Stream-bed stability: how best to measure it?

Posted on December 18, 2015

Most research on the impacts of water flow on stream environments has been carried out in low-gradient channels. As a result, relationships between flow strength and stream bed mobility in steep mountain systems haven’t been well described. To characterise high-flow disturbance in mountain streams, an international research team investigated twenty headwater streams in the Upper East River catchment in western Colorado. They compared four different ways of assessing streambed stability, namely: (1) Repeat photography, where all rocks larger than small gravel that appeared in transect photographs were marked and GIS software was used to observe
whether the same rocks were present in the rephotographed transects one year later; (2) the use of data loggers to collect information on the variability and rate of change of streamflow; (3) calculations of critical shear stress, to measure the capacity of different flows to mobilize particles of a certain size; and (4) the visual assessment of channel stability based on substrate features, the evidence of bank erosion and other information. Because repeat photography provided the most direct indication of benthic disturbance, the photographic index (i.e. the proportion of photographed rocks that moved during the study period) was used as a basis for comparing the other indicators. The photographic index was well predicted by a multivariate equation that combined the visual index and one of the flow measures (the maximum daily increase in discharge). Even when used in isolation, the visual index proved to be a reliable indicator of streambed stability. This is good news because this visual method is very simple and much less expensive in time, effort and money than the other methods.

Reference: Peckarsky, B.L. et al. 2014. Characterizing disturbance regimes of mountain streams. Freshwater Science. 33(3), 716–730.