I think we have different understandings for the use of the tag "wetland". It is my understanding that wetland does not need always to be wet - especially in the Australian content. Gwyder wetlands and Macquarie Marshes are both intermittent in nature, as are many other wetland areas. 

I found two OSM definitions for wetland:
1. "A natural area subject to inundation or with waterlogged ground, further specified with wetland=*" source: https://wiki.openstreetmap.org/wiki/Key:natural

2. "A wetland is a land area that is saturated with water, either permanently or seasonally." source: https://wiki.openstreetmap.org/wiki/Tag:natural=wetland

Referring to the first definition, an area subject to inundation will be wet when inundated but will not always be wet. The extent and duration of inundation and subsequent period of damp or bogginess varies depending on many factors. 

 And the second definition also makes it clear that the saturation with water does not need to be permanent. 

I believe that most wetland in Australia is intermittently wet rather than always so. 

It seems to me that wetlands are less frequently covered with water than rivers and lakes and, depending on the interval between rainfall/inundation events, wetlands, rivers and lakes may all become dry for a period.
 


