Buchanan, the 2009 and 2010 UCI World Champion, qualified third, behind defending champion Anneke Beerten of the Netherlands and Romana Labounkova of the Czech Republic.
In the final, the Australian beat Germany's Franziska Meyer, who took silver, with Beerten having to settle for bronze.
The men's race was won by Mitja Ergaver of Slovenia ahead of Hannes Slavik (Austria), Luke Cryer (Great Britain).
