Non-metropolitan expansion along the coast

Since so much of Australia's population is concentrated in the capital cities, and since the Australian coastline is so extensive and the numbers of people so small by world standards, it might be thought that there would be few coastal management problems in the non-metropolitan areas. However, homes and holiday houses have spread extensively along the coast, especially in the east, and this together with the high national rate of off-road vehicle ownership, means that 19 million Australians have made a marked impact through development along considerable stretches of the coast.

A population analysis carried out for the RAC's Coastal Zone Inquiry (RAC 1993a) showed that in the latter part of the 20th century, population growth in Australia was most rapid in the coastal outer metropolitan areas, away from the older parts of the metropolitan centres, and also the New South Wales central

Table 3.4 Most rapid coastal population growth, 1971-91

Coastal region

Increase (%)

Sydney

157

Richmond-Tweed

132

NSW Mid-North Coast

126

Melbourne

202

Brisbane

271

Queensland, Far North Coast

93

Adelaide

327

Perth

604

Hobart

133

Source: Extracted from tables in RAC 1993b, pp. 99-101

and northern coasts, the south-west of Western Australia and the south-eastern Queensland coast. With the exception of Hobart and Adelaide which remained static, the trend of growth in the major population centres continued into the 1990s (ABS 1999).

Suburbanisation of the coast in recent decades has resulted in the loss of recreational amenity and conservation values. For example, Frankston on Port Phillip Bay was, in 1960, a recreational area with holiday homes, wide recreational spaces, and open beaches. Now with the spread of suburbs along the shore of the Bay it has become a dormitory suburb, not a holiday venue. Frequently the problem of linear expansion along the coast is compounded by lack of setback from the dune or cliff, often leading to protection costs.

The scale of the problem is extreme in south-eastern Queensland. In 1991, Gold Coast and Sunshine Coast had populations of 273 000 and 154 000 respectively; according to Queensland Department of Planning projections, these will increase to 486 000 and 310 000 by 2011. However, these figures alone represent a conservative view for the region, since the hinterlands of these coastal areas are currently growing even more rapidly: Albert and Logan Shires between Brisbane and the Gold Coast have easily been the Australian leaders in numbers of building approvals in recent years.

In many areas of coastal land, suburbanisation is the latest point in a typical sequence of change. This commences with clearance for farming, which begins the establishment of infrastructure in the area, usually dirt roads and power. This basic infrastructure encourages the establishment of holiday homes and shacks, as close to the sea as is practicable and often on the coastal reserve. Holiday homes in groups bring about the development of some holiday facilities: a ramp or launching facility, a shelter shed and barbecue near the foreshore, a car park and toilet. Landward of the holiday homes, rural subdivision allows the development of hobby farms. Together with retirees moving into the holiday homes, this leads to the rise of permanent resident numbers, which attract more facilities, including the first shops. Coastal strip development has thus occurred. Where intensification and consolidation of coastal strip development occurs, a consolidated urban community becomes established.

The form of this suburbanisation of the coast is that of the discontinuous strip: the various coastal ecosystems are quickly affected by even low-density development. For example, in low-density housing among natural bush:

• niches are created for exotic plants and weeds

• domesticated and feral animals are introduced

• changes in microclimate and run-off follow clearance and the construction of buildings and roads

• high sediment run-off is generated during road and house construction.

As settlement proceeds, the bush tends to become fragmented; and as the number of species is reduced, interdependent species do not recover and species loss is intensified. For example, in the period 1974-89 some 40% of the littoral vegetation was lost from the mainland coast in south-eastern Queensland, and little coastal vegetation remains in a natural state (AURDR 1995, p. 89). Supratidal areas, subcoastal lagoons and wetlands are often lost to 'improvement' at this stage; some may be drained for farming, and others become filled for building. Australia's coastal water ecosystems have evolved in low-nutrient and low-sediment conditions. Because coastal development immediately raises nutrient and sediment flow to the sea, there is a marked impact. Intertidal reef and seagrass communities are affected by sedimentation and raised nutrient levels from suburban run-off and by wastewaters. For example, in Western Port, Victoria, clearing, fanning and urbanisation of the hinterland has led to the deposition of 6.5 million m3 of silt and sand in the bay, resulting in the loss of 85% of the seagrass and a deterioration in fisheries.

A CSIRO study of the south coast of New South Wales divided the coast as a 3 km wide strip into 10 km sections and examined the population changes between 1971 and 1981, 1986 and 1991. Every section between Batemans Bay and Eden showed rapid population growth: usually of several hundred percent, and in two cases over 1300%. The study emphasised, that even though the absolute numbers are small, they are significant: 'This is because the maximum environmental impact during the urbanisation process usually occurs at the very earliest stages: direct habitat loss, infrastructure expansion, introduction of nonnative plants and animals ... ' (Hamilton & Cocks 1994).

