INTRODUCTION 



Fundamental to an understanding of the interaction of a particular 

 beach with the forces exerted upon it by the impinging water body is an 

 assessment of the dynamic behavior of the particles that comprise the 

 beach, under the expectable wave and current forces. To this end it is 

 necessary, first of all, to undertake the description of the dynamic and 

 associated properties of the existing spectrum of sand-sized particles. 

 The method of description chosen here for samples of sand from Virginia 

 Beach (Figure 1) is based upon the measured dynamic property of settling 

 velocity. Mean settling velocities of sand samples are determined from 

 fall-tube settling velocity curves by statistical methods. From a given 

 mean settling velocity the derived dynamic properties of mean Reynolds 

 number, mean drag coefficient , and mean dynamic shape factor are determined 

 for a sample. Mean grain size, in terms of nominal diameter, and sorting 

 are also determined. 



REVIEW OF PREVIOUS WORK 



The significance of the settling velocity of sediment particles in 

 the study of their dynamic properties has been stressed by many investiga- 

 tors. Brown (1950) states that many of the hydraulic properties that 

 control the entrainment, transportation, and deposition of mineral particles 

 apparently also control the dynamics of the mineral particles falling 

 through the fluid. Briggs, et al. (1962), consider that settling velocity 

 is perhaps the most fundamental of these hydraulic properties. The U. S. 

 Inter-Agency Committee on Water Resources (1958) considers that the settl- 

 ing velocity of the individual particle in quiescent water is the most 

 fundamental hydraulic characteristic which can be measured; that the 

 physical properties of the particles greatly affect their settling velocity 

 but are not in themselves adequate measures of their behavior in motion in 

 a fluid; and that studies of transport of sediments in water bodies require 

 a knowledge of the dynamic properties of the particles. 



The settling velocity of a particle through a fluid medium is essen- 

 tially determined by the force that resists motion of an immersed body. 

 Newton (1687) considered this resisting force (F) to depend upon the cross 

 sectional area of the body (A), the mass density of the particle (P s ), 

 and the square of the velocity (V). 



v 2 



F = (C) Ap s -j- (1) 



The term C is a numerical resistance coefficient which Newton believed to 

 vary only with the shape of the body and its orientation with respect to 

 the direction of motion. Rouse (1937) considers Newton's equation dimen- 

 sionally correct but states that the resistance coefficient depends not only 



