Spatial organisation of ecologically relevant high order flow properties and implications for river habitat assessment
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The turbulent properties of flow in rivers are of fundamental importance to aquatic
organisms yet are rarely quantified during routine river habitat assessment surveys
or the design of restoration schemes due to their complex nature. This thesis uses a
detailed review of the literature to highlight the various ways in which plants and
animals modify the flow field, how this can deliver beneficial effects; and how
turbulence can also generate threats to growth and survival. The thesis then
presents the results from detailed field assessments of turbulence properties
undertaken on low, intermediate and high gradient rivers to advance scientific
understanding of the hydrodynamics of rivers and inform effective habitat
assessment and restoration. A reach-scale comparison across sites reveals spatial
variations in the relationships between turbulent parameters, emphasising the need
for direct measurement of turbulence properties, while a geomorphic unit scale
assessment suggests that variations in turbulence at the scale of individual
roughness elements, and/or within the same broad groupings of geomorphic units
(e.g. different types of pools) can have an important influence on hydraulic habitat.
The importance of small-scale flow obstructions is further emphasised through
analysis of the temporal dynamics of turbulence properties with changes in flow
stage and vegetation growth. The highest magnitude temporal changes in
turbulence properties were associated with individual boulders and vegetation
patches respectively, indicating flow intensification around these sub-geomorphic
unit scale features. Experimental research combining flow measurement with
underwater videography reveals that more sophisticated turbulence parameters
provide a better explanation of fish behaviour and habitat use under field conditions,
further supporting direct measurement of turbulent properties where possible. The
new insights into interactions between geomorphology, hydraulics and aquatic
organisms generated by this work offer opportunities for refining habitat assessment
and restoration design protocols to better integrate the important role of turbulence
in generating suitable physical habitat for aquatic organisms.
Authors
Trinci, GiudittaCollections
- Theses [4125]