CHANNEL GEOMETRY OF MOUNTAIN RIVERS IN NEW ZEALAND

A dataset of 21 study reaches in the Porter and Kowai rivers (eastern side of the South Island), and 14 study reaches in Camp Creek and adjacent catchments (western side of the South Island) was used to examine downstream hydraulic geometry of mountain rivers in New Zealand. Rivers in the eastern and western regions both exhibit well-developed downstream hydraulic geometry, as indicated by strong correlations between hydraulic radius, channel top width, mean velocity, and bankfull discharge. Exponents for the hydraulic geometry relations are similar to average values for rivers worldwide. Factors such as colluvial sediment input to the channels, colluvial processes along the channels, tectonic uplift, and discontinuous bedrock exposure along the channels might be expected to complicate adjustment of channel geometry to downstream increases in discharge. The presence of well-developed downstream hydraulic geometry relations despite these complicating factors is interpreted to indicate that the ratio of hydraulic driving forces to substrate resisting forces is sufficiently large to permit channel adjustment to relatively frequent discharges.