Just as suburbanisation of the coastline has gone through a sequence of change, the development of stormwater and wastewater infrastructure has gone through a sequence of adjustments to the coastal environment. Many small coastal settlements begin with septic disposal schemes for individual houses, with impacts on the coastal environment varying with local site conditions and with planning regulations. For example, South Australia and Queensland allow subdivision to the edge of the river bank and do not control littoral clearance, leading often to septic overflow into water courses and bank erosion. At beaches, septic overflow directly to nearshore waters from beachside shacks and homes occurs where regulations allow the subdivision size to be too small for adequate septic disposal, where development has been allowed on the foredune, and where local groundwater conditions are unsuitable for septic disposal. For example, on the shore of northern Spencer Gulf south-west of Whyalla in South Australia, the siting of a group of 250 holiday homes on a thin veneer of permeable shellgrit over hard clay has resulted in frequent septic flow to the foreshore, including to mangrove areas.

Individual septic disposal has often been followed by common effluent disposal schemes by councils (STED schemes), with impacts subject to the same considerations. Thus, for example, at Streaky Bay on the far western coast of South Australia, the downslope end of the pipes of the common effluent scheme was sited near the foreshore. Stress to this system from increased visitor numbers in summer results in overflow to the beach and nearshore waters, to the considerable alarm of the developing oyster farming enterprises in the bay.

The history of urban wastewater disposal in Australia (see Smith 1998, chapter 4) shows that there was a considerable backlog in the development of sewage treatment schemes in urban areas in the 1950s and 1960s; for example, only 50% of Sydney was sewered by 1960. Federal funding in the Whitlam years (1972-75) allowed a considerable improvement but, because of the technology and habit of the times, disposal of treated effluent was to marine and estuarine waters. By the 1990s a range of disposal arrangements was in place in the non-metropolitan coastal urban areas. The 1995 State of the Environment Report for New South Wales noted that the discharge in ML/day from the 38 sewage treatment works that pump directly to the ocean was: primary 1049.5; secondary 174.3; tertiary 48; no treatment 7.1. (Primary treatment involves the screening of solids only.) In south-eastern Queensland, wastewater is discharged to streams after secondary treatment; for example, Oxley Creek which enters the Brisbane River, and the Logan and Albert River estuaries that empty directly into Moreton Bay, where deterioration to mangrove and seagrass areas has been recorded.

Federal funding again began to influence this situation in the late 1990s; the major criterion for grants under the Coasts and Clean Seas program is the reduction of marine pollution. New treatment schemes, together with aquifer storage and reuse, indicate the beginning of a change in a situation that has arisen from 40 years of urban coastal expansion. The national State of the Marine Environment. Report (Zann 1995) showed the need for an expensive continuing program of remediation in coastal urban infrastructure. Revised planning codes to ensure minimal marine disposal are essential to prevent a compounding of the impacts.

Urban spread along the coast has also been accompanied by marked changes in run-off from the rural and urban stormwater systems. Farm drain systems and urban surfaces reduce infiltration and accelerate flow to coastal creeks and to the sea, leading to higher flood peaks and greater water and sediment discharge. This process is at its peak at the time of building construction (Wolman & Schick 1967). The Willunga Basin in South Australia provides a case study of change through clearance, grazing, horticultural development and coastal urban growth.

Box 3.1 Willunga Basin

The district was cleared of native scrub shortly after European invasion in the 1840s, to be followed by a long, productive period of wheat farming and grazing, hi the 1900s almond growing and viticulture began its growth to its modern preeminence in the Basin. During this period coastal swamps were drained and the run-off from the Willunga Scarp was directed to the sea, the flow supplemented by drains from the paddocks. Much water that formerly infiltrated and fed the groundwater is now discharged directly to the sea. Along the coast Adelaide's outer southern suburbs have spread in a narrow strip. As a result of these land use changes, surface water run-off to the Gulf has been greatly increased, as shown in table 3.5. The right-hand column of the table shows the anticipated future increase in run-off as the coastal suburbs consolidate and grow.

Table 3.5 Various estimates of run-off (ML/year) from the Willunga Basin, under different development scenarios

Stream

Pre-clearance Cleared, pre-urban

Present

Ultimate

development

scenario

Pedler Creek

2600

5395

5883

6610

Maslins Creek

900

1584

1701

2180

Port Willunga Creek

700

1176

1611

2670

Washpool Drain

690

1751

1977

2400

Sellicks Creek

360

1657

1660

1290

Source: Hale 1997, p. 35

These estimates were obtained from sources that estimated pre-clearance flows through comparison with other creeks, and using surface run-off coefficients.

The table shows doubling of total run-off in today's situation, but does not reflect sharp flood peaks of fast run-off, nor the raised sediment load of high flows, which affect the Aquatic Reserves, Aldinga Reef and Noarlunga Reef.

