The paper describes data collected in a 158-km2 basin for testing hypotheses underpinning the optimal channel network concept. Over a 4-day period, discharge, channel cross sections, and longitudinal slope were measured at 300 sites. Measured channel widths range from 0.050 to 16.60 m, mean depths range from 0.010 to 0.546 m, and mean water velocities range from 0.004 to 0.575 m/s. Bias in the site selection was checked by comparing measurements made at predefined distances upstream or downstream of the measurement section. Slope measurements were based on channel reach lengths typically of the order of 0.5 km. Since the data may be of use to other researchers, we have archived them on the World Wide Web (site http://www.cri.nz/hydrology/taieripage.htm) along with a 1:50,000 scale map and the associated time series of streamflow at the basin outlet during the measurement interval. ¿ 1998 American Geophysical Union