LSTF

Experimental Setup

The Large-Scale Sediment transport Facility (LSTF) at the Engineer Research and Development Center of U.S. Army Corps of Engineers (shown in Figure 1) is capable of simulate oblique (6.5º incident angle) regular and random waves and a uniform longshore current by adjusting a series of 20 pumps in the cross-shore direction therefore simulating an infinite beach. The test cases shown here represent natural beaches with uniform longshore currents (Cases 1-4). Each experiment was 160 minutes long. In Case 1, a longshore current was induced by oblique random waves and the pumps where adjusted to match the measured longshore current. Case 2 was ran with the same wave heights as Case 1, but the pumps were set to recirculate twice the measured longshore flux of Case 1. Because the model does not have a variable flux boundary condition, this is was not simulated. In Case 3, the wave generator was turned off, and only the pumps were run. For this reason, Case 3 was also not used to test the model.

Figure 1. LSTF configuration (Gravens and Wang 2007)

Model Setup

The computational domain was generated based on the interpolation of measured beach profiles from profile Y14 to Y34 (see Figure 1). A constant grid resolution of 0.2 and 0.4 m where was used in the cross-shore and longshore directions respectively. A TMA spectrum was assumed at the offshore boundary with the parameter values γ = 3.3, and n = 100. The offshore water level during the experiment is not equal to the Still Water Level (SWL) because of the wave setup. The offshore water level was approximated for each experiment based on the most offshore water level gauge.

Table 2. CMS-Flow Settings

Setting	Value
Solver	Implicit
Time step	60 sec
Wetting and drying depth	0.001 m
Simulation duration	3 hr
Ramp duration	3 hr
Clock time	2.08 min

Table 3. CMS-Wave settings

Setting	Value
Wave breaking	Jansen and Battjes
Diffraction coefficient	3
Bottom friction	Off
Steering interval	0.25 hr

Results

Measured wave heights, water levels, and depth-averaged current velocities were compared to the center line profile measurements in Figures 1 through 6.

Table 4. Offshore significant wave height H_mo, peak wave period T_p,, incident wave period Θ_o, water level η₀ for the LSTF test cases.

	Hmo, m	Tp, s	Θo, deg	η0, m
Case 1	0.228	1.465	6.5	-0.001
Case 2	0.228	1.465	6.5
Case 4	0.222	1.465	6.5

Figure 1. Computed and measured significant wave heights for LSTF Case 1.

Figure 2. Computed and measured longshore currents for LSTF Case 1.

Figure 3. Computed and measured mean water levels for LSTF Case 1.

Table 5. Goodness of fit statistics for LSTF Case 1 for waves, water levels and longshore currents

	Hs, m	Eta, m	V, m/s
RMSE	0.0083	0.0012	0.0393
RMAE	0.0201	0.0261	0.0393
R2	0.982	0.934	0.665
Bias	0.005	0.0001	-0.017,

Table 6. Goodness of fit statistics for LSTF Case 1 for waves, water levels and longshore currents

	Lund-CIRP Qt, m3/m/year	van Rijn Qt, m3/m/year	Soulsby-van Rijn Qt, m3/m/year
RMSE	57.21	87.82	72.90
RMAE	0.118	0.357	0.1738
R2	0.20	0.57	0.10
Bias	26.43	79.92	38.93

Figure 4. Computed and measured longshore sediment transport rates LSTF Case 1 using the Lund-CIRP formulas.

Figure 5. Computed and measured longshore sediment transport rates LSTF Case 1 using the Soulsby-van Rijn formulas.

Figure 6. Computed and measured longshore sediment transport rates LSTF Case 1 using the van Rijn formulas.

References

• Gravens, M.B., Wang, P. (2007). "Data report: laboratory testing of longshore sand transport by waves and currents; morphology change behind headland structures". Technical Report, ERDC/CHL TR-07-8, Coastal and Hydraulics Laboratory, US Army Engineer Research and Development Center, Vicksburg, MS.

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