These variables were included because of their statistical association with independently derived measures of human disturbance in the riparian zone and the catchment, and because they are considered important in other habitat protocols or to the ecology of large rivers. The proposed NWHI included seven variables: riparian width, large woody debris, aquatic vegetation, bottom deposition, bank stability, thalweg substrate, and off-channel habitat. We used correlation and principal components analysis to reduce the number of variables, and examined the spatial pattern of retained variables to exclude any that appeared to reflect spatial location rather than reach condition, resulting in 12 variables to be considered in the habitat index.

We measured 171 individual habitat variables over 2-km reaches at 35 locations on 14 rivers during 2000–2002, where mean wetted width was found to range from 32 to 185 m and mean thalweg depth from 0.8 to 8.3 m. This identified 22 candidate rivers that ranged in length from 103 to 825 km and in drainage area from 1620 to 16,860 km2. We developed and tested a non-wadeable habitat index (NWHI) for rivers of Michigan, where non-wadeable rivers were defined as those of order ≥5, drainage area ≥1600 km2, mainstem lengths ≥100 km, and mean annual discharge ≥15 m3/s. However, little effort has been devoted to habitat evaluation in non-wadeable rivers, where it is likely that protocols will differ and field logistics will be more challenging. Habitat evaluation of wadeable streams based on accepted protocols provides a rapid and widely used adjunct to biological assessment. Once implemented, the habitat assessment protocol will provide a standardised tool for the assessment of river habitat condition at a variety of governance levels.

There are four sequential components to the implementation of the protocol: reference site selection, data collection, predictive model construction and assessment of test sites using the predictive models.

However, the protocol has been augmented with geomorphological variables and incorporates principles of hierarchy and geomorphological river zonation. Habitat Predictive Modelling forms the basis for the protocol because it can predict the occurrence of local-scale features from large-scale data, uses the reference condition concept, can be modified to incorporate a range of biologically and geomorphologically relevant variables, and employs a rapid survey approach. Existing habitat assessment methods are not suitable for implementation on a national scale, so we present a new habitat assessment protocol that incorporates favorable elements of existing methods. Despite the demonstrated utility of the Australian River Assessment Scheme (AUSRIVAS) to provide national-scale information on the biological condition of rivers, there is no commensurate scheme that can provide standardised information on physical habitat.

Mountains to Sea by Mike Joy