Lake Illawarra Research Articles

Using Ocean Accounting towards an integrated assessment of ecosystem services and benefits within a coastal lake

Coasts lie at the interface between terrestrial and marine environments, where complex interrelationships and feedbacks between environmental, social and economic factors provide a challenge for decision-making. The knowledge and data needed to link and measure these multiple domains are often highly fragmented and incoherent. Ocean Accounting provides a means to organise relevant ocean data into a common framework, grounded in existing international statistical standards for national and environmental-economic accounting. Here, we test Ocean Accounting within Lake Illawarra, New South Wales (Australia), compiling accounts for the years between 2010 and 2020, inclusive, to measure the extent of coastal vegetation (mangrove, tidal marsh and seagrass) and associated ecosystem services flows (climate change mitigation, eutrophication mitigation) in physical and monetary terms and associated production and employment within sectors of the ocean economy. The accounts show an increase in mangroves by 2 ha and a decrease in seagrass of 80 ha. A net increase was observed in the amount of carbon, nitrogen and phosphorus sequestered across coastal vegetation, due to the expansion of mangroves. Alongside changes in ecosystem extent, a 2-fold increase in full-time ocean-related employment was observed. Fisheries catch also showed significant variation over the 10-year period, where dependencies were observed between commercial species with seagrass and tidal marsh. The relationships and measures derived from accounts provide a cohesive and integrated understanding to provide information for the management and standardised ecosystem service assessments.

Sediment dynamics at different timescales on an embayed coast in southeastern Australia

The concept of coastal sediment compartments has recently been adopted at a national scale in Australia to better understand sediment and shoreline dynamics and to underpin management of future shoreline behaviour in response to impacts of climate change. Geomorphological studies in southern NSW have provided a foundation for development of conceptual models of estuary and sandy barrier evolution. Geochronological reconstructions using radiocarbon, optically-stimulated luminescence, and other dating techniques, reviewed in this paper, demonstrate that adjacent compartments are at successive stages. Three compartments, Illawarra, Shoalhaven and Moruya, are compared, each with different catchment characteristics and different levels of human intervention. Landform change and sediment accumulation at millennial timescales enable estimates of past sediment accretion (vertical accumulation) and horizontal displacement of shorelines (particularly progradation), as a first step towards quantifying volumetric changes of morphology. Lake Illawarra is a barrier estuary at an early stage of infill, but land-use change, urbanisation, and engineering structures at the entrance have accelerated rates of sediment accumulation. The Shoalhaven River has infilled its estuary and delivers sand to the coast. It has been subject to several conspicuous anthropogenic interventions. At Moruya, ongoing supply of sand, primarily from offshore rather than from the catchment, has resulted in beach-ridge plains (strandplains) with changes in their alongshore inter-connectivity driven by differential embayment infilling. Millennial-scale geomorphology indicates landform change providing a means to determine natural trajectories of sediment transfer. However, variability is apparent at century and decadal timescales, compounded by various anthropogenic interventions. Disentangling natural and anthropogenic influences will be necessary to provide greater confidence in estimating past and present sediment budgets. Assessing sand sources and transport rates is important in relation to engineering interventions at entrances, and long-term resilience of coastal habitats. Such issues are the focus of coastal management programs, and this synthesis emphasises the relevance of a sediment budget approach to understand contemporary sediment pathways and provide an indication of future response to engineering interventions and sensitivity to climate change.

Holocene evolution and depositional model of a bayhead delta, Lake Illawarra, Australia

AbstractExtensive research into the evolution of wave‐dominated estuaries has been documented since the 1960s. However, there has only been limited research on the prograding bay‐head deltas that are the primary drivers for the rate and stage of estuary evolution. This paper presents the findings of a high‐resolution spatial study into the evolution of the Macquarie Rivulet bayhead delta in the Lake Illawarra barrier estuary. The delta’s evolution has been established based on sedimentological analysis of 74 cores, two14C ages and 45 amino acid racemization ages. This study intersected two Pleistocene and 10 Holocene sedimentary facies associations representing both the retrogradational and progradational phases of delta development. The distribution of bayhead delta facies associations in shallow barrier estuaries is initially controlled by the antecedent morphology, but, in contrast to deeper estuaries, this influence decreases as sedimentation proceeds. Changing relative sea level also has a major control on facies distribution with transgressive facies deposited as relative sea‐level rises being replaced by prograding deltaic facies during the highstand and subsequent minor relative sea‐level fall. Fluvial sediment supply and river flood events affect the rate of delta progradation, and produce low and high flow sediment deposits within the overall deltaic sequence. The low tidal flux in barrier estuaries, the muddy cohesive nature of the sediments and the prevalence of bioturbation means that primary sedimentary structures are rarely preserved in these bayhead delta facies. The depositional model of bayhead delta evolution shown by the Macquarie Rivulet delta would be widely applicable to other similar barrier estuary settings.