The effect of storm drain construction on coastal dunes can be spectacular, especially at a high-energy beach subject to heavy rainstorms, as the following account from Noosa in Queensland testifies:

Sunshine Beach is the northern end of the strip of sandy coastline that extends from the Noosa National Park southwards to Coolum. Behind the beach there is a triangular sand mass having dimes which rise about 250 feet above sea level. Much of this sand mass was freeholded early in the century, but remained undeveloped until about 20 years ago.

Since then, seaside development has progressed at an accelerating rate so that there are now several miles of roads and more than 100 houses in the area. Most of this development has occurred in the last ten years and it is in the latter part of this period that we have witnessed the predictable effects of discharging stormwater on to or near the beach.

Instead of falling on to vegetated dunes where it can be harmlessly absorbed and discharged later into swamps at the rear of the dunes, rain now falls on to impervious road surfaces where it is concentrated by kerbing and channelling into a few outlets located on or near the beach. So instead of a gradual flow to the sea by means of the existing creeks, there is now an explosive discharge every time rain occurs. When tliis is combined with storm surge, as it so often is, the results can be catastrophic.

Before Sunshine Beach was developed there were four natural creeks which carried water steadily all the year round from the swamps. There are now six additional outlets, all of which have been associated at some time or another during the past three years with severe scouring. (Three examples chosen.)

'The first outlet was damaged when Cyclone 'Daisy' struck the coastline in February 1972. This outlet was originally constructed so that stormwater was discharged into a depression 100 feet behind the foredune. Instead of being absorbed into the depression, as was intended, concentrated stormwater rapidly filled it, overtopped the dune and flowed in a torrent towards the ocean, which meanwhile entered the scour and enlarged it to a depth of 15 feet and a width of 20 feet.

The second outlet was grafted into a seepage fine behind two dunes which, when it ran under normal conditions, carried only a minimal flow of water. It survived until May 1973, when stormwater from a rain depression suddenly caused it to collapse right back to the road. At the same time, a scour, 20 feet deep, formed in front of it, right down to beach level, and much of the foredune disappeared.

The third outlet originally carried storm water across the beach to highwater. It began breaking up with Cyclone 'Daisy' and with each storm it disintegrated further as lengths of pipe broke away and lay on the beach. Finally, the pipe fractured beneath the road some distance away during heavy rain and formed a completely new scour, 150 feet long, as the water forced its way through to the ocean.

The story of these three stormwater outlets illustrates graphically the failure of three different methods of storm water disposal. In each case the fault lay in directing storm water from sub-divisions directly towards the sea, in underestimating the volume and the force of the stormwater discharge, and in not anticipating the force of the accompanying storm surge. Consequently, whether the water was conveyed to a depression in the dimes, channelled into a seepage line or taken directly to the beach, the effect was the same, namely gross overloading at the outlet, with severe scouring and local destruction of the foredune, all of which are factors which contribute needlessly to beach erosion.

'Beach Conservation '21, Beach Protection Authority, Queensland (1975)

Experiences such as this have caused many coastal management authorities around Australia to look seriously at rerouting piped flows inland, to avoid the problems of discharge through the dunes or across the beach. However, this may not always be practicable. Thus, examination of the alternatives to a proposed piped discharge of farm drainage waters from near Kingston in the south-east of South Australia, left little choice but a pipeline over the Coorong lagoon and through the Younghusband Peninsula, to exit 100 metres back from the shore among aeolianite and modem dunes. An average coastal recession of 1.5m/year, calculated from land title surveys of 1890 and 1990, is an added hazard to the structure at this particular location.

Rapid urbanisation in low-lying coastal land in New South Wales and southern Queensland has lead to unexpected drainage impacts, which have been the focus of considerable recent research. Acid sulfate soils – soils containing iron sulfides – accumulated in some low-lying coastal sediments following the sea level rise at the end of the postglacial marine transgression. When the sea inundated coastal sediments, sulfates in the seawater combined with iron oxides and organic matter in the sediments, producing quantities of iron sulfides.

It has been estimated that there are 2 million ha of potential acid sulfate soils throughout the coastal lands of all Australian states. While these soils and sediments are waterlogged the iron sulfides come in contact with the air on very rare occasions, but where excavation or drainage has exposed these sediments to the air the resulting oxidation has produced quantities of sulfuric acid. Large amounts of acid groundwater may thus be released to estuarine streams, affecting estuarine biota. In recent years, incidents of fish kills in New South Wales and Queensland estuaries have been linked to adjacent clearance and drainage for development, such as housing, marina development or farm improvement. The release of acid from drained acid sulfate soils in slow-draining clays can continue for decades. Current management action involves identification of potential areas and the development of drainage techniques to minimise acid release. The CSIRO and state government agencies are involved in disseminating advice on this problem.

 
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