Beach Investigation

Name: __________________________

Introduction The coastline is a place of continuous modification and change by wave action. Waves

can quickly build or erode beaches and thus change the shoreline profile. The profile of

the shoreline at any given time is an expression of the available energy; it changes as the

energy varies. When wave action is at a minimum, new beach deposits may form,

building the beach seaward and producing a long, gentle profile. Larger, more

energetic waves, on the other hand, tend to erode beaches producing short, steep

profiles. A typical undisturbed beach profile is shown in Figure 1. Moving towards the

ocean it consists of sand dunes (formed by wind action), that berm (the nearly

horizontal section of beach usually preferred to as “the beach”), and the foreshore (the

section between the low tide mark in the beginning of the berm).

Figure 1. Generalized beach profile

Beach Profiles An important method of analyzing a shoreline is to construct a cross-section or profile

of the beach. In order to do this, two sets of data must be gathered: distances and

elevations. We began with a point of known elevation near where the beach begins and

at set distances (example, 10 feet apart) move directly toward the shore while recording

the change in elevation at each station.

Figure 2. Beach drift and longshore drift of sand on the beach

Erosion and Restoration at John U. Lloyd Beach

Because of wave action sand is constantly being moved along the coastline. This

process, known as longshore drift (Figure 2), moves sand mainly from the north to the

south along both coasts of Florida. It is estimated that each year 35,000 cubic yards of

sand enters Broward Country along the coast from Palm Beach County to the north.

Likewise, the same amount leaves the county to the south annually.

In 1926, the Port Everglades Inlet to the intercoastal waterways was completed (Figure

3). The inlet effectively acted as a barrier for sand moving immediately to the beach

south of the inlet. The beach, now part of John U. Lloyd Park, deprived of its supply of

sand, was severely eroded landward, almost ¼ mile from 1926 to 1989. To restore the

beach, 500,000 cubic yards of sand was dredged and added to a 1.5 mile stretch at John

U. Lloyd Park in July 1989.

Figure 3. Mercator map of Port Everglades Inlet (Source: NOAA)

Exercise 1

Construct profiles for John U. Lloyd State Park for, (1) eroded beach just prior to

restoration, (2) immediately after restoration in July 1989, and (3) two years after the

restoration in July 1991. Be sure to use different colors for each profile and label them.

Materials:

Beach profile data for John U. Lloyd Park

Colored pencils

Beach grid graph paper

Directions:

From the knowledge you have acquired and with their profile data for John U. Lloyd Park,

accurately draw the three profiles on the graph paper provided using data from Table 1. Be

sure to use a different colored pencil for each profile, clearly label each profile, and connect the

points with a smooth line.

Distance from

base (ft)

Eroded Beach

May 1989

Restored Beach

July 1989

Post-restoration

July 1991

0 8.8 8.8 8.8

25 8.2 8.2 8.2

50 7.8 7.8 7.9

75 6.0 9.7 9.7

100 3.8 10.0 9.8

125 0.6 9.7 9.8

150 -1.0 9.9 9.8

175 -1.5 9.8 9.8

200 -2.0 9.8 9.8

225 -2.7 9.8 9.0

250 -3.4 9.8 3.7

275 -4.0 9.7 1.5

300 -5.4 9.1 -2.5

325 -7.7 6.7 -2.5

350 -8.4 4.4 -2.5

375 -9.0 0.8 -2.6

400 -9.7 -1.8 -2.6

425 -10.2 -3.8 -3.4

450 -10.7 -7.5 -4.0

475 -10.3 -9.8 -4.7

500 -10.2 -10.5 -5.2

Table 1. Beach profile data for John U. Lloyd Park pre- and post-restoration

Questions:

1. How many feet was the shoreline extended outward immediately after beach restoration

in July 1989?

