Accuracy of channel measurements and the implications in estimating streamflow characteristics

Regional relations between flow characteristics and stream-channel size offer a promising alternative to available methods of estimating flow characteristics for ungauged sites, particularly in semiarid regions. The reliability of such relations and of flow estimates made from them is partly dependent on the user's ability to recognize a suitable reach and the reference levels in that reach. A test was made in northern Wyoming to determine how consistently trained individuals could measure channel size for three different reference levels. Seven participants independently visited 22 sites and measured channel dimensions in sections of their choosing. Assuming that the functional relation between a discharge characteristic (Q) and channel width (W) is log Q=f(1.5 log W) and that the average log W from seven measurements is the best estimate of log W at a site, an average standard error for discharge of about 30 percent was attriluted to differences in width measurements alone.