A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
A geomorphological outline of the Spit
and the southern Broadwater,
Gold Coast, Queensland :
their environmental history &
modifications
Dr Richard Whitlow
July 2005
Prepared for Gold Coast Combined Chambers of Commerce
ALL FIGURES CONTAINED IN THIS REPORT ARE
COPYRIGHT TO DR R.WHITLOW
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
This summary outlines the environmental history of the Spit and the
southern Broadwater offshore Southport on the Gold Coast,
Queensland. It also notes some of the major human impacts on this
part of the coast. A list of selected references is supplied at the end.
Introduction – some key questions and issues related to the
characteristics and development of the Spit and the state of the
southern Broadwater addressed here include :
•
•
•
•
•
What is a spit and how do they form ?
How has the Spit changed in historic times ?
Dynamics of the Spit as a landform feature.
Sources of sediments associated with the Spit.
How much sediment has accumulated within the southern
Broadwater ?
• How has human activity modified the Spit and the
Broadwater ?
• What are the characteristics of the sediments within the
southern Broadwater ?
1.
What is a spit and how do they form ?
• A spit is a long narrow accumulation of sediment (sand or
pebbles) with one end attached to the land and the other
projecting into the sea or across the mouth of an estuary.
• Typically, on the east Australian coast, the sediment that feeds
spits is derived from longshore movement (or littoral drift)
northwards up the coast. The sediment accumulates (progrades)
where the flow from rivers is not strong enough to push the
material back out to sea. During storm events major erosion can
result in reduction in the extent of a spit and change its shape.
• The Nerang River spit, now referred to simply as The Spit
(sometimes also called The Southport Spit), is a classic example
of how a river outlet has migrated northwards as a result of the
formation of a blocking spit at the mouth of the river.
2.
How has the Spit changed in historic times ?
Historical map, aerial photography and ground observation sources
related to The Spit dating from 1887 to the present are summarised in the
table below, with selected maps shown in Figures 1 to 6. Jubilee Bridge,
noted in this table, is shown on these maps. The measurement ‘chain’ is
used in past geological reports; a chain is a distance of 22 yards or
around 20.1 metres. As a comparison, the distance from what was the
eastern end of the former Jubilee Bridge to the present Seaway (cnr of
Waterway Drive & Main Beach Parade) is about 4,230 metres.
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
DATE
SOURCE
STATUS OF THE SPIT
1887
Department of Lands map
(Fig.1)
The Spit is 35 chains (774m) north of eastern end of
Jubilee Bridge; southern tip of South Stradbroke Island
was about a mile (1,600m) north of this.
1901
Ground observation by local
officials/residents (Fig.1)
Northern end of The Spit was ‘a few chains’ (over
44m) north of eastern end of Jubilee Bridge.
1924
Department of Lands map
The Spit is about 60 chains (1,206m) north of eastern
end of Jubilee Bridge.
1930
Department of Lands survey
(Fig. 2)
The Spit is about 130 chains (2,613m) north of eastern
end of Jubilee Bridge.
1937
Harbours & Marine Dept.
ground survey (Fig.2)
The Spit is about 2 miles (3,220m) north of eastern end
of Jubilee Bridge.
1944
RAAF aerial photo (April)
(Fig.7)
The Spit is about 175 chains (3,520m) north of eastern
end of Jubilee Bridge.
1952
1:63,360 scale topographical
mapping (aerial photography
1944 & 1952) (Fig.3)
The Spit is 3,960m north of eastern end of Jubilee
Bridge.
1966
1:50,000 scale topographical
mapping (aerial photography
1966) (Fig. 4)
The Spit is 4,315m north of eastern end of the former
Jubilee Bridge which has been replaced by the Nerang
Bridge further west and orientated north-south.
1990
1:25,000 scale topographical
mapping & 1990 aerial
photography (Fig.5)
The Spit is 4,230m north of eastern end of the former
Jubilee Bridge (marked approximately by the
intersection of Waterway Dv & Main Beach Pde)
2004
1:10,000 aerial photography
(Fig.6)
Same position as in 1990, with Seaway stabilising the
entrance to the Broadwater, but sand banks within this
shallow basin constantly changing in extent and shape.
3.
Dynamics of the Spit as a landform feature.
The supporting historical maps (Figs. 1 to 6) were compiled from a
variety of sources including a study in 1946 of ‘Stradbroke Island erosion
and Broadwater silting, Southport’, along with charts of varying dates
and scales housed in the Queensland Department of Transport, Marine
Division at the Spit. These maps demonstrate clearly that :
• The Spit is a relatively young landform feature, certainly not
‘centuries old’, since it did not extend much beyond Main Beach
and Southport Yacht Club marina at the turn of the 19th century.
