WATERSHED-SCALE IMPLICATIONS OF HACK'S SLOPE-DRAINAGE AREA RELATIONSHIP AND APPLICATION TO THE PREDICTION OF IN-CHANNEL FEATURES OF ECOLOGICAL INTEREST

Hack proposed a relationship that expressed stream gradient as a function of the ratio of substrate size to drainage area raised to some power. Subsequent research has demonstrated that the general form of this relationship is valid across a broad range of spatial scale, substrate size and stream gradient. However, this relationship has received relatively little attention with respect to potential applications or important implications for watershed-scale analysis of geomorphic processes and habitat characteristics. Preliminary work suggests that Hack’s relationship may be used as a surrogate variable for stream power to develop associations between slope-drainage area, channel unit morphology, and substrate size. Because channel morphology is an important driving factor in aquatic ecosystem structure and health, such a relationship could provide a critical link between hydrologic processes at larger scales and local scale aquatic ecosystem variables. The author will outline the effort to use Hack’s relationship along with widely available Geographic Information System software and remotely sensed data to predict channel morphologic units that are ecologically relevant. Three principle topics will be discussed: (1) the appropriate length of stream to sample to calculate gradient from channel networks derived from elevation data to ensure adequate representation of the variability in relief of the network structure and minimization of redundancy in calculations of gradient, (2) techniques utilized in an attempt to predict unit morphology using only remotely sensed data, and (3) demonstration that Hack’s relationship can be used to associate stream power with in-channel ecological features.