characteristics of slow water channel units. Location denotes whether the unit is like to be associated with the thalweg of the channel (the main part of the flow) or adjacent to a bank. Longitudinal and cross-sectional profiles refer to the deepest point in the unit relative to the head, middle,or tail region of the unit. substrata characteristics refer to the extent of particle sorting (i.e,particle uniformity) and resistance to scour. the channel unit forming constraint describes the feature most likely to cause pooling. Modified from Hawkins et al.(1993)