2. How many feet inland did the shoreline recede from July 1989 to July 1991?

3. Give a possible explanation for the change and beach profile from July 1989 to July 1991.

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4. Examine the completed profile of John U. Lloyd Park. What is the area of each

rectangular unit of the profile in square feet? Show your calculations for credit. Area

per unit square (ft2):

__________ ft (elevation) x __________ ft (beach distance) = __________ ft2

5. Count the number of rectangles which like completely within the area between the

eroded and reconstructed beaches above sea level, use Table 2).

6. Count the number of rectangles which are crossed by the eroded and reconstructed

beaches above sea level, use Table 2).

Interval (ft) Number of complete

rectangles (Question 5)

Number of crossed

rectangles (Question 6)

50-75

75-100

100-125

125-150

150-175

175-200

200-225

225-250

250-275

275-300

300-325

325-350

350-375

375-400

Total rectangles

Table 2. Worksheet calculation for number or eroded and reconstructed areas

7. Calculate the area, in square feet, of the sand added to the eroded beach in July 1989.

For those rectangles crossed by the profile lines assume an average area of ½ a full

rectangle. Show your calculations for credit.

Beach calculation Total complete rectangles *

25 ft2

(Total crossed rectangles *

25 ft2 ) / 2

Area of sand added (ft2)

8. From the information you just obtained, calculate the volume of sand headed for a 300 ft

length of beach and cubic feet. Show your calculations for credit.

Total area of sand added (ft2)

from Question 7

Total volume of sand(ft3) =

area (ft2) x length of beach (ft)

That Beach Face The sloping part of the beach is a result of wave action upon them billions of sediments which

comprise the shore. The active part of the beach is commonly called the foreshore or beach face.

The angle which the beach face makes with the horizontal is closely related to the size of

sediments making up the beach. The table below it displays this relationship.

One simple way to measure the angle of the beach face is to use some basic trigonometry. A

right triangle is one in which one angle equals 90°. Consider the example below where the

length of side (y) and (x) are known (Figure 3). For this exercise, angle is the angle of the

beach face. To derive angle , it is necessary to use the trigonometric function tangent. Where

tangent = (y/x). Once the value of (y/x) is known, it is then necessary to use the tangent table

(Table 1) to find angle . x is the length of the slope in feet, y is the height of the slope in feet.

Figure 3. A right triangle

Notice that the angle at the beach face is about the same for all three profiles at the park. This is

because the energy conditions have remained the same throughout the period studied.

Exercise 2

Questions:

1. Using your graphed profile, calculate the angle of each beach face at John U. Lloyd Park

using the tangent table below (Table 3). Show your calculations for credit.

Beach slope May-89 Jul-89 Jul-91 Average

Length of slope (x) ft

Height of slope (y) ft

Tan (y/x)

Angle (degree)

Table 3. Tangent table

2. Calculate the average particle size of sand that would be expected there using Table 4.

Note: You may have to estimate particle size. For example, if the slope is 21º then the

particle size would be cobble. If the slope was 19º then the particle size would be

pebble.

Particle size: _________________________

Wentworth particle size Millimeters Mean slope

Cobble 64 - 256 24º

Pebble 4 - 64 17º

Granule 2 - 4 11º

Very coarse sand 1 - 2 9º

Coarse sand 0.5 - 1 7º

Medium sand 0.25 - 0.5 5º

Fine sand 0.125 - 0.25 3º

Very fine sand 0.063 - 0.125 1º

Table 4. Wentworth particle sizes

Exercise 3 (Optional) Go to John U. Lloyd Beach in Dania Beach, FL. It costs $6.00 to get into the park. You

can do a search on the web for directions. To get the extra credit you must:

o Take a picture of yourself at the beach in front one of the signs by the pavilions

o Take at least two other pictures of the beach profile

Resize the pictures. If they are too big they can’t be submitted.

o Write a brief description of the beach, its profile, and your visit.

o Estimate the particle size of the sand; how did you come up with that particle

size? Describe what you could do to get a more precise particle size?