Drag of emergent and submerged rectangular obstacles in turbulent flow above bedrock surface

Flume experiments quantify the force balance equation for initial motion of isolated blocks. Experiments: (1) Initial motion on smooth concrete surface; (2) Initial motion on simulated rough bedrock. Three cases of initial motion: (1) the block is emergent and pivots; (2) the block is emergent and slides; (3) the block is submerged and slides. The drag coefficient (C d ) on rough bedrock was related to relative water depth and particle orientation. For submerged cases C d = 0.95 for sliding, but for near emergent/emergent conditions C d increases rapidly as relative depth reduces. For shallow water and emergent conditions large values of C d pertain as the relative depth decreases and blocks pivot. For…