have a quantifiable knowledge of natural IWH load, the results of the present study provide some guidance. The predicted IWH loadings are a useful first step in identifying broad areas for further investigation and a natural condition base for current IWH condition modelling.

Accumulation of sulfidic sediments in a channelised inland river system, southern Australia

Accumulation of sulfidic sediments in freshwater environments is a relatively recent phenomenon and an emerging environmental issue. In the present study, benthic sediments along short (~250m) reaches of an inland freshwater river in south-eastern Australia were examined to determine the abundance and vertical distribution of fine-grained organic sulfidic sediments, identified by acid volatile sulfide (AVS) and chromium-reducible sulfur (SCR) contents. Sulfidic sediments (up to 404mmolkg–1 SCR) preferentially accumulated in zones immediately overlying coarse sandy bed material. Conversely, where bed material was clay or silt dominated, comparatively limited sulfidic sediment had accumulated (where AVS and SCR were not detected). This suggests that the hydraulic conductivity of the underlying bed material could play a role in the formation of sulfidic sediments and that the overlying water column is not the sole source of SO42–. Evidence suggests that accumulation of sulfidic materials occurred preferentially downstream of channel obstructions, such as submerged logs or in scour pools. However, sediment accumulation was not limited to lower-energy parts of the channel, as would be expected for fine-grained organic sediments. Evidence of reworking, burial or sulfide formation at depth highlights the dynamism of the system and its differences to many coastal systems where these sediments are commonly found.

The Use of Evolutionary Trajectories to Guide ‘Moving Targets’ in the Management of River Futures

AbstractRiver histories provide important guidance with which to inform river management. Evolutionary trajectories and appraisals of system responses to changing flux conditions and disturbance events can be used to determine the range of potential future states and associated behavioural regimes, assessing the likelihood that that these states will be attained over a given timeframe. In these analyses, natural or historical reference reaches may not provide a realistic basis to set target conditions for management actions, as what has gone before does not necessarily provide a complete and reliable picture of prospective future conditions. This paper outlines the use of a conceptual tool, the river evolution diagram, as a geomorphic platform to assess river history and the potential range of river futures for any given system. Evolutionary adjustments of a sand bed river in southeastern Australia are used to demonstrate the application of this approach. Applying adaptive management principles, ‘moving targets’ for river management are framed in relation to the range of likely future states and trajectories of adjustment. Copyright © 2015 John Wiley & Sons, Ltd.

Response of the Snowy River Estuary to two environmental flows

The Snowy River is a major river in south-eastern Australia, discharging to the Tasman Sea via a barrier estuary, with its entrance constricted by marine sands. Since the construction of the Snowy Mountains Scheme, river flows have not been sufficient to maintain the river channel. A program of environmental flow releases (EFR) is returning water to the river to restore the fluvial reaches and is now trialling flow regimes that may also benefit the estuarine reaches. This paper documents the response of the estuarine segments of the Snowy River to two EFRs; the release in 2010 was designed to scour the upper reaches of the Snowy River while the larger 2011 release was intended to extend the scouring downstream. For each release, the effects on the entrance morphology, tides and salinity through the flow peak and recovery are described. Each EFR caused minor increases in depth and very minor longshore movement of the entrance channel, although each EFR had been preceded by a larger fresh flow that would have scoured the channels. The small increase in fresh water inflow in the 2010 EFR pushed salinity contours seawards and steepened vertical salinity gradients. The larger inflow in the 2011 EFR purged the upper estuary of saltwater. After the peak flow, salinity recovery was rapid in the principal estuarine channels but took weeks where poorly connected wetlands could store fresh flood waters. Critical flows for scouring the entrance and purging salinity are estimated.