Floodplains and billabongs
Floodplains undergo dramatic seasonal changes. Following wet season rains, a sea of shallow freshwater spreads over the plains for hundreds of square kilometres. As the floodplains start to dry, waterbirds and crocodiles seek refuge in the remaining wet areas such as Yellow Water.
Nutrient-rich soils carried in the floodwaters add nutrients to the floodplains, which, along with an abundance of water and sunlight, make the floodplains an area of prolific plant and animal life. During the dry season the water recedes into rivers, creeks and isolated waterholes or billabongs. Kakadu's wetlands are listed under the Convention on Wetlands of International Importance (the Ramsar convention) for their outstanding ecological, botanical, zoological and hydrological features.
The most accessible places to view the floodplains are Yellow Water, Mamukala, Iligadjarr, Ubirr and Bubba wetland.
The wetlands of Kakadu are registered as a Ramsar site for their rare and unique wetlands, and importance in conserving biological diversity. Find out more
Wildlife
The floodplains and wetlands of Kakadu are important refuges and feeding grounds for many Australian waterbirds, especially during the dry season. The populations of some waterbirds that are abundant in Kakadu are largely restricted in Australia to a narrow band along the northern coastline. Typical of these birds are the magpie goose, the green pygmy goose, the Burdekin duck, and the wandering whistling duck.
Other commonly seen and more widespread waterbirds are the jabiru, the comb-crested jacana (or lotus bird), cormorants, darters, egrets, ibises and herons.
Kakadu's wetlands are visited each wet season by about 30 species of migratory birds, such as the little curlew, the snipe and the godwit. The birds' breeding grounds are in the Northern Hemisphere, in places such as Siberia, China and Japan. Each year they leave their breeding grounds at the end of the northern summer to fly south to warmer climates. Most migratory birds visit Kakadu during the wet season. As noted, the wetlands of Kakadu are on the list of Wetlands of International Importance and Australia has entered into agreements with the governments of China and Japan to protect the breeding and summer grounds of migratory birds.
A number of reptiles live on Kakadu's floodplains. Northern snake-necked turtles are perhaps the most frequently seen turtles; they bury themselves in mud as the water dries up at the end of the dry season.
The larger pig-nosed turtles are more secretive; it was recent Aboriginal rock art paintings of the pig-nosed turtle that first suggested to scientists that these animals occurred in the area. The Arafura file snake is abundant but rarely seen because it lives in billabongs among the roots of the river pandanus. Freshwater and Macleay's water snakes are sometimes seen swimming gracefully through the water. King brown snakes and water pythons are common on the floodplains; dusky rats form a large part of their diets.
Forest kingfisher
Estuarine crocodiles are found in both freshwater and saltwater. They are often seen on the Yellow Water and East Alligator River boat cruises. Their nests are usually mounds of mud and rotting vegetation next to permanent water. Nesting occurs during the wet season (between December and April), and about 80 per cent of mature females nest each year, laying about 50 eggs. Generally, at least 75 per cent of the eggs laid fail to hatch because the nest becomes flooded.
The paperbark forests that fringe the floodplains provide ideal nesting sites for wetland birds such as the jabiru, the white-bellied sea eagle, the whistling kite and the green pygmy goose. Paperbark forests are also home to the brush cuckoo, the lemon-bellied flycatcher, the rufous-banded honeyeater, and the restless flycatcher.
When they are in flower paperbarks provide food for nectar-feeding birds such as honeyeaters and lorikeets. Kingfishers such as the blue-winged kookaburra and the forest kingfisher, with its white wing patches, are often seen darting through the paperbark forest. The rainbow bee-eater and several species of flycatcher are also often seen. The mistletoe bird feeds on the berries of the parasitic mistletoe plant on the paperbarks, spreading the plant's seed to other parts of the forest.
Paperbark forests also provide a safe haven for agile wallabies, who must leave the safety of treed areas to drink and graze at the water's edge.
Flora
Red lily
Where floodplains are inundated for two to six months a year grasses and sedges such as spike rush occur. Clumps of freshwater mangroves (itchy tree), pandanus and paperbarks are found on slightly higher ground. Herbaceous swamp vegetation dominates areas covered by water for six to nine months a year. A variety of waterlilies, such as the blue, yellow and white snowflake, are commonly found in these areas.
Tall, dense stands of paperbark trees grow on the margins of Magela Creek, Yellow Water, Anbangbang billabong and other floodplains and permanent waterholes. The dominant species are the broad-leafed and weeping paperbarks. Freshwater mangroves and water pandanus are also common.
Common flora
- Blue lily Nymphaea violacea Barradjungga
Commonly seen along the margins of billabongs. Its violet-tipped white flowers appear between January and July. The seeds and stems can be eaten raw; the tuberous underground bulbs can be eaten after cooking. - Red lily Nelumbo nucifera Wurrmarninj
Grows in lowland wetlands. Its leaves are very large and stand erect above the water. Large, fragrant deep-pink flowers appear between March and November.