• The Spit is a very dynamic landform, to be expected given its
exposure to both marine and river processes, with major storms and
runoff events remoulding the unconsolidated sandy embankments
quite dramatically from time to time e.g. as took place in the 1930’s
with rapid northerly extension of the Spit at the expense of the
southern portion of South Stradbroke Island.
• Periodic (although rare) cyclonic events, with storm waves up to
8m or more, have also resulted in major alteration of the Spit. In
addition, natural changes, like the breaching at Jumpinpin in the
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
late 1800s, and man-made changes, like construction of training
walls on the Tweed River in 1962-65 restricting sediment supply to
Gold Coast beaches and the Spit, have also brought about
significant geomorphological adjustments of the Spit in recent
times.
• The Spit has more or less been ‘stabilised’ since completion of the
Gold Coast Seaway in 1986, with limited changes to the
morphology of the landform since this time.
4.
Sources of sediments associated with the Spit.
The sediment that enters into the southern Broadwater is derived from
two main sources. These are sandy material transported by marine action
through the Seaway entry from the east and finer sediments transported
by fluvial action down the Nerang River and, to some extent, the urban
creeks that drain into this part of the Broadwater. The dynamic nature of
sediment influx from the sea is demonstrated well in the 1944 aerial
photography of this area shown in Figure 7. This shows a distinctive
deltaic feature with strong flow lines evident in the outlines of the
sandbanks.
This sediment flux has since been modified by construction of the Gold
Coast Seaway in 1985-86 which is described later. The offshore
northward flux of sediment on the Gold Coast offshore the Spit has been
calculated at around 480,000 m3 to 500,000 m3 annually. It seems likely
that this flux may have increased, however, since the construction of the
Tweed River Entrance Sand Bypass (TRESB, see comments later),
possibly to as much as 700,000 m3 annually. Consequently, more
sediment may be finding its way through the Seaway entry than in the
past, but there is no definite data to confirm this.
5.
How much sediment has accumulated within the southern
Broadwater ?
The 1946 paper by Connah, a Queensland Department of Mines geologist
was prompted by official concerns at that time about the ongoing siltation
within the Broadwater and the problems that this created for boating. To
quote from his paper :
“As the mouth of the Nerang River has migrated northwards larger
quantities of sand have been deposited in the Broadwater between
Southport pier and Land’s End, resulting in banks which have
seriously restricted the area of deep navigable water. Over the
same period considerable silting of the Nerang River has taken
place and this river is now navigable only by the smallest craft”
(Connah, 1946, p 373).
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
These same observations are repeated in later geological reports on this
area, with recommendations to carry out dredging to at least keep major
channels clear of sediment and open for free access of commercial and,
later, recreational boats. Both topographical maps and aerial photography
since the Second World War demonstrate the persistence of massive, but
shifting, sediment banks within the southern Broadwater (see Figs. 2 to
6). Whilst monitoring of seabed contours and slope profiles has been
carried out systematically in relation to assessing the effects of the Gold
Coast Seaway and to assist in management of the sand bypass system (see
comments below), no similar work has been done for the southern
Broadwater. It is evident, however, that within the last decade or so, the
expanses of sand exposed at low tide appear to be greater than in the past
and that even small boats can get into difficulties if they stray off the
main ‘deep water’ channels.
6.
How has human activity modified the Spit and the Broadwater ?
The Spit and the Broadwater are clearly not natural nor pristine, given
they have been subjected to well over a century of progressively more
varied and intensive disturbance from human activities, with the township
of Southport established in 1874 (about a decade after Nerang which
dates from 1865 – see www.goldcoastaustralia.com – virtual tours – Nerang a
local study). Some of these impacts include :
• Mining for black minerals, an activity that began on the Gold
Coast at Tugun in 1928 (although this initial mining for zircon,
gold & tin did not last long). Mining really got underway during
1939-1945, when demand for rutile for wartime uses increased.
Mining was extended from Broadbeach in 1945 through to the Spit
and constituted the first major human disturbance of this coastal
strip.
• Construction of the Gold Coast Seaway and associated sand
bypass system between September 1984 and May 1986 (officially
opened on May 31, 1986), a major capital works project costing
around $50 million. This project involving construction of two
enormous rockwalls (South Wall, 600m; North Wall, 400m) was
carried out to stabilise the entry to the Broadwater for commercial
and recreational boats following several major coastal engineering
studies by the Delft Hydraulics Laboratory in the Netherlands in
the 1970s. Wavebreak Island was built at this time, mainly from
dredged material, to block storm waves and protect the western
shores of the Broadwater opposite the 320 metre wide Seaway
entry (see Fig. 5).
