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Study of Sand Particle Size at Crystal Cove Beach

by Dan Williamson, Aimee Bacayo, Ha Nguyen and  Arthur Sanchez.

Introduction

Webster's Dictionary defines sand as a lose glandular material that results from the disintegration of rock, consisting of particles smaller than gravel but coarser than silt. From this definition one could speculate that not all grains of sand are the same. But to find how sand particles are spread along the beach we went to Crystal Cove to do field studies on sand particle size.

Methods

Our investigation started at 9 am, on September 7, 1999, by collecting twelve samples of sand. There were three starting points (in front of the stairs at the North end, in front of the ramp in the middle of the beach and in front of the stairs at the South end.) >From each of these points a sample of 11 ml. of sand was collected. Then a sample every 20 ft. was taken to give us four samples from all three sections of the beach.

After the sand had been gathered it was sifted to sort it by size. The sieves used sorted sand particles by .0394 in., .0197 in., .0049 in. and .0098 in. Some of the sand was too wet to sift so it had to be taken home and dried out The beach is ever changing and results of the sand could change from week to week. To make sure that our results were accurate for this day we collected all samples on the same day. The samples that needed to be dried out were collected at the same time as all of the other samples. After the sand was sifted it was logged and graphed. A table was set up to show the amounts of sand which pass through each of the sieves.

Results

As shown in Table 1 the sand particle distribution varied across the beach. Based on the samples taken the table shows how sand particle distribution differs from one end of the beach to the other but also across the beach, from the cliff to the water.

Changes are most evident between the large particle (over .0197 in.) and the medium (between .0149 in. to .0196 in.) to small (between .0099 in. to .0148 in.) particles. Taking the average of the stations in each section of the beach you can see the increase of large sand particles as you move from the North end to the South. That same increase is seen in the medium and small particles as you move the opposite direction, from the South end to the North. However the biggest difference in the sand particle size along the beach is in the sand from .0197 in. to.0393 in. The South end of the beach had over 3 times the amount of these particles as the North end

Discussion

Sand is moved from one end of the beach to the other by the wind as well as the ocean. The long shore current picks up smaller particles and moves them along the beach until it loses enough momentum and the particles fall. This lead us to believe that the long shore current was moving North picking up the smaller particles and then losing speed as it runs into the North cliff where it would leave the sand. One of the groups which was doing their study on long shore currents confirmed that the long shore current was moving North on September 7. This gives even more detail to our findings on sand particle distribution.

A further investigation of this project would be to repeat the study in the spring when the long shore current runs South and compare the two.

TABLE 1: SAND PARTICLE SIZE DISTRIBUTIONS FOR VARIOUS LOCATIONS AT CRYSTAL COVE STATE PARK ON
TUESDAY, SEPTEMBER 7, 1999
1.  North End of Beach  (References: Starting directly in front of North end staircase)
ML of Sand Particles EXTRA LARGE LARGE MEDIUM SMALL EXTRA SMALL
A)  START 113 370 550 40 15
B)  20 feet from starting point 10 10 1000 35 3
C)  40 feet from starting point trace 25 1060 5 trace
D)  60 feet from starting point 2 5 1030 50 2
Average 31.25 102.5 910 32.5 5
2.  Middle of Beach  (References: Starting directly in front of lifeguard tower)
ML of Sand Particles EXTRA LARGE LARGE MEDIUM SMALL EXTRA SMALL
A)  START trace 325 725 13 trace
B)  20 feet from starting point 15 275 740 45 10
C)  40 feet from starting point 2 50 995 40 10
D)  60 feet from starting point 7 60 995 20 10
Average 6 177.5 863.75 29.5 7.5
3.  South End of Beach  (References: Starting directly in front of South end staircase)
ML of Sand Particles EXTRA LARGE LARGE MEDIUM SMALL EXTRA SMALL
A)  START 75 350 560 45 5
B)  20 feet from starting point 10 270 800 5 trace
C)  40 feet from starting point 7 320 760 10 trace
D)  60 feet from starting point 5 400 670 15 trace
Average 24.25 335 697.5 18.75 1.25