Ferreira, C.C.; Abreu, T.; Silva, P.A.; Bernabeu, A.; Romao, S., and Staudt, F., 2020. Sediment transport with mixed sand in nonlinear regular waves. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 408–411. Coconut Creek (Florida), ISSN 0749-0208.This work presents the results of an experiment carried out in the Large Wave Flume (Groser Wellenkanal, GWK) in Hannover, which enables full-scale wave experiments to be conducted above sand beds. The experiment consisted of a set of regular waves propagating over a 30 m long horizontal bed composed of a bimodal mixture of fine (F) and coarse (C) sands. Wave gauges placed along the test section and an ADV (Acoustic Doppler Velocimeter) placed above the wave bottom boundary layer allow characterizing the wave nonlinearity parameters (skewness and asymmetry). Fluorescent sand was inserted at the beginning of each experiment and subsequent bed samples allowed tracking its movement, differentiating between the coarse and fine sand fractions.This study presents the results obtained with a particular sediment mixture (75%F+25%C) for two regular trochoidal wave conditions with the same wave period, 7 s, but different wave heights, 1.0 and 1.5 m. The total net transport rates estimated from a practical sediment transport formula, which includes both effects of wave asymmetry and skewness, are comparable with those obtained with the fluorescent tracer.

Sediment Transport with Mixed Sand in Nonlinear Regular Waves

Fractional formula of sediment transport rate for graded sediment in wave-driven sheet flow

层移输沙现象因为对应巨大的底床切应力和输沙量，对海岸工程和海岸地貌影响十分显著而备受关注。自然界中的泥沙绝大多数都是级配沙。现有研究对波浪层移输运级配沙的复杂运动机理的认识仍不够完善，同时缺乏级配沙瞬时输沙率的计算方法。本文针对近岸常见波浪诱导的非对称往复流建立了级配沙层移输运的瞬时输沙率公式。该公式综合了往复流输沙的相位差、加速度效应和紊流非对称边界层发展的作用。公式通过引入暴露和隐藏概率描述的暴露隐藏因子和不同组分相互影响的颗粒沉速来考虑级配效应。通过往复流水槽实验数据对瞬时输沙率公式进行了验证。结果表明，本文建立的瞬时输沙率公式对级配沙的瞬时输沙率、各组分净输沙率和总净输沙率均能取得较好的预测效果，并且优于传统的瞬时和半周期平均公式。基于该瞬时输沙率公式进一步探讨了随最大流速变化泥沙级配对各组分净输沙率和总净输沙率的影响。 

波浪层移输运级配沙的瞬时输沙率公式及其验证

This paper presents new net transport data from the STENCIL full-scale wave flume experiments with a sediment mix of a fine (0.21 mm) and a coarse (0.58 mm) sand fraction. These and existing mixed sand transport data from full-scale oscillatory flow tunnel experiments were used to validate the SANTOSS practical sand transport formula, which includes size-selective transport mechanisms and hiding and exposure effects. The STENCIL data show a strong effect of the sediment mix on the bed form regime and net transport rates. The SANTOSS formula predicts the flow tunnel net sand transport data well, and does a reasonable job in reproducing the net sand transport per fraction in the mix. The new STENCIL net transport data are generally underpredicted. In further research the SANTOSS formula will be further tested and improved using more detailed STENCIL data of flow and sand transport processes.

S. Schimmels

Papers

Understanding and modelling wave-driven mixed sand transport