Saltwater Intrusion and Morphological Change at the Mouth of the East Alligator River, Northern Territory

Morphological changes associated with saltwater intrusion of a small salt-affected floodplain in the vicinity of the mouth of the East Alligator River were examined through interpretation of aerial photography and ground surveys. The floodplain, in the Alligator Rivers Region of the Northern Territo...

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Bibliographic Details
Published in:	Journal of coastal research Vol. 22; no. 1; pp. 137 - 149
Main Authors:	Winn, K. O., Saynor, M. J., Eliot, M. J., Elio, I.
Format:	Journal Article
Language:	English
Published:	Lawrence, KS Coastal Education and Research Foundation (CERF) 01-01-2006 Coastal Education and Research Foundation Allen Press Inc
Subjects:	Aerial photography Alligator Alligator Rivers Region Aquatic reptiles Beach ridges Brackish Coastal plains Creeks Desiccation Dry season Earth sciences Earth, ocean, space East Alligator River Eolian processes Exact sciences and technology Floodplains Floods Floodwater Fresh water Freshwater Geomorphology, landform evolution Kakadu National Park Marine and continental quaternary Melaleuca morphological change Mud flats National parks Plant morphology Point Farewell Rivers Saline water Saline water intrusion Saltwater Saltwater intrusion Sea level rise Sediments Surficial geology THEMATIC SECTION Thematic Section: Australian Coastal Geomorphology, 1984–2004 Water levels South Pacific Coral Sea West Pacific Australia Northern Territory Australia Alligator River National Wildlife Refuge ISEW, Australia, Northern Terr., Alligator Rivers Region Australia, Northern Terr., Alligator Rivers Region morphological change Australasia vegetation Alligator Rivers Region modern East Alligator River cheniers retention rivers saltwater intrusion salt aerial photography salt-water intrusion chemically precipitated rocks evaporites coastal environment desiccation floodplains sedimentary rocks Kakadu National Park coastal plains interpretation Pacific Ocean landform evolution sea level national parks Point Farewell
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Summary:	Morphological changes associated with saltwater intrusion of a small salt-affected floodplain in the vicinity of the mouth of the East Alligator River were examined through interpretation of aerial photography and ground surveys. The floodplain, in the Alligator Rivers Region of the Northern Territory, Australia, includes mudflats, tidal creeks, upper and lower floodplains, and a freshwater basin impounded by cheniers. Significant morphological change has occurred since 1950, with the tidal creek extending 4 km inland. By 2000, bare saline mudflats on the coastal plain had undergone a ninefold increase, and 64% of Melaleuca spp. forest had been lost. Saltwater intrusion and associated morphological change over time appears to have been driven by drier-than-average monsoonal conditions, low-frequency and low-intensity cyclonic events, and above-average ocean water levels experienced since 1950 and particularly since the mid-1980s. Loss of vegetation on the lower coastal plain was facilitated by expansion of the tidal creek. As a result, deflation of sediment followed sediment desiccation in the dry seasons. Arguably, the deflation contributes to basin formation and promotes favourable conditions for continuation of tidal-creek development. In turn, this promotes favourable conditions for subsequent retention of floodwater and continuation of tidal-creek development. There is interplay between the two processes. Historical records and field observations indicate that the floodplains may grow in elevation, responding to slight rise in sea level, through alternation of their freshwater and saltwater states. In sequence, the change occurs as a result of shallow basin formation by aeolian processes, saltwater intrusion by tidal creeks, basin infilling by tidal creeks and river deposition, and reestablishment of the freshwater body at a slightly higher level.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 ObjectType-Article-2 ObjectType-Feature-1
ISSN:	0749-0208 1551-5036
DOI:	10.2112/05A-0011.1