Characterization of Hydraulic Habitat and Retention Characteristics Across Different Channel Types; Introducing a New Field-based Technique

Understanding the interactions between
physical habitat and aquatic biodiversity has become a
key research objective in river management. River
research and management practitioners are increasingly
seeking new methodologies and techniques for
characterizing physical habitat heterogeneity. The
physical biotope has been widely employed as the
standard mesoscale unit in river surveys. However,
few surveys have quantified the combined physical
heterogeneity at the meso- and microscale scale via a
single technique. This paper describes a new field
methodology for assessing variations in hydraulic
habitat and retention across different channel types
(e.g. step-pool, bedrock, plane-bed and pool-riffle).
Hydraulic habitat and retention was measured by
timing 100 flow tracers across a 100-m stream length,
and recording the types of trapping structures. The
pattern of flow tracers and retention varied significantly
between channel types and structures. Rocks
(boulders and cobbles) were more important retentive
structures than eddies and snags (woody material and
vegetation). The results indicate the importance of a
diverse hydraulic environment, woody material and
channel substrate character in increasing physical
heterogeneity within a stream reach. The findings
suggest that the field methodology may be an effective
tool to assess differences in physical heterogeneity pre
and post river restoration activities.