The official gov data is 'PSMA' available on the OSM Australian Data page. Get that as the basis of replacing any creek boundaries. 

When you work on a creek .. download the OSM creek, then 'File' 'download along' -(I set it to 1m distance and not more than 1 km)  and using 'more tools' 'replace geometry' replace the old with your new.  This should don the job .. but any side creeks might get displaced where they join the new entry. 
The 'down load along' gets the side creeks and should get any boundaries that use the creek. 

I think that will work. 