A methodological framework for reconstructing historical delta front morphology: case study at Macquarie rivulet delta within Lake Illawarra, Australia

Reconstructing past delta front morphology is a challenging task, due to complex morphological formation processes. We have developed a methodological framework to reconstruct the delta front morphology by integrating the information from historical shorelines, spatial distribution of depositional environments, relative sea-level changes and a modern Digital Elevation Model (DEM). The delta front morphology was reconstructed based on spatial connections between mud basin morphology, subaerial DEM and the historical shoreline. In addition, available sedimentation data at the delta front was utilized to aid in reflecting complex morphological formation processes. Taking Macquarie Rivulet delta within Lake IlIawarra, Australia, as an example, we generated the historical delta morphology for 1892. The modelled sedimentation rate appears to be consistent with the measured ones. We have also applied this method to reconstruct the historical morphology in 1938 and 1981. The model results indicate a progressive infilling influenced by switching river mouth locations. The cautions and implications of this method are also discussed. An increased resolution of sedimentation data should be able to improve the accuracy of the model. The reconstructed morphologies, elucidating fundamental information about delta evolution and sediment mass volumes in the past, can be employed in management activities.

Wind influence on the orientation of estuarine landforms: An example from Lake Illawarra in southeastern Australia

AbstractWe propose a type of a quasi‐equilibrium, which describes a convergence of the estuarine system towards a form whose planimetric orientation is along the prevailing winds. By using the microtidal Lake Illawarra in southeastern Australia as an example, we describe sediment convergent and divergent processes that induce such an equilibrium controlled by the complex configuration of the shoreline relative to the prevailing winds. For a complex estuarine sedimentary system with a mixture of non‐cohesive and cohesive sediments, alongshore distribution of fluvial or marine sand deposition and associated subaqueous morphology reflects alongshore redistribution of sediments from rivers and the tidal inlet. The orientation of the second‐order polynomial trend surface of estuarine morphology is consistent with prevailing wind directions. Along the lake shore, there are extensive narrow flats mainly covered by fluvial or marine sands shaped by the prevailing winds. The implementation of the Delft3D flow model coupled with the SWAN wave model driven by idealized prevailing winds indicates the potential of sediment convergent and divergent transport at the embayment and promontory shoreline, which appears to be similar to the alongshore distribution of sandy sediments and the nearshore flats. Alongshore transport of sandy sediments is primarily induced by the wave refraction on the shore, while the currents are more effective in transporting fine‐grained sediments such as mud or clay. Finally, we suggest a conceptual model that describes potential sediment transport of convergence and divergence on the embayment or promontory shoreline that is normal to the prevailing winds. Orientation of the estuary follows the convergence centre of sediment transport driven by the prevailing winds with the largest fetch. A quantitative threshold for such sediment redistribution may be determined in the future. © 2018 John Wiley & Sons, Ltd.

Using modelling to predict impacts of sea level rise and increased turbidity on seagrass distributions in estuarine embayments

Climate change induced sea level rise will affect shallow estuarine habitats, which are already under threat from multiple anthropogenic stressors. Here, we present the results of modelling to predict potential impacts of climate change associated processes on seagrass distributions. We use a novel application of relative environmental suitability (RES) modelling to examine relationships between variables of physiological importance to seagrasses (light availability, wave exposure, and current flow) and seagrass distributions within 5 estuarine embayments. Models were constructed separately for Posidonia australis and Zostera muelleri subsp. capricorni using seagrass data from Port Stephens estuary, New South Wales, Australia. Subsequent testing of models used independent datasets from four other estuarine embayments (Wallis Lake, Lake Illawarra, Merimbula Lake, and Pambula Lake) distributed along 570 km of the east Australian coast. Relative environmental suitability models provided adequate predictions for seagrass distributions within Port Stephens and the other estuarine embayments, indicating that they may have broad regional application. Under the predictions of RES models, both sea level rise and increased turbidity are predicted to cause substantial seagrass losses in deeper estuarine areas, resulting in a net shoreward movement of seagrass beds. Seagrass species distribution models developed in this study provide a valuable tool to predict future shifts in estuarine seagrass distributions, allowing identification of areas for protection, monitoring and rehabilitation.

