Half Moon Bay Sand

Half Moon Bay sand is a naturally sorted sand sourced from Half Moon Bay beach in Providenciales, TCI. The beach is a sand bar located between the uninhabited islands of Water Cay and Little Water Cay, approximately 4 km from Grace Bay. In 1960, a channel was created by Hurricane Donna between the two islands. The channel gradually filled in over time and all water movement ceased by approximately 2000. The material in the bay was deposited in what used to be the channel, and presently it is a pristine low energy environment. The sand is classified as a mixture of Subangular to Subrounded particles, as shown in Fig. 4.163. Selected DIA images of Half Moon Bay sand are also presented in Fig. 4.164.

Grain size distributions of Half Moon Bay sand are presented using several size descriptors in Fig. 4.165. Fig. 4.166 also depicts variation between number and volume distribution. The size of the number distribution is dominated by the finer particles while volume distribution is dominated by the larger particles. The grain size D₅₀ of Half Moon Bay is 255 µm. Typical particle size diameters in µm corresponding to several particle size descriptors are presented in Table 4.110. Comparison between EQPC sizes corresponding to various particle size diameters by weight/volume and number distributions are also presented in Table 4.111.

The density distribution for a number of commonly used shape descriptors is presented in Fig. 4.167 and summarized in Table 4.112. The distributions are clearly non gaussian and are thus fit with Johnson’s parameters. The fitting parameters are summarized in Table 4.113, and the goodness of fit is depicted in Fig. 4.168.

Fig. 4.163. Photo of Half Moon Bay sand with a 19 mm diameter US Penny for scale.

Fig. 4.164. Images of Half Moon Bay sand acquired using 2D DIA.

Table 4.110 Typical particle size diameters in µm corresponding to several particle size descriptors (by weight/volume distribution).

Half Moon Bay	D1	D5	D10	D30	D50	D60	D90	D99
Feret-max	150	171	195	252	316	361	597	1052
EQPC	121	150	162	209	255	286	435	848
Feret-min	106	127	143	182	223	245	385	832

Table 4.111 Typical EQPC corresponding to various particle size diameters by weight/volume and number distributions.

Half Moon Bay	D1	D5	D10	D30	D50	D60	D90	D99
Volume	121	150	162	209	255	286	435	848
Number	3	4	4	6	98	133	217	339

Table 4.112 Statistics of particle shape descriptors for Half Moon Bay sand by number and volume distributions.

Half Moon Bay	AR	S	Cx	Rwadell
Number
Mean	0.67	0.81	0.92	0.75
Median	0.68	0.84	0.95	0.76
Standard Deviation	0.13	0.10	0.06	0.10
Volume
Mean	0.67	0.80	0.92	0.75
Median	0.67	0.83	0.94	0.76
Standard Deviation	0.13	0.10	0.06	0.10

Table 4.113 Johnson fitting parameters for Half Moon Bay sand.

Half Moon Bay	γ	δ	ξ	λ
AR	-0.33	1.39	0.23	0.79
S	-0.64	0.66	0.53	0.40
Cx	-1.13	0.66	0.69	0.29
Rwadell	2.53	2.58	0.95	0.17

Fig. 4.165. Particle size distributions using various size descriptors.

Fig. 4.166. Particle size volume and number distributions.

Fig. 4.167. Particle shape density distributions (based on volume) for Half Moon Bay sand.

Fig. 4.168. Johnson fitting of shape descriptors for Half Moon Bay sand.