• Sand bypass pumping associated with the operation of the Gold
Coast Seaway has a capacity to pump up to 500 cubic metres of
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
sediment per hour. Although the annual northward flux of sediment
at the time of construction of the Seaway was around 500,000 m3,
considerable amounts of sediment may be moved during a single
cyclonic storm. Hence the pumping of sand from offshore so that it
can continue its northerly progression along the shores of South
Stradbroke Island is vital to the ongoing maintenance of this now
heavily modified section of coastline.
• Construction of the TRESB to the south has resulted in further
coastal adjustments in the 1990s to the present day. The TRESB,
instigated to make the lower Tweed River safer for navigation, has
involved offshore dredging and beach nourishment (1995-1996 and
1998, with 3 million m3 of sediment relocated mainly onto Gold
Coast beaches) and subsequent installation of a sand bypass system
which began operating in mid 2001. Currently, it pumps close to
700,000 m3 of sediment, material which continues to shift
northwards up the coast resulting in active progradation of southern
Gold Coast beaches. Some of this ‘additional’ sediment must work
its way up to the Spit reaches of the coast and enter into the
southern Broadwater through normal tidal processes.
• Commercial and recreational boating activities also influence the
environmental conditions in and around the Broadwater and the
Spit. There is now major infrastructure on the margins of the
Broadwater to accommodate the needs of boating, notably large
marinas and jetties (see Fig. 5 as compared to earlier figures). As of
June 30, 2005 there were over 24,000 registered recreational boats
on the Gold Coast with adjoining regions (Brisbane, Logan and
Redland Shire) accounting for a further 35,500 boats. The
breakdown of recreational boats according to size of craft on the
Gold Coast, is given in the table below :
Boast size (metres)
Number 30/06/2005
4m and under
9,498
4.01 to 8.00m
12,179
8.01 to 15.00.
2,126
Over 15m
243
Source : Queensland Department of Transport, July 2005.
Swash from growing numbers of boats must affect localised
erosion of shorelines, although many of these are now armoured by
rock and concrete walls. Possibly of greater concern, and there is
no specific data on this issue, is the environmental effects of large
numbers of recreational boats on water quality and hence on
marine life.
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
7.
What are the characteristics of the sediments within the southern
Broadwater ?
There have been no major published studies related to the textural and
geochemical characteristics of sediments within the Broadwater (at least
as far as we are aware). The only two recent investigations of relevance
are the following :
• a PhD thesis (1999) from Queensland University of Technology
by Micaela Preda (see references), with a summary paper
related to trace metal distribution within marine and estuarine
sediments in western Moreton Bay (Cox & Preda, 2005)
concluding that
• Sediments within Moreton Bay have relatively low
metal content, but concentrations within fine-grained
estuarine sediments are at least 2 to 3 times higher than
those of sandy sediments;
• Compared with Australian & New Zealand
Environment & Conservation Council Guidelines,
elements with most commonly elevated levels include
nickel (Ni), mercury (Hg), lead (Pb) and zinc (Zn).
• Main sources of introduced trace metals are likely to be
light industry, landfills, agriculture, intensive fertilizing
(e.g. golf courses) and composite effects of urban
centres.
• a Bsc Geology honours dissertation (2001) from Adelaide
University by Amanda Elliott. This project involved collection
of 31 sediment and 31 water samples, about 500m intervals,
along a 15 km reach of the Nerang River and throughout the
Broadwater system. Samples were analysed for formaniferal
content as an indicator of pollution conditions, quartz sand grain
textures (scanning electron microscopy) to assess origins of
sediments, and chemical analyses (organic material , total
carbonate). Water analysis data supplied by Gold Coast Water
laboratories was also used in this study. Not unexpectedly, the
study demonstrated spatial and temporal variability in sediment
and water characteristics associated with tidal activity and
seasonal fluxes of water through the river and estuarine system.
It also demonstrated that heavy metal levels increased and the
overall water quality decreased significantly for about two
weeks following any heavy rainfall and flooding activity. More
importantly, it tested a range of simple methods that could be
applied in routine monitoring of the health of the southern
Broadwater, the Nerang River and the associated canals.
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
Conclusions on the environmental history and modifications of the Spit
and southern Broadwater
Previous studies of the Spit and southern Broadwater, along with research
on comparable features elsewhere along the eastern coast of Australia,
demonstrate the following :
• spits are made up of unconsolidated, mainly sandy, sediments
and are constantly changing landform features as a result of
exposure to both marine and fluvial (river) processes.
