Scour process, flow dynamics, hydrodynamic forces, around a series of repelling spur dikes - Experimental study under clear-water conditions

Q: Where does the maximum scour occur, and what drives it?

Maximum scour occurs at the tip of the first spur dike. It is associated with intense vortex activity and sediment mobilisation, reflected by elevated Reynolds shear stress near the base of that first dike.

Q: How are the flow turbulence and hydrodynamic forces quantified in the experiment?

Instantaneous velocity components are measured using an acoustic Doppler velocimeter across longitudinal and transverse directions. The study then evaluates Reynolds shear stress, drag forces and drag coefficient, turbulent kinetic energy, and vortex strength over the evolved bed.

Q: What happens to turbulence intensity downstream of successive spur dikes?

Downstream, reductions in Reynolds shear stress, drag, and vortex strength correspond to weaker turbulence. However, renewed vortex shedding between the second and third dikes sustains scour and sediment resuspension.

Sep 30, 2026

Upload by Connor

Experimental research investigates turbulence effects around spur dikes on scour dynamics under clear-water conditions. A straight rectangular flume (15 m length, 0.91 m width, 0.70 m flow depth) measures instantaneous velocity components with an acoustic Doppler velocimeter across longitudinal and transverse directions over the evolved bed. Reynolds shear stress, drag forces/coefficient, turbulent kinetic energy, and vortex strength quantify hydrodynamics. Maximum scour occurs at the first dike tip; RSS peaks at its base and links to intense vortex activity and sediment mobilisation, while downstream changes reflect weaker turbulence and renewed shedding.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages17

Reading Time43 min

AccessFree to download

Experimental setup and clear-water conditions

Velocity measurements and hydrodynamic metrics

Scour distribution and turbulence indicators

Roles of vortex activity and drag trends

Background on river scour and spur dike stabilization

Scour, sediment deposition, and bank erosion

Spur dike geometry and classification (attracting/deflecting/repelling)

Review of related studies and design considerations

[www. nature.com/scientificreports](www. nature.com/scientificreports) OPEN Scour process, flow dynamics, hydrodynamic forces, around a series of repelling spur dikes Sandeep Kumar1, Prashanth Reddy Hanmaiahgari1􀀍 & Jaan H. Pu2 This experimental study examined the turbulence effects around spur dikes on scour dynamics under clear-water conditions. An experiment was conducted in a straight rectangular flume of length, width, and flow depth: 15, 0.91, and 0.70 m, wherein instantaneous flow velocity components were measured using an acoustic doppler velocimeter (ADV) across longitudinal and transverse directions over the evolved bed to evaluate Reynolds shear stress (RSS), drag forces, drag coefficient, turbulent kinetic energy (TKE), and vortex strength to capture the detailed hydrodynamics. The results indicate maximum scour occurred at the tip of the first spur dike. The RSS peaked at the base of the first spur dike, correlating with intense vortex activity and sediment mobilisation. Downstream, reductionsin RSS, drag, and vortex strength corresponded to weaker turbulence; however, renewed vortex shedding between the second and third dikes sustained scour and sediment resuspension. Negative RSS values near the third dike indicated complex recirculation and vertical mixing that enhanced local deposition. TKE profiles mirrored the RSS trends, with the highest values near the first dike, driven by vortex formation and recirculation. The drag force and drag coefficient values consistently decreased across successive spur dikes. Similarly, vortex strength was much greater ahead of the first spur dike and decreased in the downstream direction. The findings provide new insights into the coupling between flow turbulence, vortex dynamics, and local scouring around the dikes. Keywords Deposition, Drag coefficient, Erosion, Spur dike, Scour depth, Reynolds shear stress, Turbulent kinetic energy, Vortex strength Rivers and streams are vital sources of water. Typically, riverbanks experience soil particle displacement from their original location, resulting in scour. Eroded sediments are deposited downstream (d/s), causing additional harm to rivers1. Riverbank erosion destabilises the bank, causing the loss of fertile soil and damage to existing structures along it and in the floodplain. The sediments deposited d/s cause morphological changes, including alterations to the riverbed and riverbank2,3. Bank protection is the primary concern in hydraulic river engineering as it is critical to secure significant structures and restore the ecosystem4. Spur dikes have been widely utilised as river stabilization and erosion control structures. They are built perpendicularly or at an angle, projecting slightly into the flow. It redirects water from vulnerable areas to reduce bank degradation and achieve optimal channel width or alignment5. In spur design, the most important physical factors to consider are the spur dike length (L), angle (θ), elevation of the spur crest, cross-sectional profile, expected scour, and materials used for construction4–7. Yazdi et al.8 simulated flow patterns using a 3D numerical model and recommended that the spur dike’s maximum length (Lmax) should be Lmax = (1/3)B, where B denotes the channel width. Richardson et al.,5 suggested a spacing range of 1.5–6 * the projected length of the spur into the flow, depending on site-specific conditions. The orientation of spur dikes has a significant influence on flow patterns, scouring, sedimentation, and riverbank stability. Depending on their angle, spur dikes are classified as “attracting,” “deflecting,” or “repelling.” Attracting spur dikes ( θ > 900 ) draw flow toward the near bank and are effective for navigation by increasing flow depth5. Deflecting dikes ( θ = 900 ) alter flow direction without reversing it, while repelling dikes ( θ < 900 ), directed u/s, push flow toward the opposite bank, aiding in bank protection by facilitating sediment deposition9, 10.

FAQs

Where does the maximum scour occur, and what drives it?

Maximum scour occurs at the tip of the first spur dike. It is associated with intense vortex activity and sediment mobilisation, reflected by elevated Reynolds shear stress near the base of that first dike.

How are the flow turbulence and hydrodynamic forces quantified in the experiment?

Instantaneous velocity components are measured using an acoustic Doppler velocimeter across longitudinal and transverse directions. The study then evaluates Reynolds shear stress, drag forces and drag coefficient, turbulent kinetic energy, and vortex strength over the evolved bed.

What happens to turbulence intensity downstream of successive spur dikes?

Downstream, reductions in Reynolds shear stress, drag, and vortex strength correspond to weaker turbulence. However, renewed vortex shedding between the second and third dikes sustains scour and sediment resuspension.

Sep 30, 2026

Upload by Connor