History of metal contamination in Lake Illawarra, NSW, Australia

Lake Illawarra has a long history of sediment contamination, particularly by metals, as a result of past and current industrial operations and land uses within the catchment. In this study, we examined the history of metal contamination in sediments using metal analysis and 210Pb and 137Cs dating. The distributions of copper, zinc, arsenic, selenium, cadmium and lead concentrations within sediment cores were in agreement with historical events in the lake, and indicated that metal contamination had been occurring since the start of industrial activities in Port Kembla in the late 1800s. Most metal contamination, however, has occurred since the 1960s. Sedimentation rates were found to be 0.2cmyear−1 in Griffins Bay and 0.3cmyear−1 in the centre of the lake. Inputs from creeks bringing metals from Port Kembla in the northeast of the lake and a copper slag emplacement from a former copper refinery on the Windang Peninsula were the main sources of metal inputs to Lake Illawarra. The metals of highest concern were zinc and copper, which exceeded the Australian and New Zealand sediment quality guideline values at some sites. Results showed that while historical contamination persists, current management practices have resulted in reduced metal concentrations in surface sediments in the depositional zones in the centre of the lake.

Case study: Assessment of the entrance stability of the Lake Illawarra Estuary

Prior to completion of entrance improvements in 2007, Lake Illawarra behaved as an ICOLL (Intermittently Closed and Open Lakes and Lagoons) with entrance conditions dependent on prevailing conditions. Since construction of twin training breakwaters and dredging in 2007, the entrance has remained permanently open, with water level stations within the estuary recording an increasing tidal signal. This paper provides a case study describing methods to assess the stability of the entrance to Lake Illawarra through preliminary analysis of aerial photography, hydrosurvey, continuous water level records, consecutive tidal gauging and Escoffier analysis. Regarding the case study of entrance stability, consideration is given to data for analysis, limitations of the analysis and its reliance on local or site specific empirical data, needs for ongoing monitoring and tuning to represent further data, potential implications for Lake Illawarra and on similar estuaries and possible management responses. The likely effects of expected sea level rise on stability of the entrance are also estimated based on the understood key physical processes. Since completion of the entrance works, the lake is characterised by an 'unstable scouring' entrance as indicated by empirical analysis supported by lake water level and catchment rainfall data, tidal flow gauging, hydrosurveys and aerial photography. Ongoing monitoring and evaluation will determine further action that may be required.

Case study: Assessment of the entrance stability of the Lake Illawarra Estuary

Prior to completion of entrance improvements in 2007, Lake Illawarra behaved as an ICOLL (intermittently closed and open lakes and lagoons) with entrance conditions dependent on prevailing conditions. Since construction of twin training breakwaters and dredging in 2007, the entrance has remained permanently open, with water level stations within the estuary recording an increasing tidal signal. This paper provides a case study describing methods to assess the stability of the entrance to Lake Illawarra through preliminary analysis of aerial photography, hydro-survey, continuous water level records, consecutive tidal gauging and Escoffier analysis. Regarding the case study of entrance stability, consideration is given to data for analysis, limitations of the analysis and its reliance on local or site specific empirical data, needs for ongoing monitoring and tuning to represent further data, potential implications for Lake Illawarra and on similar estuaries and possible management responses. The likely effects of expected sea level rise on stability of the entrance are also estimated based on the understood key physical processes. Since completion of the entrance works, the lake is characterised by an ’unstable scouring’ entrance as indicated by empirical analysis supported by lake water level and catchment rainfall data, tidal flow gauging, hydro-surveys and aerial photography. Ongoing monitoring and evaluation will determine further action that may be required.

