The Ord River floodplain is the floodplain of the lower Ord River in the Shire of Wyndham-East Kimberley, in the Kimberley region of northern Western Australia. It lies within the Victoria Bonaparte IBRA bioregion and contains river, seasonal creek, tidal mudflat and floodplain wetlands, with extensive stands of mangroves, that support saltwater crocodiles and many waterbirds. It is recognised as an internationally important wetland area, with of it designated on 7 June 1990 as Ramsar Site 477 under the Ramsar Convention on Wetlands.
Description
The site lies about east of the town of Wyndham, extending from to . It comprises the Ord River and Parry Lagoons nature reserves, with some additional land. It lies downstream of two large impoundments on the Ord River, Lakes Argyle and Kununurra, which have had a major impact on the river's hydrology through changing its flow pattern so that there are now constant flows through the dry season. In effect, the lower Ord has been transformed through flow regulation at the dams from a ‘dry tropics’ to a ‘wet tropics’ river.
The southern part of the site is dominated by Parry Creek, including of seasonal creek and an alluvial floodplain which is flooded during the wet season. It dries out quickly in the dry season, except for waterholes associated with incised channels and claypans. The southern, or upstream, part of the floodplain is freshwater, while the northern, or downstream part, is either regularly flooded with saltwater or contains saline soils.
The lower reaches of the Ord River extend from the Parry Creek floodplain northwards to the Cambridge Gulf. The upper reaches of the Ord River are permanently fresh; the lower reaches, when not in flood, become saline due to the tidal cycle which, at the coast, has an amplitude of up to . Within the site the upstream end of the river channel is around wide with broad sand and gravel spits, while unstable mud bars and islands characterise the wide mouth. From the mouth of the Ord River, the site extends northwards around the coast to include the False mouths of the Ord, consisting of a maze of deltaic channels, intertidal mudflats and low muddy islands, an area which receives only a little fresh water from small and ephemeral creeks.
Climate
The site has a dry tropical climate. Rainfall is monsoonal, with the hot and humid wet season occurring from November to March. Wyndham has an average annual rainfall of . The dry season is mild, with periods of steady south-easterly winds. The average maximum temperature varies from in July to in December.
Flora and fauna
Vegetation
Within the site ten main vegetation associations have been identified: mudflats, mangroves, dune systems, grassland, low woodland, sandstone range open woodland, riverine woodland, rainforest (aquifer forest) and spring vegetation, major rivers and lagoons (permanent and ephemeral), and savanna woodland. Some 335 native vascular plants from 89 families have been recorded from the site, with 16 introduced species.
The eastern coast of the Cambridge Gulf is one of the richest places for mangroves in the Kimberley region in terms of species diversity, structural complexity, and area, with 14 species occurring within the site. Zonation is evident; mangrove species in the seaward zone form a woodland about high, dominated by Sonneratia alba, Avicennia marina and Aegiceras corniculatum. Behind this, in a woodland high, are Bruguiera parviflora, Avicennia marina and Aegiceras corniculatum, and then a belt of Rhizophora stylosa high. On the landward edge is a high thicket of Avicennia marina, Ceriops tagal and Aegialitis annulata. Sporobolus virginicus grassland and samphire grow on the mudflats behind the mangroves. Other occasional species of mangrove include Xylocarpus moluccensis, Excoecaria agallocha and Camptostemon schultzii.