Sand mass density and borrow material compatibility for beach nourishment

Abstract

Design of successful and cost-effective beach nourishment schemes requires a sound understanding of the hydraulic character of both borrow material and native beach sand. Techniques for assessing borrow material compatibility exist, but have proven inadequate in some situations. Most methods use a particle size parameter to represent sand transportability, although hydraulic theory and the nature of post-erosional lag deposits on Durban beaches suggest that mass density may also be a factor of importance. Results of a flume test on natural and artificialy constituted samples of Durban beach sand showed that transport of sand particles was unrelated to median particle size, but inversely correlated with sample mass density. The study concludes that where beaches consist of mineralogically heterogeneous material, a density factor should be included in any attempt to assess sediment transport rates and borrow material compatibility.