Abstract
The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes. Step-pools display spatio-temporal variations in bed and flow characteristics due to meso-scale units such as step, tread, base of step, and pool. Exclusive research on the effects of bed variations in step-pools on the flow dynamics is limited. Here, we conducted laboratory experiments on a physical model downscaled from a field site in the Western Ghats, Kerala, India. The results of Kruskal–Wallis ANOVA show significant differences in the velocity and turbulent intensities for the morphological units. A regression equation of the form Power-Allometric1 has been proposed to relate the normalized turbulent kinetic energy with the velocity magnitude. The present study also estimated the range of Reynolds shear stress and energy dissipation factor existent in the step-pool systems. The normalized values of Reynolds shear stress in the x–z plane ranged from − 19.477 to 13.729, and energy dissipation factors obtained for the three step-pool systems are 321, 207, and 123 W/m3; both the results reveal insufficient pool volume for adequate energy dissipation. The study concludes that while designing close-to-nature step-pool fish passes, pool dimensions should be finalized with respect to the target aquatic species.
Highlights
The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes
Step-pools are characterized by unique morphological units and spatially varying hydrodynamics
Better understanding about the flow characteristics in a self-formed step-pool will aid in the design of artificial fish structures and in improving hydraulic models of varied applications
Summary
The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes. Exclusive research on the effects of bed variations in step-pools on the flow dynamics is limited. Step-pools are natural geomorphologic forms developed under the action of extreme floods[1] in mountain streams with bed slopes ranging from 3 to 20%2,3. The variations in hydrodynamics within step-pool systems do not furnish considerable differences in the sediment transport estimation since the measured and computed magnitudes differ up to an order of three because of the limited sediment availability in mountain s treams[27,28]. Updated knowledge on the flow dynamics at different regions within the step-pool reach will aid in providing guidelines for designing close-to-nature fish passes to enable target species to pass through the fluvial system[29,30]. With increased demands to implement and maintain environmental flow schemes, cost-effective and eco-friendly structures such as step-pools provide a promising tool to facilitate economic development together with ecological conservation
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