While in Malmsbury a few days ago I noticed the Malmsbury Reservoir flowing into the Coliban Main Channel - first time I had seen it for over 3 years When flowing, tunnels, dissipators and similar devices will be great viewing. An enquiry to Coliban Water revealed that the channel runs intermittently on demand to cater for town water and irrigator needs. So its pot luck really.
You can start either end of the rideable channel at Harcourt North or Sandhurst Reservoir or a few cross roads in between. This is generally a fast ride as it is mainly on the channel embankment. However there are 2 or 3 short grunty hills and a lovely treed bypass.
Make the most of it as these channel devices are quite spectacular in good flows. Castlemaine and Bendigo Tourist Info Centres have leaflets on the Coliban Channel (free) and also the GDTA Leanganook Track brochure which includes a map ($) http://www.gdt.org.au And if you geocache, there are some along the way.