• The Spit, as we know it today, is a relatively young landform
feature, with historical sources (maps, aerial photographs,
ground observation) confirming that it only extended as far as
Main Beach at around 1900.
• the Gold Coast Seaway project completed in mid 1986 has
effectively ‘stabilised’ the Spit in recent years, although a major
cyclonic storm could result in reconfiguration of the
unconsolidated portions of the Spit to the south of the seaway.
All the northern end of the Spit and the southern portion of
South Stradbroke Island are man-made features.
• sedimentation of the southern Broadwater has been an ongoing
problem for decades with early references to this issue and the
dangers it poses for boating dating from the 1930s. Much of this
sediment is derived from longshore drift up the coastline, but
some of it, mainly the finer material, is of fluvial origin.
• although there are no systematic studies of the current extent of
sediment accumulation within the southern Broadwater,
sequential aerial photography and casual ground observation
suggest that sand banks are more extensive now than in the past
creating difficulties for both recreational and commercial boats.
• sediment characteristics are only known at a general level, but
there is reason to believe that heavy metals may have
accumulated in association with the finer-grained sediments
within the southern Broadwater over many years; for example,
it is no accident that official warnings are given to avoid
consuming oysters because of possible high levels of mercury !
• clearly, the Spit and the southern Broadwater have been
impacted heavily by human activities, especially during the last
two decades which has seen construction of the Gold Coast
Seaway and major foreshore and marina construction around
the fringe of this water body. These features are far from natural
or pristine and require ongoing management to maintain
environmental health and allow ongoing, legitimate uses by
residents and visitors to this city.
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 1 : The Spit from 1865 to 1901 (note the location of Jubilee Bridge)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 2 : The Spit 1930 to 1937 (note shape of South Stradbroke Island point)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 3 : The Spit 1952 (note sandbanks within the southern Broadwater)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 4 : The Spit 1966 (note change in outline of Nerang Head & Porpoise Point)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 5 : The Spit 1990 (note Seaway infrastructure & Wave Break Island)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 6 : The Spit 2004 (note limited changes between 1990 and 2004)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
FIGURE 7 : The Spit in April 1944 (note bare sandbanks and extensive deltaic deposits)
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005
A GEOSCIENTIFIC SUMMARY OF THE SPIT AND SOUTHERN BROADWATER
ENVIRONMENTAL HISTORY AND MODIFICATIONS
KEY SELECTED REFERENCES
Connah T. H. (1946) Stradbroke Island erosion and Broadwater silting,
Southport, Queensland Government Mining Journal, December, 370-373.
Connah T. H. (1961) Beach Sand Heavy Mineral Deposits in Queensland,
Geological Survey of Queensland Publication 302.
Cox M.E. and Preda M. (2005) Trace metal distribution within marine
and estuarine sediments in western Moreton Bay, Queensland, Australia :
relation to land use and setting, Geographical Research, 43(2) 173-193.
Elliott, A.E. (2001) Sedimentology and ecological health of man-made
canal and marina systems : an example from the Gold Coast, Australia,
unpublished Geology honours dissertation, Adelaide University.
Hails J R. (1964) The coastal depositional features of south-eastern
Queensland, Australian Geographer, 9, 207-217.
Hopley D. (1986) The Queensland coastline : attributes and issues, pp 7394 in Queensland, A Geographical Interpretation edited by J.H.Holmes,
Queensland Geographical Journal, Vol 1.
Morley I.W. (1982) Black Sands ; a history of the mineral sand mining
industry in eastern Australia, University of Queensland Press, St Lucia.
Preda M. (1999) Distribution, lithology and geochemistry of pyritic
sediments, and implications for coastal evolution and water quality,
Pimpama estuarine plain, southeast Queensland. Unpublished PhD thesis,
School of Natural Resource Sciences, Queensland University of
Technology, Brisbane.
Queensland Transport (undated) The Gold Coast Seaway. The Nerang
River Mouth Stabilisation & Sand Bypass System – innovative and
unique, pamphlet.
Thompson C.H. Coastal areas of southern Queensland : some land-use
conflicts, Proceedings of Royal Society of Queensland, 86(18), 109-120.
Witt C.L and Hill P.C. (1987), Gold Coast Seaway : An overview of the
project’s design and construction and it’s subsequent performance, 8th
Australian Conference on Coastal and Ocean Engineering, Launceston,
30 November – 4 December 1987, pp 259-266.
Websites : www.tweedsandbypass.nsw.gov.au
Prepared by Dr Richard Whitlow, TriMap Pty Ltd, Geoscience & Mapping Consulting
(PhD, London; MPhil, Reading; MAIG, MSIA, MISSA) – JULY 2005