The Richmond floodplain with predicted areas of inundation marked in red.
The Richmond floodplain with predicted areas of inundation marked in red.

Study of sea-level rises

A one-metre rise in sea level, predicted by 2100, would submerge large areas of the Richmond River floodplain, according to the latest research.

The study, by Southern Cross University environmental scientist Clement Akumu, looks at land that is now less than 20 metres above sea level in the area from Tweed Heads to Evans Head.

In the study area, a one-metre sea-level rise would flood about one third of the land now occupied by towns and farms, according to the research.

Clement, from the Centre for Geoinformatics Research and Environmental Assessment Technology (GREAT), in the SCU School of Environmental Science and Management, is using satellite data and a range of geoinformatics software to assess the potential impacts of climate change on coastal wetlands in the study area.

Geoinformatics is the science and technologies that use information-science infrastructure to address the problems of geography, geosciences and related branches of engineering. It combines geospatial analysis and modelling, development of geospatial databases, information systems design, human-computer interaction and networking technologies.

Clement said, when assessing the possible effects of climate change, the most commonly used estimate was a one-metre sea-level rise by 2100, which was a conservative estimate.

His modelling predicts areas of inundation at Cumbalum, inland from Lennox Head and Skennars Head, East Ballina, Ballina, North Creek, West Ballina, South Ballina, Keith Hall, Pimlico, Empire Vale, East Wardell, Patchs Beach, Goat Island, Broadwater, Green Forest, Dungarubba, Rileys Hill, Kilgin, East Coraki, Tuckurimba, Bungawalbyn, Bora Ridge, Swan Bay, Woodburn, Doonbah, Trustums Hill and Moonem.

He said that for the purposes of the project, areas that were ‘inundated’ were those where water would be visible on the surface.

The research originally focussed on wetland areas and did not include farmland or urban land. However, once the modelling neared completion the software started to indicate that large areas of farmland and urban land also would be affected.

Across the entire study area, upland developed dry land (urban land), which now totals 95 square kilometres, is predicted to decrease to 78 sq km by 2025 and 62 sq km by 2100.

In the same area, upland undeveloped dry land (agricultural land), which now totals 968 sq km, is predicted to decrease to 804 sq km by 2025, and 662 sq km by 2100.

Areas of forested wetlands, inland fresh marshes and inland open water are predicted to decrease, while wetlands such as mangroves and salt marshes, transitional marshes, and estuarine open water are predicted to increase.

The research predicted that by the year 2100 the area of forested wetlands will decrease from about 149 sq km to 125 sq km; inland fresh marshes (coastal swamps and dunal wetlands) will decrease from about 226 sq km to 168 sq km; transitional marsh will increase from zero to about 250 sq km; mangroves and salt marshes will increase from 37 sq km to about 102 sq km; tidal flats will increase from zero to about 1 sq km; inland open water (lakes and rivers) will decrease from 33 sq km to 9 sq km and estuarine open water will increase from 36 sq km to about 161 sq km.

PhD candidate Clement used satellite data from 1989, 2001 and 2009 to produce maps of the study region showing wetland change during those years.

He used digital elevation model (DEM) data with a pixel size of 25 metres, supplied by the Richmond River County Council (RRCC) and Tweed Shire Council, to produce an inundation map for the one-metre sea-level rise.

Overlaying the inundation map on the wetland map produced a map of wetlands which would be inundated by the sea-level rise.

Clement said the model’s parameters included DEM, slope, the wetland maps, offshore direction (the direction to the ocean), historic trends of sea-level rise, tide information, marsh erosion, swamp erosion, tidal-flat erosion, accretion rates, beach sedimentation rates and the frequency of storms.

The project’s aim is to assess the potential impacts of climate change on the coastal wetland communities in north- eastern NSW.

The project identifies the following wetland types:

Mangroves and salt marshes, coastal swamps, forested wetlands, dunal wetlands, transitional wetlands, tidal flats, coastal upland water bodies and estuarine water bodies.

Clement said there were several options for mitigating the effects of sea-level rise.

“In some cases it may be possible to give protection using buffer zones,” he said. “In other instances the best thing may be to do nothing.

“Depending on land use, retreat may be an appropriate strategy, or, in other cases, it may be possible to accommodate the impact by staying there but raising the level of buildings and other structures.”

Clement used another complex process, based on satellite data and Bureau of Meteorology (BOM) climate data, to estimate methane emissions from the wetlands in the winter month of June. He modelled the possible effect of a one-degree Celsius rise in temperature on methane emission from the wetlands (not including agricultural and urban land).

In his paper, ‘Modelling methane emission from wetlands in North-Eastern NSW, Australia using Landsat ETM+’, in the Remote Sensing Journal, he says that natural wetlands constitute a major source of methane emission to the atmosphere, accounting for about 32% of the total methane emission.

He found that for the month of June, a 1 degree C rise in temperature would increase by about 50% the amount of methane produced in the wetlands (from about 1,900,000 kilograms to about 2,700,000 kilograms). Methane produced in mangroves and salt marshes would rise from 13,000kg to around 18,000kg, from forested wetlands about 1,600,000 kg to 2,200,000 kg and coastal swamps about 310,000 kg to 440,000 kg.

The sea-level research is also the subject of papers in the Journal of Wetlands Ecology and Management and the Journal of Coastal Conservation.

Clement said he wanted to thank SCU, doctoral supervisors Dr Sumith Pathirana, Dr Daniel Bucher and Professor Serwan Baban, SCU geographic information systems manager Greg Luker, RRCC, Tweed Shire Council, the NSW Department of Environment and Climate Change, BOM, and the National Tides Centre for their support.

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