Small Step Hydraulics

Submerged and Unsubmerged Natural Hydraulic Jumps in a Bedrock Step-pool Mountain Channel

Participants

Gregory B. Pasternack and Brett L. Valle

Overview

High-resolution digital elevation models (DEMs) for natural submerged and unsubmerged jump regions were tested against the classical hydraulic jump (CHJ) and engineering analogues that have dominated previous geomorphic and engineering research. DEMs were compared for two discharge conditions. The data showed bed and water surface features of the natural jump regions differ significantly from CHJ conditions and engineering analogues with respect to boundary conditions. Roughness elements were highly irregular in frequency, spacing, size, and orientation, and were comprised of form obliquity and bed scour in boulder-bed and pure-bedrock conditions. The data also showed bed and water surface features of natural jump regions have similarities and deviations from CHJ conditions and engineering analogues with respect to hydraulic characteristics. Several order of magnitude variations were observed in the hydraulic characteristics between the ballistic and sloping jets. Revised conceptual models based on idealized corollaries were developed for the natural jump regions based on upstream energy head relative to the downstream tailwater depth and step geometry. The DEMs highlight the importance of recognizing the interrelationship between spatial transcritical flow structures and localized topographic heterogeneities in bedrock channels.

Map of Study Area

Photos of the Two Hydraulic Jumps Investigated

PUBLICATION

Valle, B. and Pasternack, G. B. 2006. Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step-pool channel. Earth Surface Processes and Landforms 31:6:646-664.