Phosphorus speciation and changes with depth in the sediment of Lake Illawarra, New South Wales, Australia

In order to better understand phosphorus (P) cycling and origins in the sediment of the Lake Illawarra, two sediment cores were extracted in November, 2010 and a modified sequential extraction scheme (SEDEX) was used to profile the exchangeable P (Pex), reactive Fe/Al-bound P (Preac), reductive Fe/Al-bound P (Predu), authigenic apatite P (Pauth), detrital P (Pdet), organic P (Porg) and residual P (Presi). The total sedimentary P (TP) ranged from 93 to 437 μg g−1, and was dominated by inorganic P. The average percentage of each fraction of P in the sediment followed the sequence: Preac (28.6 %) > Presi (23.5 %) > Pauth (19.1 %) > Predu (17.0 %) > Porg (4.9 %) > Pex (4.7 %) > Pdet (2.2 %). The profiles of TP and Porg showed two peak values with depth, which were matched to land use history in the Lake Illawarra catchment. The sediment depth profiles indicated that Fe oxyhydroxides play a predominant role in the P cycle in the sediments of the lagoon. This is supported by significant positive correlation between Preac and reactive Fe and a negative correlation between Pauth and Fe. Pauth and Preac concentrations were also well negatively correlated, possibly a result of competitive equilibrium between Fe and Ca for P. The estimated P burial efficiency was up to 82 % for this lagoon, which is likely related to the high sediment accumulation rate and the high value of R Fe-P. In addition, the bioavailable P, which consists of Pex, Preac, and Porg, represented a significant proportion of the sedimentary P pool, accounting, on average, for 38 % of the TP. This result indicates that the sediment is a potential internal source of P for this lake ecosystem.

Phytoplankton assemblages of two intermittently open and closed coastal lakes in SE Australia

Species composition and biomass of phytoplankton assemblages of a heavily impacted lake (Lake Illawarra) and a less impacted lake (Burrill Lake) in the South-Eastern region of Australia were compared based on bimonthly samples from three sites in each lake collected between April 2005 and April 2007. Lake Illawarra was generally characterized by higher nutrient concentrations and lower salinity than Burrill Lake. Phytoplankton assemblages displayed significant differences between the two lakes in terms of the dominant species composition and patterns of seasonal change rather than biomass. Diatoms were the dominant species in Lake Illawarra on most sampling occasions. In contrast, dinoflagellates (including toxic species) dominated in Burrill Lake during most seasons. Seasonal succession of phytoplankton in the two lakes did not follow the strict spring maximum that is generally observed in temperate waters. In Burrill Lake, maximum phytoplankton biomass often occurred in winter, while the maximum biomasses in Lake Illawarra occurred in autumn, winter and spring. The significant difference of nutrient structure between two lakes and warm temperate regime was regarded as important factors to affect these results. The results suggested care should be taken when relying on estuary health “indicators”, such as chlorophyll a, rather than more detailed investigations of phytoplankton species compositions.

Matrix-bound phosphine in sediments from Lake Illawarra, New South Wales, Australia

Matrix-bound phosphine (MBP) has been measured in sediment from two cores in Lake Illawarra on the south east coast of Australia. The sediments were also dated in the upper layers. MBP concentrations found range from 142 to 1813ngkg−1, dw (dry weight of sediment) with some values being amongst the highest ever measured. Values of MBP in deeper sediments were higher than for near surface samples, but the patterns with depth were not consistent. Strong correlations were noted between MBP and organic phosphorus (OP, r>0.8) and with total phosphorus (TP, r>0.7), but only moderate correlations were found with organic carbon (OC, r>0.5). No correlations were found between MBP concentrations and the age of the sediments. It was confirmed that high MBP concentrations are indicative of a phosphorus rich environment. The results tend to support the premise that MBP is generated by microbial attack on OP under anaerobic conditions.

Contrasting sedimentation rates in Lake Illawarra and St Georges Basin, two large barrier estuaries on the southeast coast of Australia

Sedimentation rates over the last 100 years within two lagoons on the southeast coast of Australia, Lake Illawarra and St Georges Basin, have been quantified to determine the effects of catchment land use change and native vegetation clearance on infill rates, and spatial variations in the rate at which the estuaries have filled. Both catchments have similar lake and catchment area but have experience different degrees of modification due to land clearing for agriculture practices, urbanisation and industrialisation. Results indicate that in the heavily modified catchment of Lake Illawarra sedimentation rates close to fluvial deltas can be in excess of 16 mm/year, and between 2 and 4 mm/year in the adjacent central basin. This is approximately an order of magnitude greater than the pre-European rates. In contrast, at St Georges Basin, where the catchment has experienced much less modification, sedimentation rates in the central basin appear to have remained close to those prior to European settlement. However, sedimentation rates in the urbanized margin of St Georges Basin are relatively high (up to 4.4 mm/year). This rapid modern sedimentation in the margin of the estuarine embayments has been detected in several other estuaries in the region. However the degree of sedimentation within the bay-head deltas, and more significantly in the central basin appears proportional to the degree clearance of native vegetation (forest) in the catchment, urban expansion and development of heavy industry in the respective catchment areas.

