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Sediment Scour & Bed Load Transport Model

Scour and deposition is an important consideration in the design of bridges, dams and reservoirs. The sediment scour model in FLOW-3D enables users to study the erosion and deposition of sediments caused by powerful currents and complex flow patterns.

The sediment scour model handles multiple components such as sands, silts, and fine gravel in one simulation. The bedload transport model describes the transport of heavier debris by the currents along the bottom of the reservoir and the entrainment model predicts the lifting of the sediments into the bulk flow of the fluid.

Related links:

Modeling Local Bridge Scour during Flood Event

Improved Sedimentation & Scour Model

Modeling Tidal Erosion

Below is a FLOW-3D simulation of the erosion that occurs around a group of three 2.4 m diameter piers as river water flows past at 1.5 m/s. The river depth is 15.8 m and the mean sediment size was presumed to be 0.35 mm. Go here to read about this modeling project completed by Northwest Hydraulics Consultants.

3D Pier Example Simulation

These images show the results of a flow of 3m/s of clear water flowing past a 2m diameter pier. The sediment bed is composed of a bottom layer 2m thick of gravel (1cm diameter), a 1m thick layer of coarse sand (3mm diameter) and a 1m thick layer of sand (1mm diameter). The first plot shows the free surface interface colored by the elevation change of the packed sediment; this setup is strongly erosive. The second plot shows the conformation of the packed bed interface colored by the sand concentration; most of the sand had been eroded away, leaving only some sheltered by the apron. The final plot shows the gravel concentration, which is present only when the packed bed has eroded down to that level (at least 2m below the original bed height).

Free surface colored by the change in elevation of the packed bed due to erosion and sedimentation.
Free surface colored by the change in elevation of the packed bed due to erosion and sedimentation.
FLOW-3D's sediment scour model simulates the packed bed interface colored by the local sand concentration.
Packed bed interface colored by the local sand concentration.
FLOW-3D sediment scour model simulations the packed bed interface colored by the local gravel concentration.
Packed bed interface colored by the local gravel concentration.

Scour Potential and Scouring Downstream of Spillways

The scour potential model computes the shear stress beyond which scouring can occur along a surface. For example, a river bed can be simulated and regions where the scour is above a defined critical shear value are captured during postprocessing. Local scour downstream of hydraulic structures such as low head and high head structures, spillways and culverts is an important research field. The images below show FLOW-3D simulations of local scouring process downstream of various structures.


Simulating scouring downstream of spillways   Predicting excess shear stress using FLOW-3D's hydraulics models
Local scouring of overflow triple spillways. Courtesy of The Royal Institute of Technology
 
Excess shear stress on the riverbed
downstream of a powerplant.

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