The bedrock topography and origin of Broken Bay, N.S.W.

Albani, A. D.; Johnson, Bruce D.

doi:10.1080/00167617408728846

Cited by 20 publications

(17 citation statements)

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“…The conductivity-depth section also identifies an area of sediment (marker D,Figs 12,13) in the Pittwater area. This sediment deposit is consistent with the results of a study by Albani and Johnson (1974), which identified a steepsided V-shaped bedrock channel in Pittwater that reached the sea through the Palm Beach tombolo, with a depth of approximately 50 m in Pittwater. This feature is referred to as the Pittwater paleovalley.…”

Section: Figure 13supporting

confidence: 90%

“…This feature is referred to as the Pittwater paleovalley. The contour data presented by Alabani and Johnson (1974) is very sparse and did not warrant digitization and gridding and is therefore not represented in Fig. 13.…”

Section: Resultsmentioning

confidence: 99%

“…Between L8010 and L8235, the deepest section of the Hawkesbury paleovalley is estimated to be approximately 140 m below sea level, gradually deepening to 190 m as the paleovalley progresses seawards (Albani et al 1988). Southeast of Barrenjoey Head, the Pittwater paleovalley that lies to the south of the larger Hawkesbury paleovalley is evident (Albani and Johnson 1974).…”

Section: Resultsmentioning

confidence: 99%

“…The Pleistocene lowering of the sea level enabled the existing valleys to be further eroded by coastal streams, which in the case of the Hawkesbury River, led to excavations exceeding depths of 125 m below present sea level. At the end of the Pleistocene, the eustatic rise of the sea level resulted in the drowning of the estuary, accompanied by the redistribution of unconsolidated sediment that was present offshore and which now presently fills the seaward portion of the drowned valleys (Albani and Johnson 1974). Figure 2 shows a section of the 2 m bathymetric contour and sediment distribution chart draped over the gridded bathymetry data, obtained by digitizing the depth contours on this chart.…”

Section: B R O K E N B a Y T R I A L S I T Ementioning

confidence: 99%

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An investigation of seawater and sediment depth using a prototype airborne electromagnetic instrumentation system – a case study in Broken Bay, Australia

Vrbancich¹

2009

Geophysical Prospecting

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A B S T R A C TPrevious studies using commercial airborne electromagnetic equipment that is not optimized for marine surveying have demonstrated the use of airborne electromagnetic methods for measuring water depth and estimating sediment thickness. A new prototype helicopter time-domain airborne electromagnetic system, SeaTEM (0), is now under development for bathymetric surveying. The first sea trial of the SeaTEM(0) system took place over Broken Bay, New South Wales, Australia, in shallow water up to ∼30 m in depth. Broken Bay was chosen because the separate paleodrainage systems for the Hawkesbury River, Brisbane Water and Pittwater, which join in Broken Bay give rise to paleovalleys infilled with unconsolidated sediments, ranging in thickness between 0 m (bedrock outcrop) and ∼200 m. The survey area also included a tombolo with a beach either side, which provided the opportunity to measure water depth through a surf zone. Sediment thickness and water depth is predicted from stitched layered-earth inversion of data based on a simplified two-layer model that represents seawater and sediment overlying a resistive half-space basement (bedrock). The resulting bathymetric profiles show agreement typically to within ∼ ±1 m and ∼ ±0.5 m with known water depths in areas less than 20 and 6 m deep respectively. The inverted depth profile of the second (sediment) layer is noisy; however, the profiles reveal coarse topographic features of paleovalleys to depth limits of ∼60 to 80 m below sea level in 20 to 30 m water depth, as well as resolving bedrock ridges and exposed reefs in shallow waters. I N T R O D U C T I O NThe use of airborne electromagnetic methods to detect seawater depth in turbid waters is under investigation because a significant proportion of Australia's coastal waters within depths of about 50 m is affected by water turbidity. If one assumes that the turbidity levels found in seawater do not affect the bulk seawater conductivity, then the interpreted layer thickness of the upper conductive layer (seawater) of a layeredearth model derived from the inversion of airborne electromagnetic data should not be influenced by water turbidity. *