Analysis of macrobenthic assemblages of Lake Illawarra, New South Wales, Australia

1 - A survey of the macrobenthos community was carried out in Lake Illawarra, NSW, Australia, during April and May 2011. 2 - The aim of this study was to understand the current status of the characteristic macrobenthic fauna community, and the temporal changes over the past 30 years, as well as the impacts of anthropogenic activities on the benthic ecosystem. 3- Fifteen stations were selected as representative of three main areas of the lake (the entrance channel, the central basin and the sublittoral fringe), which might be impacted by different kinds of human activities. 4 - A total of 45 macrobenthic species were identified. Mollusca represented the most abundant taxon with 17 species, followed by Crustacea with 16 species. Three species were dominant, i.e., the mollusk Nassarius burchardi, and the polychaeta Lumbrineris sp. and Nephtys australiensis. 5 - The abundance and biomass of the macrobenthos were variable between the three main areas. Based on Bray Curtis similarity of macrobenthos, the 15 sites also divided largely into three groups. 6 - M-AMBI index analysis indicated that eight stations (57.1%) had ‘good’ to ‘high’ ecological status (EcoQ), four stations (28.6%) ‘moderate’ EcoQ, and two stations (14.3%) with ‘poor’ to ‘bad’ EcoQ, which indicates the Lake Illawarra was in reasonably good condition, but evidence of disturbance and impact on benthic communities was obvious at several sites.

Foreshore vegetation of Lake Illawarra.

Lake Illawarra is located approximately 8km south of Wollongong. The Lake is a coastal lagoon formed as a result of the change in ocean level during the Pleistocene period. The last rise in sea level was dated 6000-6500 years ago and since the time of submergence, the area of the Lake has decreased about 17% and sedimentation has filled out about 90% of the original basin. The present Lake is linked to the sea via an entrance channel 3.2km long, the mouth of which changes continuously in position, shape, depth and width, depending on rainfall, wind and wave action. Consequently, lake-ocean exchange is restricted and there is very little tidal effect extending into the Lake (see Figure 1).

The seagrasses of Lake Illawarra, New South Wales.

Ecological studies on seagrasses and seagrass communities in eastern Australia date back only as far as those of Wood (1959a, b). The most detailed studies in New South Wales have been made on the central coast lakes, Lake Macquarie (see King 1986, for references) and Tuggerah Lakes (see King & Holland 1986). Detailed studies in those lakes over five years (King & Hodgson 1986) showed that in terms of the area occupied by seagrasses, species composition of the communities, and the biomass of the eelgrass Zostera capricorni Ascherson, there are marked fluctuations which cannot be correlated easily with seasonal or environmental changes. Such variation appears to be inherent in the nature of seagrass communities but has not often been properly documented. In some cases aerial photographs can be used to give an overview of the (recent) history of the distribution of seagrass beds but without concurrent field survey there is no information on species present or biomass. The biota of Lake Illawarra is of special interest, not only because it is in a region of rapid urbanisation with associated recreational use, but also because of proposals to refurbish and upgrade the existing Tallawarra Power Station. Lake Illawarra is already subject to environmental problems, especially eutrophication which has resulted in excessive algal growth (LIMC 1986b), but while this is a major immediate problem the most severe long-term concern is with the infilling of the lake (LIMC 1986a). Lake Illawarra has, as a consequence, been the subject of a range of intensive studies most of which are summarized in the ‘Environmental Audit’ (SPCC 1986).

Thermal pollution and algal growth in the Tuggerah Lakes.

