Observations and Analysis of the Horizontal Structure of a Tidal Jet at Deep Scour Holes

Broekema, Y.B.; Labeur, R.J.; Uijttewaal, W.S.J.

doi:10.1029/2018JF004754

Observations and Analysis of the Horizontal Structure of a Tidal Jet at Deep Scour Holes

Title

Observations and Analysis of the Horizontal Structure of a Tidal Jet at Deep Scour Holes

Author

Broekema, Y.B. (TU Delft Environmental Fluid Mechanics)
Labeur, R.J. (TU Delft Environmental Fluid Mechanics)
Uijttewaal, W.S.J. (TU Delft Environmental Fluid Mechanics)

Date

2018

Abstract

Scour in the vicinity of a hydraulic structure may compromise its geotechnical stability or that of nearby structures. Much fundamental research has been dedicated to the understanding and prediction of these processes, in order to enable the efficient design of mitigation measures. While most of these efforts consider laterally uniform flows, nonuniformity is the rule rather than the exception. This study presents field observations near the storm surge barrier in the Eastern Scheldt estuary, The Netherlands, where significant scour holes have developed. The tidal flow through this semi-open barrier exhibits characteristics of a shallow jet. A pronounced contraction of this jet toward the nearby scour hole during particular stages of the tidal cycle is revealed, attributed to potential vorticity conservation; the depth-averaged vertical vorticity increases proportionally to the depth increase. Measurements show a vertically uniform velocity profile in the scour hole that is attributed to a reduction of the adverse pressure gradient due to the contraction, that suppresses boundary layer separation from the upstream slope of the scour hole. A positive feedback mechanism is thus revealed; lateral velocity gradients lead to relatively high near-bed velocities in the scour hole which enhances erosion—causing an even stronger horizontal contraction—maintaining the scouring potential. If the upstream flow field is laterally uniform (observed around slack tide), horizontal contraction does not occur, and the boundary layer separates from the upstream slope. The scour depth will then tend to an equilibrium. The results infer the importance of the nonuniformity of the horizontal flow field.

Subject

field data
flow separation
potential vorticity
scour hole
shallow tidal jet
storm surge barrier

To reference this document use:

http://resolver.tudelft.nl/uuid:6fffb5ee-60a0-4503-9943-610ab0f8f552

DOI

https://doi.org/10.1029/2018JF004754

ISSN

2169-9003

Source

Journal of Geophysical Research: Earth Surface, 123 (12), 3162-3189

Part of collection

Institutional Repository