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Section: Figure 13supporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: B R O K E N B a Y T R I A L S I T Ementioning

confidence: 99%

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An investigation of seawater and sediment depth using a prototype airborne electromagnetic instrumentation system – a case study in Broken Bay, Australia

Vrbancich¹

2009

Geophysical Prospecting

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“…1) the position of the bedrock drainage channels beneath the unconsolidated sediment was determined using seismic methods [ 1 ]. The geological history of Botany Bay and of similar estuaries along the east coast of New South Wales [2,3] was strongly influenced by the climatic events of the Quaternary Period, During conditions of low sea level, the numerous coastal streams were rejuvenated and river valleys were entrenched and accentuated; the large volume of eroded material was deposited on the inner shelf, as shown by recent seismic data (unpublished data). During high sea-level stands, some of the newly deposited sediment was remobilized by marine processes and transported into the drowned river valleys causing partial siltation.…”

Section: Introductionmentioning

confidence: 97%

Sedimentary environments and Pleistocene chronology of the Botany Basin, N.S.W., Australia

Albani

1981

Geo-Marine Letters

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The sedimentary sequence of the Pleistocene deposits of the Botany Basin were investigated using borehole samples and seismic data. A succession of environments from marine to terrestrial, separated by erosional surfaces, were recognized and, although absolute dating is not possible, a relative "minimum" chronology was established correlating erosional surfaces with sea-level fluctuations. Seismic surveys and borehole material from other sites indicate that the model presented here is applicable to other estuaries of N.S.W.

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Wave direction shift triggered severe erosion of beaches in estuaries and bays with limited post‐storm recovery

Gallop

Vila‐Concejo

Fellowes

et al. 2020

Earth Surf Processes Landf

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Many estuaries contain sandy beaches that provide habitats and offer protective buffers for wetlands and infrastructure, alongside cultural and recreational resources. Research underpinning coastal management tends to focus on tide‐ and swell‐dominated sandy beaches, but little attention is given to beaches in estuaries and bays (BEBs) that exist along a continuum of wind/swell wave, tide and riverine influence. BEBs are subject to less wave energy than open coast locations because of the generally narrow window of directions for which ocean waves can propagate through the entrance. However, when storm wave direction coincides with the orientation of the estuary or bay entrance, waves can penetrate several kilometres inside. Here we focus on eight BEBs in two major bays/estuaries in Sydney, Australia and present observations from before and after a major extratropical storm with waves from an atypical direction in June 2016. We quantify magnitudes of beach erosion and recovery rates for 3 years post‐storm. We show that when high‐energy storm waves penetrate bays and estuaries, BEBs can undergo up to 100% of subaerial beach erosion. Three years after the storm, only 5 of the 29 (17%) eroded subaerial beach profiles had recovered to their pre‐storm volume. This is likely due to the lack of low‐frequency, beach‐building waves at BEBs under modal weather conditions in between storms, in contrast to open coast beaches. We also show that the recovery of BEBs may be limited by the absence of adjacent sediment reservoirs due to the dominance of tidal processes mid‐channel. Our study highlights the unique behaviour of BEBs relative to beaches on the open coast, and that shifting wave direction needs to be considered in long‐term beach resilience under climate change. © 2020 John Wiley & Sons, Ltd.

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The bedrock topography and origin of Broken Bay, N.S.W.

Cited by 20 publications

References 1 publication

An investigation of seawater and sediment depth using a prototype airborne electromagnetic instrumentation system – a case study in Broken Bay, Australia

An investigation of seawater and sediment depth using a prototype airborne electromagnetic instrumentation system – a case study in Broken Bay, Australia

Sedimentary environments and Pleistocene chronology of the Botany Basin, N.S.W., Australia

Wave direction shift triggered severe erosion of beaches in estuaries and bays with limited post‐storm recovery

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