Abundant growth of ‘weed’ and its accumulation and decomposition in inshore waters and on the shoreline are seen as increasing problems in estuaries and lakes in regions of expanding populations. The weed may be visually unacceptable, become malodorous as it decomposes, and can considerably reduce the amenity value of the water-way if it interferes with activities such as swimming and boating. In Australia, the phenomenon has been studied in detail in the Peel-Harvey estuarine system in Western Australia (Hodgkin et al. 1985) and the Swan River estuary (John 1987). In New South Wales, Yassini (1985) has provided an overview of the problem of algal growth in Lake Illawarra. In Tuggerah Lakes on the central coast of New South Wales, the problem of excessive weed growth is one of the problems being tackled by Wyong Shire Council in relation to the overall management of the lake system. In this case, as elsewhere in Australia, the weed problem is due to macroalgae (seaweeds) and not aquatic angiosperms (seagrasses). There is no evidence of an explosion in seagrass growth in the last 20 or so years, though there have been changes in the overall distribution (See King & Hodgson 1986, and King & Hodgson 1986 for relevant literature). When the Munmorah Power Station was planned, algal growth was not perceived as a likely outcome of power station operation but seagrasses were studied because of suggestions that the growth of particular ‘reeds’ would accelerate, thereby reducing the cooling field and potentially offering resistance to the pumping of water through the lake. This possibility has not been realised in the 21 years of power station operation.

Community Valuations of Environmental Quality in Coastal Lakes: Lake Illawarra Case Study*

This is the first Australian study to apply the hedonic pricing method to value environmental quality of an urban water body. It demonstrates the technique using a case study of a degraded urban lake that is currently undergoing a programme of water quality restoration and foreshore improvements. The results show that the community places significant value on proximity to the lake and on waterfront location. A range of other data was also generated that adds to the usefulness of this approach for general planning purposes. It is suggested that this technique would be a useful tool to aid in the allocation of public funds among competing environmental improvement projects.

Jellyfish modify the response of planktonic assemblages to nutrient pulses

The short-term effects of pulses of nutrients and jellyfish Catostylus mosaicus on planktonic assemblages were investigated in field-based experiments using 3 m3 mesocosms. Experiments ran for 5 d and were repeated in autumn and spring at Lake Illawarra, a coastal lagoon in New South Wales, Australia. Experiments consisted of 2 orthogonal treatments, addition/non-addition of nutrients and presence/absence of jellyfish, and were designed to determine how bottom-up (i.e. addition of nutrients) and top-down (i.e. predation by jellyfish) processes influence planktonic assemblages, both independently and in combination. During both experiments, nutrients stimulated primary production and caused changes in phytoplankton assemblages. Nutrients also stimulated production of large tintinnids, suggesting that bottom-up processes may influence 2 trophic levels. Mesozooplankton were consistently depleted in mesocosms containing jellyfish. Jellyfish also caused changes in microzooplankton assemblages, indicating that top-down processes also cascade to at least 2 trophic levels. In mesocosms to which both nutrients and jellyfish were added during spring, concentrations of the red-tide forming, heterotrophic dinoflagellate Noctiluca scintillans were 20 times greater than in mesocosms to which nutrients were added alone. We hypothesize that addition of nutrients stimulated production of centric diatoms, the main prey of N. scintillans, but that a bloom of N. scintillans only formed when jellyfish were also present because jellyfish grazed on populations of herbivorous mesozooplankton (particularly the calanoid copepod Gladioferens), which generally out-competed N. scintillans for diatom prey. These data provide the first empirical evidence linking jellyfish to the formation of red tides.

Assessing the recent (1834 – 2002) morphological evolution of a rapidly prograding delta within a GIS framework: Macquarie Rivulet delta, Lake Illawarra, New South Wales

The recent morphological evolution of Macquarie Rivulet delta, Lake Illawarra, New South Wales, has been assessed from historical parish maps from 1834, 1892, 1916 and 1927 along with aerial photographs from 1938 to 2002. These images were digitised, georeferenced and analysed in a GIS framework. The 1834 sketch map could not be georeferenced and it was excluded from the calculation of delta progradation areas. Between 1892 and 1927 morphological changes were minimal, probably because the areas were not resurveyed between these map editions. A significant change in morphology between 1927 and 1938 reflects a change in source material from maps to aerial photographs. The research highlights that great care must be taken when utilising historical data. Major morphological changes observed between 1938 and 2002 included the development of a large crevasse splay in the 1960s to 1970s and the abandonment and infilling of the delta's previously active distributary channels. The research shows that the morphological changes observed on the delta can be related to both natural processes and anthropogenic modifications to the catchment and thus could be used in the development of catchment management plans.