I was recently party to a discussion on analysing ADCP velocity profiles in order to develop suitable alpha coefficients for wider use with surface velocity. I'm aware there is a lot of work happening in this area, and a lot of historical evidence already collected, so won't dwell on that, but it did remind me that I'd like evidence (empirical or theoretical) of velocity profiles in a super critical concrete channel. In this situation it is very difficult to measure flow using current meters or ADCPs, and there are possibly some concerns with edge effects, air bulking etc. I have since received some material from Ray Maynard, and I understand he may have joined this forum so I'll let him speak to that. The other thing I'd like to encourage is the production of a handbook of alpha coefficients, rather like the texts for estimating Mannings n, versions of which have been released by the USGS, The Swiss National Hydrography Service, and our own New Zealand version.
Martin Doyle, Tasman District Council, New Zealand.