EXAMPLE PROBLEM III-2-11

FIND:

The width of the beach at the ends of the fill after 3 days and after 12 weeks of design wave action

on the beach fill.

GIVEN:

A beach nourishment 5,000 m in length is placed on a reasonably stable shoreline to widen the beach

as a protective measure for upland construction during storms. The new beach width is to be 50 m and

is to be placed at the same berm elevation as the natural beach *d*B = 3 m. Depth of appreciable sand

transport as estimated from historical profiles in the region is assumed *d*c = 7 m. A design wave for the

area is estimated to be *H*b = 3 *m*, *T *= 12 sec, αb = 10 deg. The sediment size of the natural beach is the

same size as the fill sediment size and ratio of sediment density to water density (i.e., specific gravity)

is 2.65. The porosity of beach is *n *= 0.4. The *K *factor is assumed = 0.77, and *κ *is assumed = 1.

SOLUTION:

a = 5,000/2 = 2,500 m ; YO = 50 m

At fill ends x/a = 1.0

From Equation 2-26

0.77 (3)2 9.81 @ 3

1

1

1

ε'

8

2.65 & 1

1 & 0.4

3%7

0.47 m 2/s

After 3 days (*t *= 259,200 sec)

2,500

' 3.58

'

2 ε*t*

2 0.47 (259,200)

From Figure III-2-36, for

' 1.0

' 0.56 hence, *y *' 0.56 (50) ' 28 m

After 12 weeks (*t *= 7,257,600 sec)

2,500

' 0.68

'

2 ε*t*

2 0.47 (7,257,600)

From Figure III-2-36, for

' 1.0

' 0.46 hence, *y *' 0.46 (50) ' 23 m

III-2-70

Longshore Sediment Transport

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